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6.1 Commentary
Parodi and associates reported the first successful endovascular aneurysm repair of an abdominal aortic aneurysm in 1991.1 Dake et al. followed in 1994 with the first report of EVAR for a thoracic aortic aneurysm (TEVAR).2
TEVAR and open surgical repair (OSR) share similar indications for treatment of TAA. These indications include: TAA ³ 6 cm, symptomatic thoracic aneurysm regardless of size, and TAA growth rate >3 mm/year.3,4 However, whereas OSR is appropriate only for relatively physiologically fit patients, TEVAR has the advantage of being able to treat less fit patients who might otherwise be turned down for open repair. Most surgeons treating this pathology favour TEVAR as their first option given the fact that the chest cavity does not need to be opened thus avoiding the common pulmonary complications that are associated with OSR. Perhaps the most important advantage of TEVAR is that the thoracic aorta does not need to be cross-clamped. This can obviously lead to deleterious consequences in any patient with cardiac insufficiency or valvular abnormalities. Relative contraindications for standard TEVAR include inadequate proximal and distal landing zone (<2 cm in length), significant tortuosity, extensive aortic arch thrombus, and extensive calcification at the proximal and distal fixation sites.5,6 Patient selection should be based on CTA findings, clinical presentation, and past medical history. [Q2: A, B, D]
Compared to OSR, TEVAR has demonstrated a reduction in 30-day mortality from 11.7% to 2.1%, decreased length of hospital stay, and a lower risk of stroke, end organ failure, spinal cord ischemia, and cardiopulmonary complications. However, TEVAR does result in a higher number of re-interventions compared to OSR, although the majority of these are minimally invasive in nature. There is no difference between TEVAR and OSR of the thoracic aorta in terms of late mortality.7
Preoperative cardiac investigation is indicated for patients who display active ischemic heart symptoms and signs but is not necessary in the majority of patients as balloon aortic occlusion is limited to a few seconds during the procedure. CTA is the preferred imaging modality as it demonstrates the most useful information for both planning and sizing of the endograft procedure. [Q1: B] [Q9: B]
In general TAA occurs in patients with advanced age who commonly have a diseased, angulated and tortuous aortic arch. For this reason, proximal fixation of the thoracic stent graftisoftenthegreatestchallengetosuccess.Twocentimetersofnormalhealthycylindrical aorta (neck) is the absolute minimum for optimal results, with a 20–30% oversizing recommended for the endoprosthesis.3
Positioning may vary depending on surgeon preference. The authors generally prefer the supine patient’s left arm tucked in and the right arm extended. If the case is performed under C-arm fluoroscopy, and lateral views are necessary in order to identify the celiac artery for accurate distal graft placement, then positioning both arms extended is recommended to improve the lateral image. Femoral cutdown is performed on the intended side of delivery of the endoprosthesis. The authors prefer accessing the vessel through concentric double pursestring 5–0 prolene sutures of the femoral artery instead of formal arteriotomy. Contralateral percutaneous access is obtained in standard fashion. After obtaining
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appropriate sheath access to both femoral arteries, standard endovascular technique is used to gain access to the ascending aorta with an extra stiff double curved lunderquist wire (Cook Medical, Inc., Indiana, USA) and the distal wire tip is placed above the aortic valve. A pigtail catheter is placed via the contralateral access just proximal to the subclavian artery. The device is delivered on the stiff wire to the desired location. Digital subtraction angiography (DSA) is preformed under breath holding/apnea state. If absolute accurate positioning is required in reference to the supra-aortic vessels, induced hypotension is recommended using rapid ventricular pacing technique during deployment of the device. This is very well tolerated in the majority of cases but may be contraindicated in patients with significant cardiac insufficiency. The pigtail is retrieved with wire support. In general, we recommend compliant balloon molding of the proximal stent only in the event of obvious type I endoleak and certainly in the presence of induced hypotension to reduce the chance of migration. [Q3: B] [Q4: C]
Permissive hypotension is a technique that permits accurate device deployment, as well as avoiding migration during balloon molding. It can be accomplished by permissive “low grade” hypotension during the deployment and molding balloon phase with the help of nitrates.8 Acute short acting hypotension can be achieved by the use of adenosine, which usually results in resumption of normotension within seconds of hypotension but can often be unpredictable.9,10 The authors prefer rapid ventricular pacing which is safe, reliable, and short acting with resumption of normotension usually occurring only a few seconds after turning off the pacing device.11–13 [Q6: A, B, D]
TEVAR devices generally require a large-profile delivery system ranging in size 22-27 French (Fr). This clearly necessitates the presence of large, femoral-iliac arteries and represents a significant contributor to the risks of access vessel injury. Access vessel injury is the most significant cause of serious morbidity and mortality. The most common site of rupture is the proximal external iliac artery. Iliac accessibility can often be tested with careful use of endovascular dilators, which should clarify the issue of whether the operator should attempt transfemoral introduction or proceed to an iliac conduit.14 As an alternative to conduit placement, the authors prefer directly accessing the common iliac vessel through double concentric 4–0 prolene sutures. Other intra-operative complicationsincludeaorticrupture,dissection,aorticbranchvesselocclusions,andlowerextremity embolism. During deployment, the utmost care should be exercised to avoid an unnecessary windsock effect that may, in some cases, lead to instability or even migration or displacement of the proximal end of the device. This undesirable consequence may be avoidedbycontinuousfluoroscopicvisualizationduringdeployment,permissivehypotension techniques described, and the use of devices with modifications designed to counter this effect such as the newest generation Cook TX2 thoracic device. Severely angulated aortic arches can often lead to non-apposition of the inferior aortic wall with the fabric of the proximal covered stent leading to the characteristic “Birds Beak” appearance on angiography with possible consequential type I endoleak. This issue appears to be resolved with a technological modification of the Cook TX2 thoracic graft with Cook’s most recent generation TX2 Pro-Form graft.
