- Email: [email protected]
Sizing and planning for TEVAR: How to do?
Reviews in Vascular Medicine 1 (2013) 43–47
Contents lists available at ScienceDirect
Reviews in Vascular Medicine journal homepage: www.elsevier.com/locate/rvm
REVIEW
Sizing and planning for TEVAR: How to do? Bernd Muehling n Division of Vascular Surgery, Department of Cardiothoracic and Vascular Surgery, University of Ulm, Albert Einstein Allee 23, 89081 Ulm, Germany
art ic l e i nf o Article history: Received 3 July 2013 Accepted 9 July 2013
Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Stentgraft planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Get adequate Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Create centreline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Perform measurements of lengths and diameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Access vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Specific features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Overstenting of the left subclavian artery (LSA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Traumatic aortic injury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Stanford B-dissections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Adjunctive procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Introduction Since the milestone publication by Dake et al. thoracic endovascular aortic repair (TEVAR) has become a standardized procedure in endovascular aortic surgery [1]. It is performed in various pathologies of the thoracic aorta, e.g. aneurysms, traumatic rupture, dissections and penetrating aortic ulcers. Midterm results are encouraging with up to 97% technical success, 30-d mortality of 5.5% and neurological complications about 2–3% [2,3]. For some indications TEVAR is nowadays considered to be treatment of first choice: patients with blunt traumatic aortic injuries who undergo TEVAR show significant better survival as compared to open repair in this situation [4]. For degenerative aortic aneurysm there is consensus that TEVAR demonstrates low early operative mortality rates of about 5.7% [5]. However in the long term late complications such as endoleaks and graft migration may occur and require secondary interventions [6,7]. Nonetheless the good results in
terms of morbidity and mortality have driven the endovascular approach to the thoracic aorta and reduced numbers of open repair in the descending part of it [8]. Like in open surgery that requires years of training TEVAR also requires adequate surgical and interventional skills including proper planning of the procedure. However there are hardly any reports or reviews dealing with this issue. This is predominantly attributed to the fact that TEVAR is more complicated and not as standardizable as infrarenal endovascular repair. Pathologies are diverse, the anatomy is not as straight as in the infrarenal aorta and most pathologies involve supraaortic vessels, predominantly the lefts subclavian artery. Hence the aim of this review is to give a hand to all those endovascular surgeons who plan and perform TEVAR procedures.
Stentgraft planning Get adequate Images
n
Tel.: +49 731 500 54004; fax: +49 731 500 54003. E-mail address: [email protected]
2212-0211/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rvm.2013.07.001
The first step in stentgraft planning be it infrarenal or thoracic is to get a multidetector CT as it provides better resolution especially for
44
B. Muehling / Reviews in Vascular Medicine 1 (2013) 43–47
vascular imaging [9]. From these scans 3D reconstructions can be generated for planning of the procedure; for carotid artery stenting it has been shown that 3D CT angiographic assessment prior to stenting significantly influenced the endovascular plan [10]. As a consequence planning TEVAR requires imaging systems that are able to create 3D CT angiographic assessment of the aorta along with image processing techniques that allow proper measurements. For planning of TEVAR it is necessary to scan the aorta as a whole, i.e. the scan should include the pathology itself, the ascending aorta, origin of supraaortic trunks, aortic arch, descending and abdominal aorta and access vessels. Create centreline After having scanned the aorta with a multislice CT the next step is to create the centreline for the subsequent measurements of lengths and diameters. There are several companies that provide software for centreline measurements. No matter which company one chooses the principle is always the same. After having loaded the pictures the next step is to place seeds in order to segment the aorta for post processing (Fig. 1). One should place the seeds always in a manner that the first and last seed is central and distal enough to the pathology. In TEVAR the first seed should always be central to the brachiocephalic trunk so that the origins of the supraaortic vessels are included. After having placed the seeds the centreline is created by the software using a “auto track” or “create centreline” button. The result is a stretched view of the aorta itself (Fig. 2). Perform measurements of lengths and diameters To choose the appropriate stentgraft it is important to define central and distal landing zones. Companies provide measurement sheets that can help to carry out the complete measurements needed (Fig. 3). As for the diameters the measurements should be performed in the central and distal non diseased segment of the aorta (Fig. 4a and b). To obtain optimal sealing in the central and distal landing zones stentgrafts are usually oversized. There is a lack of evidence how excessive this oversizing should be. For endovascular repair of
Fig. 2. Centerline reconstruction of a posttraumatic thoracic aortic aneurysm. Brachiocephalic trunk, left common carotid artery and left subclavian are visible.
