Moderate Aortic Stenosis and Coronary Artery Bypass Grafting: Clinical Update for the Perioperative Echocardiographer

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Moderate Aortic Stenosis and Coronary Artery Bypass Grafting: clinical update for the perioperative echocardiographer Yasdet Maldonado MD, Saket Singh MD, John G. Augoustides MD, FASE, FAHA, Brenda MacKnight MD, Elizabeth Zhou MD, Jacob T. Gutsche MD, Harish Ramakrishna MD FASE www.elsevier.com/locate/buildenv

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S1053-0770(15)00256-6 http://dx.doi.org/10.1053/j.jvca.2015.04.007 YJCAN3258

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Journal of Cardiothoracic and Vascular Anesthesia

Cite this article as: Yasdet Maldonado MD, Saket Singh MD, John G. Augoustides MD, FASE, FAHA, Brenda MacKnight MD, Elizabeth Zhou MD, Jacob T. Gutsche MD, Harish Ramakrishna MD FASE, Moderate Aortic Stenosis and Coronary Artery Bypass Grafting: clinical update for the perioperative echocardiographer, Journal of Cardiothoracic and Vascular Anesthesia, http://dx.doi.org/10.1053/j.jvca.2015.04.007 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 galley proof before it is published in its final citable 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.

Moderate Aortic Stenosis and Coronary Artery Bypass Grafting: clinical update for the perioperative echocardiographer

Yasdet Maldonado MD Department of Anesthesiology Allegheny Health Network Temple University School of Medicine Pittsburgh, Pennsylvania, USA

Saket Singh MD Department of Anesthesiology Allegheny Health Network Temple University School of Medicine Pittsburgh, Pennsylvania, USA

John G. Augoustides MD, FASE, FAHA Associate Professor Cardiovascular and Thoracic Section Department of Anesthesiology and Critical Care Perelman School of Medicine University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Brenda MacKnight MD Department of Anesthesiology Allegheny Health Network Temple University School of Medicine Pittsburgh, Pennsylvania, USA

Elizabeth Zhou MD Fellow Cardiovascular and Thoracic Section Department of Anesthesiology and Critical Care Perelman School of Medicine University of Pennsylvania, Philadelphia, Pennsylvania, USA

Jacob T. Gutsche MD Assistant Professor Cardiovascular and Thoracic Section Department of Anesthesiology and Critical Care Perelman School of Medicine University of Pennsylvania, Philadelphia, Pennsylvania, USA

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Harish Ramakrishna MD, FASE Associate Professor Vice-Chair for Research Chief of Cardiovascular and Thoracic Anesthesiology Department of Anesthesiology Mayo Clinic, Scottsdale, Arizona Conflicts of Interest: None Financial Support: Institutional

Corresponding Author John G. T. Augoustides MD, FASE, FAHA Associate Professor Cardiothoracic Section Anesthesiology and Critical Care Dulles 680, HUP 3400 Spruce Street Philadelphia, PA, 19104-4283 Tel: (215) 662-7631 E-mail: [email protected] Key Words: aortic stenosis; coronary artery bypass grafting; risk stratification; transesophageal echocardiography; aortic valve area; minimally invasive; port access; sutureless; transcatheter aortic valve replacement; apicoaortic conduit; three-dimensional imaging; ellipse; pressure recovery; continuity equation; geometric orifice area; effective orifice area; Gorlin area

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Abstract

Incidental aortic stenosis in the setting of coronary artery bypass surgery may be a perioperative challenge. The accurate assessment of the degree of aortic stenosis remains an important determinant. Although severe aortic stenosis is an indication for valve replacement, current guidelines advise a balanced approach to the management of moderate aortic stenosis in this setting. Multiple factors should be considered in a team discussion to balance risks versus benefits for the various management options in the given patient. The rapid progress in aortic valve technologies also offer alternatives for definitive management of moderate aortic stenosis in this setting that will likely become even safer in the near future.