Post-implantation syndrome can sometimes occur with transient elevation of body tem- peratureandC-reactiveproteinwithmildleukocytosis.Thisphenomenonisoftenobserved in cases of large segment coverage and the use of multiple devices and/or extensions.2,15
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Stroke has been identified as a common complication of TEVAR, with an incidence rangingfrom0%to8%.Riskfactorsforstrokeincludehistoryofpreoperativestroke,CTgrade IV atheroma (5 mm) in the aortic arch, proximal descending aorta coverage, and long segment coverage.16 [Q5]
TEVAR is also associated with a 3–6% incidence of spinal cord ischemia. Risk factors for spinal cord ischemia include prior abdominal aortic repair, length of thoracic aortic coverage, hypogastric artery interruption, subclavian artery coverage, emergent repair, intra-operative hemorrhage and sustained hypotension.17–20
Coverage of the thoracic aorta may be categorized as in Fig. 6.5 below.
A-coverage from the origin of the left subclavian artery to the T6 vertebral level, B-coverage from T6 to the diaphragm and C-coverage of the entire descending thoracic aorta from the left subclavian artery to the diaphragm.20,21 This can often be helpful in conveying spinal cord ischemia risk to patients and their families. Category C obviously has the highest risk of paraplegia (5–10%).
With respect to post-procedural care, all patients should be transferred to a monitored settingpostoperatively.Multipleparametersshouldbemonitoredclosely.Mostimportantly, blood pressure should be controlled (MAP > 80 mmHg), avoiding high blood pressure (SBP > 160) to minimize the chance of stent migration as well as hypertensive medical complications such as stroke. Urine output should be recorded, and regular neurological assessment should be carried out to assess for stroke and spinal cord ischemia. Patients with cerebrospinal fluid (CSF) drains should have continuous CSF pressure monitoring and CSF should be drained according to a standardized protocol.22,23 [Q7] [Q8: A, B, C, D]
Case number 2 describes a situation in which there is inadequate length of healthy aorta distal to the left carotid artery for an adequate seal. A hybrid procedure consisting ofextra-anatomicbypass(righttoleftcarotid-carotidbypasswithorwithoutaleftcarotid- subclavian bypass) and TEVAR was chosen as the treatment option.24 Recently, technological innovation has demonstrated the possibility of circumventing debranching
Extent A |
Extent B |
Extent C |
(L. subclavian a. to T6) |
(T6 to diaphragm) |
(L. subclavian a. to diaphragm) |
Fig. 6.5 Extent of aortic coverage during TEVAR
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procedures with fenestrated/scalloped and branched arch grafts. However, further cases and published case series are necessary before these procedures become ready for prime time. [Q10: A, B]
Ifextra-anatomicbypassisbeingconsideredforaorticarchdebranching,carotidduplex ultrasound is mandatory to assess for occlusive disease as well as vertebral artery flow dynamics. Carotid endarterectomy may need to be performed in conjunction with the bypass. [Q11: C]
In some instances, it is acceptable to cover the origin of the subclavian artery with the thoracic aortic stent graft without subclavian revascularization, however carotid-subcla- vian bypass should be considered in patients who have radiological evidence of a dominant left vertebral artery and in patients who demonstrated the following: aberrant origin of the left vertebral artery, history of CABG using the left internal mammary artery, history of AAA repair, occluded or diseased hypogastric arteries, patent left axillary-femoral bypass graft, functional left arm arteriovenous fistula, and in any patients who require long segment coverage with TEVAR (B, C extent).16,25 [Q12: A. B, C]
The authors prefer staging the extra-anatomic debranching procedures when possible. Advantages to this method include minimizing operative time, and identifying the etiology of potential neurological complications after each procedure. [Q13]
References
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2. 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. N Engl J Med. (Dec 29) 1994;331(26):1729-1734.