infrarenal aortic aneurysms van Prehn and co-workers published a review and concluded that an oversizing of 10–20% “appears to be relatively safe and preferable” [11]. For TEVAR no data exist dealing with this issue. From our clinical experience the same oversizing (10–20%) in degenerative aneurysmas causes usually no problems; however there are specific conditions in which oversizing of 20% might be too much (see below). As for stentgrafts lengths the graft should cover the pathology itself and (depending on the instructions for use of the companies) have a distal and central non diseased segment of the aorta of at least 15 mm in order to achieve good sealing of the graft itself. Access vessels Endovascular access to the thoracic aorta is usually achieved via the femoral and iliac arteries. Hence during planning it is important to look at these access vessels. They should have a diameter of at least 8 mm and no severe kinking or calcifications. As an alternative in case of femoral calcifications or access vessel problems the iliac artery can be exposed via a retroperitoneal approach. In case of occlusion of an iliac artery the other one has to be used (Fig. 5a and b) Specific features Overstenting of the left subclavian artery (LSA) Overstenting of the LSA be it intentionally or accidentally in TEVAR is always an issue of debate. Some authors claim that the risk for stroke and paraplegia is increased in LSA overstenting; in contrast there are also publications that do not confirm these risks. Our policy is a selective approach in this topic according to Lee et al. [12]. Indications for LSA revascularization in our department include:
Patent LIMA bypass Dominant left vertrebral artery Left upper extremity dialysis access Status after infrarenal aortic repair Long thoracic aortic stentgraft (20 cm) Aortic dissection
Usually we achieve revascularization by transposition, if not possible by carotid-subclavian bypass (Fig. 6a and b).
Fig. 1. Placement of several seeds for centreline creation.
Traumatic aortic injury In traumatic rupture there are specific features to be aware of: First these are usually younger patients with a so called “gothic arch” which means that the aortic arch in the region of the rupture forms a sharp curve which can lead to misalignment and the so
B. Muehling / Reviews in Vascular Medicine 1 (2013) 43–47
45
Fig. 3. Sizing sheet for TEVAR procedures.
Fig. 4. (a) and (b) Diameter measurements of the central and distal landing zone.
called “bird beak configuration”. Second patients with traumatic rupture are usually in shock after loss of their blood volume so that the initial diameter of the aorta in the intended landing zones can differ up to 12% as compared to hemodynamically stable patients [13]. As a consequence stentgrafts in traumatic rupture should be oversized approximately 10–20% and the left subclavain artery (LSA) should be intentionally covered in order to achieve acceptable alignment at the inner curve of the aortic arch. In our experience intentional overstenting of the LSA in these cases requires revascularization very rarely and causes no harm.
Stanford B-dissections Endografting of B-dissections requires first of all accurate assessment of the access vessels. Typically the dissection involves the iliac arteries and it is easier to come into the true lumen from one side. Apart from that a transesophageal echocardiography should be used to verifiy the guide wire location in the true lumen. As for sizing of diameters the diameter of the stentgraft is determined by the diameter of the central landing zone as the distal landing zone in the true lumen is habitually half moon
shaped. In our experience TEVAR in dissections requires revascularization of the LSA prior to endografting in order to reduce the risk of paraplegia. Some spinal arteries arise from the false lumen and thrombose after entry sealing. Nonetheless permanent paraplegia can occur.
