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Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review
Accepted Manuscript Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review Chi Wei Ong, Ian Wee, Nicolas Syn, Sheryl Ng, Hwa Liang Leo, Arthur Mark Richards, Andrew MTL. Choong PII:
S0890-5096(19)30487-X
DOI:
https://doi.org/10.1016/j.avsg.2019.04.032
Reference:
AVSG 4465
To appear in:
Annals of Vascular Surgery
Received Date: 29 December 2018 Revised Date:
9 March 2019
Accepted Date: 18 April 2019
Please cite this article as: Ong CW, Wee I, Syn N, Ng S, Leo HL, Richards AM, Choong AM, Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review, Annals of Vascular Surgery (2019), doi: https://doi.org/10.1016/ j.avsg.2019.04.032. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Chi Wei Ong1,2 Ian Wee2,3 Nicolas Syn2,3 Sheryl Ng2,4 Hwa Liang Leo1 Arthur Mark Richards4,5,6,7 Andrew MTL Choong2,4,8,9
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Department of Biomedical Engineering, National University of Singapore, Singapore SingVaSC, Singapore Vascular Surgical Collaborative, Singapore 3 Yong Loo Lin School of Medicine, National University of Singapore, Singapore 4 Cardiovascular Research Institute, National University of Singapore, Singapore 5 Department of Cardiology, National University Heart Centre, Singapore 6 Christchurch Heart Institute, University of Otago, Christchurch, New Zealand 7 Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 8 Department of Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 9 Division of Vascular Surgery, National University Heart Centre, Singapore 2
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Corresponding Author Assistant Professor Andrew MTL Choong MBBS, FRCS (Gen Surg), FEBVS (Hons), MFSTEd, FAMS (General Surgery) Consultant Vascular, Endovascular and Aortic Surgeon Division of Vascular and Endovascular Surgery National University Heart Centre, Singapore Address: Level 9, NUHS Tower Block, 1E Kent Ridge Road, Singapore 119228
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Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review
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Telephone: Fax: Email:
+65 67736512 +65 67766475 [email protected]
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Abstract
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Background:
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The analysis of the correlation between blood flow and aortic pathology through
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Computational Fluid Dynamics (CFD) shows promise in predicting disease progression,
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the effect of operative intervention and guiding patient treatment. However, to date, there
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has not been a comprehensive systematic review of the published literature describing
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CFD in aortic diseases and their treatment.
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Methods
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This review includes 136 published articles which have investigated the application of
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CFD in all types of aortic disease (aneurysms, dissections and coarctation). We took into
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account case studies of both, treated or untreated pathology, investigated with CFD. We
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also graded all studies using an author-defined GRADE approach based on the validation
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method used for the CFD results.
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Results
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There are no randomised controlled trials assessing the efficacy of computation fluid
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dynamics as applied to aortic pathology, treated or untreated. Whilst a large number of
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observational studies are available, those using clinical imaging tools as independent
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validation of the calculated CFD results, exist in far smaller numbers. Only 21% of all
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studies used clinical imaging as a tool to validate the CFD results and these were graded
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as high qualities studies.
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Conclusion
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Contemporary evidence shows that computational fluid dynamics can provide additional
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hemodynamic parameters such as wall shear stress, vorticity, disturbed laminar flow and
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recirculation regions in untreated and treated aortic disease. These have the potential to
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predict the progression of aortic disease, the effect of operative intervention and
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ultimately help guide the choice and timing of treatment to the benefit of patients and
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clinicians alike.
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Keywords: computational fluid dynamics, CFD, aneurysm, aorta, dissection, stent,
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EVAR, TEVAR, coarctation
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1. Introduction
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Aortic disease represents a subset of a much broader spectrum of arterial disease,
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comprising of aortic aneurysms; aortic dissections; intramural haematomata; penetrating
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atherosclerotic ulcers; blunt traumatic aortic injuries; pseudoaneurysms; aortic ruptures
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and associated inflammatory diseases1. Epidemiological trends have been disappointingly
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poor, with a 12% increase of annual death rate due to aortic aneurysm (2.8/100,000(>20
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million)) in the past twenty years2. Despite significant improvements in peri-operative
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care, surgical technique and the maturity of the endovascular therapy of aortic aneurysms,
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challenges in limiting aortic aneurysm growth and rupture persist3, 4.
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Although computed tomography (CT) aortography is widely considered to be the gold
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standard for delineating aortic pathologies, given the geometrical and functional
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complexities of the aorta, a multi-modal approach to imaging (computed tomography,
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chest x-ray, magnetic resonance imaging, ultrasound, echocardiography) is sometimes
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required for optimal aortic disease management1. Whilst we know that additional
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anatomical predictors such as aortic size, luminal size and patency have value in the
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assessment of the progression of aortic disease, recent research suggests that intra-aortic
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hemodynamics indices may also be an independent predictor of patient outcome. CT
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aortography is currently limited by only being capable of capturing a snapshot of the
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blood flow at a singular points in time. In time, increased use and uptake of 4D magnetic
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resonance imaging (MRI) may improve our understanding of the inherent dynamicity of
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aortic blood flow, but CFD has the ability to model such intra-aortic hemodynamic
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indices, based on current CT aortographic images, now.
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CFD has emerged in recent years as a complementary tool to ameliorate our
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understanding on the biomechanical behavior of blood flow in both normal and diseased
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vessels. It is essentially a branch of engineering that studies fluid flow and associated
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phenomena using computer-based simulation. One of the earliest applications came from
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the Massachusetts Institute of Technology in the 1950s, where they used computer
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simulation to solve numerical equations related to supersonic flow over sharp cones5.
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Since then, several studies6-15 have attempted to analyze blood flow in diseased aorta
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using CFD, including flow patterns in aortic aneurysm12, 15, aortic dissections7, 14, 16, 17,
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and changes pre- and post-endovascular aortic repair (EVAR)8.
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Significant technological advances in computing power and a concomitant cost reduction
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in the equipment necessary for supercomputing, have made it possible to analyze, in
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detail, the complex hemodynamics of blood vessels in the human body. The
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"computational" of CFD describes the use of computing resources to solve a set of
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mathematical equations, namely the Navier-Stokes equation which delineate the motion
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of blood. Representation of realistic blood flow and pressure waveforms can be achieved
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using properly framed model parameters to investigate the rate of change of blood
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velocity in relation to the pressure and density, as well as the different stresses and forces
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that are driving blood flow. The terms "fluid dynamics" in CFD can describe both
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moving blood (dynamic) and blood at rest (static). However, modern CFD studies tends
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to espouse the “dynamic” definition as it is a more accurate depiction of the body’s
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normal physiology 18, 19.
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Several computational software packages such as ANSYS FLUENT20, Open Foam21,
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SIMVascular22, ADINA23 and in-house coding24 can all be employed to execute CFD
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models, by calculating a few fundamental parameters such as wall shear stress (WSS) and
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vorticity for fluid behavior quantification. Wall shear stress is an important indicator for
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aneurysm rupture, thrombus formation and prediction of disease progress. It is included
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in all the CFD models to make the computational models clinically relevant. A useful
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glossary table of commonly used terms can be found in Table 1. The purpose of this
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systematic review is to provide a comprehensive overview from an assemblage of current
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literature available on the use of CFD in the assessment of both the normal human
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healthy aorta, the diseased aorta as well as the endovascularly treated aorta. This rigorous
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review of the literature will also help to delineate the clinical validity, and the application
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of, CFD simulations in predicting the progression of diseased aortas.
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2. Material and Methods
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The review protocol is registered at PROSPERO (registration number CRD42017070449;
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http://www.crd.york.ac.uk/prospero/).
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2.1 Search strategy
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This systematic review was conducted in accordance to the Preferred Reporting Items for
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Systematic Reviews and Meta-Analyses (PRISMA) checklist25, and in line with The
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Cochrane Library recommendations26. A comprehensive electronic search was performed
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in four electronic databases (Pubmed, Ovid, Cochrane, and Scopus) from inception to 4th
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September, 2017 to identify all articles describing the application of CFD in the human
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aorta, with language restriction to English and Chinese articles. Chinese articles were
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translated by a native Chinese speaker (OCW) and the data was extracted by two
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independent reviewers (OCW and AC). A repetitive and exhaustive search was
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conducted using a combination of these search terms: 'computational', ‘fluid’, ‘dynamics’
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and 'human aorta’.
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2.3 Inclusion and exclusion selection criteria
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Studies that reported the use of CFD in the analysis of hemodynamic parameters and
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factors contributing to aortic disease progression, aortic repair, and/or replacement, pre-
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/post-treatment comparisons with endovascular stent graft implantations were included.
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Studies evaluating idealized geometry were included, only if the analysis demonstrated
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meaningful results that could potentially contribute to the understanding of disease
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progression.
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Studies that solely focused on medical imaging rather than evaluating the impact of flow
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patterns in the human aorta were excluded. Studies presenting aortic flow patterns using
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newly developed numerical methods, but not new findings in human aortic flow patterns,
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were excluded. Studies applying a newly developed algorithm for aortic flow patterns,
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without validation, were also excluded. For studies that only took into consideration, wall
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strength measurements in vitro, without taking into account, fluid pressures or only finite
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elements of wall material stress-strain relationships, were also excluded.
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With regards to studies focusing on aortic intervention, we defined this as open or
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endovascular surgery of the aorta, not involving the aortic valve or coronary arteries,
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distal to the sino-tubular junction down to the iliac bifurcation. Therefore, coronary
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artery-related
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cardiopulmonary bypass or studies evaluating the effect of an external device such as a
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left ventricular assist device were excluded. Studies reporting cell factors that contributed
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to the growth of endothelium cells in the microscale, mass transport models and those
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involving the glucose level which facilitates the nutrient change in aorta were similarly
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excluded. The eligibility of studies was independently assessed by two independent
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reviewers (OCW, LHL) and disagreements were resolved by consensus or appeal to a
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third author (AC).
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surgical
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2.4 Validation and Quality Assessment of Studies
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The quality of the overall body of evidence was appraised using an author-modified and
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defined version of the Grading of Recommendations Assessment, Development and
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Evaluation (GRADE) system27, which originally considers five main domains: statistical
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heterogeneity; publication bias; risk of bias; indirectness; and statistical imprecision. The
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overall confidence in the reliability of the pooled data is then rated from ‘very low’, ‘low’,
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‘moderate’, to ‘high’.
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4D flow MRI is also referred to as time-resolved phase-contrast magnetic resonance
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imaging (PC-MRI). Velocity is encoded along three axes and provides 3D anatomical
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coverage28. The authors deemed this imaging modality the most accurate validation
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method of calculated CFD results as it allows a complete evaluation of complex flow
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patterns and quantification of flow parameters in real time29,
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patient-specific 4D MRI or invasive measurements like direct aortic pressure
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measurements via a catheter, as their validation methodology, were rated as high quality.
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For simulation studies that relied on external published MRI results, rather than their own,
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we rated the quality of these studies as "moderate to high".
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We accept that 4D MRI involves high cost which can be prohibitive and thus,
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preliminary results which are able to provide minimum physical validation are often seen
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as acceptable alternative validation methods. Generally, in vitro validation can be divided
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into idealized or phantom models. Idealized models are drawn out using computer aided
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design software based on published statistical results. Phantom models can be derived
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from idealised models or patient-specific images. Phantom models are fabricated in
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polymers like silicone and run in a flow loop employing a pump that generates similar
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pressures and velocity waveforms similar to human physiology. Next, this fluid flow
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pattern is captured with the particle image velocimetry (PIV) or particle tracking
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velocimetry (PTV) allowing evaluation. We rate the quality of those studies validated
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with in vitro measurement, be it idealised or phantom models, as 'moderate'. The CFD
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models that only provided claims of biological plausibility, such as the prediction of
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aneurysm rupture without other validation, are rated 'low' or 'very low'.
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3. Results
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3.1 Study Selection
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The systematic search yielded a total of 716 results. On the basis of title and abstract
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review, irrelevant publications or those not fitting our inclusion criteria were excluded.
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This left a total of 136 studies that were included in the qualitative analysis for the
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systematic review. See Figure 1.
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3.2 Overview of Studies
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Studies were categorised by pathology type, organised into treated and untreated
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subcategories and further subdivided into anatomical categories where appropriate. The
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studies were also ordered by the author-defined level of evidence and presented in
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reverse chronological order of publication.
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3.3 Results Summary
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In our summary, we found out that only 21% of CFD studies were rated 'high' given that
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they provide physical validation of the studied flow patterns via 4D MRI. Many of the
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reviewed CFD models claim some kind of biological relevance, such as the prediction of
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aneurysm rupture.
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physical validation, none of them seem to be properly validated with respect to such
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biological claim.
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Whilst some of the CFD models might have undergone proper
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3.3.1 Aortic Aneurysm
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The 59 included studies (Table 2- Table 5) were published from 2001 to 2017 (with
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patient-specific model and idealized models). Of these, 40 examined the relationship
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between hemodynamic changes and the risk of rupture (including 6 idealized geometry),
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5 studies compared the risk of thrombus formation between resting and exercise
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conditions, and 3 studies investigated the relationship between intraluminal thrombus
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formation14,
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validation whilst only 1 study attempted to model the in-vitro deposition of monocytes33.
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Overall 285 patients (42 males, 16 females, the others unknown) were included. The
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cohort ranged from ages 33 to 79.9 years old. Most studies looked at patient CT images
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to reconstruct aortic geometry, with only a handful utilising MRI. The biggest pre-
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treatment aneurysm size reported was 7.0cm, but few studies reported post-treatment
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aneurysm parameters. Only one study reported the cross-sectional area and volume of
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aneurysm but did not report aneurysm diameter34. In terms of aortic wall conditions, ten
and risk of aortic rupture. Four studies conducted in vitro CFD
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studies performed fluid-structure interaction (FSI) with a uniform wall thickness of 2 mm
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outside the AAA, while the remaining studies assumed a rigid wall in the CFD simulation
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studies.
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Six studies, comprising 105 patients, focussed on CFD modeling on untreated thoracic
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aortic aneurysms (TAA) geometry as shown in Table 2. The most recent study conducted
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by Callaghan et al combined the modalities of 4D MRI and CFD to study aortic flow
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patterns35. Tan et al. demontrated that both a numerical model with fluid structure
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interaction and turbulence model provided realistic flow patterns in a TAA associated
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with previous coarctation of the aorta, which could be further validated by MRI36. This
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was consistent with what Callaghan et al described in his study, where the TAA led to the
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formation of a vortex distal to the aortic branches, which was further validated by CFD
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analysis. A similar phenomenan was also reported by Hu et al37, albeit without CFD
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validation.
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Fourty four studies comprising of 145 patients evaluated untreated infrarenal abdominal
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aortic aneurysms (IRAAA) (Table 3). Whilst the majority of studies evaluated IRAAAs
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with a defined maximum diameter size of <5.5 cm, 6 studies included aneurysms which
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were larger than 5.5 cm. Four studies benchmarked their findings with the observation
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from clinical studies, for which, we graded the quality of evidence as high. Only one
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presented cases, compared their results with an idealized phantom model e.g. a straight
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tube in PC MRI which they used to validate their numerical model29. Three cases30-32
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employed the PIV and PTV methods to validate flow patterns in the patient-specific
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phantom model. The authors observed a strong recirculation region in the aneurysm sac,
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which they hypothesized may increase the risk of intraluminal thrombus formation. The
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majority of the remaining studies looked at the hemodynamics changes in AAA, with and
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without the wall of the aneurysm, to predict the potential of rupture, through qualitative
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and qualitative comparison of biomechanical parameters such as disturbed flow pattern,
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vortex formation, WSS and mechanical stress in various conditions and individual
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patient-specific geometry.
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Seven studies comprising 23 patients conducted a CFD analysis of TAAs that have
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undergone repair (Table 4). The majority of TAAs with a stent-graft repair demonstrated
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marked improvements in blood flow pattern . Midulla et al. showed an improvement in
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hemodynamic flow patterns after stent graft implantation38. Lei et al.39 proposed to
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combine WSS, luminal surface LDL concentration, and oxygen flux parameters to
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optimise the assessemnt of stent graft efficacy. The use of overlapping stent grafts has
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been shown to be effective in isolating the TAA, resulting in decreased WSS and risk of
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rupture. Filipovic et al. demonstrated an increased shear stress distribution in the
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aneurysm site post-surgery, the clinical signficance of which is uncertain but may
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predispose to increased risk of aneurysm rupture24. Two studies evaluated the
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hemodynamic changes in TAAs that were repaired with a chimney stent graft, and
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identified regions of stagnated flow and WSS alterations that could predispose to
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thrombotic events. It appears from CFD analysis that wall shear stress distribution is
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higher in the aneurysm post-repair, which may promote vascular reconstruction and
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endothelium remodelling. However, these findings must be interpreted with caution,
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since WSS threshold varies amongst studies and hence requires further experimental
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validation with MRI results. Future studies should consider implementing a more
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comprehensive and detailed measurement of flow patterns by combining various
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modalities such as both CFD and MRI.
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Only two studies analysed treated IRAAA with CFD modelling (Table 5), by comparing
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flow pattern parameters in pre and post treatment. Their findings identified an
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improvement of flow pattern, as evident from reductions of wall pressure, WSS, and an
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improvement in the degree of smoothness of the blood flow, hence reducing the risk of
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thrombosis formation.
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3.3.2 Aortic Dissection
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The degree of complexity in the geometry of dissections limits the potential combination
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of MRI and CFD for validation purposes. Consequently, the overall quality of evidence is
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poorer compared to those studies evaluating aortic coarctation. Only three studies
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demonstrated a high quality of evidence with MRI flow patterns used for comparison and
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only one study compared their CFD results with MRI flow patterns from other groups.
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Two studies provide in vitro validation with CFD results but these are mostly are in
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idealized geometry which undermines the value of validation. 17 studies are rated as
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“moderate low” with two studies rated low since their CFD data is presented without
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validation. Three studies used idealized geometry while the rest used Type-B aortic
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dissection (TB-AD) geometry.
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Twenty studies comprising of a total of 75 patients evaluated the changes in flow
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patterns in patients with untreated type B aortic dissection as shown in Table 6. Only two
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studies validated their results with PC-MRI flow to look at the residual dissection flap
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following occlusion of the entry tear. Two cases presented in vitro validation using
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idealized models and validated their CFD results using a phantom model. Both cases
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demonstrated that tear size can result in haemodynamic changes.
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Four studies (Table 7) comprising of 10 patients evaluated type B aortic dissections that
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were treated endovascularly.1 case looked at the differences in the pre and post treatment
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haemodynamic flow patterns. The other 3 cases reported significant improvements in
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hemodynamic pattern, hence reducing the risk of thrombus formation.
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3.3.3 Coarctation
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As would be expected from the pathology of aortic coarctation, almost all the CFD
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studies done, were performed on younger (<30 years old) patients with only three patients
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more than 30 years old as shown in Table 8 and Table 9. Fifteen studies reported using
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CFD to studying hemodynamic changes in coarctation, before and after treatments. One
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study evaluated the hemodynamic alterations of a CoA with a concomitant bicuspid
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aortic valve. A more comprehensive study published on congenital heart diseases by
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LaDisa et al examined the hemodynamic changes in postoperative age and gender-
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matched CoA, treated by resection with end-to-end anastomosis (RWEA) through WSS40.
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More than half (76%) studies utilised invasive catheter measurement results as validation,
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hence the overall quality of evidence is deemed to be good. There are only 3 studies that
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combined MRI and CFD studies in CoA, which reinforced the point that MRI-based CFD
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studies can provide more information on flow patterns compared to other imaging
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modalities.
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We found 2 studies presenting data on untreated CoA patients, with validation from in
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vivo studies. The changes in hemodynamic flow patterns are validated via intra-aortic
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catheter pressure measurements, pre- and post CoA, demonstrating the pressure gradient.
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Table 9 shows 16 studies which present the CFD modelling of hemodynamic changes for
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treated CoA. 5 studies showed an improvement in the pressure gradient, as expected, in
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the treated CoA population. For the rest of studies, a reduction of pressure difference
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before and after the coarctation site demonstrated the effectiveness of CoA treatment.
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Stent grafts consist of an expandable wire (usually nitinol - nickel-titanium alloy) mesh
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covered with fabric (usually Dacron, a polymer, polyethylene terephthalate) forming a
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tube when expanded. They isolate the diseased aortic aneurysmal sac from the circulation
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by preventing blood flow into the aneurysm. The alteration of blood flow after stent graft
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implantation can be represented by common parameters like velocity, pressure, WSS,
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OSI and TAWSS. Eight studies evaluated external forces acting on the stent graft that
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could account for migration, by calculating the displacement force and drag force from
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the blood pressure and shear stress. Only one study investigated the oxygen flux and low-
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density lipoprotein concentration before and after stent graft implantation. Five high-
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quality studies compared the simulation with migration results in patient specific imaging
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during follow-up. Two studies were classified as low quality as they did not have any
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form of validation from either the published literature or in vivo/in vitro evidence. In
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seven FSI studies involving blood-aortic wall interactions, the stent wall is assumed to be
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rigid without any movement. Only one study considered the stent graft as linear elastic
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material (Young modulus) and validated it using particle image velocimetry (PIV)41. One
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study examined the forces acting on stent grafts used for treating type B aortic dissection
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and compared velocities, before and after treatment in thoracic aortic aneurysms (TAA).
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Only 9 studies focussed on the treatment of TAAs by comparing the hemodynamic
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differences and forces acting on the stent graft.
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3.3.4 Characteristics of Stent Grafts
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In Table 10 and Table 11, we present studies that investigate the behavior of stent grafts
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by estimating the displacement forces exerted on the stent grafts based on hemodynamic
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flow patterns, before and after their use. The design and positioning of the stent graft are
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paramount to understanding aortic remodeling and changes in hemodynamic patterns.