3. Katzen BT, Dake MD, MacLean AA, Wang DS. Endovascular repair of abdominal and thoracic aortic aneurysms. Circulation. (Sept 13) 2005;112(11):1663-1675.
4. Cambria RP, Crawford RS, Cho JS, et al. A multicenter clinical trial of endovascular stent graft repair of acute catastrophes of the descending thoracic aorta. J Vasc Surg. (Dec) 2009;50(6):1255-1264. e1251-1254.
5. Jones LE. Endovascular stent grafting of thoracic aortic aneurysms: technological advancements provide an alternative to traditional surgical repair. J Cardiovasc Nurs. (Nov–Dec) 2005;20(6):376-384.
6. Patel HJ, Williams DM, Upchurch GR Jr, et al. A comparison of open and endovascular descending thoracic aortic repair in patients older than 75 years of age. Ann Thorac Surg. (May) 2008;85((5):1597-1603. discussion 1603-1594.
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9. DorrosG,CohnJM.Adenosine-inducedtransientcardiacasystoleenhancesprecisedeployment of stent-grafts in the thoracic or abdominal aorta. J Endovasc Surg. (Aug) 1996;3(3):270-272.
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10.Kahn RA, Moskowitz DM, Marin ML, et al. Safety and efficacy of high-dose adenosineinduced asystole during endovascular AAA repair. J Endovasc Ther. (Aug) 2000;7(4):292-296.
11.Pornratanarangsi S, Webster MW, Alison P, Nand P. Rapid ventricular pacing to lower blood pressure during endograft deployment in the thoracic aorta. Ann Thorac Surg. (May) 2006;81(5):e21-23.
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14.CriadoFJ.Iliacarterialconduitsforendovascularaccess:technicalconsiderations.JEndovasc Ther. (Jun) 2007;14(3):347-351.
15.Criado FJ, Barnatan MF, Rizk Y, Clark NS, Wang CF. Technical strategies to expand stentgraft applicability in the aortic arch and proximal descending thoracic aorta. J Endovasc Ther. 2002;9(Suppl 2):II32-38.
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17.Buth J, Harris PL, Hobo R, et al. Neurologic complications associated with endovascular repair of thoracic aortic pathology: incidence and risk factors. A study from the European Collaborators on Stent/Graft Techniques for Aortic Aneurysm Repair (EUROSTAR) registry. J Vasc Surg. (Dec) 2007;46(6):1103-1110. discussion 1110-1101.
18.Chiesa R, Melissano G, Marrocco-Trischitta MM, Civilini E, Setacci F. Spinal cord ischemia after elective stent-graft repair of the thoracic aorta. J Vasc Surg. (Jul) 2005;42(1):11-17.
19.Kawaharada N, Morishita K, Kurimoto Y, et al. Spinal cord ischemia after elective endovascular stent-graft repair of the thoracic aorta. Eur J Cardiothorac Surg. (Jun) 2007;31(6): 998-1003. discussion 1003.
20.GutscheJT,CheungAT,McGarveyML,etal.Riskfactorsforperioperativestrokeafterthoracic endovascular aortic repair. Ann Thorac Surg. (Oct) 2007;84(4)):1195-1200. discussion 1200.
21.Feezor RJ, Martin TD, Hess PJ Jr, et al. Extent of aortic coverage and incidence of spinal cord ischemia after thoracic endovascular aneurysm repair. Ann Thorac Surg. (Dec) 2008;86(6): 1809-1814. discussion 1814.
22.Estrera AL, Miller CC 3rd, Chen EP, et al. Descending thoracic aortic aneurysm repair: 12-year experience using distal aortic perfusion and cerebrospinal fluid drainage. Ann Thorac Surg. (Oct) 2005;80(4):1290-1296. discussion 1296.
23.Hnath JC, Mehta M, Taggert JB, et al. Strategies to improve spinal cord ischemia in endovascular thoracic aortic repair: outcomes of a prospective cerebrospinal fluid drainage protocol. J Vasc Surg. (Oct) 2008;48(4):836-840.
24.Cina CS, Safar HA, Lagana A, Arena G, Clase CM. Subclavian carotid transposition and bypass grafting: consecutive cohort study and systematic review. J Vasc Surg. (Mar) 2002;35(3):422-429.
25.Feezor RJ, Lee WA. Management of the left subclavian artery during TEVAR. Semin Vasc Surg. (Sept) 2009;22(3):159-164.