Adjunctive procedures Cerebrospinal fluid drainage (CSFD). Just like in open repair of the descending aorta TEVAR carries the risk of paraplegia. As for open repair rates of spinal cord ischemia (SCI) are approximately 20% depending upon the extent of repair, for TEVAR spinal damage rates are about 4%. Risk factors that contribute to SCI are long segment of the aorta to be stented, prior abdominal aortic aneurysm (AAA) repair, hypotension and overstenting of the left subclavian artery. One adjunct to overcome the problem of spinal cord ischemia is the use of a CSFD. Yet a recently published review by Wong and co-workers could not demonstrate an advantage of prophylactic CSFD in patients undergoing TEVAR [3]. Hence our policy is to use prophylactic CSFD only in patients at risk as mentioned above.
46
B. Muehling / Reviews in Vascular Medicine 1 (2013) 43–47
Fig. 5. (a) and (b) not suitable access vessels: occlusion of the left iliac artery and severe kinking.
Fig. 6. (a) and (b): Carotid subclavian bypass and transposition of the left subclavian artery
Cardiac arrest. Accurate deployment of the endograft in the thoracic aorta is absolutely mandatory for the technical success of the procedure. Some newer devices provide a so called tip capture that reduces the effects of the wind sock in the thoracic aorta during deployment; nonetheless the closer the procedures is to the LSA or even in the aortic arch cardiac arrest allows precise deployment in the central landing zone. Currently tow techniques are used for cardiac arrest in order to reduce blood pressure and the windsock effect: rapid pacing and adenosine intravenously. As for rapid pacing serious complications such as ventricular tachyarrhythmia are reported to be about 1% [14]. As for adenosine no comparable severe complications are reported so far. Our strategy in this issue is to use adenosine in TEVAR procedures that involve the aortic arch or ascending aorta.
Follow up after TEVAR. Perioperative complications after TEVAR are very low. However in the long term secondary interventions may be necessary. Hence it is mandatory to follow the patients by
annual CT scans. Depending upon the pathology treated follow up regimen after TEVAR can differ: Especially in patients that have undergone endovascular entry sealing due to post-dissections aneurysms re-interventions are frequent (Oberhuber et al. [7]). So these patients should be followed very closely. In patients that have undergone TEVAR due to traumatic aortic injury follow up for 5 years is sufficient in our mind as device related secondary problems such as graft migration or stent fracture are not observed in the mid term [15] Our policy in following the patients is to perform a contrast enhanced CT before discharge, after three and twelve months and annually thereafter.
Conclusion TEVAR is safe and in some cases first line treatment of thoracic aortic disease. However technical and clinical success can only be achieved by proper planning of the procedure itself and exact sizing of the endograft. Planning of thoracic procedures is more
B. Muehling / Reviews in Vascular Medicine 1 (2013) 43–47
challenging than planning of infrarenal procedures as pathologies are miscellaneous and usually the supraaortic vessels are involved.