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Common parameters used to evaluate the performance of stent graft include drag force
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and displacement force exerted on the stent graft, which can be extrapolated to evaluate
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the risk of stent graft migration.
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4. Discussion
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From an assemblage of the latest evidence available, this systematic review has attempted
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to evaluate the clinical validity and use of computational flow dynamic (CFD) studies in
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evaluating the progression of diseased aortas, both treated and untreated.
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This review demonstrates favorable evidence that supports the use of CFD in analyzing
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hemodynamic changes, important factors potentially affecting disease progression.
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Experimental studies have postulated that hemodynamic parameters such as wall shear
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stress (WSS) can change the behavior of endothelial cells, consequently affecting
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aneurysmal degeneration42. Besides WSS, conventional alteration of hemodynamics often
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refers to the change of flow pattern and pressure gradient. WSS in particular has been
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used to form different indexes, such as oscillatory shear index (OSI) and rupture index to
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estimate the risk of rupture, apart from measuring the conventional maximum diameter of
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an aneurysm. Although maximum aneurysm diameter and growth rate are important risk
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factors for surgical intervention decision making, the association is actually less
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straightforward. A small aneurysm can rupture and vice versa, and treatment is ultimately
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down to patient choice.43. If all CFD-derived hemodynamic indexes can be combined
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with advanced imaging modalities, we may be able to better predict potential risk of
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harmful aortic disease progression and therefore provide more accurate aortic
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intervention.
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In addition, as discussed in Moris et al44, WSS is also correlated to endothelial
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homeostasis, inhibiting unnecessary endothelial cell activation and triggering adverse
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vessel remodeling. To accentuate the relationship between biomechnical parameters and
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disease state, TAWSS, OSI, RRT and other WSS-related metrics have also been linked to
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thrombus and platelet formation. Recently Azani et al45 and O Rourke et al showed that
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regions of low OSI correlated with growth of intraluminal thrombus in AAA. However,
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high OSI(>0.4) and low TAWSS (<1 dyn/cm2) did not appear to coincide with locations
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of thrombus deposition46. Tan et al36 showed that low TAWSS and high OSI can be
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attributed to flow recirculation and consequent enlargement of an aneurysm. The
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aneurysm formation index (AFI) and gradient oscillatory index were proposed by Poelma
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et al47, who then hypothesised that such metrics can identify regions prone to disease
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formation, but nonetheless requires further validation.
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Furthermore, fluid structure interaction studies (FSI) allow us to assume different vessel
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wall models (i.e. deformed wall model and rigid wall model), which enables us to draw
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accurate and realistic associations between wall strength, wall stress and aortic wall
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remodeling. The wall strength information can be useful in assessing risk of rupture once
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the flow pattern is validated with medical imaging modalities. Although most studies did
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not provide follow-up outcome data to validate the occurrence of aneurysmal rupture, we
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acknowledge that the maximum diameter of an aorta may still be one of the important
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factors in deciding surgical intervention. Hence, this warrants further research to be
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conducted with large enough sample sizes in order to form a comprehensive risk
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assessment model for aneurysmal rupture.
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A systematic review of TB-AD conducted by Sun & Chaichana48 showed various
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hemodynamic changes between the false lumen (FL) and true lumen (TL). They
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demonstrated that high WSS and TAWSS was consistently associated with the reentry
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site and the edge of the tear. By analysing pre- and post-EVAR hemodynamics changes
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in TB-AD, the authors also concluded that decreased wall shear stress was associated
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with improved flow pattern post-EVAR. With the existence of the FL, OSI is always high
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due to the unsteady flow pattern cause turbulence. TAWSS and WSS will only decrease
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following FL dilatation since flow tends to be lower. The pressure in TL was reduced
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with pressure in FL elevated given that the number of reentry tears was increased.
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Findings from this review suggest that only a few dissection models have proper
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validation from MRI images which demonstrate localized hemodynamic changes. The
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difficulty comes from the dynamic motion of the intimal flap and tear locations, both of
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which causing ever changing hemodynamic parameters. Although these can be conducted
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with CFD studies, it remains a challenge to validate it in vivo and in vitro settings given
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the limitation of current imaging modalities to analyse aortic blood flow.
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Unfortunately, evidence for the prediction of the effect of stent grafts for aortic dissection
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are still lacking. Since all the simulations were performed on completely remodeled FLs,
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it is impossible to study association between FL progression and hemodynamic factors.
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Yu et al49 showed that morphological features can significantly affect pressure and
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velocity.
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Differential impact of local stiffening and narrowing on hemodynamic in repaired CoA
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using computational modelling has been conducted50. Results showed that vessel
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obstruction can introduce the buffering of stroke volume proximal to aortic narrowing.
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An enlarged pressure drop in repaired CoA can be explained through the conversion of
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kinetic energy into pressure with the viscous losses. Furthermore, the extent of stenosis
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depends on both pressure drop and flow rate. Ralovich et al showed that pressure drop
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across the coarctation can be accurately predicted in CFD after validation with MRI
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measurement51. This potentially provides for a noninvasive measurement rather than
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invasive measurement like catheter measurement reduce complications. Ladisa et al
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showed that low TAWSS and OSI was measured in the doA of COA treated by RWEA,
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suggesting that plaque formation may be influenced by surgical repair40. Kwon et al52
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showed that TAWSS measurements in a stented CoA can be significantly different along
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the posterior dAo, and with different stent types. This may assist in proper selection of
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stents for different types of patients. Goubergrits et al.
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can potently improve clinical treatment of CoA with 15 patients. They showed that a
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slight reduction of post-treatment pressure can decrease WSS in the stenotic segment,
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hence reducing the chance of stenosis. Based on these findings, CFD serves as an
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alternative , noninvasive tool to improve clinical diagnosis.
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showed that MRI-based CFD
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Despite the advent of endovascular treatments such as stent-graft implantations, it should
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not be a one-size-fits-all approach. To address this limitation, virtual implantation can
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assist in determining whether a stent graft is suitable for a patient based on unique
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anatomical features.
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modalities, coupled with flow waveform measurements derived from the MRI, it is
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possible to examine the impact of stent grafts on hemodynamics outcomes before any
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implantation. Given the invasive nature of open surgeries, an accurate noninvasive
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By reconstructing patient-specific geometry from imaging
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assessment of stent graft suitability would not only eliminate this drawback but also help
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lower the overall treatment cost.
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Midulla et al observed an increase of WSS in the inner wall of descending aortic
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aneurysm (doA) corresponding to an infold of the stent graft tissue38. Frauenfelder et al41
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found a reduction of wall pressure and WSS and turbulence after implantation, consistent
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with results published by Li and Kleinstreuer54. This may help to reduce complications
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like thrombosis and stent migration. Van Bogerjien et al showed that the bird-beak
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configuration post-thoracic endovascular aortic repair (TEVAR) can reduce flow
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disturbances in TAA despite significant hemodynamic turbulence in the distal descending
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aorta that could be attributed to dissection55. Rinourdo et al56 showed that the protrusion
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extension (PE) of endograft can be linked to marked intramural stress and principal strain
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distribution on the protruded segment of endograft depending on the length of endograft
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PE. Besides WSS, Lei et al39 showed that luminal surface concentration of lipoprotein
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(LDL) and oxygen flux on the wall can affect the stent graft performance in virtual
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implantations. The LDL concentration is calculated based on convective diffusion
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equation for the plasma while the oxygen flux is evaluated using the Sherwood number
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based on diffusivity and mass transfer coefficient. Overlapping bare-metal stents may
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reduce WSS and pressure to protect aneurysms from rupture57.
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The magnitude of load under the influence of hemodynamic factors like WSS is
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important to evaluate and estimate device migration. These loads can be referred to as
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displacement forces, migration forces or drag forces. Figueroa et al showed that increased
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curvature of the aortic graft changes the flow patterns, which may increases the risk of
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stent graft migration in vivo58. Pasta et al
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angle and extension can lead to an increase of transmural pressure across the stent graft
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wall leading to stent graft collapse. Gallo et al showed that low TAWSS and high OSI
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were associated with bird-beak configuration in TAA whilst low OSI suggests the risk of
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thrombus60. Complications like stenosis in the descending aorta still present with low
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TAWSS, hence suggesting that secondary complications may still occur after TEVAR. In
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addition, studies61, 62 showed that displacement forces exerted on stent grafts are sensitive
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to neck angle and positions that the stent graft can adapt to . Evaluation of the renal
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arteries’ flow dynamics could detect misalignment of the renal stent graft and potential
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sites for thrombus formation or stenosis. Jones et al63 showed that distraction forces
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related to morphological features of at the aortoiliac vessel generated by blood pressure
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and viscous force acting against fixation force can encourage stent graft migration. As
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such, an alternative choice of seal zone or even device can be developed based on CFD
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results to reduce the risk of migration.
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further showed that increase of stent graft
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To the authors’ knowledge, this is the first systematic review to assess the application of
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CFD on the human aorta, treated and untreated as well as the clinical relevance of such
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studies. The assemblage of evidence in this systematic review demonstrates the effective
520
use of CFD in studying a wide array of aortic pathologies. A concomitant large
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population screening study would be the most robust method of assessing the usefulness
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of CFD in the diseased aorta. However, such a study confers high cost, would take a long
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time due to technical limitations, and require many years of follow-up. Nonetheless, we
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acknowledge the importance and usefulness of CFD simulations as an adjunct to the
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armamentarium of currently available tools.
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4.1 Limitations
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Whilst we believe this comprehensive review to be the first of its kind, examining all
529
CFD studies looking at human aortic disease, treated and untreated, in the published
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literature covering both engineering and medical disciplines, we found out that only 596
531
patients are studied in 136 studies. Out of 136 studies, only 29 are rated as high quality
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which is only approximate 21% of all the studies (representing 270 patients).
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None of the studies had a high clinical impact and additionally, the risk of publication
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bias is high in this new area. The collected literature are too heterogeneous to perform
536
meta-analysis. It is worth highlighting that there is no universal threshold of WSS to
537
indicate disease progression, given that most models are different in geometry. The use of
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both the Newtonian and non-Newtonian model in the studied simulations make the
539
literature even more heterogeneous, hence we do not include the deviation between them
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in this systematic review. The risk of rupture of aneurysm or mortality are not directly
541
confirmed with clinical end points and many studies also only compare their findings
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with previously reported literature making their claims weaker. Thus, overall the clinical
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value of reported studies is relatively low, with heterogeneity and bias high, and this must
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be considered in the analysis of these simulated results.
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5. Conclusion
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The benchmarks for computational fluid dynamics results differ widely in the literature.
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As such, the utility of CFD to guide decision making for the treatment of aortic disease,
549
remains experimental for now. To date, high quality of evidence to support its use
550
remains sparse, but consistent results of the analysis of the hemodynamic changes in the
551
course of aortic disease, pre- and post-treatment are encouraging. This review has
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highlighted key areas for the development of CFD research as applied to aortic disease.
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Ultimately, by combining all the different numerical CFD parameters available, with
554
proper and consistent validation, it may be possible to create a highly accurate patient-
555
specific aortic disease progression and or prediction model. This could revolutionise
556
aortic treatment decisions including who, when and how aortic patients should be
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intervened upon.
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6. Acknowledgement
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The author would like to thanks Mr. Julian Siew Tze Kang for assisting in correcting the
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reference for the current manuscript.
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7. Disclosure Statement
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None
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Table 1 Glossary Summary of Common Terminology in Computational Fluid Dynamics
Mathematical Modeling Term
Definition/ Explanation
A branch of fluid mechanics that solves complex fluid behavior, as described by the
(CFD)
Navier-Stoke equation, using computational algorithms
Fluid-structure interaction
Similar to CFD but includes the deformation of adjacent solid material when
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SC
Computational fluid dynamics
analyzing fluid behavior. It can be used for evaluating the change in fluid behavior due to wall motion and properties
A variable represent the gradient of velocity in the flowing fluid
Wall Shear stress
Normal velocity gradient at the wall multiplied by dynamic viscosity. It is used to
TE D
Shear rate
(WSS)
express the force exerted on the wall by the fluid passing through it.
Vortex
A whirling fluid which rotates either clockwise or counterclockwise
Vorticity
A vector (a variable that has magnitude and direction) describing the tendency of the
AC C
Reynolds number
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fluid particle to rotate or circulate at a particular point.
Dimensionless quantity that is used to classify different fluid flow patterns
Viscosity
A measure of a fluid resistance to gradual deformation caused by shear stress
Newtonian vs Non-Newtonian
The viscosity of fluid is independent of shear rate is defined as Newtonian fluid, for non-Newtonian fluid, the viscosity change is dependent of shear rate
Deformation
Deformation can be defined as relative movement with respect to another point on the same body
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Wall strength
The ability of aortic wall material to resist deformation under an applied load without failure
Internal forces within a solid material that balance and react to the fluid pressure applied to it
RI PT
Wall stress
Relative deformation or change in a solid wall
Elasticity vs hyperelasticity
Elasticity refers to a linear relationship between stress and strain. While hyperelastic
SC
Wall strain
material has a nonlinear relationship between stress and strain
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WSS-Derived Parameters
Wall shear stress gradient
The difference of shear stress between two close locations at the same time point
(WSSG)
The difference of shear stress between two time points over a small period of time at
(TAWSS)
the same location
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Time-averaged wall shear stress
Oscillatory shear index
Temporal oscillation of WSS during a period of time. It is calculated as a dimensionless metric of changes in the WSS direction13
(OSI)
(RRT)
The time of residence of fluid particle stay in particular location. This metric is
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Rupture potential index (RPI)
inversely proportional to the magnitude of the TAWSS vector(OSI)13
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Relative residence time
Ratio of local wall stress to local wall strength
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Table 2: Untreated Thoracic Aortic Aneurysms
n
Age
M:F
CFD
(Years)
/FSI
74 ±6.9
CFD
Pathology
Size of
Parameters
aneurys
Quality of Evidence
m 100
Thoracic and Cardiovascular Surgery,2017
8
64
aortic
-
v, WSS, OSI
aneurysm
healthy: 70±6.9 and 40±9.9
Nauta, The Annals of
74
M
CFD
TAA
-
Platelet Activation
65
Callaghan, Callaghan,
1
47
M
CFD
TAA
Biomed Engin,2015 35 1
1
-
-
-
-
FSI
TAA with
-
CFD
Investigate hemodynamics change in
Saccular arch aneurysm dilate without much elongation
the saccular and fusiform aortic
compared with fusiform. The low WSS in inner
aneurysm and their relationship with
curvature of saccular arch aneurysm may cause the
WSS and OSI.
aneurysm act malignantly.
compare hemodynamic flow pattern
High platelet activation potential was found correlated
on 3 virtual surgical repair (1) open
with aortic thrombus. Aortic repair resolved pathologic
surgical repair, (2) conformable
flow patterns, reducing PLAP. Branched endografting
endografting, and (3) single-branched
also relieved complex flow patterns reducing PLAP.
endografting High
Vortex found after aortic branches in the aneurysm and
4D MRI for the understanding of
low wall WSS was found at the aneurysm wall which
aneurysm development and risk
may cause wall remodeling
to examine the hemodynamic
Vortex and regions of low WSS was identified in the
behviour in a thoracic aortic
aneurysm which can help to predict the aneurysm
repair
Mises stress,
aneurysm and compared with MRI
rupture.
CoA
repair
-
High
compare the flow field in CFD and
TAWSS, OSI, von
TAA with
v, wall displacement,
Clinical relevance
CoA
AC C
Tan, Comput Struct,200936
66
v, WSS, vorticity
EP
Comput Methods Biomech
Tan, Int J Appl Mech,2009
High
Potential (PLAP)
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Thoracic Surgery,2017
1
High
M AN U
Natsume, The Journal of
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(6 studies representing 105 patients with an untreated TAA)
turbulence intensity V, WSS, OSI turbulence intensity
results High
examine hemodynamic change in
The correlation-based transitional model was found to
TAA using transitional model
produce results in closer agreement with the MR data than the laminar flow simulation where a vortex found
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Hu, X. Z., National Medical
1
33
M
CFD
TAA
-
v. P, WSS
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moderate-
To investigate growth and rupture
Large vortex found at the aneurysm the growth and
low
mechanism of TAA
rupture mechanisms of TAA may be analyzed based on
RI PT
a constructed patient specific model and hemodynamic simulation.
TAA=Thoracic Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; Platelet Activation Potential (PLAP); OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational
AC C
EP
TE D
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Fluid Dynamics; FSI: Fluid structure interaction
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RI PT
Table 3: Untreated Infrarenal Abdominal Aortic Aneurysms
n
Age
M:
CFD
Patholog
Size of
(Years)
F
/FSI
y
aneurys
Parameters
-
CFD
Arzani, Am. J. Physiol. Heart
10
-
-
CFD
Circ. Physiol.,2014 45
Suh, Ann Biomed Eng,2011
69
Les, Ann Biomed Eng,201070
Kung, J Biomech Eng,2011
71
8
10
8
1
70.5±7.8
71.2 ± 7.9
73.3
-
8:0
9:1
7:1
-
CFD
CFD
small
(MRI)
(<5cm)
CFD
CFD
v, P
AAA
small
(MRI)
(<5cm)
distance, t mean exposure
AAA
small
v , PRT
(MRI)
(<5cm)
TAWSS, OSI
AAA(
small
v, MWSS
MRI)
(<5cm)
OSI, PRT
AC C
Suh, Ann Biomed Eng,2011
68
AAA
TE D
-
EP
5
Biomed Eng.,2014 67
AAA
small
v, P, MWSS, OSI,
(MRI)
(<5cm)
TKE, normal stresses
AAA
-
v
(MRI)
Specific study interest using CFD
Clinical relevance
compare the topology of blood
Exercise resulted in higher and more uniform mixing
transport and mixing during rest and
and reduced the overall residence time in all aneurysms
exercise
compared to exercise.
Evidence
m Arzani, Int J Numer Method
Quality of
M AN U
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SC
(44 studies comprising 145 patients with an untreated IRAAA)
High
High
investigate
hemodynamic
change
with ILT progression High
Low OSI(<0.1) and high TAWSS can be related with ILT growth
investigate
hemodynamic
through
MRI
changes
Longer duration of PRT in AAA under resting
CFD
conditions can be used to compared with exercise to
and
examine potential benefits of physical activity High
examine hemodynamic change in
Exercise decrease the PRT, an increase of WSS and a
different exercise condition
decrease OSI in AAA which suggest that mild exercise may reduce flow stasis in AAA
High
investigate hemodynamics in eight
An increase mean WSS and a decrease OSI suggest that
AAAs during rest and exercise
exercise may attenuate AAA growth
moderate-
validate
high
pressure using PC MRI, and an in-
simulated
vitro phantom
velocity
and
-
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7
-
-
CFD
AAA
8.3±
v, P, WSS
moderate
0.91cm
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a
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1
75 until
M
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78
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-
-
CFD
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v, WSS
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-
CFD
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AAA
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PTV
O'Rourke, Proc. Inst. Mech.
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68
F
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14
-
-
-
CFD
AAA
76
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-
Lozowy, Cardiovasc Eng
Arzani, J Biomech Eng. 2016
FSI
ted
&CFD
AAA
untrea
CFD
AAA
ted
79
6
CFD
AAA
-
Suprarenal AAA promotes thrombosis initial within
zone, TAWSS, OSI,
ow
of
AAA
3
65:66:70
M
AC C
Manage.,201580
CFD
AAA
1-5cm
aneurysm
on
the
renal
and
increase
the
chance
for endothelial
hemodynamics
dysfunction and atherosclerosis in renal arteries. -
v,WSS,von Mises
moderate-
investigate the impact of FSI and
stress
low
CFD on the flow pattern in AAA
v, WSS, OSI,
moderate-
Investigated pulsatile blood flow
the impingement of blood flow change the recirculation
TAWSS
low
dynamics in patient-specific AAA.
region may prevent ILT deposition and influences the
WSS
(MRI)
Filardi, Vasc. Dis.
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EP
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23
78
untrea
Strong P gradient and presence of vortex structure
with CFD results
moderate-
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compare flow field measured in vitro
v, WSS, recirculation
RT Lin, Biomed Research
moderate
overall aneurysm shape. moderate-
investigate hemodynamic parameter
The correlation between spatial/temporal gradients of
low
in aneurysm
WSs magnitude can be used to predict aneurysm growth.
v, P, WSS
moderate-
to
low
parameters with aneurysm diameter
investigate
hemodynamic
Flow separation streamline regions found on the neck of the aneurysm and there is high WSS found at the aneurysmal wall
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5
-
-
CFD
AAA(MR
3-5cm
I)
time averaged action
moderate-
understand
potential
low
developing ILT in AAA
the
mechanisms
for
v, p
moderate-
examine
WSS
low
before and after aneurysm
wall deformation
moderate-
examine
VMS, p, WSS
low
under realistic AAA with different
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-
-
CFD
Technol.,201582
-
Fusiform
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1
-
M
FSI
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hemodynamic
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the laminar flow model is desirable for normal aorta and smaller aneurysm while transitional flow model should be applied on the larger aneurysm models Higher WSS was observed at the distal part and lower WSS at the proximal part of the aneurismal sac
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Fluid,2014
-
-
-
FSI
83
Chandra, J Biomech Eng,2013
Idealized
6cm
WSS, VMS
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23
1
73
M
CFD
AAA
moderate low
-
investigate the influence of spiral
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flow to the AAA
with beneficial and detrimental effects in terms of
M AN U
Javadzadegan, Eur J Mech B-
change of wall stress and WSS
v, P, WSS
moderate-
examine hemodynamic changes in
High WSS were observed near the inlet and in the
wall stress
low
AAA with different inlet boundary
common iliac arteries. The location of high wall stress
conditions
was found where ILT was absent.
strain
and
one
way
FSI
compared to 2 way.