Key Words: aortic stenosis; coronary artery bypass grafting; risk stratification; transesophageal echocardiography; aortic valve area; minimally invasive; port access; sutureless; transcatheter aortic valve replacement; apicoaortic conduit; three-dimensional imaging; ellipse; pressure recovery; continuity equation; geometric orifice area; effective orifice area; Gorlin area

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Introduction Patients requiring coronary artery bypass grafting (CABG) may often undergo comprehensive intraoperative transesophageal echocardiography (TEE) as part of perioperative management.1-2

In this setting, TEE may reveal associated cardiac

pathology that may require incidental cardiac conditions that may require surgical intervention at the time of CABG.2-5 A retrospective analysis of patients undergoing isolated CABG from 1990-2005 (N = 12 566) revealed that intraoperative TEE influenced surgical decisions in 5.4% of procedures.6 Furthermore, in this large analysis, 3.3% of study subjects had an additional mitral or aortic valve procedure added to their CABG procedure as a result of incidental findings from intraoperative TEE.6 Even though recent CABG guidelines recommend that aortic intervention is reasonable for moderate aortic stenosis (AS), the perioperative decision as to whether to intervene is complicated factors such as patient age, associated comorbidities, expanding surgical and percutaneous options, and advances in imaging techniques.7 The purpose of this expert review is to evaluate these important questions to both provide a guide for decisionmaking and a clinical update for the perioperative echocardiographer. 1. Incidental Moderate Aortic Stenosis at the Time of CABG Although there have been dramatic advances in the medical and percutaneous management of coronary artery disease, recent trials have highlighted the therapeutic value of CABG in scenarios such as left main or three-vessel coronary artery disease, especially in the setting of diabetes mellitus.8-10 Besides the enduring clinical indications

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for CABG, the prevalence of significant aortic stenosis requiring surgical intervention is steadily increasing due to factors such as an aging population, advances in aortic intervention such as transcatheter aortic valve replacement, and advances in cardiac imaging such as three-dimensional TEE.11-15

The incidence of incidental AS in

contemporary patients presenting for CABG has recently been estimated as about 2.5%.13 Although recent guidelines recommend severe AS as a Class I indication for severe surgical aortic valve replacement (AVR), lesser grades of AS present a complex clinical dilemma at the time of CABG since it is unclear at which threshold untreated AS impacts long-term outcome.15-16 A recent Mayo Clinic analysis (N = 624) evaluated the outcome effects of mild or moderate AS (defined as aortic valve area from 1.0 – 2.0 cm2) in patients who underwent isolated CABG.16 Although mild/moderate As did not affect perioperative mortality (P=0.1), it did result in an increased risk for future aortic valve intervention (as high as 21% for patients with moderate AS, defined as an aortic valve area from 1.0 to 1.5 cm2).16 Furthermore, in the Mayo analysis, moderate AS was an independent risk factor for late mortality (P=0.001) following isolated CABG.16 This mortality risk was also inversely related to aortic valve area. Patients with aortic valve areas of (1.0 -1.25) cm2 had 2.5-fold increase in mortality (hazard ratio 2.45; 95% confidence interval 1.57 – 3.82; P < 0.001) as compared to patients with aortic valve areas (1.25-1.50) cm2 who had a 1.8-fold increase in mortality (hazard ratio 1.83; 95% confidence interval 1.28 – 2.61; P = 0.001).16

The investigators concluded that

untreated moderate AS independently predicts excess late mortality after CABG with the greatest risk in patients with moderate-to-severe AS (defined as aortic valve area 1.0 –

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1.25 cm2).16 Future trials are indicated to test whether aortic valve intervention mitigates this identified mortality risk. The estimated average progression of AS is a decline of aortic valve area of approximately 0.1cm2/year.17 Hence, patients with aortic valve areas of 1-1.25 cm2 at time of diagnosis can be expected to develop severe AS within 5 years. According to the 2014 ACC/AHA valvular heart disease guidelines, expert opinion has recommended AVR as reasonable for patients with moderate AS (defined as an aortic velocity of 3.03.9 m/s or an aortic mean pressure gradient of 20-30 mmHg) who are undergoing cardiac surgery (Class IIa Recommendation IIA; Level of Evidence C).