[8]
References [1] Dake MD, Miller DC, Semba CP, Mitchell RS, Walker PJ, Liddell RP. Transluminal placement of endovascular stent-grafts for the treatment of descending thoracic aortic aneurysms. The New England Journal of Medicine 1994;331 (26):1729–1734 (PubMed PMID: 7984192). [2] Sayed S, Thompson MM. Endovascular repair of the descending thoracic aorta: evidence for the change in clinical practice. Vascular 2005;13(3):148–157 (Review. PubMed PMID: 15996372). [3] Wong CS, Healy D, Canning C, Coffey JC, Boyle JR, Walsh SR. A systematic review of spinal cord injury and cerebrospinal fluid drainage after thoracic aortic endografting. Journal of Vascular Surgery 2012;56(5):1438–1447, http: //dx.doi.org/10.1016/j.jvs.2012.05.075 (Epub 2012 Aug 9. Review. PubMed PMID: 22884456). [4] Azizzadeh A, Charlton-Ouw KM, Chen Z, Rahbar MH, Estrera AL, Amer H, Coogan SM, Safi HJ. An outcome analysis of endovascular versus open repair of blunt traumatic aortic injuries. Journal of Vascular Surgery 2013;57(1):108–114, http://dx.doi.org/10.1016/j.jvs.2012.05.110 (discussion 115. Epub 2012 Nov 8. PubMed PMID: 23141678). [5] Svensson LG, Kouchoukos NT, Miller DC, Bavaria JE, Coselli JS, Curi MA, Eggebrecht H, Elefteriades JA, Erbel R, Gleason TG, Lytle BW, Mitchell RS, Nienaber CA, Roselli EE, Safi HJ, Shemin RJ, Sicard GA, Sundt 3rd TM, Szeto WY, Wheatley 3rd GH. Society of thoracic surgeons endovascular surgery task force. Expert consensus document on the treatment of descending thoracic aortic disease using endovascular stent-grafts. The Annals of Thoracic Surgery 2008;1 Suppl:S1–41, http://dx.doi.org/10.1016/j.athoracsur.2007. 10.099 (PubMed PMID: 18083364). [6] Lee CJ, Rodriguez HE, Kibbe MR, Malaisrie SC, Eskandari MK. Secondary interventions after elective thoracic endovascular aortic repair for degenerative aneurysms. Journal of Vascular Surgery 2013;57(5):1269–1274, http://dx. doi.org/10.1016/j.jvs.2012.10.124 (Epub 2013 Jan 24. PubMed PMID: 2335 2360). [7] Oberhuber A, Winkle P, Schelzig H, Orend KH, Muehling BM. Technical and clinical success after endovascular therapy for chronic type B aortic
[9]
[10]
[11]
[12]
[13]
[14]
[15]
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dissections. Journal of Vascular Surgery 2011;54(5):1303–1309, http://dx.doi. org/10.1016/j.jvs.2011.05.020 (Epub 2011 Jul 13. PubMed PMID: 21741793). Jonker FH, Verhagen HJ, Lin PH, Heijmen RH, Trimarchi S, Lee WA, Moll FL, Atamneh H, Rampoldi V, Muhs BE. Open surgery versus endovascular repair of ruptured thoracic aortic aneurysms. Journal of Vascular Surgery 2011;53 (5):1210–1216, http://dx.doi.org/10.1016/j.jvs.2010.10.135 (Epub 2011 Feb 5. PubMed PMID: 21296537). Duddalwar VA. Multislice CT angiography: a practical guide to CT angiography, in vascular imaging and intervention. British Journal of Radiology 2004;77 (Spec No 1):S27–38 (Review. PubMed PMID: 15546840). Wyers MC, Powell RJ, Fillinger MF, Nolan BW, Cronenwett JL. The value of 3DCT angiographic assessment prior to carotid stenting. Journal of Vascular Surgery 2009;49(3):614–622, http://dx.doi.org/10.1016/j.jvs.2008.10.015 (PubMed PMID: 19268765). van Prehn J, Schlösser FJ, Muhs BE, Verhagen HJ, Moll FL, van Herwaarden JA. Oversizing of aortic stent grafts for abdominal aneurysm repair: a systematic review of the benefits and risks. European Journal of Vascular and Endovascular Surgery 2009;38(1):42–53, http://dx.doi.org/10.1016/j.ejvs.2009.03.025 (Epub 2009 May 9. Review. PubMed PMID: 19428273). Lee TC, Andersen ND, Williams JB, Bhattacharya SD, McCann RL, Hughes GC. Results with a selective revascularization strategy for left subclavian artery coverage during thoracic endovascular aortic repair. The Annals of Thoracic Surgery 2011;92(1):97–102, http://dx.doi.org/10.1016/j.athoracsur.2011.03.089 (discussion 102-3. PubMedPMID: 21718834; PubMed Central PMCID: PMC32 73700). Jonker FH, Verhagen HJ, Mojibian H, Davis KA, Moll FL, Muhs BE. Aortic endograft sizing in trauma patients with hemodynamic instability. Journal of Vascular Surgery 2010;52(1):39–44, http://dx.doi.org/10.1016/j.jvs.2010.02. 256 (Epub 2010 May 23. PubMed PMID: 20494542). Murphy JJ. Current practice and complications of temporary transvenous cardiac pacing. British Medical Journal 1996;312(7039):1134 (PubMed PMID: 8620131; PubMed Central PMCID: PMC2350635). Thiere M, Oberhuber A, Link J, Riepl C, Orend KH, Muehling B. Successful endovascular repair of blunt traumatic thoracic aortic injury has no effect on acute or mid-term outcom of poly-traumatized patients: a demand for an excellent initial endovsacular treatment. The Italian journal of Vascular and Endovacular Surgery 2013;20:27–34.