1
62
-
CFD
AAA
middle-
Biomech. Biomed. Eng.,201384
Soudah, Comput Math Methods
-
M
CFD
AAA
3
-
-
CFD
Part H J. Eng. Med.,201333 68;53;58
2:1
Mech. Eng. Part H J. Eng. Med.,201221 O'Rourke, Proc. Inst. Mech. Eng. H J. Eng. Med.,201286
3
68:53:58
1:2
FSI
CFD
AAA
AAA
downstream to the protuberant apex of the
2.5-4.0cm
v, P, WSS
moderate-
examine
changes
the greater the asymmetry and tortuosity of the AAA,
low
which linked to the main AAA
the higher the possibility of blood recirculation, ILT
geometric parameter
formation, and a possible rupture
model the deposition of monocytes
Peak monocyte residence time was found to increase
-
WSS
+MRI) 3
The regions of high TAWSS appeared upstream and
variation
low
AC C
Kelly & O'Rourke ,Proc Inst.
AAA(CT
investigate hemodynamic parameter
RPI,
85
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moderate-
size
EP
Med.,2013
5
VMS, TAWSS
TE D
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4.9-5.2cm
3.6-4.5cm
v , WSS, P
during
the
AAA
development
moderate-
hemodynamic
growing aneurysm.
low
with aneurysm sac size
moderate-
investigate the effect that fluid flow
simulation should include solid stress to predict the
low
has on the stress in an aneurysm wall
maximum stress in an aneurysm wall
v, TAWSS, OSI
moderate-
investigate flow field in AAA under
low OSI (OSI<0.1) is linked to thrombus growth
shear strain rate
low
steady condition
showed the link of biomechanical predictor to thrombus
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-
-
CFD
AAA
-
v, P,OSI
Shabestari, Biomed. Eng. Appl.
4
55-65
-
CFD
AAA
5.37±1.28
Basis Commun.,201188 Wang, Comput. Biol. Med.,2011
v, P, WSS
cm -
-
-
-
FSI
89
moderate-
examine hemodynamic changes with
shows validation of 2D MRI for comparison of AAA
low
different inlet boundary conditions
hemodynamics
moderate
investigate hemodynamic changes
increase WSS found at the distal and proximal location
low
9
-
-
CFD
AAA
v, WSS
moderate-
study dynamic behaviors of aortic
the correlations between blood viscosity and the
Aneurys
Strain rate
low
aneurysm subject to physiological
dynamic behaviors of aortic aneurysm help to
m
wall axial
blood flow with normal and high
individualize endovascular treatment for patient with
4.35-
Eng,2010 34
99.07cm2 -
-
FSI
Bluestein, Comput Methods
Idealized
-
3
2
-
-
-
-
FSI
FSI
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AAA
6.2-7.0cm
AAA
4.3-6.5cm
with ILT
200892
-
-
Khanafer, Ann Vasc Surg,200794
-
-
-
CFD+
Idealized
FSI
model
CFD
idealized
-
-
geometry
aortic aneurysm
investigate the impact of blood flow
disturbed flow found right after the neck of aneurysm
low
on thrombus development
that can be linked to platelet activation and adhesion
moderate-
examine
hemodynamic
change
FSI is unnecessary for purely mechanical modelling,
low
between CFD and FSI
wall stress
moderate-
examine
WSS, v
low
between CFD and FSI
moderate-
examine hemodynamic change with
higher WSS on the anterior side of the AAA in the
low
ILT and without ILT
patient with the smallest AAA may affect aneurysm
v, WSS, VMS
with the aim of evaluating the current rupture probability
hemodynamic
change
wall stress and WSS magnitude are influenced by the shape of aneurysm and ILT that may affect the prediction on risk of rupture.
growth. There is reduced stress at the location of ILT compared to aneurysm without the ILT.
v, P, Wall stress
moderate-
examine pressure condition for the
Change of flow field can affect rupture risk of aneurysm
displacement
low
evaluation of AAA wall mechanics
such as change of pressure at the aneurysm site.
v, shear stress,
moderate-
examine
Turbulence induce higher WSS on the aneurysmal wall
relative pressure
low
under rest and exercise
EP
-
Biomech Biomed Eng,200893
AC C
Scotti,Comput Methods
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displacement Biasetti, Ann Biomed
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Hardman, Int J Numer Method
hemodynamic
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that maybe responsible for wall dilation and bigger dilation of wall may trigger greater turbulence, possibility
a
self-perpetuating
aneurysmal growth.
mechanism
for
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-
-
FSI
Online,200595
idealized
-
fusiform
v, P, wall
moderate-
investigate
displacement
low
cause rupture
hemodynamic
change
thickness has higher mechanical stresses under effect of
-
-
-
-
-
FSI
CFD
AAA
-
idealized
-
v, principal wall
moderate
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low
AAA under FSI
v, P, WSS
fusiform
Venez.,2003
2
-
-
CFD
AAA
5.8-
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-
-
CFD
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low v ,P,WSS
6.55cm -
low
v, P,WSS
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-
-
FSI
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v ,P ,s, VMS
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-
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88
-
FSI
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101
Piccinelli, Biomech. Model.Mechanobiology,2013102
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TAWSS
-
-
CFD
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<5cm,
v, WSS, displacement
distribution in the aneurysm that may change the risk of rupture. larger aneurysms in vivo may be subject to turbulence
lead to aneurysm rupture
than smaller aneurysms may change risk of rupture
examine hemodynamic change in the
vortex are linked to the stress distributions in aneurysm
aneurysm
examine hemodynamic change in the
Maximum WSS at peak flow and appearance of
low
aneurysm
secondary flows in late diastole at the aneurysmal wall
moderate-
investigate
low
cause AAA rupture
low
low
OSI , VMS
10
Vortex and WSS formation may affect the wall stress
moderate-
OSI
are affected by effect of asymmetry hemodynamic
change
Localized interaction of aneurysmal wall and blood flow may affect the thrombus formation and help to determine the aneurysm risk of rupture.
examine
transitional
flow
in
Transitional flow pattern was found in AAA on systolic
aneurysms
phase that may affect thrombus
investigate hemodynamic parameter
the anterior part of the aneurismal wall (2D) was a
to assess rupture risk
potential region of rupture based on the vortex formation displacements
anisotropic displacement of AAA were reported to have
experienced by AAA and correlate
relationship with hemodynamic forces related to the
6.5cm,>6.
them
impingement of the blood on the lumen boundary that
5cm
hemodynamics
5cm-
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v, P, Vorticity. TKE,
EP
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1
flow conditions and risk of rupture than a more fusiform
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low
investigate
with
the
the
local
bulk
affect ILT.
AAA= Abdominal Aortic Aneurysm; ILT=intraluminal thrombus; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
SC
RI PT
ACCEPTED MANUSCRIPT
Table 4: Treated Thoracic Aortic Aneurysms
n
Age
M:F
(Years) Midulla, Eur Radiol,201238
Lei, J Biomech,2015
39
Zhang,J. Biomech.,2014
20
1
57
-
62.2
-
-
CFD
Pathology
14:6
-
-
CFD
CFD
CFD
TAA
v , WSS
TAA(pre
WSS, LDL
and post-
concentration oxygen
operative)
flux
Idealized
v, P, WSS
stent -
-
CFD
TAA with
v, WSS, OSI
AC C
1
EP
overlapping
Programs Biomed,201124
Quality of
High
moderate-
aortic
low
Ong, Artif Organs
1
-
-
CFD
Clinical relevance
examine hemodynamics change after
increased WSS found along the inner wall of the descending aorta that
TEVAR
may correspond to an in-fold of the stent-graft tissue. There is increase
TAA with
v,p,WSS, TAWSS,
microporou
OSI, RR
s stent graft
WSS at the proximal and distal part of the stent-graft
examine hemodynamic changes pre
WSS, luminal surface LDL concentration, and the oxygen flux on the wall
and post-operative treatment
have to be considered together to evaluate the performance of SG comprehensive.
moderate-
To
hemodynamic
overlapping stents intervention may effectively isolate the TAA ,
low
performance of overlapping bare-
protecting it from rupture. Decrease of WSS found at aneurysm after
metal stents
implantation of overlapping of SG
moderate-
to examine the hemodynamic
CFD results shows that aneurysm site after surgical intervention has
low
parameters before and after aortic
higher shear stress distribution that may promote vascular reconstruction
repair
and benefit endothelium
to examine hemodynamic pattern
improved flow pattern after microporous stent graft restore blood flow in
before and after preferential covered
aneurysm to physiological flow condition(Figure 2).
repair
20
Specific study interest using CFD
Evidence
TAA with
Filipovic, Comput Methods
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/FSI
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low
investigate
stent graft
the
ACCEPTED MANUSCRIPT
-
-
-
CFD
Idealized
investigate hemodynamic behaviour
hybrid procedure produce better hemodynamic performances over
aortic arch
v,WSS, Pressure
low
of aortic arch in aneurysm and treated
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cased in surgery graft, hybrid stent-
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-
-
-
CFD
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the presence of chimney stent graft results in stagnation regions and WSS
aorta vs aorta post'chimney' stent
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grafts inserted into each renal artery
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in parallel to the aortic SG
TAA= Thoracic Aortic Aneurysm; ILT=intraluminal thrombus; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
M AN U
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n
Age
M:F
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-
Pathology
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FSI
76
M
CFD
Quality of
Specific study interest using CFD
Clinical relevance
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reduction of wall P and WSS and less turbulence
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flow pattern found at the AAA after implantation
Evidence AAA
41
1
Parameters
/FSI
AAA
P,WSS
v, P
EP
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11
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low
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AC C
AAA=Abdominal Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
Postoperative case showed improve blood v in the intravascular lumen after implantation of stent graft.
SC
RI PT
ACCEPTED MANUSCRIPT
Table 6: Untreated Type B Aortic Dissection
n
Age
M:F
(Years) Osswald,, Eur J Vasc
20
Endovasc Surg,
Treated/
CFD/FSI
Pathology
44-79
7:3
38-77
9:1
Untreated
1
56
M
untreated
Quality of
Specific study interest using CFD
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TB-AD with a relatively stiff dissection flap can affect the
data to examine hemodynamic changes
flow dynamics
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Simulated EVAR treatment by virtually occluding the
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-
-
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untreated
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OSI, turbulence
high
aneurysmal dilatation of the thoracic aorta
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as long as the tear size was large enough so that the effect
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hemodynamic
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in
intensity P
the flow pattern in the dissected aorta is extremely complex with recirculating and disturbed flow dominating in the FL and TL.
the in vitro results from a previous study
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untreated
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moderate
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-
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-
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the presence of an additional re-entry tear provided an
low
entry tear on hemodynamic parameters in
extra return path for blood flowing back to the TL during
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moderate-
diastole
to assess hemodynamic implications of
can help predict which patients will suffer adverse events and facilitate the clinical decision-making process related
TAWSS
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CFD simulations can be used as a diagnostic tool for
low
Windkessel as boundary condition
AD
moderate-
to elucidate the underlying hemodynamic
The interluminal ∆P may be a contributing factor in the
low
mechanisms involved in the longitudinal
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investigate hemodynamic for a case of pre-
CFD can be used as both a diagnostic and an
including a
OSI
low
and post-stenting(virtual stent-graft)
interventional tool.
coarctation
ACCEPTED MANUSCRIPT
54
F
untreated
FSI
TB-AD
Karmonik,, Vasc
45
M
untreated
CFD
Phys,2013
Online,2013
chronic
P, WSS
hemodynamic
70
-
untreated
CFD
chronic
-
-
untreated
CFD
118
and oscillatory WSS
models evaluate hemodynamic changes during
potential to deliver information about hemodynamics
aneurysmal dilatation in chronic type B AD
thereby improving management of type B AD
moderate-
quantitatively
identify entries and relevant reentries between true
low
hemodynamic features of AD.
v,P, WSS
moderate-
study the flow exchange between true and
contributes to evaluating potential thrombotic behavior in
TKE
low
false lumen during the cardiac cycle and
the false lumen and is pivotal in guiding endovascular
quantifying
intervention
v , P, WSS
TB-AD
FSI can help to identify certain collocated regions of low
low
TB-AD
-
parameters'
moderate-
type III AD 1
117
Chen, Biomed Eng
difference between FSI and rigid wall
DeBakey
116
Chen, Med Eng
compare
low
TAWSS. OSI 1
Endovascular Surg,2013
moderate-
displacement
investigate
the
and false lumen and potentially assist in stent-graft
SC
Online,2015
6
v, P, WSS
RI PT
1
Biomed Eng
M AN U
Alimohammadi,
the
flow
across
planning
specific
passages.
1
45
M
untreated
CFD
Surg,201212
Karmonik, Eur J Vasc Endovascular Surg,2011
10
1
53
M
untreated
CFD
chronic
P, WSS
TB-AD
v
DeBakey
v, P
type III AD
moderate
determine the potential value of CFD
to
low
simulations in prediction of aneurysmal
characterization of this severe disease entity, thereby
growth and rupture.
predicting false lumen progression in individual patients
moderate-
TE D
Karmonik, J Vasc
low
quantify
hemodynamic
changes
provide
additional
surrogate
markers
for
the
with
occlusion of exit tear caused increase in FL pressure.
interventional treatment or with disease
Simulating TEVAR treatment by occluding entrance tear
progression
depressurised the FL. Removing the IS lowered pressure of the combined lumen compared with TL pressure of the original model.
EP
RATD=Retrograde Type A aortic dissection; TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy;
AC C
TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction; FL=False Lumen; TL=true lumen; EVAR=endovascular aortic repair; IS=intra-luminal septum;
ACCEPTED MANUSCRIPT
Table 7: Treated Type B Aortic Dissection
n
Karmonik, Vasc
1
Age
M:F
(Years) 60
Treated/
CFD/FSI
Pathology
Parameters
CFD
TB-AD
v, P ,WSS
Untreated M
treated
Quality of evidence High
Endovascular
Eng.,2015
8
52.75
7:1
treated
CFD
TB-AD
v, P, TAWSS
120
Chitsaz, J Cardiovasc
-
-
-
treated
CFD
Surg,2012121
Idealized
P
geometry
2011
15
1
38
F
treated
CFD
TB-AD
forces
Quantitative assessment of hemodynamic wall forces in
moderate-
examine hemodynamic changes in TB-AD
high RRT is a strong predictor of subsequent FL
low
between medically treated and stented cases
thrombosis, whereas ∆P between the TL and FL
moderate-
determine
low
dissection
the
as well as the location of the largest ∆P may be associated with the likelihood of subsequent aortic expansion relationship
propagation
in
between the
distal
TEVAR should ideally cover both entry and reentry tears to reduce risk of retrograde propagation of AD.
longitudinal direction(the tearing force) and dp/dt of endovascular stent grafting in idealized geometry
v, P, WSS,
moderate-
examine hemodynamics parameters in TB-
relatively high TAWSS (in the range of 4–8 kPa) may be
TAWSS
low
AD and relate it to progression of dissecting
associated with tear initiation and propagation
EP
Tse， J Biomech，
hemodynamic
TB-AD can assist in follow-up examinations.
TE D
for AD
quantify
Clinical relevance
pretreatment /post-treatment
119
Cheng, Ann Biomed
to
M AN U
Surg,2011
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(4 studies comprising 10 patients with a treated type B aortic dissection)
aneurysm
TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational Fluid Dynamics; FSI: Fluid
AC C
structure interaction; FL=False Lumen; TL=true lumen; EVAR=endovascular aortic repair; IS=intra-luminal septum
ACCEPTED MANUSCRIPT
Table 8: Untreated Coarctation of the Aorta
Age
M:F
(Years) Keshavarz-Motamed, PLoS
1
-
Treated/
CFD/FSI
Pathology
-
untreated
Quality of evidence
CFD
CoA
v, P,TAWSS ,
One,2013122 Valverde, J Cardiovasc
Parameters
Untreated
High
OSI 7
20 (mean)
-
untreated
CFD
CoA
P
Magn Reson,2011 123
Specific study interest using CFD
SC
n
to examine hemodynamic changes with
Clinical relevance
the presence of a BAV in the CoA raise the TAWSS to around 14 Pa
the presence of a CoA and a BAV High
To predict the aortic P distribution in
predict the hemodynamic conditions in the aorta and avoid invasive cardiac
patients with aortic coarctation model
catheterization. An invasive pressure gradient drop across the coarctation.
M AN U
Author, Journal, Year
RI PT
(2 studies representing 8 patients with an untreated coarctation of the aorta)
CoA=coarctation of aorta; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; TKE=turbulent kinetic energy; CFD: Computational Fluid Dynamics; FSI:
AC C
EP
TE D
Fluid structure interaction; BAV=bicuspid aortic valve
ACCEPTED MANUSCRIPT
Table 9
Treated Coarctation of the Aorta
n
Age
M:F
(Years) Mirzaee,J Magn Reson
12
Treated/
CFD/FSI
Pathology
Parameters
Quality of
Untreated 5:7
treated
evidence CFD
Imaging,201729
aortic
p
High
coarctatio
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(16 studies representing 107 patients with treated coarctation of the aorta)
investigate the numerical method Lattice Bozman
for
pressure drop found across aortic coarctation.
noninvasively
measurement of pressure gradients in
M AN U
n
method
Clinical relevance
patients with a coarctation of the aorta
Goubergrits, J Magn Reson Imaging,2015
6:7
treated
CFD
CoA
P
6
-
-
treated
CFD
CoA
P
5
-
-
untreated
CFD
126
1
60
F
treated
CFD
Eng.,2012127
CoA
5
treated
MICCAI,2012 51
Coogan, Catheter Cardiovasc Interv., 2011
2
15;25
0:2
CFD
CoA
AC C
Ralovich,
Restenosis
treated
CFD
v,P
TKE
EP
Arzani, Ann Biomed
128
CoA
TE D
125
Itu, Ann Biomed Eng,2013
25±14
124
Ralovich, Med. Phys.,2015
13
CoA
P
High
High
High
High
High
compared MRI based CFD with catheter-
Peak systolic P drops can be reliably calculated
derived peak systolic P drops
using MRI-based CFD in a clinical setting
estimate the pre- and postoperative
the study can be integrated into a clinical setting,
hemodynamics for coarctation patients
where manual interaction is required in a mostly
a mean absolute error of less than 2 mmHg in all
pre- and post-operative coarctation of
the patient between CFD results and catheter
aorta (CoA) patients
measurements
provide a comparison between in vivo
Results indicate relative agreement (error ≈10%)
and numerical estimates of turbulence
between the in vivo measurements and the CFD
intensity in a patient specific model
predictions of TKE
estimate the pre- and post-operative hemodynamics
v, P
High
supervisional manner
examine hemodynamic change between
for
both native
and
High correlation of our results and catheter measurements(∆P>20mmHg)
is
shown
on
recurrent coarctation patients.
corresponding pre and post-operative examination
compare the effects of surgical and stent
CoA stenting may not affect cardiac work to any
based treatments on aortic compliance
significant degree as is commonly believed in the
and
clinical community.
ventricular
coarctation
workload
in
aortic
ACCEPTED MANUSCRIPT
Szopos, J Thorac
30
15±5.1
-
treated
CFD
CoA
v, P, WSS
Cardiovasc Surg,2014 129
moderate-
quantify the geometric factor that leads to
patients with an angulated ‘‘gothic’’ aortic arch
high
abnormal
might warrant increased surveillance for aortic
blood
flow
patterns
and
6:8:10:5:4
3:2
treated
FSI
CoA
Eng,2011130
LaDisa, Congenit Heart
6
15±8
4:2
treated
CFD
Dis,2011 40
CoA
moderate-
Examine hemodynamic alterations under
Local patterns of hemodynamic indices reported to
displacement
high
resting and non-resting
correlate with atherosclerosis in normal patients
WSS, TAWSS, OSI
treated by
examine
in
Localized differences in WSS indices within the
high
postoperative age- and gender-matched
descending aorta of CoA patients treated by
CoA patients treated by resection with
RWEA suggest that plaque may form in unique
Biomech ,2017
63
F
treated
CFD
131
aortic
end-to-end anastomosis (RWEA).
locations influenced by the surgical repair
WSS, KE, TKE, TI
coarctatio n
Comput,2016
1
39
M
treated
FSI
CoA
132
Kwon,Pediatr.
1
15
-
treated
CFD
Cardiol.,2014133
v, P
TE D
Taelman, Med Biol Eng
M AN U
1
CoA with
TAWSS
different
hemodynamic
changes
were accentuated by CoA.
moderate-
RWEA
Andersson,, J
complication due to eccentric WSS.
v ，TAWSS
SC
5
RI PT
modified indexes of WSS LaDisa, J Biomech
Moderate-
investigate the transWSS properties in
Results showed that regions of strong near-wall
low
flows
turbulent
turbulence were collocated with regions of elevated
characteristics in an aortic coarctation
dominated
by
transWSS and turbulent WSS, while in more
before and after treatment
transitional-like near-wall flow regions a closer resemblance was found between transWSS and low, and oscillatory WSS
moderate
predict
the hemodynamic impact of
low
(coexisting) stiffening and narrowing in
A
residual
narrowing
of
CoA
affect
the
hemodynamics significantly by decreasing the WSs
CoA repair moderate-
compare
low
between stents in CoA
hemodynamic
alterations
it help to select most appropriate stent for each
moderate-
compare
low
treatment hemodynamics in CoA
treatment pressure drop
moderate-
investigate hemodynamic changes under
4D MRI-based in vivo v profile in CFD
low
different flow conditions
studies may be an important step towards a patient-
patient, and ultimately reduce long-term morbidity
Goubergrits, Ann
13
25±14
6:7
treated
CFD
Goubergrits, Ann
3
40:23:29
0:3
Biomed Eng,2013134
Olivieri, Cardiovasc Eng Technol.,2011135
3
-
-
CoA
AC C
Biomed Eng.,2014 53
EP
stents
treated
treated
CFD
CFD
CoA
CoA
v, P, WSS
v, P, WSS
pre,
post-treatment,
virtual
MRI-based CFD allow the evaluation of the post-
specific analysis of CoA hemodynamics v, WSS
moderate-
examine hemodynamic changes in native
varied patterns and locations of WSS resulting
low
and surgically repaired aortic arches
from abnormal arch remodeling may exhibit a primary effect on clinical vascular dysfunction
ACCEPTED MANUSCRIPT
CoA=coarctation of aorta; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; TKE=turbulent kinetic energy; CFD: Computational Fluid Dynamics; FSI:
AC C
EP
TE D
M AN U
SC
RI PT
Fluid structure interaction; BAV=bicuspid aortic valve
ACCEPTED MANUSCRIPT
Table 10
Characteritsics of stent grafts after the treatment of TAA and TB-AD
M:F
(Years) Prasad, J. Endovasc.