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In a recent thoracic

aortic guideline, the Society of Thoracic Surgeons has also supported performing an AVR in patients with moderate AS undergoing CABG (Class IIa Recommendation IIA; Level of Evidence B).18 Since AS is a progressive disease, symptom onset is likely within 5 years once moderate AS is present. It is also important in patients with both coronary artery disease and AS for the clinician to be able to differentiate the origin of the symptomatology since symptomatic AS has a poor prognosis. Individuals with AS are relatively symptom-free until late in the disease. However, once symptoms manifest, the interval from onset of symptoms to time of death is approximately 2 years for individuals with dyspnea, 3 years for those with syncope, and 5 years for those with angina.19 The rate of progression of AS often is a function of etiology, age, and comorbidities. Rheumatic AS has a slower progression than degenerative AS. The rate of progression is intermediate in patients with bicuspid aortic valves.20 Aortic stenosis with morphological features such as advanced leaflet calcification and/or leaflet motion

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restriction typically has a rapid progression.21

Comorbidities such as smoking,

hypercholesterolemia, and renal dysfunction can accelerate the progression of AS. 22-23 The rate of progression may also be more rapid in patients older than 80 years.24 Patients with incidental AS presenting for CABG with these risk factors may merit special consideration, given their higher risk of rapidly progressive AS. Further studies are required to investigate the factors that govern the progression of AS so that therapeutic interventions can be designed to improve the prognosis for this disease even further.25 There are currently no proven medical interventions that delay the progression of AS, although statins have shown some promise in this regard.26-27 Medical treatment for AS is typically directed in treating concurrent cardiovascular conditions. The maintenance of sinus rhythm remains an important consideration in these high-risk patients, given the excessive dependence of atrial kick for preservation of left-ventricular end-diastolic volume in AS. Patients with medically-treated AS have mortality rates of 25% at 1 year and 50% at 2 years after onset of symptoms, highlighting that medical therapy is not definitive management in this disease.28 Recent multisociety guidelines from 2012 have also supported timely intervention in patients with symptomatic AS.29 The decision-making process in the geriatric population is complicated by the question as to whether the elderly patient will outlive the rate of disease progression in aortic stenosis. Early surgical management exposes the patient to operative and prosthetic valve-related risks whereas a delay in management may subject the patient to higher risk secondary to disease progression and/or late reoperation.30 A recent prospective analysis (N = 236: age > 70 years) in patients with moderate AS who underwent CABG demonstrated that AVR should be performed with CABG in patients with minimal

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comorbidities and aortic gradients greater than 26/15 mmHg.30 The data analysis in this clinical trial identified a peak gradient of 26 mmHg and a mean gradient of 15 mmHg as risk factors for AVR downstream after CABG.30 In their opinion, patients with multiple comorbidities such as renal failure and pulmonary disease should only have a CABG performed due to their increased perioperative risk and limited lifespan.30 The risk-benefit ratio of AVR for the patient with incidental moderate AS first encountered during CABG should be individualized.

The operative risks include

prolonged cardiopulmonary bypass and cross-clamp times, a repeat sternotomy, and the long-term valve-related complications such as embolism, endocarditis, and/or anticoagulation-related bleeding. With conservative medical management, there are risks from significant AS such as angina, left heart failure and sudden death. The advent and rapid progress of transcatheter AVR (TAVR) will significantly affect the risk profile for high-surgical risk patients.31 2. Aortic Valve Replacement after Prior CABG According to compiled data from important trials published in the past decade, the rate of progression to AVR in patients with asymptomatic AS is approximately 25% in the first year after diagnosis and 12% every year thereafter.32 In those patients who require AVR after CABG, this redo procedure can be performed with acceptable outcomes, including a perioperative mortality of 4.4% in patients with patent grafts, as demonstrated in a recent multicenter clinical registry (N = 113).33 This clinical registry analysis also reported the following morbidity rates: prolonged tracheal intubation 20.8%, intensive care unit stay longer than five days 19.5%, low cardiac output syndrome 14.1%, and stroke 8.0 %.33 Furthermore, in a large study (N = 1400), the type of aortic valve prosthesis (mechanical,