Contents lists available at ScienceDirect
Reviews in Vascular Medicine journal homepage: www.elsevier.com/locate/rvm
REVIEW
Sizing and planning for TEVAR: How to do? Bernd Muehling n Division of Vascular Surgery, Department of Cardiothoracic and Vascular Surgery, University of Ulm, Albert Einstein Allee 23, 89081 Ulm, Germany
art ic l e i nf o Article history: Received 3 July 2013 Accepted 9 July 2013
Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Stentgraft planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Get adequate Images. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Create centreline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Perform measurements of lengths and diameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Access vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Specific features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Overstenting of the left subclavian artery (LSA). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Traumatic aortic injury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Stanford B-dissections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Adjunctive procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Introduction Since the milestone publication by Dake et al. thoracic endovascular aortic repair (TEVAR) has become a standardized procedure in endovascular aortic surgery [1]. It is performed in various pathologies of the thoracic aorta, e.g. aneurysms, traumatic rupture, dissections and penetrating aortic ulcers. Midterm results are encouraging with up to 97% technical success, 30-d mortality of 5.5% and neurological complications about 2–3% [2,3]. For some indications TEVAR is nowadays considered to be treatment of first choice: patients with blunt traumatic aortic injuries who undergo TEVAR show significant better survival as compared to open repair in this situation [4]. For degenerative aortic aneurysm there is consensus that TEVAR demonstrates low early operative mortality rates of about 5.7% [5]. However in the long term late complications such as endoleaks and graft migration may occur and require secondary interventions [6,7]. Nonetheless the good results in
terms of morbidity and mortality have driven the endovascular approach to the thoracic aorta and reduced numbers of open repair in the descending part of it [8]. Like in open surgery that requires years of training TEVAR also requires adequate surgical and interventional skills including proper planning of the procedure. However there are hardly any reports or reviews dealing with this issue. This is predominantly attributed to the fact that TEVAR is more complicated and not as standardizable as infrarenal endovascular repair. Pathologies are diverse, the anatomy is not as straight as in the infrarenal aorta and most pathologies involve supraaortic vessels, predominantly the lefts subclavian artery. Hence the aim of this review is to give a hand to all those endovascular surgeons who plan and perform TEVAR procedures.