1
69
Treated/
CFD/FSI
Pathology
Parameters
CFD
TAA with 4-module
displacement
thoracic stent-graft
force, v, VMS
Untreated F
treated
evidence
Ther.,2011136
Rinaudo,Comput. Biol.
4
32±9
-
treated
CFD
TAA
High
-
-
-
treated
CFD
1
51
M
treated
CFD
Van Bogerijen,J.
1 55
51
M
treated
TAA with stent graft
AC C
201660
EP
Gallo, Comput Fluids,
Stent graft in TAA
The region of larger intermodular stresses and highest frictional instability correlated with the
Slippage
intermodular junctions of a multi-component
zone where a type III endoleak developed 4 years
coefficient
thoracic endograft
in CT after thoracic stentgraft placement.
examine hemodynamic changes acting on the
Greater displacement and transmural pressure
bird-beak configuration after TEVAR
across the stent-graft wall were found for a
P
CFD
Dissecting thoracic aorta aneurysm with stent graft
the
biomechanical
Clinical relevance
the
moderate
moderate
TE D
Endovasc. Surg., 2011 137
evaluate
hemodynamic
displacement
Vardoulis, Eur. J. Vasc.
Specific study interest using CFD
and
v, P, VMS,
Med.,201556
Endovasc. Ther.,2014
Quality of
SC
Age
forces
acting
on
M AN U
n
RI PT
(8 studies representing 21 patients with stent grafts in TAA and TB-AD)
protrusion extension(PE) longer than 21 mm.
analyses the mechanisms by which grafts,
Patients who receive ascending aorta grafts
placed in the ascending aorta (proximal) and
maybe more prone to systolic hypertension and
descending aorta (distal)
therefore
deserve
proximal
aortic
closer
BP
graft
presented
monitoring. more
haemodynamic alterations than the distal graft
OSI
moderate-
examine hemodynamic change with different
Comparison
TAWSS
low
geometrical features after TEVAR
indicates a partial restoration of normal flow in
of the
different morphologies
v, P
moderate-
evaluate the impact of TEVAR on aortic
Less chaotic flow at the bird-beak location with
low
hemodynamics, focusing on the implications
higher velocity and more flow disturbance found
of a bird-beak configuration
at the aortic narrowing in the descending TAA.
the region of interest.
ACCEPTED MANUSCRIPT
-
treated
CFD
TAA with stent graft
Biomed Engin,2012
Cheng, J Vasc
138
P, WSS
moderate-
determine the orientation and magnitude of
High magnitude of displacement was found
displacement
low
maximal displacement forces (DFs) in the
as35.01 (standing) and 37.32 N (supine). The
TAA endograft
orientation of the resultant DF vector is
force
12
56
11:1
treated
CFD
TB-AD
drag force
Surg,2008139
Lam, Med Biol Eng Comput,2008 140
1
-
-
treated
CFD
RI PT
1
Methods Biomech
perpendicular to the greater curvature of the thoracic aorta,
moderate-
study the forces acting on thoracic stent grafts
A significant change in stent-graft diameter
low
and their relationship to geometry and flow,
occurs after endovascular repair for TB-AD, may
and its impact with stentgraft remodeling
increase the hemodynamic drag force.
SC
Krsmanovic, Comput
Thoracic aorta with
Drag force
moderate-
investigate the biomechanical factors which
Larger internal diameter and smaller diameter of
stent graft
v
low
may affect the drag force on stent-graft wall
curvature affect drag force on the stent-graft.
M AN U
induced by the blood flow
TAA=Thoracic Aortic Aneurysm; TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational
AC C
EP
TE D
Fluid Dynamics; FSI: Fluid structure interaction; TEVAR=Thoracic endovascular aortic repair; BP=Blood pressure
ACCEPTED MANUSCRIPT
Characteristics of stent grafts after the treatment of IRAAA
RI PT
Table 11
n
Age
M:F
(Years) Konoura,J. Artif. Organs,2013
-
-
Treated/
CFD/FSI
3
-
-
CFD
-
treated
CFD
Eng.,2012142 Figueroa, J Vasc
5
76
Parameters
4:1
treated
Quality of evidence
141
Segalova,J. Biomech.
Pathology
Untreated
CFD
Idealized geometry
v, Energy
with stent graft
loss
AAA with novel
v , P , stress
endograft
NIH
AAA
v, P
Surg,201022
High
High
High
TE D
displacement force
Figueroa, J Endovasc
1
-
-
treated
CFD
AAA
Ther, 200958
v, WSS, P
High
Force
3
-
-
treated
CFD
Ther, 2008143
3 postoperative
v, WSS
patient specific
drag force
EP
Molony, J Endovasc
moderate
Biomech Biomed Engin,2017
144
15
5
AC C
model
Raptis, Comput Methods
untreated
10 treated
CFD
AAA
Specific study interest using CFD
Clinical relevance
to evaluate blood flow distribution in the 3
estimate blood flow distribution of a newly
branch graft
developed vascular graft prior to its clinical use,
M AN U
Author, Journal, Year
SC
( 27 studies representing 90 patients with stent grafts in AAA)
for safe use of the graft.
examine hemodynamic change that may
The magnitude of the NIH in all models was well
occur due to unique position of stent graft
below the accepted design and safety threshold
to determine whether the direction of aortic
the magnitude and direction of the displacement
endograft
force acting on aortic endografts can affect the
movement
is
related
to
the
directional displacement force
endografts movement
determine the effect of curvature on the
Curvature of endograft can change the blood
magnitude and direction of displacement
flow. It can be used to evaluate the risk of
forces acting on aortic endografts
endograft migration in vivo
To compare the function of conventional
WSS appeared to be higher in the conventional
Dacron stent-graft and tapered stent graft
stent-graft compared to the tapered stent graft
designs for EVAR WSS,
Moderate-
compare the hemodynamic patterns before
a decrease of peak WSS on the part of the EG
Helicity, p, v
low
and after the EVAR implantation
that resides in the iliac arteries,
significant
variations were observed in the iliac arteries part that may require an improvement of EG designs
ACCEPTED MANUSCRIPT
20
treated
CFD
AAA
Device,2017145
v, WSS,
Moderate-
compare hemodynamic patterns on two
The results showed that two similar endografts
helicity,
low
different
can induce different flow characteristic that could
displacement
-
treated
CFD
-
WSS
146
Polanczyk, J
10
Biomech,2015147 Kandail,J. Endovasc.
61–76
treated
CFD
AAA
-
-
-
-
treated
CFD
Idealized geometry
-
-
treated
CFD
Sughimoto,Heart
1
54
M
treated
CFD
Vessels,2014 149 Jones,J. Vasc.
1
-
-
treated
CFD
-
treated
CFD
Vasc Endovasc
Pasta,J. Vasc. Surg.,201359
1
-
M
treated
One way FSI
Pa-s
that
may
be
important
to
predict
thromboembolic events. thrombus growth model can be applied to predict the risk of thrombus formation in stent-grafts
v. TAWSS
moderate-
examine hemodynamic changes in branched
Displacement forces exerted on stent-grafts are
displacement
low
stent-grafts (BSGs) for different anatomic
very sensitive to lateral neck angle but not on the
variations
configuration of the stent-graft.
moderate-
to assess durability of F-EVAR through
Blood flow patterns are better in post-operative
displacement
low
analyze the displacement forces acting on
AAA, demonstrating that with FSG in place,
standard non FSGs
force
AAA&TAA with
WSS
AAA with
AAA
AC C
Surg.,201362
does have particles with WSS accumulation>3.5
v ,WSS, P
EP
-
graft with diaphgram
and one with a
fenestrated stent
1
low
5 AAA with FSGs
grafts Georgakarakos, Eur J
The stent graft configuration with the diaphragm
and growth in the stent-graft
FSGs.
restore blood flow in aneurysm sac
moderate-
use novel indices to characterize and quantify
Grafting not only to ameliorate WSS or OSI but
low
energy loss of pulsatile blood flow
also to improve blood flow
distraction
moderate-
determine morphologic features which were
Distraction force acts against endovascular
forces
low
associated with greater distraction force
fixation to provoke stent graft migration.
displacement
moderate-
study the hemodynamic effects of positional
differences in the values of shear stress exerted
force
low
variations of SG
on the stented arteries, depending on different
aneurysm repair
Surg.,201463
investigate shear accumulation in the stent
determine the process of thrombus formation
TE D
6
Biomech,2014148
patients.
Moderate-
low
forces Kandail, J
affect design of endografts for individual
moderate-
years
Ther.,201561
their
SC
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on
M AN U
2017
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endografts
postimplantation position
force Suess, J Vasc Surg,
aortic
RI PT
Raptis, J Med
AAA with TASG
shear stress
positions that SG can adapt after the deployment of fenestrated EVG
v, P
moderate-
To assess the biomechanical implications of
It helps in identifying patients with high risk of
VMS
low
excessive stent protrusion into the aortic arch
TASG
in relation to TASG collapse
intervention.
collapse
and
guide
preventive
ACCEPTED MANUSCRIPT
5
-
-
treated
CFD
Methods Biomed. Eng.,2013
AAA with
v, P
moderate-
to examine hemodynamic change under
No difference in drag forces with the SG
bifurcated stent graft
drag force
low
different input boundary flow for four
containing the full human aorta and those
patient-specific bifurcated stent graft no
without. A twisted leg configuration promoted a
150
RI PT
Stefanov, Int. J. Numer.
twisted and twisted leg configurations with
spiral flow formation along its distal legs
the inclusion of the full human aorta. 2
-
-
treated
FSI
AAA
v, P, WSS
Radiol,2010151 Fung, Comput. Biol.
1
-
-
treated
CFD
AAA
P, force
Med,2008152
6
-
-
treated
CFD
Radiol.,2008153
Howell, J Endovasc
4
-
-
treated
CFD
AAA with Zenith®
P, v
bifurcated stent-
Total shearing
grafts
force
AAA
Force
-
-
-
untreated
untreated
FSI
FSI
AAA
AAA
hemodynamic
effect
of
the renal arteries is insignificant
moderate-
examine the dynamic factors linked to actual
hemodynamic factors can be linked to drag force
low
motions of blood and related it to drag force
that may play a significant role in the risk of
acting on the endoluminal stentgraft
stent-graft failure.
moderate-
estimate the pressure which occurred in the
increase of shear stress and higher P drop for
low
aorta after stent-grafting
short body graft compared to long body graft.
Phys,200644
1
-
-
treated
CFD
AAA
The highest WSS occurred near bifurcation area.
To assess the hemodynamic forces on a
Forces on a stent-graft are also affected by the P
bifurcated abdominal aortic stent-graft
within the aneurysm sac, which depends on stent-
moderate-
quantitatively assess the impact of type II
the risk of type II endoleaks depends on the P
P
low
endoleaks on AAA rupture risk and potential
level of the inlet branch
drag force
moderate-
Investigate the biomechanical factors based
sac pressure caused by these endoleaks depends
wall stress ,v
low
on SG–AAA interaction dynamics
largely on the inlet branch pressure. the stent
wall stress ,v,
AC C
Morris, Med Eng
hemodynamic effect of fenestrated renal stents on
low
TE D
1
-
the
graft performance.
stent-graft migration
graft migration force can be reduced by type II
EP
Li, J Biomech, 200654
1
fenestrated stents on the renal arteries
moderate-
Ther, 2007154
Li, J Biomech, 2006155
investigate
low
M AN U
Stefańczyk, Pol J
moderate-
SC
Sun,Korean J
endoleak since it depends on the pressure difference between stent graft and aneurysm cavity. v
moderate-
investigate geometrical effect of stent graft
geometry has the greatest influence on the outlet
low
to the flow pattern in AAA
flow rates, flow patterns and drag forces
ACCEPTED MANUSCRIPT
1
Treated
FSI
AAA
2005156
wall stress, v
moderate-
analyze the pulsatile flow and its impact on
The time-varying drag force on the EVG exerted
drag force
low
EVG placement, EVG/AAA wall stress
by physiological blood flow is unavoidable,
distributions, sac P generation, and EVG drag
where for patients with severe hypertension the
P
force -
-
-
FSI
157
Liffman, J Endovasc
-*
-
-
-
CFD
Ther, 2001158
P
moderate-
graft
VMS
low
Idealized AAA with
v , P, Force
graft
Pless, Stud Health Technol Inform,2001
Idealized AAA with
1
-
-
treated
CFD
investigate the AAA-stent graft interaction
AAA
v ,P,WSS
159
risk of EVG migration is very high sac pressure and maximum aneurysm wall stress both follow closely the endoleak flow rate.so both parameters can be used to predict post EVAR complications.
moderate-
investigate the forces acting within the
downward force on a bifurcated stent-graft may
low
pressurized aorta and upon a stent-graft
exceed the force required to dislodge it when
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2003
-
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Li, J Biomech Eng,
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Li, Med Eng Phys,
low
investigate blood flow change by stent grafts
relying on radial attachment alone which is largely depends on proximal graft diameter CFD can be used to evaluate risk of AAA rupture and optimize stent graft design
AAA=Abdominal Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction; TEVAR=Thoracic endovascular aortic repair; NIH= normalized index of hemolysis; EVAR= endovascular aortic repair; EG=endograft; F-EVAR=Fenestrated-EVAR; FSG=Fenestrated Stent Graft; EVG=endovascular graft; TASG=thoracic
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aortic stent graft
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Table 12 Summary of the application of CFD in the diseased aorta
Disease Management
Future perspective
Aneurysm
be
Stent graft manages to reduce the pressure in
A comprehensive aneurysm model should include aortic wall,
Aneurysm
correlated with hemodynamic factors
the aneurysm sac and improved the flow
intraluminal thrombus with realistic flow condition derived
like WSS, velocity, and pressure to
pattern which can reduce the chance of platelet
from MRI. More realistic aortic wall strength and wall
fully determine the risk of rupture.
activation. Difference forces, energy loss,
properties should be derived from advanced imaging technique
The hemodynamic factors can be
morphologic features should be taken into
in vivo to enhance the credibility of the model160. An
linked to the platelet activation,
account on stent graft design in order to
integrative
intraluminal thrombus, and monocyte
optimize the performance of stent graft and
combination of fluid properties should be used in order to
deposition
avoid stent graft malposition and migration.
understand the aneurysm progression. Stent graft material
should
approach
like
taking
the
diffusivity
and
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diameter
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Pre and post treatment
Aortic
properties should be integrated into the treated aneurysm model to evaluate the durability and strength of design to withstand stent migration. More malposition case and bird
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peak configuration should be done in order to design new treatment for faulty implantation. More follow up case on Image-based CFD should be presented in order to confirm the assessment of rupture risk.
The geometry of CoA affects the
Pre and posttreatment of coarctation show that
The future of CFD in coarctation focus on the impact of
hemodynamics
with
post operation can reduce the pressure drop.
surgical repair on the CoA. Different repair has been repaired
hemodynamic factors e.g. WSS that
However, the surgical repair may also change
but the complications still occur after the repair like plaque
can
be
flow
pattern
plaque
the hemodynamic patterns in CoA which may
formation due the abnormal aorta geometry even after repair.
formation. Good agreement between
correlated
with
trigger the complications e.g. plaque formation
A more realistic flow condition and compliance of the aorta in
catheter
in some unique locations.
CoA should be measured through the in vivo and in vitro in
measurement
and
CFD
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CoA
results shows that CFD can be used in
order to evaluate the performance of surgical repair.
diagnosing the severity of coarctation through pressure evaluation. Aortic
Hemodynamics
dissection
pressure
of
TB-AD
like
A stent graft treatment shows that it can reduce
CFD in dissection should be done in FSI given the intimal flap
in
and
the pressure difference in FL and TL and also
motion which only simulated through FSI. It is still not sure
FL
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difference
circulation and disturbed flow found
reduce the disturbed flow pattern.
whether the motion will cause a highly turbulent flow if the flap is taking into consideration. The intimal flap motion is
identify the entries and relevant
important to study since it may relate to disease progression. A
entries between TL and FL.
more comprehensive model will include a dissecting aneurysm
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between FL and TL can help to
with intimal flap motion and compliance of aorta with realistic boundary condition from MRI-derived with and catheter-based pressure measurement. It should give more realistic flow pattern to predict the dissection progression. There is not direct approach to validate the blood flow in dissection due to the complex
geometry
which
should
combination of 4D MRI and CFD.
be
addressed
with
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n=196
Other sources (Ovid, Cochrane, and Scopus) n=520
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Records after duplicates removed (n=358)
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Pubmed (from 2001)
Full text articles excluded with reasons (n=216)
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Records screened by title and abstract (n=352)
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Figure 1: PRISMA Flowchart of Systematic Search Strategy
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Early diastole
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(c)
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(b)
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Figure 2 Velocity streamlines in the (a) healthy, (b) aneurysm before treatment, and
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(c) aneurysm after stent graft implantation at early diastole in the cardiac cycle20
S0890-5096(19)30487-X
DOI:
https://doi.org/10.1016/j.avsg.2019.04.032
Reference:
AVSG 4465
To appear in:
Annals of Vascular Surgery
Received Date: 29 December 2018 Revised Date:
9 March 2019
Accepted Date: 18 April 2019
Please cite this article as: Ong CW, Wee I, Syn N, Ng S, Leo HL, Richards AM, Choong AM, Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review, Annals of Vascular Surgery (2019), doi: https://doi.org/10.1016/ j.avsg.2019.04.032. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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38 39
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Chi Wei Ong1,2 Ian Wee2,3 Nicolas Syn2,3 Sheryl Ng2,4 Hwa Liang Leo1 Arthur Mark Richards4,5,6,7 Andrew MTL Choong2,4,8,9
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Department of Biomedical Engineering, National University of Singapore, Singapore SingVaSC, Singapore Vascular Surgical Collaborative, Singapore 3 Yong Loo Lin School of Medicine, National University of Singapore, Singapore 4 Cardiovascular Research Institute, National University of Singapore, Singapore 5 Department of Cardiology, National University Heart Centre, Singapore 6 Christchurch Heart Institute, University of Otago, Christchurch, New Zealand 7 Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 8 Department of Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 9 Division of Vascular Surgery, National University Heart Centre, Singapore 2
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Corresponding Author Assistant Professor Andrew MTL Choong MBBS, FRCS (Gen Surg), FEBVS (Hons), MFSTEd, FAMS (General Surgery) Consultant Vascular, Endovascular and Aortic Surgeon Division of Vascular and Endovascular Surgery National University Heart Centre, Singapore Address: Level 9, NUHS Tower Block, 1E Kent Ridge Road, Singapore 119228
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Computational Fluid Dynamics Modelling of Hemodynamic Parameters in the Human Diseased Aorta – A Systematic Review
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Telephone: Fax: Email:
+65 67736512 +65 67766475 [email protected]
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Abstract
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Background:
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The analysis of the correlation between blood flow and aortic pathology through
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Computational Fluid Dynamics (CFD) shows promise in predicting disease progression,
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the effect of operative intervention and guiding patient treatment. However, to date, there
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has not been a comprehensive systematic review of the published literature describing
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CFD in aortic diseases and their treatment.
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Methods
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This review includes 136 published articles which have investigated the application of
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CFD in all types of aortic disease (aneurysms, dissections and coarctation). We took into
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account case studies of both, treated or untreated pathology, investigated with CFD. We
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also graded all studies using an author-defined GRADE approach based on the validation
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method used for the CFD results.
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Results
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There are no randomised controlled trials assessing the efficacy of computation fluid
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dynamics as applied to aortic pathology, treated or untreated. Whilst a large number of
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observational studies are available, those using clinical imaging tools as independent
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validation of the calculated CFD results, exist in far smaller numbers. Only 21% of all
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studies used clinical imaging as a tool to validate the CFD results and these were graded
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as high qualities studies.
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Conclusion
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Contemporary evidence shows that computational fluid dynamics can provide additional
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hemodynamic parameters such as wall shear stress, vorticity, disturbed laminar flow and
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recirculation regions in untreated and treated aortic disease. These have the potential to
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predict the progression of aortic disease, the effect of operative intervention and
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ultimately help guide the choice and timing of treatment to the benefit of patients and
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clinicians alike.
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Keywords: computational fluid dynamics, CFD, aneurysm, aorta, dissection, stent,
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EVAR, TEVAR, coarctation
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1. Introduction
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Aortic disease represents a subset of a much broader spectrum of arterial disease,
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comprising of aortic aneurysms; aortic dissections; intramural haematomata; penetrating
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atherosclerotic ulcers; blunt traumatic aortic injuries; pseudoaneurysms; aortic ruptures
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and associated inflammatory diseases1. Epidemiological trends have been disappointingly
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poor, with a 12% increase of annual death rate due to aortic aneurysm (2.8/100,000(>20
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million)) in the past twenty years2. Despite significant improvements in peri-operative
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care, surgical technique and the maturity of the endovascular therapy of aortic aneurysms,
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challenges in limiting aortic aneurysm growth and rupture persist3, 4.