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stented, or stentless) was not an independent risk factor for perioperative mortality (within 30 days).34 Due to these favorable outcomes, a history of a prior CABG is not necessarily a contraindication to surgical AVR, although the clinical drift to lower risk patient cohorts currently in progress with TAVR may challenge this perspective in the near future.35 Furthermore, besides TAVR, there are refined approaches for AVR including minimally invasive AVR, port access AVR, and sutureless AVR.36 A large systematic review (N = 4586) demonstrated that compared to conventional AVR, minimally invasive AVR via ministernotomy was associated with shorter intensive care unit and hospital stays, shorter ventilation times, and less blood loss.37 Although not as common, port access AVR procedures have also been shown to be effective.38 In this technique, the patient undergoes peripheral endovascular catheter placement for cardiopulmonary bypass and surgical access to the aortic valve is via right minithoracotomy.38 In a retrospective matched analysis (N =90), port access AVR as compared to conventional AVR had longer aortic cross-clamp times (91 versus 75 minutes: P = 0.033) but shorter intensive care stay (44.4 versus 65.7 hours: P = 0.01), length of hospital stay (7.2 versus 8.5 days: P = 0.033), and ventilation times (9.2 versus 16.3 hours: P < 0.001). 38 Finally, sutureless AVR has emerged as a therapeutic option for those patients whose perioperative risk lies in the “gray zone” between conventional AVR and TAVR.39 These patients are considered high risk for a conventional AVR but are not deemed inoperable. Sutureless AVR allows faster aortic valve implantation on conventional cardiopulmonary bypass. In a multicenter matched analysis (N=76: 38 sutureless AVR versus 38 balloon-expandable TAVR), it was demonstrated that the sutureless AVR

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technique was as effective as TAVR with a lower rate of paravalvular leak (15.8% versus 44.7%; P = 0.0001) yet a higher rate of postoperative atrial fibrillation (42.1% versus 18.4 %; P = 0.04).39 The therapeutic options have recently expanded for patients requiring AVR after CABG both in surgical and transcatheter AVR. The patient should be matched on an individual basis to the best option, taking into account the entire clinical scenario. 3. Transcatheter Aortic Valve Replacement after Prior CABG In the patient with previous CABG presenting with moderate or greater AS, the avoidance of a redo-sternotomy may be a reason to consider TAVR rather than a standard AVR. A recent observational study reflects the growing importance of percutaneous valve replacement in high- risk surgical patients.40 In a prospective analysis, TAVR patients with and without prior CABG were compared in a risk-stratified fashion.40 Out of 372 patients who underwent TAVR during a six year period (2007-2013), 32.8% had previously undergone CABG.

It was noted that those patients that had previously

undergone CABG had more high-risk features such as a prior myocardial infarction, peripheral vascular disease, cerebrovascular disease, and/or a lower ejection fraction. Despite these higher risk comorbidities, these patients had similar short- and long-term outcomes when compared to patients who had not previously had a CABG.40 Patients with AS selected for TAVR are currently typically high-risk for conventional AVR.29 The rapid progress in technology and procedural conduct for TAVR will further expand the selection criteria for this therapy in AS.31;

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Since these

advances will lead to improved outcomes, it is highly likely that TAVR with an

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appropriate bioprosthesis will become a leading choice to manage significant AS in patients who have undergone prior CABG.41 4. Aortic Stenosis and Off-Pump CABG Although off-pump CABG continues to be favored by many surgeons, long-term data compared with standard on-pump CABG tend to be equivocal.42-43

A recent large

(N=2539) randomized controlled trial found no difference in outcomes at 30 days and 1 year between on- and off-pump CABG in patients greater than 75 years of age.42 The primary end point was a composite of death, myocardial infarction, stroke, repeat revascularization, and acute renal failure requiring renal-replacement therapy. According to this study and recent guidelines, it appears that both on- and off- pump CABG procedures can result in excellent outcomes.7;

42-43

The skills and experience of the

operative team likely influences the choice of CABG technique, given the equivalence in clinical outcomes. Inevitably, the management dilemma arises when an off-pump CABG is considered in the setting of a heavily calcified or atherosclerotic aorta and AS is encountered.

First, the aortic valve needs to be thoroughly evaluated in order to

determine the necessity for AVR. Consideration must also be given to the effects of untreated residual AS on postoperative and long-term outcomes. Bottiger and colleagues have suggested that if the aortic valve must be replaced, the decision of changing to an on-pump procedure versus determining if the patient is a candidate for TAVR at a later date should first be deliberated.44 If conversion to an on-pump procedure is determined, further management considerations are required to minimize the risk of stroke due to the severe ascending

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aortic disease.