Stentgraft planning Get adequate Images
n
Tel.: +49 731 500 54004; fax: +49 731 500 54003. E-mail address: [email protected]
2212-0211/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rvm.2013.07.001
The first step in stentgraft planning be it infrarenal or thoracic is to get a multidetector CT as it provides better resolution especially for
44
B. Muehling / Reviews in Vascular Medicine 1 (2013) 43–47
vascular imaging [9]. From these scans 3D reconstructions can be generated for planning of the procedure; for carotid artery stenting it has been shown that 3D CT angiographic assessment prior to stenting significantly influenced the endovascular plan [10]. As a consequence planning TEVAR requires imaging systems that are able to create 3D CT angiographic assessment of the aorta along with image processing techniques that allow proper measurements. For planning of TEVAR it is necessary to scan the aorta as a whole, i.e. the scan should include the pathology itself, the ascending aorta, origin of supraaortic trunks, aortic arch, descending and abdominal aorta and access vessels. Create centreline After having scanned the aorta with a multislice CT the next step is to create the centreline for the subsequent measurements of lengths and diameters. There are several companies that provide software for centreline measurements. No matter which company one chooses the principle is always the same. After having loaded the pictures the next step is to place seeds in order to segment the aorta for post processing (Fig. 1). One should place the seeds always in a manner that the first and last seed is central and distal enough to the pathology. In TEVAR the first seed should always be central to the brachiocephalic trunk so that the origins of the supraaortic vessels are included. After having placed the seeds the centreline is created by the software using a “auto track” or “create centreline” button. The result is a stretched view of the aorta itself (Fig. 2). Perform measurements of lengths and diameters To choose the appropriate stentgraft it is important to define central and distal landing zones. Companies provide measurement sheets that can help to carry out the complete measurements needed (Fig. 3). As for the diameters the measurements should be performed in the central and distal non diseased segment of the aorta (Fig. 4a and b). To obtain optimal sealing in the central and distal landing zones stentgrafts are usually oversized. There is a lack of evidence how excessive this oversizing should be. For endovascular repair of
Fig. 2. Centerline reconstruction of a posttraumatic thoracic aortic aneurysm. Brachiocephalic trunk, left common carotid artery and left subclavian are visible.
infrarenal aortic aneurysms van Prehn and co-workers published a review and concluded that an oversizing of 10–20% “appears to be relatively safe and preferable” [11]. For TEVAR no data exist dealing with this issue. From our clinical experience the same oversizing (10–20%) in degenerative aneurysmas causes usually no problems; however there are specific conditions in which oversizing of 20% might be too much (see below). As for stentgrafts lengths the graft should cover the pathology itself and (depending on the instructions for use of the companies) have a distal and central non diseased segment of the aorta of at least 15 mm in order to achieve good sealing of the graft itself. Access vessels Endovascular access to the thoracic aorta is usually achieved via the femoral and iliac arteries. Hence during planning it is important to look at these access vessels. They should have a diameter of at least 8 mm and no severe kinking or calcifications. As an alternative in case of femoral calcifications or access vessel problems the iliac artery can be exposed via a retroperitoneal approach. In case of occlusion of an iliac artery the other one has to be used (Fig. 5a and b) Specific features Overstenting of the left subclavian artery (LSA) Overstenting of the LSA be it intentionally or accidentally in TEVAR is always an issue of debate. Some authors claim that the risk for stroke and paraplegia is increased in LSA overstenting; in contrast there are also publications that do not confirm these risks. Our policy is a selective approach in this topic according to Lee et al. [12]. Indications for LSA revascularization in our department include:
Patent LIMA bypass Dominant left vertrebral artery Left upper extremity dialysis access Status after infrarenal aortic repair Long thoracic aortic stentgraft (20 cm) Aortic dissection
Usually we achieve revascularization by transposition, if not possible by carotid-subclavian bypass (Fig. 6a and b).
Fig. 1. Placement of several seeds for centreline creation.
Traumatic aortic injury In traumatic rupture there are specific features to be aware of: First these are usually younger patients with a so called “gothic arch” which means that the aortic arch in the region of the rupture forms a sharp curve which can lead to misalignment and the so
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Fig. 3. Sizing sheet for TEVAR procedures.