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Although computed tomography (CT) aortography is widely considered to be the gold
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standard for delineating aortic pathologies, given the geometrical and functional
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complexities of the aorta, a multi-modal approach to imaging (computed tomography,
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chest x-ray, magnetic resonance imaging, ultrasound, echocardiography) is sometimes
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required for optimal aortic disease management1. Whilst we know that additional
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anatomical predictors such as aortic size, luminal size and patency have value in the
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assessment of the progression of aortic disease, recent research suggests that intra-aortic
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hemodynamics indices may also be an independent predictor of patient outcome. CT
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aortography is currently limited by only being capable of capturing a snapshot of the
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blood flow at a singular points in time. In time, increased use and uptake of 4D magnetic
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resonance imaging (MRI) may improve our understanding of the inherent dynamicity of
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aortic blood flow, but CFD has the ability to model such intra-aortic hemodynamic
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indices, based on current CT aortographic images, now.
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CFD has emerged in recent years as a complementary tool to ameliorate our
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understanding on the biomechanical behavior of blood flow in both normal and diseased
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vessels. It is essentially a branch of engineering that studies fluid flow and associated
101
phenomena using computer-based simulation. One of the earliest applications came from
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the Massachusetts Institute of Technology in the 1950s, where they used computer
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simulation to solve numerical equations related to supersonic flow over sharp cones5.
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Since then, several studies6-15 have attempted to analyze blood flow in diseased aorta
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using CFD, including flow patterns in aortic aneurysm12, 15, aortic dissections7, 14, 16, 17,
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and changes pre- and post-endovascular aortic repair (EVAR)8.
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Significant technological advances in computing power and a concomitant cost reduction
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in the equipment necessary for supercomputing, have made it possible to analyze, in
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detail, the complex hemodynamics of blood vessels in the human body. The
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"computational" of CFD describes the use of computing resources to solve a set of
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mathematical equations, namely the Navier-Stokes equation which delineate the motion
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of blood. Representation of realistic blood flow and pressure waveforms can be achieved
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using properly framed model parameters to investigate the rate of change of blood
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velocity in relation to the pressure and density, as well as the different stresses and forces
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that are driving blood flow. The terms "fluid dynamics" in CFD can describe both
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moving blood (dynamic) and blood at rest (static). However, modern CFD studies tends
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to espouse the “dynamic” definition as it is a more accurate depiction of the body’s
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normal physiology 18, 19.
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Several computational software packages such as ANSYS FLUENT20, Open Foam21,
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SIMVascular22, ADINA23 and in-house coding24 can all be employed to execute CFD
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models, by calculating a few fundamental parameters such as wall shear stress (WSS) and
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vorticity for fluid behavior quantification. Wall shear stress is an important indicator for
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aneurysm rupture, thrombus formation and prediction of disease progress. It is included
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in all the CFD models to make the computational models clinically relevant. A useful
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glossary table of commonly used terms can be found in Table 1. The purpose of this
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systematic review is to provide a comprehensive overview from an assemblage of current
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literature available on the use of CFD in the assessment of both the normal human
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healthy aorta, the diseased aorta as well as the endovascularly treated aorta. This rigorous
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review of the literature will also help to delineate the clinical validity, and the application
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of, CFD simulations in predicting the progression of diseased aortas.
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2. Material and Methods
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The review protocol is registered at PROSPERO (registration number CRD42017070449;
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http://www.crd.york.ac.uk/prospero/).
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2.1 Search strategy
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This systematic review was conducted in accordance to the Preferred Reporting Items for
141
Systematic Reviews and Meta-Analyses (PRISMA) checklist25, and in line with The
142
Cochrane Library recommendations26. A comprehensive electronic search was performed
143
in four electronic databases (Pubmed, Ovid, Cochrane, and Scopus) from inception to 4th
144
September, 2017 to identify all articles describing the application of CFD in the human
145
aorta, with language restriction to English and Chinese articles. Chinese articles were
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translated by a native Chinese speaker (OCW) and the data was extracted by two
147
independent reviewers (OCW and AC). A repetitive and exhaustive search was
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conducted using a combination of these search terms: 'computational', ‘fluid’, ‘dynamics’
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and 'human aorta’.
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2.3 Inclusion and exclusion selection criteria
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Studies that reported the use of CFD in the analysis of hemodynamic parameters and
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factors contributing to aortic disease progression, aortic repair, and/or replacement, pre-
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/post-treatment comparisons with endovascular stent graft implantations were included.
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Studies evaluating idealized geometry were included, only if the analysis demonstrated
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meaningful results that could potentially contribute to the understanding of disease
157
progression.
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Studies that solely focused on medical imaging rather than evaluating the impact of flow
160
patterns in the human aorta were excluded. Studies presenting aortic flow patterns using
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newly developed numerical methods, but not new findings in human aortic flow patterns,
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were excluded. Studies applying a newly developed algorithm for aortic flow patterns,
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without validation, were also excluded. For studies that only took into consideration, wall
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strength measurements in vitro, without taking into account, fluid pressures or only finite
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elements of wall material stress-strain relationships, were also excluded.
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With regards to studies focusing on aortic intervention, we defined this as open or
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endovascular surgery of the aorta, not involving the aortic valve or coronary arteries,
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distal to the sino-tubular junction down to the iliac bifurcation. Therefore, coronary
170
artery-related
171
cardiopulmonary bypass or studies evaluating the effect of an external device such as a
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left ventricular assist device were excluded. Studies reporting cell factors that contributed
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to the growth of endothelium cells in the microscale, mass transport models and those
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involving the glucose level which facilitates the nutrient change in aorta were similarly
175
excluded. The eligibility of studies was independently assessed by two independent
176
reviewers (OCW, LHL) and disagreements were resolved by consensus or appeal to a
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third author (AC).
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surgical
operations
such
as
the
FORTAN
procedure,
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2.4 Validation and Quality Assessment of Studies
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The quality of the overall body of evidence was appraised using an author-modified and
181
defined version of the Grading of Recommendations Assessment, Development and
182
Evaluation (GRADE) system27, which originally considers five main domains: statistical
183
heterogeneity; publication bias; risk of bias; indirectness; and statistical imprecision. The
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overall confidence in the reliability of the pooled data is then rated from ‘very low’, ‘low’,
185
‘moderate’, to ‘high’.
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4D flow MRI is also referred to as time-resolved phase-contrast magnetic resonance
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imaging (PC-MRI). Velocity is encoded along three axes and provides 3D anatomical
189
coverage28. The authors deemed this imaging modality the most accurate validation
190
method of calculated CFD results as it allows a complete evaluation of complex flow
191
patterns and quantification of flow parameters in real time29,
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patient-specific 4D MRI or invasive measurements like direct aortic pressure
193
measurements via a catheter, as their validation methodology, were rated as high quality.
194
For simulation studies that relied on external published MRI results, rather than their own,
195
we rated the quality of these studies as "moderate to high".
. Studies that utilised
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We accept that 4D MRI involves high cost which can be prohibitive and thus,
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preliminary results which are able to provide minimum physical validation are often seen
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as acceptable alternative validation methods. Generally, in vitro validation can be divided
200
into idealized or phantom models. Idealized models are drawn out using computer aided
201
design software based on published statistical results. Phantom models can be derived
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from idealised models or patient-specific images. Phantom models are fabricated in
203
polymers like silicone and run in a flow loop employing a pump that generates similar
204
pressures and velocity waveforms similar to human physiology. Next, this fluid flow
205
pattern is captured with the particle image velocimetry (PIV) or particle tracking
206
velocimetry (PTV) allowing evaluation. We rate the quality of those studies validated
207
with in vitro measurement, be it idealised or phantom models, as 'moderate'. The CFD
208
models that only provided claims of biological plausibility, such as the prediction of
209
aneurysm rupture without other validation, are rated 'low' or 'very low'.
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3. Results
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3.1 Study Selection
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The systematic search yielded a total of 716 results. On the basis of title and abstract
215
review, irrelevant publications or those not fitting our inclusion criteria were excluded.
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This left a total of 136 studies that were included in the qualitative analysis for the
217
systematic review. See Figure 1.
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3.2 Overview of Studies
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Studies were categorised by pathology type, organised into treated and untreated
221
subcategories and further subdivided into anatomical categories where appropriate. The
222
studies were also ordered by the author-defined level of evidence and presented in
223
reverse chronological order of publication.
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3.3 Results Summary
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In our summary, we found out that only 21% of CFD studies were rated 'high' given that
227
they provide physical validation of the studied flow patterns via 4D MRI. Many of the
228
reviewed CFD models claim some kind of biological relevance, such as the prediction of
229
aneurysm rupture.
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physical validation, none of them seem to be properly validated with respect to such
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biological claim.
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3.3.1 Aortic Aneurysm
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The 59 included studies (Table 2- Table 5) were published from 2001 to 2017 (with
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patient-specific model and idealized models). Of these, 40 examined the relationship
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between hemodynamic changes and the risk of rupture (including 6 idealized geometry),
238
5 studies compared the risk of thrombus formation between resting and exercise
239
conditions, and 3 studies investigated the relationship between intraluminal thrombus
240
formation14,
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validation whilst only 1 study attempted to model the in-vitro deposition of monocytes33.
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Overall 285 patients (42 males, 16 females, the others unknown) were included. The
243
cohort ranged from ages 33 to 79.9 years old. Most studies looked at patient CT images
244
to reconstruct aortic geometry, with only a handful utilising MRI. The biggest pre-
245
treatment aneurysm size reported was 7.0cm, but few studies reported post-treatment
246
aneurysm parameters. Only one study reported the cross-sectional area and volume of
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aneurysm but did not report aneurysm diameter34. In terms of aortic wall conditions, ten
and risk of aortic rupture. Four studies conducted in vitro CFD
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studies performed fluid-structure interaction (FSI) with a uniform wall thickness of 2 mm
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outside the AAA, while the remaining studies assumed a rigid wall in the CFD simulation
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studies.
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Six studies, comprising 105 patients, focussed on CFD modeling on untreated thoracic
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aortic aneurysms (TAA) geometry as shown in Table 2. The most recent study conducted
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by Callaghan et al combined the modalities of 4D MRI and CFD to study aortic flow
255
patterns35. Tan et al. demontrated that both a numerical model with fluid structure
256
interaction and turbulence model provided realistic flow patterns in a TAA associated
257
with previous coarctation of the aorta, which could be further validated by MRI36. This
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was consistent with what Callaghan et al described in his study, where the TAA led to the
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formation of a vortex distal to the aortic branches, which was further validated by CFD
260
analysis. A similar phenomenan was also reported by Hu et al37, albeit without CFD
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validation.
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Fourty four studies comprising of 145 patients evaluated untreated infrarenal abdominal
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aortic aneurysms (IRAAA) (Table 3). Whilst the majority of studies evaluated IRAAAs
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with a defined maximum diameter size of <5.5 cm, 6 studies included aneurysms which
266
were larger than 5.5 cm. Four studies benchmarked their findings with the observation
267
from clinical studies, for which, we graded the quality of evidence as high. Only one
268
presented cases, compared their results with an idealized phantom model e.g. a straight
269
tube in PC MRI which they used to validate their numerical model29. Three cases30-32
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employed the PIV and PTV methods to validate flow patterns in the patient-specific
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phantom model. The authors observed a strong recirculation region in the aneurysm sac,
272
which they hypothesized may increase the risk of intraluminal thrombus formation. The
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majority of the remaining studies looked at the hemodynamics changes in AAA, with and
274
without the wall of the aneurysm, to predict the potential of rupture, through qualitative
275
and qualitative comparison of biomechanical parameters such as disturbed flow pattern,
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vortex formation, WSS and mechanical stress in various conditions and individual
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patient-specific geometry.
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Seven studies comprising 23 patients conducted a CFD analysis of TAAs that have
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undergone repair (Table 4). The majority of TAAs with a stent-graft repair demonstrated
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marked improvements in blood flow pattern . Midulla et al. showed an improvement in
282
hemodynamic flow patterns after stent graft implantation38. Lei et al.39 proposed to
283
combine WSS, luminal surface LDL concentration, and oxygen flux parameters to
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optimise the assessemnt of stent graft efficacy. The use of overlapping stent grafts has
285
been shown to be effective in isolating the TAA, resulting in decreased WSS and risk of
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rupture. Filipovic et al. demonstrated an increased shear stress distribution in the
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aneurysm site post-surgery, the clinical signficance of which is uncertain but may
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predispose to increased risk of aneurysm rupture24. Two studies evaluated the
289
hemodynamic changes in TAAs that were repaired with a chimney stent graft, and
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identified regions of stagnated flow and WSS alterations that could predispose to
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thrombotic events. It appears from CFD analysis that wall shear stress distribution is
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higher in the aneurysm post-repair, which may promote vascular reconstruction and
293
endothelium remodelling. However, these findings must be interpreted with caution,
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since WSS threshold varies amongst studies and hence requires further experimental
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validation with MRI results. Future studies should consider implementing a more
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comprehensive and detailed measurement of flow patterns by combining various
297
modalities such as both CFD and MRI.
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Only two studies analysed treated IRAAA with CFD modelling (Table 5), by comparing
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flow pattern parameters in pre and post treatment. Their findings identified an
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improvement of flow pattern, as evident from reductions of wall pressure, WSS, and an
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improvement in the degree of smoothness of the blood flow, hence reducing the risk of
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thrombosis formation.
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3.3.2 Aortic Dissection
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The degree of complexity in the geometry of dissections limits the potential combination
308
of MRI and CFD for validation purposes. Consequently, the overall quality of evidence is
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poorer compared to those studies evaluating aortic coarctation. Only three studies
310
demonstrated a high quality of evidence with MRI flow patterns used for comparison and
311
only one study compared their CFD results with MRI flow patterns from other groups.
312
Two studies provide in vitro validation with CFD results but these are mostly are in
313
idealized geometry which undermines the value of validation. 17 studies are rated as
314
“moderate low” with two studies rated low since their CFD data is presented without
315
validation. Three studies used idealized geometry while the rest used Type-B aortic
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dissection (TB-AD) geometry.
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Twenty studies comprising of a total of 75 patients evaluated the changes in flow
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patterns in patients with untreated type B aortic dissection as shown in Table 6. Only two
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studies validated their results with PC-MRI flow to look at the residual dissection flap
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following occlusion of the entry tear. Two cases presented in vitro validation using
322
idealized models and validated their CFD results using a phantom model. Both cases
323
demonstrated that tear size can result in haemodynamic changes.
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Four studies (Table 7) comprising of 10 patients evaluated type B aortic dissections that
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were treated endovascularly.1 case looked at the differences in the pre and post treatment
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haemodynamic flow patterns. The other 3 cases reported significant improvements in
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hemodynamic pattern, hence reducing the risk of thrombus formation.
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3.3.3 Coarctation
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As would be expected from the pathology of aortic coarctation, almost all the CFD
332
studies done, were performed on younger (<30 years old) patients with only three patients
333
more than 30 years old as shown in Table 8 and Table 9. Fifteen studies reported using
334
CFD to studying hemodynamic changes in coarctation, before and after treatments. One
335
study evaluated the hemodynamic alterations of a CoA with a concomitant bicuspid
336
aortic valve. A more comprehensive study published on congenital heart diseases by
337
LaDisa et al examined the hemodynamic changes in postoperative age and gender-
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matched CoA, treated by resection with end-to-end anastomosis (RWEA) through WSS40.
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More than half (76%) studies utilised invasive catheter measurement results as validation,
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hence the overall quality of evidence is deemed to be good. There are only 3 studies that
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combined MRI and CFD studies in CoA, which reinforced the point that MRI-based CFD
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studies can provide more information on flow patterns compared to other imaging
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modalities.
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We found 2 studies presenting data on untreated CoA patients, with validation from in
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vivo studies. The changes in hemodynamic flow patterns are validated via intra-aortic
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catheter pressure measurements, pre- and post CoA, demonstrating the pressure gradient.
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Table 9 shows 16 studies which present the CFD modelling of hemodynamic changes for
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treated CoA. 5 studies showed an improvement in the pressure gradient, as expected, in
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the treated CoA population. For the rest of studies, a reduction of pressure difference
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before and after the coarctation site demonstrated the effectiveness of CoA treatment.
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Stent grafts consist of an expandable wire (usually nitinol - nickel-titanium alloy) mesh
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covered with fabric (usually Dacron, a polymer, polyethylene terephthalate) forming a
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tube when expanded. They isolate the diseased aortic aneurysmal sac from the circulation
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by preventing blood flow into the aneurysm. The alteration of blood flow after stent graft
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implantation can be represented by common parameters like velocity, pressure, WSS,
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OSI and TAWSS. Eight studies evaluated external forces acting on the stent graft that
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could account for migration, by calculating the displacement force and drag force from
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the blood pressure and shear stress. Only one study investigated the oxygen flux and low-
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density lipoprotein concentration before and after stent graft implantation. Five high-
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quality studies compared the simulation with migration results in patient specific imaging
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during follow-up. Two studies were classified as low quality as they did not have any
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form of validation from either the published literature or in vivo/in vitro evidence. In
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seven FSI studies involving blood-aortic wall interactions, the stent wall is assumed to be
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rigid without any movement. Only one study considered the stent graft as linear elastic
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material (Young modulus) and validated it using particle image velocimetry (PIV)41. One
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study examined the forces acting on stent grafts used for treating type B aortic dissection
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and compared velocities, before and after treatment in thoracic aortic aneurysms (TAA).
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Only 9 studies focussed on the treatment of TAAs by comparing the hemodynamic
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differences and forces acting on the stent graft.
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3.3.4 Characteristics of Stent Grafts
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In Table 10 and Table 11, we present studies that investigate the behavior of stent grafts
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by estimating the displacement forces exerted on the stent grafts based on hemodynamic
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flow patterns, before and after their use. The design and positioning of the stent graft are
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paramount to understanding aortic remodeling and changes in hemodynamic patterns.
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Common parameters used to evaluate the performance of stent graft include drag force
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and displacement force exerted on the stent graft, which can be extrapolated to evaluate
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the risk of stent graft migration.
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4. Discussion
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From an assemblage of the latest evidence available, this systematic review has attempted
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to evaluate the clinical validity and use of computational flow dynamic (CFD) studies in
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evaluating the progression of diseased aortas, both treated and untreated.
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This review demonstrates favorable evidence that supports the use of CFD in analyzing
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hemodynamic changes, important factors potentially affecting disease progression.
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Experimental studies have postulated that hemodynamic parameters such as wall shear
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stress (WSS) can change the behavior of endothelial cells, consequently affecting
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aneurysmal degeneration42. Besides WSS, conventional alteration of hemodynamics often
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refers to the change of flow pattern and pressure gradient. WSS in particular has been
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used to form different indexes, such as oscillatory shear index (OSI) and rupture index to
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estimate the risk of rupture, apart from measuring the conventional maximum diameter of
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an aneurysm. Although maximum aneurysm diameter and growth rate are important risk
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factors for surgical intervention decision making, the association is actually less
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straightforward. A small aneurysm can rupture and vice versa, and treatment is ultimately
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down to patient choice.43. If all CFD-derived hemodynamic indexes can be combined
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with advanced imaging modalities, we may be able to better predict potential risk of
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harmful aortic disease progression and therefore provide more accurate aortic
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intervention.
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In addition, as discussed in Moris et al44, WSS is also correlated to endothelial
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homeostasis, inhibiting unnecessary endothelial cell activation and triggering adverse
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vessel remodeling. To accentuate the relationship between biomechnical parameters and
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disease state, TAWSS, OSI, RRT and other WSS-related metrics have also been linked to
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thrombus and platelet formation. Recently Azani et al45 and O Rourke et al showed that
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regions of low OSI correlated with growth of intraluminal thrombus in AAA. However,
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high OSI(>0.4) and low TAWSS (<1 dyn/cm2) did not appear to coincide with locations
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of thrombus deposition46. Tan et al36 showed that low TAWSS and high OSI can be
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attributed to flow recirculation and consequent enlargement of an aneurysm. The
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aneurysm formation index (AFI) and gradient oscillatory index were proposed by Poelma
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et al47, who then hypothesised that such metrics can identify regions prone to disease
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formation, but nonetheless requires further validation.
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Furthermore, fluid structure interaction studies (FSI) allow us to assume different vessel
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wall models (i.e. deformed wall model and rigid wall model), which enables us to draw
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accurate and realistic associations between wall strength, wall stress and aortic wall
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remodeling. The wall strength information can be useful in assessing risk of rupture once
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the flow pattern is validated with medical imaging modalities. Although most studies did
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not provide follow-up outcome data to validate the occurrence of aneurysmal rupture, we
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acknowledge that the maximum diameter of an aorta may still be one of the important
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factors in deciding surgical intervention. Hence, this warrants further research to be
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conducted with large enough sample sizes in order to form a comprehensive risk
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assessment model for aneurysmal rupture.
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A systematic review of TB-AD conducted by Sun & Chaichana48 showed various
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hemodynamic changes between the false lumen (FL) and true lumen (TL). They
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demonstrated that high WSS and TAWSS was consistently associated with the reentry
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site and the edge of the tear. By analysing pre- and post-EVAR hemodynamics changes
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in TB-AD, the authors also concluded that decreased wall shear stress was associated
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with improved flow pattern post-EVAR. With the existence of the FL, OSI is always high
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due to the unsteady flow pattern cause turbulence. TAWSS and WSS will only decrease
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following FL dilatation since flow tends to be lower. The pressure in TL was reduced
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with pressure in FL elevated given that the number of reentry tears was increased.