The management options include the following: alternate arterial

cannulation sites, including the axillary and femoral vessels; deep hypothermic cardiac arrest to avoid cross-clamping the native ascending aorta; on-pump fibrillating heart technique to avoid aortic cross clamping.45-46 If the decision is made not to replace the aortic valve, an off-pump CABG can still be performed with careful attention to the ascending aortic manipulation for the proximal anastomotic sites. All of these decisions options should consider the risks of an alternative strategy versus the stroke risk due to the diseased ascending aorta. An alternative off-pump approach in high-risk patients with coronary artery disease and AS is concomitant percutaneous coronary intervention and TAVR in a hybrid operating room.47-48 When a patient is not a candidate for an on-pump AVR or a TAVR, an aortic valve bypass can be considered as an off-pump alternative.49-50 This procedure places a left ventricular apex to descending aorta bypass with a constructed valve conduit that can be performed via a midline sternotomy or left thoracotomy approach without cardiopulmonary bypass.49-50This specialized procedure requires teamwork, high-quality communication, expert echocardiographic guidance, rapid left ventricular pacing, and strict hemodynamic monitoring.49

A retrospective review of 21 high-risk patients

presenting with AS and a challenging aorta demonstrated acceptable short-term mortality results for aortic valve bypas.50 There were no intraoperative deaths in these high-risk patients, but there were 3 in-hospital mortalities (14.3%).50 Further patient follow-up revealed an additional 4 deaths at a median of 1.3 years. These numbers indicate that 1/3 of the patients will die despite operative repair, which must be appreciated prior to commencing this surgical approach. The management of AS in the setting of off-pump

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CABG presents multiple management considerations including patient consent and operative risk. The clinical decisions should be made in the patient’s best interest and weighed against immediate versus later alternative management options.44-50 5. Echocardiographic Assessment of Aortic Stenosis Diagnostic Modalities for Assessing Aortic Stenosis Aortic stenosis can be evaluated by multiple diagnostic modalities, including angiography, catheterization, echocardiography, computed axial tomography, and magnetic resonance.13-15;

18;29

In the preoperative setting, 2D transthoracic

echocardiography (TTE) is most commonly utilized for initial diagnosis and subsequent routine follow-up, as it is safe, convenient and economical. Echocardiography has largely replaced cardiac catheterization, which was once considered the gold standard for quantification.51 However, in situations where there is a discrepancy between clinical data and echocardiographic measurements, catheterization, with or without dobutamine challenge, may be required to resolve the dilemma The current guidelines utilize criteria to define AS that have been derived in part from outcome data obtained from cardiac catheterization. However, the discrepancy that may occur between measurements obtained during catheterization and echocardiography due to pressure recovery and other factors are oftentimes not taken into account.13 There are several reasons that could lead to the degree of AS being over- or underestimated, and a thorough understanding of the causative factors and fundamental principles is essential.13 These reasons are important because the accurate assessment of AS may significantly influence decision-making.13 Reasons for Error and Discrepancy in Aortic Valve Area Measurements

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There are three aortic valve area measurements that are currently utilized in clinical practice--the geometric orifice area (GOA) estimated by imaging planimetry, the effective orifice area (EOA) estimated by Doppler and the Gorlin area (GA) estimated by cardiac catheterization (Table 1; Figure 1). The same valve could potentially have three different measurements depending on the technique utilized. For example, if the valve area by planimetry is calculated at 1.0 cm2, the EOA and Gorlin area could range from 0.6 cm2 to 1.5 cm2 due to the three dimensional structure of the aortic valve and the diameter of the proximal ascending aorta. The GOA is formed by the free edges of the aortic valve while the EOA is the region that corresponds to the vena contracta (Figure 1). Computational fluid dynamics model has shown that AS leads to a funnel-shaped flow profile and flow acceleration through a convergent orifice. The maximum velocity is not at the GOA but rather a little distal to it at the vena contracta, which is the smallest crosssectional area.52-53 The EOA correlates better with clinical outcomes when compared to GOA, even though there is still some debate about the clinical relevancy.52-54 The EOA does not account for the energy loss and pressure recovery downstream from the vena contracta, which is highly dependent on aortic cross sectional area. The measurement of the aortic valve area by catheterization is obtained by the use of the Gorlin formula, which can be inaccurate under low flow conditions.55 Doppler derived values can overestimate the degree of stenosis in patients with moderate AS and small diameter aortas when compared to catheterization (EOA catheterization> EOA Doppler). These concepts have been reviewed further in detail both in the journal and beyond.13;