Fig. 4. (a) and (b) Diameter measurements of the central and distal landing zone.
called “bird beak configuration”. Second patients with traumatic rupture are usually in shock after loss of their blood volume so that the initial diameter of the aorta in the intended landing zones can differ up to 12% as compared to hemodynamically stable patients [13]. As a consequence stentgrafts in traumatic rupture should be oversized approximately 10–20% and the left subclavain artery (LSA) should be intentionally covered in order to achieve acceptable alignment at the inner curve of the aortic arch. In our experience intentional overstenting of the LSA in these cases requires revascularization very rarely and causes no harm.
Stanford B-dissections Endografting of B-dissections requires first of all accurate assessment of the access vessels. Typically the dissection involves the iliac arteries and it is easier to come into the true lumen from one side. Apart from that a transesophageal echocardiography should be used to verifiy the guide wire location in the true lumen. As for sizing of diameters the diameter of the stentgraft is determined by the diameter of the central landing zone as the distal landing zone in the true lumen is habitually half moon
shaped. In our experience TEVAR in dissections requires revascularization of the LSA prior to endografting in order to reduce the risk of paraplegia. Some spinal arteries arise from the false lumen and thrombose after entry sealing. Nonetheless permanent paraplegia can occur.
Adjunctive procedures Cerebrospinal fluid drainage (CSFD). Just like in open repair of the descending aorta TEVAR carries the risk of paraplegia. As for open repair rates of spinal cord ischemia (SCI) are approximately 20% depending upon the extent of repair, for TEVAR spinal damage rates are about 4%. Risk factors that contribute to SCI are long segment of the aorta to be stented, prior abdominal aortic aneurysm (AAA) repair, hypotension and overstenting of the left subclavian artery. One adjunct to overcome the problem of spinal cord ischemia is the use of a CSFD. Yet a recently published review by Wong and co-workers could not demonstrate an advantage of prophylactic CSFD in patients undergoing TEVAR [3]. Hence our policy is to use prophylactic CSFD only in patients at risk as mentioned above.
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Fig. 5. (a) and (b) not suitable access vessels: occlusion of the left iliac artery and severe kinking.
Fig. 6. (a) and (b): Carotid subclavian bypass and transposition of the left subclavian artery
Cardiac arrest. Accurate deployment of the endograft in the thoracic aorta is absolutely mandatory for the technical success of the procedure. Some newer devices provide a so called tip capture that reduces the effects of the wind sock in the thoracic aorta during deployment; nonetheless the closer the procedures is to the LSA or even in the aortic arch cardiac arrest allows precise deployment in the central landing zone. Currently tow techniques are used for cardiac arrest in order to reduce blood pressure and the windsock effect: rapid pacing and adenosine intravenously. As for rapid pacing serious complications such as ventricular tachyarrhythmia are reported to be about 1% [14]. As for adenosine no comparable severe complications are reported so far. Our strategy in this issue is to use adenosine in TEVAR procedures that involve the aortic arch or ascending aorta.
Follow up after TEVAR. Perioperative complications after TEVAR are very low. However in the long term secondary interventions may be necessary. Hence it is mandatory to follow the patients by
annual CT scans. Depending upon the pathology treated follow up regimen after TEVAR can differ: Especially in patients that have undergone endovascular entry sealing due to post-dissections aneurysms re-interventions are frequent (Oberhuber et al. [7]). So these patients should be followed very closely. In patients that have undergone TEVAR due to traumatic aortic injury follow up for 5 years is sufficient in our mind as device related secondary problems such as graft migration or stent fracture are not observed in the mid term [15] Our policy in following the patients is to perform a contrast enhanced CT before discharge, after three and twelve months and annually thereafter.
Conclusion TEVAR is safe and in some cases first line treatment of thoracic aortic disease. However technical and clinical success can only be achieved by proper planning of the procedure itself and exact sizing of the endograft. Planning of thoracic procedures is more
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challenging than planning of infrarenal procedures as pathologies are miscellaneous and usually the supraaortic vessels are involved.
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