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Findings from this review suggest that only a few dissection models have proper
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validation from MRI images which demonstrate localized hemodynamic changes. The
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difficulty comes from the dynamic motion of the intimal flap and tear locations, both of
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which causing ever changing hemodynamic parameters. Although these can be conducted
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with CFD studies, it remains a challenge to validate it in vivo and in vitro settings given
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the limitation of current imaging modalities to analyse aortic blood flow.
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445
Unfortunately, evidence for the prediction of the effect of stent grafts for aortic dissection
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are still lacking. Since all the simulations were performed on completely remodeled FLs,
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it is impossible to study association between FL progression and hemodynamic factors.
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Yu et al49 showed that morphological features can significantly affect pressure and
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velocity.
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Differential impact of local stiffening and narrowing on hemodynamic in repaired CoA
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using computational modelling has been conducted50. Results showed that vessel
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obstruction can introduce the buffering of stroke volume proximal to aortic narrowing.
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An enlarged pressure drop in repaired CoA can be explained through the conversion of
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kinetic energy into pressure with the viscous losses. Furthermore, the extent of stenosis
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depends on both pressure drop and flow rate. Ralovich et al showed that pressure drop
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across the coarctation can be accurately predicted in CFD after validation with MRI
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measurement51. This potentially provides for a noninvasive measurement rather than
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invasive measurement like catheter measurement reduce complications. Ladisa et al
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showed that low TAWSS and OSI was measured in the doA of COA treated by RWEA,
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suggesting that plaque formation may be influenced by surgical repair40. Kwon et al52
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showed that TAWSS measurements in a stented CoA can be significantly different along
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the posterior dAo, and with different stent types. This may assist in proper selection of
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stents for different types of patients. Goubergrits et al.
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can potently improve clinical treatment of CoA with 15 patients. They showed that a
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slight reduction of post-treatment pressure can decrease WSS in the stenotic segment,
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hence reducing the chance of stenosis. Based on these findings, CFD serves as an
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alternative , noninvasive tool to improve clinical diagnosis.
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showed that MRI-based CFD
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Despite the advent of endovascular treatments such as stent-graft implantations, it should
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not be a one-size-fits-all approach. To address this limitation, virtual implantation can
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assist in determining whether a stent graft is suitable for a patient based on unique
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anatomical features.
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modalities, coupled with flow waveform measurements derived from the MRI, it is
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possible to examine the impact of stent grafts on hemodynamics outcomes before any
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implantation. Given the invasive nature of open surgeries, an accurate noninvasive
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By reconstructing patient-specific geometry from imaging
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assessment of stent graft suitability would not only eliminate this drawback but also help
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lower the overall treatment cost.
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Midulla et al observed an increase of WSS in the inner wall of descending aortic
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aneurysm (doA) corresponding to an infold of the stent graft tissue38. Frauenfelder et al41
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found a reduction of wall pressure and WSS and turbulence after implantation, consistent
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with results published by Li and Kleinstreuer54. This may help to reduce complications
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like thrombosis and stent migration. Van Bogerjien et al showed that the bird-beak
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configuration post-thoracic endovascular aortic repair (TEVAR) can reduce flow
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disturbances in TAA despite significant hemodynamic turbulence in the distal descending
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aorta that could be attributed to dissection55. Rinourdo et al56 showed that the protrusion
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extension (PE) of endograft can be linked to marked intramural stress and principal strain
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distribution on the protruded segment of endograft depending on the length of endograft
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PE. Besides WSS, Lei et al39 showed that luminal surface concentration of lipoprotein
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(LDL) and oxygen flux on the wall can affect the stent graft performance in virtual
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implantations. The LDL concentration is calculated based on convective diffusion
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equation for the plasma while the oxygen flux is evaluated using the Sherwood number
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based on diffusivity and mass transfer coefficient. Overlapping bare-metal stents may
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reduce WSS and pressure to protect aneurysms from rupture57.
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The magnitude of load under the influence of hemodynamic factors like WSS is
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important to evaluate and estimate device migration. These loads can be referred to as
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displacement forces, migration forces or drag forces. Figueroa et al showed that increased
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curvature of the aortic graft changes the flow patterns, which may increases the risk of
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stent graft migration in vivo58. Pasta et al
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angle and extension can lead to an increase of transmural pressure across the stent graft
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wall leading to stent graft collapse. Gallo et al showed that low TAWSS and high OSI
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were associated with bird-beak configuration in TAA whilst low OSI suggests the risk of
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thrombus60. Complications like stenosis in the descending aorta still present with low
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TAWSS, hence suggesting that secondary complications may still occur after TEVAR. In
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addition, studies61, 62 showed that displacement forces exerted on stent grafts are sensitive
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to neck angle and positions that the stent graft can adapt to . Evaluation of the renal
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arteries’ flow dynamics could detect misalignment of the renal stent graft and potential
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sites for thrombus formation or stenosis. Jones et al63 showed that distraction forces
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related to morphological features of at the aortoiliac vessel generated by blood pressure
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and viscous force acting against fixation force can encourage stent graft migration. As
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such, an alternative choice of seal zone or even device can be developed based on CFD
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results to reduce the risk of migration.
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further showed that increase of stent graft
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To the authors’ knowledge, this is the first systematic review to assess the application of
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CFD on the human aorta, treated and untreated as well as the clinical relevance of such
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studies. The assemblage of evidence in this systematic review demonstrates the effective
520
use of CFD in studying a wide array of aortic pathologies. A concomitant large
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population screening study would be the most robust method of assessing the usefulness
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of CFD in the diseased aorta. However, such a study confers high cost, would take a long
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time due to technical limitations, and require many years of follow-up. Nonetheless, we
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acknowledge the importance and usefulness of CFD simulations as an adjunct to the
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armamentarium of currently available tools.
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4.1 Limitations
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Whilst we believe this comprehensive review to be the first of its kind, examining all
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CFD studies looking at human aortic disease, treated and untreated, in the published
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literature covering both engineering and medical disciplines, we found out that only 596
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patients are studied in 136 studies. Out of 136 studies, only 29 are rated as high quality
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which is only approximate 21% of all the studies (representing 270 patients).
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None of the studies had a high clinical impact and additionally, the risk of publication
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bias is high in this new area. The collected literature are too heterogeneous to perform
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meta-analysis. It is worth highlighting that there is no universal threshold of WSS to
537
indicate disease progression, given that most models are different in geometry. The use of
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both the Newtonian and non-Newtonian model in the studied simulations make the
539
literature even more heterogeneous, hence we do not include the deviation between them
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in this systematic review. The risk of rupture of aneurysm or mortality are not directly
541
confirmed with clinical end points and many studies also only compare their findings
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with previously reported literature making their claims weaker. Thus, overall the clinical
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value of reported studies is relatively low, with heterogeneity and bias high, and this must
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be considered in the analysis of these simulated results.
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5. Conclusion
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The benchmarks for computational fluid dynamics results differ widely in the literature.
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As such, the utility of CFD to guide decision making for the treatment of aortic disease,
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remains experimental for now. To date, high quality of evidence to support its use
550
remains sparse, but consistent results of the analysis of the hemodynamic changes in the
551
course of aortic disease, pre- and post-treatment are encouraging. This review has
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highlighted key areas for the development of CFD research as applied to aortic disease.
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Ultimately, by combining all the different numerical CFD parameters available, with
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proper and consistent validation, it may be possible to create a highly accurate patient-
555
specific aortic disease progression and or prediction model. This could revolutionise
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aortic treatment decisions including who, when and how aortic patients should be
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intervened upon.
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6. Acknowledgement
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The author would like to thanks Mr. Julian Siew Tze Kang for assisting in correcting the
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reference for the current manuscript.
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7. Disclosure Statement
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None
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Table 1 Glossary Summary of Common Terminology in Computational Fluid Dynamics
Mathematical Modeling Term
Definition/ Explanation
A branch of fluid mechanics that solves complex fluid behavior, as described by the
(CFD)
Navier-Stoke equation, using computational algorithms
Fluid-structure interaction
Similar to CFD but includes the deformation of adjacent solid material when
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SC
Computational fluid dynamics
analyzing fluid behavior. It can be used for evaluating the change in fluid behavior due to wall motion and properties
A variable represent the gradient of velocity in the flowing fluid
Wall Shear stress
Normal velocity gradient at the wall multiplied by dynamic viscosity. It is used to
TE D
Shear rate
(WSS)
express the force exerted on the wall by the fluid passing through it.
Vortex
A whirling fluid which rotates either clockwise or counterclockwise
Vorticity
A vector (a variable that has magnitude and direction) describing the tendency of the
AC C
Reynolds number
EP
fluid particle to rotate or circulate at a particular point.
Dimensionless quantity that is used to classify different fluid flow patterns
Viscosity
A measure of a fluid resistance to gradual deformation caused by shear stress
Newtonian vs Non-Newtonian
The viscosity of fluid is independent of shear rate is defined as Newtonian fluid, for non-Newtonian fluid, the viscosity change is dependent of shear rate
Deformation
Deformation can be defined as relative movement with respect to another point on the same body
ACCEPTED MANUSCRIPT
Wall strength
The ability of aortic wall material to resist deformation under an applied load without failure
Internal forces within a solid material that balance and react to the fluid pressure applied to it
RI PT
Wall stress
Relative deformation or change in a solid wall
Elasticity vs hyperelasticity
Elasticity refers to a linear relationship between stress and strain. While hyperelastic
SC
Wall strain
material has a nonlinear relationship between stress and strain
M AN U
WSS-Derived Parameters
Wall shear stress gradient
The difference of shear stress between two close locations at the same time point
(WSSG)
The difference of shear stress between two time points over a small period of time at
(TAWSS)
the same location
TE D
Time-averaged wall shear stress
Oscillatory shear index
Temporal oscillation of WSS during a period of time. It is calculated as a dimensionless metric of changes in the WSS direction13
(OSI)
(RRT)
The time of residence of fluid particle stay in particular location. This metric is
AC C
Rupture potential index (RPI)
inversely proportional to the magnitude of the TAWSS vector(OSI)13
EP
Relative residence time
Ratio of local wall stress to local wall strength
ACCEPTED MANUSCRIPT
Table 2: Untreated Thoracic Aortic Aneurysms
n
Age
M:F
CFD
(Years)
/FSI
74 ±6.9
CFD
Pathology
Size of
Parameters
aneurys
Quality of Evidence
m 100
Thoracic and Cardiovascular Surgery,2017
8
64
aortic
-
v, WSS, OSI
aneurysm
healthy: 70±6.9 and 40±9.9
Nauta, The Annals of
74
M
CFD
TAA
-
Platelet Activation
65
Callaghan, Callaghan,
1
47
M
CFD
TAA
Biomed Engin,2015 35 1
1
-
-
-
-
FSI
TAA with
-
CFD
Investigate hemodynamics change in
Saccular arch aneurysm dilate without much elongation
the saccular and fusiform aortic
compared with fusiform. The low WSS in inner
aneurysm and their relationship with
curvature of saccular arch aneurysm may cause the
WSS and OSI.
aneurysm act malignantly.
compare hemodynamic flow pattern
High platelet activation potential was found correlated
on 3 virtual surgical repair (1) open
with aortic thrombus. Aortic repair resolved pathologic
surgical repair, (2) conformable
flow patterns, reducing PLAP. Branched endografting
endografting, and (3) single-branched
also relieved complex flow patterns reducing PLAP.
endografting High
Vortex found after aortic branches in the aneurysm and
4D MRI for the understanding of
low wall WSS was found at the aneurysm wall which
aneurysm development and risk
may cause wall remodeling
to examine the hemodynamic
Vortex and regions of low WSS was identified in the
behviour in a thoracic aortic
aneurysm which can help to predict the aneurysm
repair
Mises stress,
aneurysm and compared with MRI
rupture.
CoA
repair
-
High
compare the flow field in CFD and
TAWSS, OSI, von
TAA with
v, wall displacement,
Clinical relevance
CoA
AC C
Tan, Comput Struct,200936
66
v, WSS, vorticity
EP
Comput Methods Biomech
Tan, Int J Appl Mech,2009
High
Potential (PLAP)
TE D
Thoracic Surgery,2017
1
High
M AN U
Natsume, The Journal of
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(6 studies representing 105 patients with an untreated TAA)
turbulence intensity V, WSS, OSI turbulence intensity
results High
examine hemodynamic change in
The correlation-based transitional model was found to
TAA using transitional model
produce results in closer agreement with the MR data than the laminar flow simulation where a vortex found
ACCEPTED MANUSCRIPT
Hu, X. Z., National Medical
1
33
M
CFD
TAA
-
v. P, WSS
Journal of China,201137
moderate-
To investigate growth and rupture
Large vortex found at the aneurysm the growth and
low
mechanism of TAA
rupture mechanisms of TAA may be analyzed based on
RI PT
a constructed patient specific model and hemodynamic simulation.
TAA=Thoracic Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; Platelet Activation Potential (PLAP); OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational
AC C
EP
TE D
M AN U
SC
Fluid Dynamics; FSI: Fluid structure interaction
ACCEPTED MANUSCRIPT
RI PT
Table 3: Untreated Infrarenal Abdominal Aortic Aneurysms
n
Age
M:
CFD
Patholog
Size of
(Years)
F
/FSI
y
aneurys
Parameters
-
CFD
Arzani, Am. J. Physiol. Heart
10
-
-
CFD
Circ. Physiol.,2014 45
Suh, Ann Biomed Eng,2011
69
Les, Ann Biomed Eng,201070
Kung, J Biomech Eng,2011
71
8
10
8
1
70.5±7.8
71.2 ± 7.9
73.3
-
8:0
9:1
7:1
-
CFD
CFD
small
(MRI)
(<5cm)
CFD
CFD
v, P
AAA
small
(MRI)
(<5cm)
distance, t mean exposure
AAA
small
v , PRT
(MRI)
(<5cm)
TAWSS, OSI
AAA(
small
v, MWSS
MRI)
(<5cm)
OSI, PRT
AC C
Suh, Ann Biomed Eng,2011
68
AAA
TE D
-
EP
5
Biomed Eng.,2014 67
AAA
small
v, P, MWSS, OSI,
(MRI)
(<5cm)
TKE, normal stresses
AAA
-
v
(MRI)
Specific study interest using CFD
Clinical relevance
compare the topology of blood
Exercise resulted in higher and more uniform mixing
transport and mixing during rest and
and reduced the overall residence time in all aneurysms
exercise
compared to exercise.
Evidence
m Arzani, Int J Numer Method
Quality of
M AN U
Author, Journal, Year
SC
(44 studies comprising 145 patients with an untreated IRAAA)
High
High
investigate
hemodynamic
change
with ILT progression High
Low OSI(<0.1) and high TAWSS can be related with ILT growth
investigate
hemodynamic
through
MRI
changes
Longer duration of PRT in AAA under resting
CFD
conditions can be used to compared with exercise to
and
examine potential benefits of physical activity High
examine hemodynamic change in
Exercise decrease the PRT, an increase of WSS and a
different exercise condition
decrease OSI in AAA which suggest that mild exercise may reduce flow stasis in AAA
High
investigate hemodynamics in eight
An increase mean WSS and a decrease OSI suggest that
AAAs during rest and exercise
exercise may attenuate AAA growth
moderate-
validate
high
pressure using PC MRI, and an in-
simulated
vitro phantom
velocity
and
-
ACCEPTED MANUSCRIPT
Boyd, J Vasc Surg,201672
7
-
-
CFD
AAA
8.3±
v, P, WSS
moderate
0.91cm
investigated the location of AAA
Rupture occurred in regions of low wall shear stress,
rupture
where flow recirculation and thrombus deposition
computationally
with
a
RI PT
comparison of rupture site showed in
predominated
Computer Tomography Angiography Boyle, CBM, 2014 73
1
75 until
M
CFD
AAA
5.01cm to
78
TAWSS
moderate
7.17cm
investigated a rapidly expanding,
Rupture occurred in the proximal, low TAWSS region
patient-specific AAA from the time
of the AAA where the flow was recirculating
of detection to rupture, over 2.5 years
Chen, J Biomech Eng,2014
2
-
-
CFD
AAA
-
v, WSS
moderate
with ILT 1
-
-
CFD
AAA
5.5cm
v, P, WSS
200974
A longer Particle resident time of recirculating flow in
AAA
aneurysm may trigger platelet activation for ILT
validate flow dynamics results with
-
PTV
O'Rourke, Proc. Inst. Mech.
1
68
F
CFD
AAA
small
Eng. H J. Eng.Med.,200875
v
(<5cm)
Javadzadegan, Eur J Mech B Fluids,2017
moderate
examine hemodynamic changes in
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Boutsianis, J Biomech Eng,
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through CT.
14
-
-
-
CFD
AAA
76
-
-
Lozowy, Cardiovasc Eng
Arzani, J Biomech Eng. 2016
FSI
ted
&CFD
AAA
untrea
CFD
AAA
ted
79
6
CFD
AAA
-
Suprarenal AAA promotes thrombosis initial within
zone, TAWSS, OSI,
ow
of
AAA
3
65:66:70
M
AC C
Manage.,201580
CFD
AAA
1-5cm
aneurysm
on
the
renal
and
increase
the
chance
for endothelial
hemodynamics
dysfunction and atherosclerosis in renal arteries. -
v,WSS,von Mises
moderate-
investigate the impact of FSI and
stress
low
CFD on the flow pattern in AAA
v, WSS, OSI,
moderate-
Investigated pulsatile blood flow
the impingement of blood flow change the recirculation
TAWSS
low
dynamics in patient-specific AAA.
region may prevent ILT deposition and influences the
WSS
(MRI)
Filardi, Vasc. Dis.
observed in the aneurysm site may trigger thrombosis
to investigate the impact of location
EP
Technol,2017
23
78
untrea
Strong P gradient and presence of vortex structure
with CFD results
moderate-
TE D
-
International, 2017 77
compare flow field measured in vitro
v, WSS, recirculation
RT Lin, Biomed Research
moderate
overall aneurysm shape. moderate-
investigate hemodynamic parameter
The correlation between spatial/temporal gradients of
low
in aneurysm
WSs magnitude can be used to predict aneurysm growth.
v, P, WSS
moderate-
to
low
parameters with aneurysm diameter
investigate
hemodynamic
Flow separation streamline regions found on the neck of the aneurysm and there is high WSS found at the aneurysmal wall
ACCEPTED MANUSCRIPT
Hansen,J Biomech Eng,201581
5
-
-
CFD
AAA(MR
3-5cm
I)
time averaged action
moderate-
understand
potential
low
developing ILT in AAA
the
mechanisms
for
v, p
moderate-
examine
WSS
low
before and after aneurysm
wall deformation
moderate-
examine
VMS, p, WSS
low
under realistic AAA with different
exercise condition and resting condition shows similar action potential level but more geometry is needed to
-
-
CFD
Technol.,201582
-
Fusiform
Ene, Proc. Inst. Mech. Eng. H J. Eng. Me,2014
Idealized
1
-
M
FSI
32
AAA
5.76cm
with ILT
hemodynamic
changes
hemodynamic
changes
SC
-
RI PT
investigate it. Vinoth,Int. J. Biomed. Eng.
the laminar flow model is desirable for normal aorta and smaller aneurysm while transitional flow model should be applied on the larger aneurysm models Higher WSS was observed at the distal part and lower WSS at the proximal part of the aneurismal sac
assumptions
Fluid,2014
-
-
-
FSI
83
Chandra, J Biomech Eng,2013
Idealized
6cm
WSS, VMS
model
23
1
73
M
CFD
AAA
moderate low
-
investigate the influence of spiral
The presence of spiral flow within AAAs is associated
flow to the AAA
with beneficial and detrimental effects in terms of
M AN U
Javadzadegan, Eur J Mech B-
change of wall stress and WSS
v, P, WSS
moderate-
examine hemodynamic changes in
High WSS were observed near the inlet and in the
wall stress
low
AAA with different inlet boundary
common iliac arteries. The location of high wall stress
conditions
was found where ILT was absent.
strain
and
one
way
FSI
compared to 2 way.
1
62
-
CFD
AAA
middle-
Biomech. Biomed. Eng.,201384
Soudah, Comput Math Methods
-
M
CFD
AAA
3
-
-
CFD
Part H J. Eng. Med.,201333 68;53;58
2:1
Mech. Eng. Part H J. Eng. Med.,201221 O'Rourke, Proc. Inst. Mech. Eng. H J. Eng. Med.,201286
3
68:53:58
1:2
FSI
CFD
AAA
AAA
downstream to the protuberant apex of the
2.5-4.0cm
v, P, WSS
moderate-
examine
changes
the greater the asymmetry and tortuosity of the AAA,
low
which linked to the main AAA
the higher the possibility of blood recirculation, ILT
geometric parameter
formation, and a possible rupture
model the deposition of monocytes
Peak monocyte residence time was found to increase
-
WSS
+MRI) 3
The regions of high TAWSS appeared upstream and
variation
low
AC C
Kelly & O'Rourke ,Proc Inst.
AAA(CT
investigate hemodynamic parameter
RPI,
85
Hardman,Proc. Inst. Mech. Eng.
moderate-
size
EP
Med.,2013
5
VMS, TAWSS
TE D
Wang, Comput. Methods
4.9-5.2cm
3.6-4.5cm
v , WSS, P
during
the
AAA
development
moderate-
hemodynamic
growing aneurysm.
low
with aneurysm sac size
moderate-
investigate the effect that fluid flow
simulation should include solid stress to predict the
low
has on the stress in an aneurysm wall
maximum stress in an aneurysm wall
v, TAWSS, OSI
moderate-
investigate flow field in AAA under
low OSI (OSI<0.1) is linked to thrombus growth
shear strain rate
low
steady condition
showed the link of biomechanical predictor to thrombus
ACCEPTED MANUSCRIPT
-
-
CFD
AAA
-
v, P,OSI
Shabestari, Biomed. Eng. Appl.