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Although a complete review of these concepts is beyond the scope of this article, it remains essential that the perioperative echocardiographer understand these concepts so

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that any clinical discrepancies do not compromise perioperative decision-making. 3D Transesophageal Echocardiographic Considerations A common intraoperative technique to calculate the aortic valve area is the continuity equation.13 The continuity equation assumes that the geometry of the left ventricular outflow tract (LVOT) is circular. Recent 3D imaging of the aortic annulus and left ventricular outflow tract by both TEE and computed axial tomography has challenged this geometric assumption since the aortic subannular plane is frequently elliptical with a major diameter, a minor diameter.14; 29; 31 Even if this circular assumption is correct in the individual patient, there are still sources of error within the equation that could lead to an erroneous calculation of the aortic valve area. The most significant cause of error occurs in estimating the LVOT true radius since the calculated value is squared. Multiple trials have demonstrated that 2D TEE can often underestimate the LVOT area because the measured LVOT diameter in the midesophageal long-axis view of the aortic valve is frequently the minor axis of the subannular ellipse.14;

58-59

Since the aortic valve is a 3D structure, customary 2D

planimetry of the aortic valve area may overestimate GOA due to oblique imaging. Aortic valve imaging with 3D TEE may allow a more reliable estimation of the AVA by planimetry because it allows cropping of the image in different planes to enable measurement of the smallest GOA in systole, when the valve is maximally opened.59-61 Comprehensive 3D imaging with echocardiography, computed axial tomography, and cardiac magnetic resonance has demonstrated that the LVOT is not a circle but an ellipse with a major and minor axis. 3D planimetry of the LVOT is more accurate than 2D measurements since it is not based on assumptions but rather is a direct

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measurement.14;

60-65

A recent imaging trial demonstrated that the severity of AS is

overestimated due to an average 17% underestimation of the cross-sectional area of the LVOT, which is due to the incorrect assumption that the LVOT is a circle.63 The measurement of the LVOT by 3D TEE is closer to that measured by cardiac computed tomographic angiography.64-65 Furthermore, 3D planimetry of the aortic valve correlates better with aortic valve area derived from 3D color Doppler than 2D area obtained by the continuity equation.61 In summary, the trials demonstrate that 3D TEE can be valuable in accurately estimating the size of the LVOT and obtaining more precise measurements of the anatomic aortic valve area compared to 2D TEE. The use of 3D data in cases where unanticipated significant AS is encountered has the potential to impact intraoperative decision- making.63-66 Conclusion Incidental AS in the setting of coronary artery bypass surgery presents a challenging set of management issues for the team involved in the operative management of these patients. While the severity of the newly diagnosed AS is the primary determinant of the therapeutic plan, it is clear from this expert review that one must take into consideration multiple surgical and non-surgical factors. Although severe AS in this setting is an indication for AVR, current guidelines advise a balanced approach to the management of moderate AS encountered during CABG. The rapid progress in TAVR and sutureless AVR also offer alternatives for definitive management of moderate AS in this setting that will likely become even safer in the near future.

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Caption

Figure 1: Spatial and Temporal Relationships of Different Aortic Valve Areas (taken from reference 13: Mahmood F, Fritsch M, Maslow A. Unanticipated mild-tomoderate aortic stenosis during coronary artery bypass graft surgery: scope of the problem and its echocardiographic evaluation. J Cardiothorac Vasc Anesth 23: 869-877, 2009 – the Journal of Cardiothoracic Vascular Anesthesia is published by Elsevier: no copyright permission required)

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Table 1: Comparison of Different Aortic Valve Areas Aortic Valve

Definition

Principle Modalities

Challenges

Effective Orifice

Cross-sectional

Continuity Echocardiography Does not

Area

area of vena

equation

Area

account for

contracta

energy loss and pressure recovery

Geometric Orifice Anatomic valve Area

Planimetry Echocardiography May

area

CT

significantly

CMR

overestimate true aortic valve area

Gorlin Area

Region

Bernoulli

Cardiac

May lead to

corresponding to

equation

Catheterization

errors in low

flow energy loss

flow states

CT-Computed Tomography Scanning, CMR-Cardiac Magnetic Resonance. This table was developed by the authors of this expert review--no copyright permission required.

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