4
55-65
-
CFD
AAA
5.37±1.28
Basis Commun.,201188 Wang, Comput. Biol. Med.,2011
v, P, WSS
cm -
-
-
-
FSI
89
moderate-
examine hemodynamic changes with
shows validation of 2D MRI for comparison of AAA
low
different inlet boundary conditions
hemodynamics
moderate
investigate hemodynamic changes
increase WSS found at the distal and proximal location
low
9
-
-
CFD
AAA
v, WSS
moderate-
study dynamic behaviors of aortic
the correlations between blood viscosity and the
Aneurys
Strain rate
low
aneurysm subject to physiological
dynamic behaviors of aortic aneurysm help to
m
wall axial
blood flow with normal and high
individualize endovascular treatment for patient with
4.35-
Eng,2010 34
99.07cm2 -
-
FSI
Bluestein, Comput Methods
Idealized
-
3
2
-
-
-
-
FSI
FSI
Biomech Biomed Engin.,
AAA
6.2-7.0cm
AAA
4.3-6.5cm
with ILT
200892
-
-
Khanafer, Ann Vasc Surg,200794
-
-
-
CFD+
Idealized
FSI
model
CFD
idealized
-
-
geometry
aortic aneurysm
investigate the impact of blood flow
disturbed flow found right after the neck of aneurysm
low
on thrombus development
that can be linked to platelet activation and adhesion
moderate-
examine
hemodynamic
change
FSI is unnecessary for purely mechanical modelling,
low
between CFD and FSI
wall stress
moderate-
examine
WSS, v
low
between CFD and FSI
moderate-
examine hemodynamic change with
higher WSS on the anterior side of the AAA in the
low
ILT and without ILT
patient with the smallest AAA may affect aneurysm
v, WSS, VMS
with the aim of evaluating the current rupture probability
hemodynamic
change
wall stress and WSS magnitude are influenced by the shape of aneurysm and ILT that may affect the prediction on risk of rupture.
growth. There is reduced stress at the location of ILT compared to aneurysm without the ILT.
v, P, Wall stress
moderate-
examine pressure condition for the
Change of flow field can affect rupture risk of aneurysm
displacement
low
evaluation of AAA wall mechanics
such as change of pressure at the aneurysm site.
v, shear stress,
moderate-
examine
Turbulence induce higher WSS on the aneurysmal wall
relative pressure
low
under rest and exercise
EP
-
Biomech Biomed Eng,200893
AC C
Scotti,Comput Methods
VMS, WSS, v
model
viscosities
moderate -
M AN U
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H.,2009 90
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v, WSS
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Fraser, Proc Inst Mech Eng
of aneurysm
Idealized
displacement Biasetti, Ann Biomed
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Biomed Eng.,2012 87
SC
Hardman, Int J Numer Method
hemodynamic
changes
that maybe responsible for wall dilation and bigger dilation of wall may trigger greater turbulence, possibility
a
self-perpetuating
aneurysmal growth.
mechanism
for
ACCEPTED MANUSCRIPT
Scotti, Biomed Eng
-
-
-
FSI
Online,200595
idealized
-
fusiform
v, P, wall
moderate-
investigate
displacement
low
cause rupture
hemodynamic
change
thickness has higher mechanical stresses under effect of
-
-
-
-
-
FSI
CFD
AAA
-
idealized
-
v, principal wall
moderate
examine hemodynamic change
stress, WSS
low
AAA under FSI
v, P, WSS
fusiform
Venez.,2003
2
-
-
CFD
AAA
5.8-
-
-
-
CFD
Idealized
98
Finol, J Biomech Eng,200399
low v ,P,WSS
6.55cm -
low
v, P,WSS
AAA
Martino, Med Eng Phys , 2001
1
-
-
FSI
AAA
-
v ,P ,s, VMS
1
-
-
CFD
AAA
-
Interface,201547 1
88
-
FSI
AAA
101
Piccinelli, Biomech. Model.Mechanobiology,2013102
-
TAWSS
-
-
CFD
AAA
<5cm,
v, WSS, displacement
distribution in the aneurysm that may change the risk of rupture. larger aneurysms in vivo may be subject to turbulence
lead to aneurysm rupture
than smaller aneurysms may change risk of rupture
examine hemodynamic change in the
vortex are linked to the stress distributions in aneurysm
aneurysm
examine hemodynamic change in the
Maximum WSS at peak flow and appearance of
low
aneurysm
secondary flows in late diastole at the aneurysmal wall
moderate-
investigate
low
cause AAA rupture
low
low
OSI , VMS
10
Vortex and WSS formation may affect the wall stress
moderate-
OSI
are affected by effect of asymmetry hemodynamic
change
Localized interaction of aneurysmal wall and blood flow may affect the thrombus formation and help to determine the aneurysm risk of rupture.
examine
transitional
flow
in
Transitional flow pattern was found in AAA on systolic
aneurysms
phase that may affect thrombus
investigate hemodynamic parameter
the anterior part of the aneurismal wall (2D) was a
to assess rupture risk
potential region of rupture based on the vortex formation displacements
anisotropic displacement of AAA were reported to have
experienced by AAA and correlate
relationship with hemodynamic forces related to the
6.5cm,>6.
them
impingement of the blood on the lumen boundary that
5cm
hemodynamics
5cm-
AC C
Eng.,2014
v, P, Vorticity. TKE,
EP
Veshkina,Bio-Med. Mater.
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100
Poelma,J. R. Soc.
moderate-
AAA with uniform wall thickness
investigate hemodynamic parameters
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Finol, Acta Cient.
moderate-
in
SC
Peattie, J Biomech Eng. 2004
97
1
flow conditions and risk of rupture than a more fusiform
RI PT
VMS, solid stress
Wolters, Med Eng Phys,2005 96
an asymmetric AAA with regional variations in wall
low
investigate
with
the
the
local
bulk
affect ILT.
AAA= Abdominal Aortic Aneurysm; ILT=intraluminal thrombus; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
SC
RI PT
ACCEPTED MANUSCRIPT
Table 4: Treated Thoracic Aortic Aneurysms
n
Age
M:F
(Years) Midulla, Eur Radiol,201238
Lei, J Biomech,2015
39
Zhang,J. Biomech.,2014
20
1
57
-
62.2
-
-
CFD
Pathology
14:6
-
-
CFD
CFD
CFD
TAA
v , WSS
TAA(pre
WSS, LDL
and post-
concentration oxygen
operative)
flux
Idealized
v, P, WSS
stent -
-
CFD
TAA with
v, WSS, OSI
AC C
1
EP
overlapping
Programs Biomed,201124
Quality of
High
moderate-
aortic
low
Ong, Artif Organs
1
-
-
CFD
Clinical relevance
examine hemodynamics change after
increased WSS found along the inner wall of the descending aorta that
TEVAR
may correspond to an in-fold of the stent-graft tissue. There is increase
TAA with
v,p,WSS, TAWSS,
microporou
OSI, RR
s stent graft
WSS at the proximal and distal part of the stent-graft
examine hemodynamic changes pre
WSS, luminal surface LDL concentration, and the oxygen flux on the wall
and post-operative treatment
have to be considered together to evaluate the performance of SG comprehensive.
moderate-
To
hemodynamic
overlapping stents intervention may effectively isolate the TAA ,
low
performance of overlapping bare-
protecting it from rupture. Decrease of WSS found at aneurysm after
metal stents
implantation of overlapping of SG
moderate-
to examine the hemodynamic
CFD results shows that aneurysm site after surgical intervention has
low
parameters before and after aortic
higher shear stress distribution that may promote vascular reconstruction
repair
and benefit endothelium
to examine hemodynamic pattern
improved flow pattern after microporous stent graft restore blood flow in
before and after preferential covered
aneurysm to physiological flow condition(Figure 2).
repair
20
Specific study interest using CFD
Evidence
TAA with
Filipovic, Comput Methods
Parameters
/FSI
TE D
Author, Journal, Year
M AN U
(7 studies comprising 23 patients with a treated TAA)
low
investigate
stent graft
the
ACCEPTED MANUSCRIPT
-
-
-
CFD
Idealized
investigate hemodynamic behaviour
hybrid procedure produce better hemodynamic performances over
aortic arch
v,WSS, Pressure
low
of aortic arch in aneurysm and treated
chimney model although it still has higher risk than surgery graft which is
aneurysm
cased in surgery graft, hybrid stent-
indicated by the WSS level
RI PT
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graft and chimney stent graft. Hila Ben Gur, EuroSim, 2016104
-
-
-
CFD
Idealized
v,WSS
low
aorta model
study the flow patterns in the healthy
the presence of chimney stent graft results in stagnation regions and WSS
aorta vs aorta post'chimney' stent
modification.
grafts inserted into each renal artery
SC
in parallel to the aortic SG
TAA= Thoracic Aortic Aneurysm; ILT=intraluminal thrombus; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy; TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
M AN U
Table 5: Treated Infrarenal Abdominal Aortic Aneurysms (2 studies representing 12 patients with a treated IRAAA)
n
Age
M:F
(Years) Frauenfelder. Cardiovasc
Shuji Yamamoto, JSRT,2006105
-
Pathology
-
FSI
76
M
CFD
Quality of
Specific study interest using CFD
Clinical relevance
investigate hemodynamic changes in AAA
reduction of wall P and WSS and less turbulence
after stent-graft placement
flow pattern found at the AAA after implantation
Evidence AAA
41
1
Parameters
/FSI
AAA
P,WSS
v, P
EP
Intervent Radiol.,2006
11
CFD
TE D
Author, Journal, Year
moderate
low
of stent graft blood P and v for pre and postoperative AAA
AC C
AAA=Abdominal Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction
Postoperative case showed improve blood v in the intravascular lumen after implantation of stent graft.
SC
RI PT
ACCEPTED MANUSCRIPT
Table 6: Untreated Type B Aortic Dissection
n
Age
M:F
(Years) Osswald,, Eur J Vasc
20
Endovasc Surg,
Treated/
CFD/FSI
Pathology
44-79
7:3
38-77
9:1
Untreated
1
56
M
untreated
Quality of
Specific study interest using CFD
Clinical relevance
to identify hemodynamic risk factors for the
P and v were not significantly increased at the entry tear
occurrence of RATD
compared with aortic arch. Increase WSS associated to the
evidence
CFD
RATD
2017106 Cheng, Med Eng
Parameters
Untreated
CFD
TB-AD
Phys,2014107
p, v, WSS
High
TE D
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(20 studies comprising 75 patients with an untreated type B)
v
High
turbulence
occurrence of RATD compare CFD results with PC-MRI flow
TB-AD with a relatively stiff dissection flap can affect the
data to examine hemodynamic changes
flow dynamics
investigate hemodynamic changes in TB-
Simulated EVAR treatment by virtually occluding the
AD with varying tear size location
entrance tear result in considerable P reduction in the
1
-
-
untreated
CFD
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TB-AD
1
58
F
13
Soudah, Comput.
Stanford
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-
-
AC C
Cheng, J Biomech
EP
intensity
Karmonik, IEEE
untreated
untreated
CFD
CFD
FL
Stanford
v, P, TAWSS
moderate-
examine
TB-AD
OSI, turbulence
high
aneurysmal dilatation of the thoracic aorta
moderate
examine hemodynamic changes in different
as long as the tear size was large enough so that the effect
dissection geometries and validate it with
of the wall compliance was negligible
Idealized
geometry
hemodynamic
change
in
intensity P
the flow pattern in the dissected aorta is extremely complex with recirculating and disturbed flow dominating in the FL and TL.
the in vitro results from a previous study
ACCEPTED MANUSCRIPT
Khanafer,J. Biomed
-
-
-
untreated
CFD
Eng Informatics,
P
moderate
geometry
were strongly correlated with the in vitro results
52
M
untreated
CFD
TB-AD
v, TAWSS
moderate-
examine
changes
Non-invasive and patient-specific tool can be developed
low
corresponding to morphological changes in
for serial monitoring of hemodynamic changes of TB-AD
TB-AD
before and after treatment.
49
Shang, J Vasc
-
untreated
CFD
TB-AD
v , TAWSS
moderate-
examine
low
different disease progression of TB-AD
v, P, WSS
moderate-
examine hemodynamic changes in an aortic
vortical structures may help to describe mechanism
vortical structure,
low
dissection patient
behind the formation of thrombus and to predict its
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-
untreated
CFD
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1
54
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FSI
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28:62:45
M
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1
54
F
untreated
CFD
changes
in
Hemodynamic parameters derived from CFD simulations of acute TB-AD were significantly different in dissections complicated by aneurysm formation.
location in TB-AD patients.
to investigate the impact of an additional re-
the presence of an additional re-entry tear provided an
low
entry tear on hemodynamic parameters in
extra return path for blood flowing back to the TL during
the dissected aorta
systole, and an extra outflow path into the FL during
moderate-
diastole
to assess hemodynamic implications of
can help predict which patients will suffer adverse events and facilitate the clinical decision-making process related
TAWSS
low
patients with patent FL of dissected aorta
v, P, WSS, OSI
moderate-
examine hemodynamic change in AD with
CFD simulations can be used as a diagnostic tool for
low
Windkessel as boundary condition
AD
moderate-
to elucidate the underlying hemodynamic
The interluminal ∆P may be a contributing factor in the
low
mechanisms involved in the longitudinal
compression of the true lumen and the cleavage force of
propagation of acute TB-ADs
the aortic wall, leading to the longitudinal propagation of
P
AD
AC C
Alimohammadi, Int J
v, P
EP
Eng Phys,2014
acute TB-
hemodynamics
moderate
TE D
Rinaudo, Cardiovasc.
hemodynamic
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1
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Yu, Cardiovasc
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validate a numerical model of TB-AD with
SC
2015
Idealized
to the treatment of TB-AD.
the dissection.
TB-AD,
v, P, TAWSS
moderate-
investigate hemodynamic for a case of pre-
CFD can be used as both a diagnostic and an
including a
OSI
low
and post-stenting(virtual stent-graft)
interventional tool.
coarctation
ACCEPTED MANUSCRIPT
54
F
untreated
FSI
TB-AD
Karmonik,, Vasc
45
M
untreated
CFD
Phys,2013
Online,2013
chronic
P, WSS
hemodynamic
70
-
untreated
CFD
chronic
-
-
untreated
CFD
118
and oscillatory WSS
models evaluate hemodynamic changes during
potential to deliver information about hemodynamics
aneurysmal dilatation in chronic type B AD
thereby improving management of type B AD
moderate-
quantitatively
identify entries and relevant reentries between true
low
hemodynamic features of AD.
v,P, WSS
moderate-
study the flow exchange between true and
contributes to evaluating potential thrombotic behavior in
TKE
low
false lumen during the cardiac cycle and
the false lumen and is pivotal in guiding endovascular
quantifying
intervention
v , P, WSS
TB-AD
FSI can help to identify certain collocated regions of low
low
TB-AD
-
parameters'
moderate-
type III AD 1
117
Chen, Biomed Eng
difference between FSI and rigid wall
DeBakey
116
Chen, Med Eng
compare
low
TAWSS. OSI 1
Endovascular Surg,2013
moderate-
displacement
investigate
the
and false lumen and potentially assist in stent-graft
SC
Online,2015
6
v, P, WSS
RI PT
1
Biomed Eng
M AN U
Alimohammadi,
the
flow
across
planning
specific
passages.
1
45
M
untreated
CFD
Surg,201212
Karmonik, Eur J Vasc Endovascular Surg,2011
10
1
53
M
untreated
CFD
chronic
P, WSS
TB-AD
v
DeBakey
v, P
type III AD
moderate
determine the potential value of CFD
to
low
simulations in prediction of aneurysmal
characterization of this severe disease entity, thereby
growth and rupture.
predicting false lumen progression in individual patients
moderate-
TE D
Karmonik, J Vasc
low
quantify
hemodynamic
changes
provide
additional
surrogate
markers
for
the
with
occlusion of exit tear caused increase in FL pressure.
interventional treatment or with disease
Simulating TEVAR treatment by occluding entrance tear
progression
depressurised the FL. Removing the IS lowered pressure of the combined lumen compared with TL pressure of the original model.
EP
RATD=Retrograde Type A aortic dissection; TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; PRT=Particle Residence Time; OSI: oscillatory shear index; TKE=turbulent kinetic energy;
AC C
TAWSS: Time average Wall Shear stress; RPI=Rupture Potential Index; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction; FL=False Lumen; TL=true lumen; EVAR=endovascular aortic repair; IS=intra-luminal septum;
ACCEPTED MANUSCRIPT
Table 7: Treated Type B Aortic Dissection
n
Karmonik, Vasc
1
Age
M:F
(Years) 60
Treated/
CFD/FSI
Pathology
Parameters
CFD
TB-AD
v, P ,WSS
Untreated M
treated
Quality of evidence High
Endovascular
Eng.,2015
8
52.75
7:1
treated
CFD
TB-AD
v, P, TAWSS
120
Chitsaz, J Cardiovasc
-
-
-
treated
CFD
Surg,2012121
Idealized
P
geometry
2011
15
1
38
F
treated
CFD
TB-AD
forces
Quantitative assessment of hemodynamic wall forces in
moderate-
examine hemodynamic changes in TB-AD
high RRT is a strong predictor of subsequent FL
low
between medically treated and stented cases
thrombosis, whereas ∆P between the TL and FL
moderate-
determine
low
dissection
the
as well as the location of the largest ∆P may be associated with the likelihood of subsequent aortic expansion relationship
propagation
in
between the
distal
TEVAR should ideally cover both entry and reentry tears to reduce risk of retrograde propagation of AD.
longitudinal direction(the tearing force) and dp/dt of endovascular stent grafting in idealized geometry
v, P, WSS,
moderate-
examine hemodynamics parameters in TB-
relatively high TAWSS (in the range of 4–8 kPa) may be
TAWSS
low
AD and relate it to progression of dissecting
associated with tear initiation and propagation
EP
Tse， J Biomech，
hemodynamic
TB-AD can assist in follow-up examinations.
TE D
for AD
quantify
Clinical relevance
pretreatment /post-treatment
119
Cheng, Ann Biomed
to
M AN U
Surg,2011
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(4 studies comprising 10 patients with a treated type B aortic dissection)
aneurysm
TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational Fluid Dynamics; FSI: Fluid
AC C
structure interaction; FL=False Lumen; TL=true lumen; EVAR=endovascular aortic repair; IS=intra-luminal septum
ACCEPTED MANUSCRIPT
Table 8: Untreated Coarctation of the Aorta
Age
M:F
(Years) Keshavarz-Motamed, PLoS
1
-
Treated/
CFD/FSI
Pathology
-
untreated
Quality of evidence
CFD
CoA
v, P,TAWSS ,
One,2013122 Valverde, J Cardiovasc
Parameters
Untreated
High
OSI 7
20 (mean)
-
untreated
CFD
CoA
P
Magn Reson,2011 123
Specific study interest using CFD
SC
n
to examine hemodynamic changes with
Clinical relevance
the presence of a BAV in the CoA raise the TAWSS to around 14 Pa
the presence of a CoA and a BAV High
To predict the aortic P distribution in
predict the hemodynamic conditions in the aorta and avoid invasive cardiac
patients with aortic coarctation model
catheterization. An invasive pressure gradient drop across the coarctation.
M AN U
Author, Journal, Year
RI PT
(2 studies representing 8 patients with an untreated coarctation of the aorta)
CoA=coarctation of aorta; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; TKE=turbulent kinetic energy; CFD: Computational Fluid Dynamics; FSI:
AC C
EP
TE D
Fluid structure interaction; BAV=bicuspid aortic valve
ACCEPTED MANUSCRIPT
Table 9
Treated Coarctation of the Aorta
n
Age
M:F
(Years) Mirzaee,J Magn Reson
12
Treated/
CFD/FSI
Pathology
Parameters
Quality of
Untreated 5:7
treated
evidence CFD
Imaging,201729
aortic
p
High
coarctatio
Specific study interest using CFD
SC
Author, Journal, Year
RI PT
(16 studies representing 107 patients with treated coarctation of the aorta)
investigate the numerical method Lattice Bozman
for
pressure drop found across aortic coarctation.
noninvasively
measurement of pressure gradients in
M AN U
n
method
Clinical relevance
patients with a coarctation of the aorta
Goubergrits, J Magn Reson Imaging,2015
6:7
treated
CFD
CoA
P
6
-
-
treated
CFD
CoA
P
5
-
-
untreated
CFD
126
1
60
F
treated
CFD
Eng.,2012127
CoA
5
treated
MICCAI,2012 51
Coogan, Catheter Cardiovasc Interv., 2011
2
15;25
0:2
CFD
CoA
AC C
Ralovich,
Restenosis
treated
CFD
v,P
TKE
EP
Arzani, Ann Biomed
128
CoA
TE D
125
Itu, Ann Biomed Eng,2013
25±14
124
Ralovich, Med. Phys.,2015
13
CoA
P
High
High
High
High
High
compared MRI based CFD with catheter-
Peak systolic P drops can be reliably calculated
derived peak systolic P drops
using MRI-based CFD in a clinical setting
estimate the pre- and postoperative
the study can be integrated into a clinical setting,
hemodynamics for coarctation patients
where manual interaction is required in a mostly
a mean absolute error of less than 2 mmHg in all
pre- and post-operative coarctation of
the patient between CFD results and catheter
aorta (CoA) patients
measurements
provide a comparison between in vivo
Results indicate relative agreement (error ≈10%)
and numerical estimates of turbulence
between the in vivo measurements and the CFD
intensity in a patient specific model
predictions of TKE
estimate the pre- and post-operative hemodynamics
v, P
High
supervisional manner
examine hemodynamic change between
for
both native
and
High correlation of our results and catheter measurements(∆P>20mmHg)
is
shown
on
recurrent coarctation patients.
corresponding pre and post-operative examination
compare the effects of surgical and stent
CoA stenting may not affect cardiac work to any
based treatments on aortic compliance
significant degree as is commonly believed in the
and
clinical community.
ventricular
coarctation
workload
in
aortic
ACCEPTED MANUSCRIPT
Szopos, J Thorac
30
15±5.1
-
treated
CFD
CoA
v, P, WSS
Cardiovasc Surg,2014 129
moderate-
quantify the geometric factor that leads to
patients with an angulated ‘‘gothic’’ aortic arch
high
abnormal
might warrant increased surveillance for aortic
blood
flow
patterns
and
6:8:10:5:4
3:2
treated
FSI
CoA
Eng,2011130
LaDisa, Congenit Heart
6
15±8
4:2
treated
CFD
Dis,2011 40
CoA
moderate-
Examine hemodynamic alterations under
Local patterns of hemodynamic indices reported to
displacement
high
resting and non-resting
correlate with atherosclerosis in normal patients
WSS, TAWSS, OSI
treated by
examine
in
Localized differences in WSS indices within the
high
postoperative age- and gender-matched
descending aorta of CoA patients treated by
CoA patients treated by resection with
RWEA suggest that plaque may form in unique
Biomech ,2017
63
F
treated
CFD
131
aortic
end-to-end anastomosis (RWEA).
locations influenced by the surgical repair
WSS, KE, TKE, TI
coarctatio n
Comput,2016
1
39
M
treated
FSI
CoA
132
Kwon,Pediatr.
1
15
-
treated
CFD
Cardiol.,2014133
v, P
TE D
Taelman, Med Biol Eng
M AN U
1
CoA with
TAWSS
different
hemodynamic
changes
were accentuated by CoA.
moderate-
RWEA
Andersson,, J
complication due to eccentric WSS.
v ，TAWSS
SC
5
RI PT
modified indexes of WSS LaDisa, J Biomech
Moderate-
investigate the transWSS properties in
Results showed that regions of strong near-wall
low
flows
turbulent
turbulence were collocated with regions of elevated
characteristics in an aortic coarctation
dominated
by
transWSS and turbulent WSS, while in more
before and after treatment
transitional-like near-wall flow regions a closer resemblance was found between transWSS and low, and oscillatory WSS
moderate
predict
the hemodynamic impact of
low
(coexisting) stiffening and narrowing in
A
residual
narrowing
of
CoA
affect
the
hemodynamics significantly by decreasing the WSs
CoA repair moderate-
compare
low
between stents in CoA
hemodynamic
alterations
it help to select most appropriate stent for each
moderate-
compare
low
treatment hemodynamics in CoA
treatment pressure drop
moderate-
investigate hemodynamic changes under
4D MRI-based in vivo v profile in CFD
low
different flow conditions
studies may be an important step towards a patient-
patient, and ultimately reduce long-term morbidity
Goubergrits, Ann
13
25±14
6:7
treated
CFD
Goubergrits, Ann
3
40:23:29
0:3
Biomed Eng,2013134
Olivieri, Cardiovasc Eng Technol.,2011135
3
-
-
CoA
AC C
Biomed Eng.,2014 53
EP
stents
treated
treated
CFD
CFD
CoA
CoA
v, P, WSS
v, P, WSS
pre,
post-treatment,
virtual
MRI-based CFD allow the evaluation of the post-
specific analysis of CoA hemodynamics v, WSS
moderate-
examine hemodynamic changes in native
varied patterns and locations of WSS resulting
low
and surgically repaired aortic arches
from abnormal arch remodeling may exhibit a primary effect on clinical vascular dysfunction
ACCEPTED MANUSCRIPT
CoA=coarctation of aorta; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time average Wall Shear stress; TKE=turbulent kinetic energy; CFD: Computational Fluid Dynamics; FSI:
AC C
EP
TE D
M AN U
SC
RI PT
Fluid structure interaction; BAV=bicuspid aortic valve
ACCEPTED MANUSCRIPT
Table 10
Characteritsics of stent grafts after the treatment of TAA and TB-AD
M:F
(Years) Prasad, J. Endovasc.
1
69
Treated/
CFD/FSI
Pathology
Parameters
CFD
TAA with 4-module
displacement
thoracic stent-graft
force, v, VMS
Untreated F
treated
evidence
Ther.,2011136
Rinaudo,Comput. Biol.
4
32±9
-
treated
CFD
TAA
High
-
-
-
treated
CFD
1
51
M
treated
CFD
Van Bogerijen,J.
1 55
51
M
treated
TAA with stent graft
AC C
201660
EP
Gallo, Comput Fluids,
Stent graft in TAA
The region of larger intermodular stresses and highest frictional instability correlated with the
Slippage
intermodular junctions of a multi-component
zone where a type III endoleak developed 4 years
coefficient
thoracic endograft
in CT after thoracic stentgraft placement.
examine hemodynamic changes acting on the
Greater displacement and transmural pressure
bird-beak configuration after TEVAR
across the stent-graft wall were found for a
P
CFD
Dissecting thoracic aorta aneurysm with stent graft
the
biomechanical
Clinical relevance
the
moderate
moderate
TE D
Endovasc. Surg., 2011 137
evaluate
hemodynamic
displacement
Vardoulis, Eur. J. Vasc.
Specific study interest using CFD
and
v, P, VMS,
Med.,201556
Endovasc. Ther.,2014
Quality of
SC
Age
forces
acting
on
M AN U
n
RI PT
(8 studies representing 21 patients with stent grafts in TAA and TB-AD)
protrusion extension(PE) longer than 21 mm.
analyses the mechanisms by which grafts,
Patients who receive ascending aorta grafts
placed in the ascending aorta (proximal) and
maybe more prone to systolic hypertension and
descending aorta (distal)
therefore
deserve
proximal
aortic
closer
BP
graft
presented
monitoring. more
haemodynamic alterations than the distal graft
OSI
moderate-
examine hemodynamic change with different
Comparison
TAWSS
low
geometrical features after TEVAR
indicates a partial restoration of normal flow in
of the
different morphologies
v, P
moderate-
evaluate the impact of TEVAR on aortic
Less chaotic flow at the bird-beak location with
low
hemodynamics, focusing on the implications
higher velocity and more flow disturbance found
of a bird-beak configuration
at the aortic narrowing in the descending TAA.
the region of interest.
ACCEPTED MANUSCRIPT
-
treated
CFD
TAA with stent graft
Biomed Engin,2012
Cheng, J Vasc
138
P, WSS
moderate-
determine the orientation and magnitude of
High magnitude of displacement was found
displacement
low
maximal displacement forces (DFs) in the
as35.01 (standing) and 37.32 N (supine). The
TAA endograft
orientation of the resultant DF vector is
force
12
56
11:1
treated
CFD
TB-AD
drag force
Surg,2008139
Lam, Med Biol Eng Comput,2008 140
1
-
-
treated
CFD
RI PT
1
Methods Biomech
perpendicular to the greater curvature of the thoracic aorta,
moderate-
study the forces acting on thoracic stent grafts
A significant change in stent-graft diameter
low
and their relationship to geometry and flow,
occurs after endovascular repair for TB-AD, may
and its impact with stentgraft remodeling
increase the hemodynamic drag force.
SC
Krsmanovic, Comput
Thoracic aorta with
Drag force
moderate-
investigate the biomechanical factors which
Larger internal diameter and smaller diameter of
stent graft
v
low
may affect the drag force on stent-graft wall
curvature affect drag force on the stent-graft.
M AN U
induced by the blood flow
TAA=Thoracic Aortic Aneurysm; TB-AD=Type B aortic dissection; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational
AC C
EP
TE D
Fluid Dynamics; FSI: Fluid structure interaction; TEVAR=Thoracic endovascular aortic repair; BP=Blood pressure
ACCEPTED MANUSCRIPT
Characteristics of stent grafts after the treatment of IRAAA
RI PT
Table 11
n
Age
M:F
(Years) Konoura,J. Artif. Organs,2013
-
-
Treated/
CFD/FSI
3
-
-
CFD
-
treated
CFD
Eng.,2012142 Figueroa, J Vasc
5
76
Parameters
4:1
treated
Quality of evidence
141
Segalova,J. Biomech.
Pathology
Untreated
CFD
Idealized geometry
v, Energy
with stent graft
loss
AAA with novel
v , P , stress
endograft
NIH
AAA
v, P
Surg,201022
High
High
High
TE D
displacement force
Figueroa, J Endovasc
1
-
-
treated
CFD
AAA
Ther, 200958
v, WSS, P
High
Force
3
-
-
treated
CFD
Ther, 2008143
3 postoperative
v, WSS
patient specific
drag force
EP
Molony, J Endovasc
moderate
Biomech Biomed Engin,2017
144
15
5
AC C
model
Raptis, Comput Methods
untreated
10 treated
CFD
AAA
Specific study interest using CFD
Clinical relevance
to evaluate blood flow distribution in the 3
estimate blood flow distribution of a newly
branch graft
developed vascular graft prior to its clinical use,
M AN U
Author, Journal, Year
SC
( 27 studies representing 90 patients with stent grafts in AAA)
for safe use of the graft.
examine hemodynamic change that may
The magnitude of the NIH in all models was well
occur due to unique position of stent graft
below the accepted design and safety threshold
to determine whether the direction of aortic
the magnitude and direction of the displacement
endograft
force acting on aortic endografts can affect the
movement
is
related
to
the
directional displacement force
endografts movement
determine the effect of curvature on the
Curvature of endograft can change the blood
magnitude and direction of displacement
flow. It can be used to evaluate the risk of
forces acting on aortic endografts
endograft migration in vivo
To compare the function of conventional
WSS appeared to be higher in the conventional
Dacron stent-graft and tapered stent graft
stent-graft compared to the tapered stent graft
designs for EVAR WSS,
Moderate-
compare the hemodynamic patterns before
a decrease of peak WSS on the part of the EG
Helicity, p, v
low
and after the EVAR implantation
that resides in the iliac arteries,
significant
variations were observed in the iliac arteries part that may require an improvement of EG designs
ACCEPTED MANUSCRIPT
20
treated
CFD
AAA
Device,2017145
v, WSS,
Moderate-
compare hemodynamic patterns on two
The results showed that two similar endografts
helicity,
low
different
can induce different flow characteristic that could
displacement
-
treated
CFD
-
WSS
146
Polanczyk, J
10
Biomech,2015147 Kandail,J. Endovasc.
61–76
treated
CFD
AAA
-
-
-
-
treated
CFD
Idealized geometry
-
-
treated
CFD
Sughimoto,Heart
1
54
M
treated
CFD
Vessels,2014 149 Jones,J. Vasc.
1
-
-
treated
CFD
-
treated
CFD
Vasc Endovasc
Pasta,J. Vasc. Surg.,201359
1
-
M
treated
One way FSI
Pa-s
that
may
be
important
to
predict
thromboembolic events. thrombus growth model can be applied to predict the risk of thrombus formation in stent-grafts
v. TAWSS
moderate-
examine hemodynamic changes in branched
Displacement forces exerted on stent-grafts are
displacement
low
stent-grafts (BSGs) for different anatomic
very sensitive to lateral neck angle but not on the
variations
configuration of the stent-graft.
moderate-
to assess durability of F-EVAR through
Blood flow patterns are better in post-operative
displacement
low
analyze the displacement forces acting on
AAA, demonstrating that with FSG in place,
standard non FSGs
force
AAA&TAA with
WSS
AAA with
AAA
AC C
Surg.,201362
does have particles with WSS accumulation>3.5
v ,WSS, P
EP
-
graft with diaphgram
and one with a
fenestrated stent
1
low
5 AAA with FSGs
grafts Georgakarakos, Eur J
The stent graft configuration with the diaphragm
and growth in the stent-graft
FSGs.
restore blood flow in aneurysm sac
moderate-
use novel indices to characterize and quantify
Grafting not only to ameliorate WSS or OSI but
low
energy loss of pulsatile blood flow
also to improve blood flow
distraction
moderate-
determine morphologic features which were
Distraction force acts against endovascular
forces
low
associated with greater distraction force
fixation to provoke stent graft migration.
displacement
moderate-
study the hemodynamic effects of positional
differences in the values of shear stress exerted
force
low
variations of SG
on the stented arteries, depending on different
aneurysm repair
Surg.,201463
investigate shear accumulation in the stent
determine the process of thrombus formation
TE D
6
Biomech,2014148
patients.
Moderate-
low
forces Kandail, J
affect design of endografts for individual
moderate-
years
Ther.,201561
their
SC
-
on
M AN U
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endografts
postimplantation position
force Suess, J Vasc Surg,
aortic
RI PT
Raptis, J Med
AAA with TASG
shear stress
positions that SG can adapt after the deployment of fenestrated EVG
v, P
moderate-
To assess the biomechanical implications of
It helps in identifying patients with high risk of
VMS
low
excessive stent protrusion into the aortic arch
TASG
in relation to TASG collapse
intervention.
collapse
and
guide
preventive
ACCEPTED MANUSCRIPT
5
-
-
treated
CFD
Methods Biomed. Eng.,2013
AAA with
v, P
moderate-
to examine hemodynamic change under
No difference in drag forces with the SG
bifurcated stent graft
drag force
low
different input boundary flow for four
containing the full human aorta and those
patient-specific bifurcated stent graft no
without. A twisted leg configuration promoted a
150
RI PT
Stefanov, Int. J. Numer.
twisted and twisted leg configurations with
spiral flow formation along its distal legs
the inclusion of the full human aorta. 2
-
-
treated
FSI
AAA
v, P, WSS
Radiol,2010151 Fung, Comput. Biol.
1
-
-
treated
CFD
AAA
P, force
Med,2008152
6
-
-
treated
CFD
Radiol.,2008153
Howell, J Endovasc
4
-
-
treated
CFD
AAA with Zenith®
P, v
bifurcated stent-
Total shearing
grafts
force
AAA
Force
-
-
-
untreated
untreated
FSI
FSI
AAA
AAA
hemodynamic
effect
of
the renal arteries is insignificant
moderate-
examine the dynamic factors linked to actual
hemodynamic factors can be linked to drag force
low
motions of blood and related it to drag force
that may play a significant role in the risk of
acting on the endoluminal stentgraft
stent-graft failure.
moderate-
estimate the pressure which occurred in the
increase of shear stress and higher P drop for
low
aorta after stent-grafting
short body graft compared to long body graft.
Phys,200644
1
-
-
treated
CFD
AAA
The highest WSS occurred near bifurcation area.
To assess the hemodynamic forces on a
Forces on a stent-graft are also affected by the P
bifurcated abdominal aortic stent-graft
within the aneurysm sac, which depends on stent-
moderate-
quantitatively assess the impact of type II
the risk of type II endoleaks depends on the P
P
low
endoleaks on AAA rupture risk and potential
level of the inlet branch
drag force
moderate-
Investigate the biomechanical factors based
sac pressure caused by these endoleaks depends
wall stress ,v
low
on SG–AAA interaction dynamics
largely on the inlet branch pressure. the stent
wall stress ,v,
AC C
Morris, Med Eng
hemodynamic effect of fenestrated renal stents on
low
TE D
1
-
the
graft performance.
stent-graft migration
graft migration force can be reduced by type II
EP
Li, J Biomech, 200654
1
fenestrated stents on the renal arteries
moderate-
Ther, 2007154
Li, J Biomech, 2006155
investigate
low
M AN U
Stefańczyk, Pol J
moderate-
SC
Sun,Korean J
endoleak since it depends on the pressure difference between stent graft and aneurysm cavity. v
moderate-
investigate geometrical effect of stent graft
geometry has the greatest influence on the outlet
low
to the flow pattern in AAA
flow rates, flow patterns and drag forces
ACCEPTED MANUSCRIPT
1
Treated
FSI
AAA
2005156
wall stress, v
moderate-
analyze the pulsatile flow and its impact on
The time-varying drag force on the EVG exerted
drag force
low
EVG placement, EVG/AAA wall stress
by physiological blood flow is unavoidable,
distributions, sac P generation, and EVG drag
where for patients with severe hypertension the
P
force -
-
-
FSI
157
Liffman, J Endovasc
-*
-
-
-
CFD
Ther, 2001158
P
moderate-
graft
VMS
low
Idealized AAA with
v , P, Force
graft
Pless, Stud Health Technol Inform,2001
Idealized AAA with
1
-
-
treated
CFD
investigate the AAA-stent graft interaction
AAA
v ,P,WSS
159
risk of EVG migration is very high sac pressure and maximum aneurysm wall stress both follow closely the endoleak flow rate.so both parameters can be used to predict post EVAR complications.
moderate-
investigate the forces acting within the
downward force on a bifurcated stent-graft may
low
pressurized aorta and upon a stent-graft
exceed the force required to dislodge it when
M AN U
2003
-
SC
Li, J Biomech Eng,
RI PT
Li, Med Eng Phys,
low
investigate blood flow change by stent grafts
relying on radial attachment alone which is largely depends on proximal graft diameter CFD can be used to evaluate risk of AAA rupture and optimize stent graft design
AAA=Abdominal Aortic Aneurysm; M=Male; F=Female; v=velocity; P=Pressure; WSS=wall shear stress; VMS=von Mises stress; OSI: oscillatory shear index; TAWSS: Time-Averaged Wall Shear stress; energy; CFD: Computational Fluid Dynamics; FSI: Fluid structure interaction; TEVAR=Thoracic endovascular aortic repair; NIH= normalized index of hemolysis; EVAR= endovascular aortic repair; EG=endograft; F-EVAR=Fenestrated-EVAR; FSG=Fenestrated Stent Graft; EVG=endovascular graft; TASG=thoracic
AC C
EP
TE D
aortic stent graft
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Table 12 Summary of the application of CFD in the diseased aorta
Disease Management
Future perspective
Aneurysm
be
Stent graft manages to reduce the pressure in
A comprehensive aneurysm model should include aortic wall,
Aneurysm
correlated with hemodynamic factors
the aneurysm sac and improved the flow
intraluminal thrombus with realistic flow condition derived
like WSS, velocity, and pressure to
pattern which can reduce the chance of platelet
from MRI. More realistic aortic wall strength and wall
fully determine the risk of rupture.
activation. Difference forces, energy loss,
properties should be derived from advanced imaging technique
The hemodynamic factors can be
morphologic features should be taken into
in vivo to enhance the credibility of the model160. An
linked to the platelet activation,
account on stent graft design in order to
integrative
intraluminal thrombus, and monocyte
optimize the performance of stent graft and
combination of fluid properties should be used in order to
deposition
avoid stent graft malposition and migration.
understand the aneurysm progression. Stent graft material
should
approach
like
taking
the
diffusivity
and
SC
diameter
RI PT
Pre and post treatment
Aortic
properties should be integrated into the treated aneurysm model to evaluate the durability and strength of design to withstand stent migration. More malposition case and bird
M AN U
peak configuration should be done in order to design new treatment for faulty implantation. More follow up case on Image-based CFD should be presented in order to confirm the assessment of rupture risk.
The geometry of CoA affects the
Pre and posttreatment of coarctation show that
The future of CFD in coarctation focus on the impact of
hemodynamics
with
post operation can reduce the pressure drop.
surgical repair on the CoA. Different repair has been repaired
hemodynamic factors e.g. WSS that
However, the surgical repair may also change
but the complications still occur after the repair like plaque
can
be
flow
pattern
plaque
the hemodynamic patterns in CoA which may
formation due the abnormal aorta geometry even after repair.
formation. Good agreement between
correlated
with
trigger the complications e.g. plaque formation
A more realistic flow condition and compliance of the aorta in
catheter
in some unique locations.
CoA should be measured through the in vivo and in vitro in
measurement
and
CFD
TE D
CoA
results shows that CFD can be used in
order to evaluate the performance of surgical repair.
diagnosing the severity of coarctation through pressure evaluation. Aortic
Hemodynamics
dissection
pressure
of
TB-AD
like
A stent graft treatment shows that it can reduce
CFD in dissection should be done in FSI given the intimal flap
in
and
the pressure difference in FL and TL and also
motion which only simulated through FSI. It is still not sure
FL
EP
difference
circulation and disturbed flow found
reduce the disturbed flow pattern.
whether the motion will cause a highly turbulent flow if the flap is taking into consideration. The intimal flap motion is
identify the entries and relevant
important to study since it may relate to disease progression. A
entries between TL and FL.
more comprehensive model will include a dissecting aneurysm
AC C
between FL and TL can help to
with intimal flap motion and compliance of aorta with realistic boundary condition from MRI-derived with and catheter-based pressure measurement. It should give more realistic flow pattern to predict the dissection progression. There is not direct approach to validate the blood flow in dissection due to the complex
geometry
which
should
combination of 4D MRI and CFD.
be
addressed
with
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n=196
Other sources (Ovid, Cochrane, and Scopus) n=520
M AN U
SC
Records after duplicates removed (n=358)
RI PT
Pubmed (from 2001)
Full text articles excluded with reasons (n=216)
TE D
Records screened by title and abstract (n=352)
EP
Eligible studies (n=136)
AC C
Figure 1: PRISMA Flowchart of Systematic Search Strategy
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Early diastole
RI PT
(t=4.47s)
(c)
SC
(b)
M AN U
(a)
Figure 2 Velocity streamlines in the (a) healthy, (b) aneurysm before treatment, and
AC C
EP
TE D
(c) aneurysm after stent graft implantation at early diastole in the cardiac cycle20