Early Results of Left Carotid Chimney Technique in Endovascular Repair of Acute Non-A Non-B Aortic Dissections

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1 J ENDOVASC THER 477 CLINICAL INVESTIGATION Early Results of Left Carotid Chimney Technique in Endovascular Repair of Acute Non-A Non-B Aortic Dissections Chang Shu, MD, PhD 1 ; Ming-Yao Luo, MD 1,2 ; Quan-Ming Li, MD 1 ; Ming Li, MD 1 ; Tun Wang, MD 1,2 ; and Hao He, MD 1,2 1 Department of Vascular Surgery, Second Xiangya Hospital, Central South University, Changsha, People s Republic of China. 2 Cardiovascular Institute and Fuwai Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. Purpose: To report our early experience with endovascular repair of acute non-a non-b aortic dissections using chimney grafts to preserve blood flow to a left common carotid artery (LCCA) located in the proximal landing zone. Methods: From June 2009 to May 2010, 8 patients (7 men; mean age 49 years, range 29 75) with acute non-a non-b aortic dissection and no adequate proximal sealing zones underwent thoracic endovascular aortic repair (TEVAR). Covered stents were placed parallel to the aortic stent-grafts to restore flow to the LCCAs while extending the proximal fixation zones; the left subclavian arteries were intentionally covered after carefully cerebrovascular assessment. Follow-up examinations included computed tomography (CT) at 2 weeks, 3 months, 6 months, 12 months, and yearly thereafter. Results: All the procedures were completed successfully, with one main aortic stent-graft deployed and one chimney graft implanted in the LCCA. Two retrograde type II endoleaks identified intraoperatively were left untreated but followed closely using CT. There were no instances of puncture site complications, stroke, paralysis, or death during the hospital stay. The 30-day mortality was 0%. During the mean 11.4-month follow-up (range 6 15), there was no mortality, and duplex ultrasound and CT showed patency of all stent-grafts, enlargement of the true lumen, and compression of the false lumen. One type II endoleak disappeared in 2 weeks postoperatively, while the other gradually faded until it was nearly gone at 11 months postoperatively. During follow-up, no renal insufficiency, new late endoleaks, endograft migration, fracture, stent-graft related complications, or deaths were observed. Conclusion: In short-term follow-up, TEVAR combined with the chimney technique seems promising for aortic dissections that involve the aortic arch with inadequate proximal sealing zones. More cases and long-term results are needed to evaluate the safety and efficiency of this alternative endovascular technique. J Endovasc Ther. Key words: thoracic aorta, dissection, non-a non-b aortic dissection, endovascular thoracic aortic repair, common carotid artery, stent-graft, chimney graft Thoracic endovascular aortic repair (TEVAR) has become the first choice for most thoracic aortic pathologies because of its safety and durability. 1 Nevertheless, when the aortic pathology involves or is in proximity to the aortic branches, the endografts must cross their ostia to achieve a good seal. 2 In this setting, a standard angioplasty/stenting technique The authors have no commercial, proprietary, or financial interest in any products or companies described in this article. Address for correspondence and reprints: Chang Shu, Professor of Vascular Surgery, Department of Vascular Surgery, Second Xiangya Hospital of Central South University, No. 139, Renmin Road, Changsha, Hunan, People s Republic of China. changshuvascular@gmail.com ß 2011 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at

2 478 LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR J ENDOVASC THER known as a chimney graft can make it possible to perform TEVAR using off-the-shelf devices. 3 9 The chimney technique is a means of gaining additional fixation length to stabilize the aortic stent-grafts while safeguarding perfusion to the vital branches, especially in emergency settings. 5 First reported by Greenberg and colleagues, 3 the chimney technique has been described in detail by several vascular groups. 4 9 However, all the experience reported thus far has been limited to case reports or small series with short follow-up. Additionally, cases involving complex aortic dissection (AD) treated in this manner are very limited, with only a few cases reported to our knowledge. 4,6,9,10 As the incidence of AD is rather high in China, we report our experience using chimney grafts to retain perfusion to the left common carotid artery (LCCA) when managing acute non-a non-b AD with inadequate proximal sealing zones. To our knowledge, there is no other English-language report on this technique from outside the US and Europe. Patient Sample METHODS Among 128 TEVAR procedures performed by the principle author between June 2009 and May 2010, 8 patients (7 men; mean age 49.0 years, range 29 75) with acute non-a non-b AD underwent TEVAR using the chimney technique during 6 elective and 2 emergent procedures (Table 1). The chimney technique was applied in these patients because the proximal entry tear was located within 1.5 cm of the LCCA origin but.2 cm distal to the origin of the innominate trunk. Informed consent was obtained from each patient, and our institutional review board approved this retrospective study. The patients were admitted to the hospital from 1 to 7 days after symptom onset, so all lesions were acute. The diagnosis of 2-channel non-a-non-b dissection (entry tear located in the arch) was confirmed by contrast-enhanced computed tomographic angiography (CTA) with 3-mm slices and 3-dimensional reconstruction. The lesions extended to the descending aorta in TABLE 1 Characteristics of 8 Patients With Non-A Non-B Aortic Dissection Age, y 49.0 (29 75) Men 7 Hypertension 6 Pregnancy-induced 1 hypertension Behçet s disease 1 Pleural effusion 7 Location of the proximal entry tear Zone 2 7 Zone 3 1 Distance between the entry 9.9 (5 13) tear and the LCCA, mm Continuous data are presented as the means (range); categorical data are given as the counts. LCCA: left common carotid artery, LSA: left subclavian artery. 1, the abdominal aorta in 3, the iliac vessels in 2, and the femoral vessels in 2. Blood pressure and heart rate were routinely controlled to an ideal level as soon as possible. One patient was a 29-year-old woman in puerperium with pregnancy-induced hypertension syndrome whose physiognomy was typical of Marfan syndrome. A 32-year-old man had a history of Behçet s disease; CTA identified a limited AD combined with a pseudoaneurysm that involved the LCCA. The other 6 patients had a 1 to 10-year history of hypertension. Except for the patient with Behçet s disease, the other 7 had pleural effusions of varying degree. As depicted in the article by Ma et al., 11 the proximal entry tear was in zone 2 in 7 patients and zone 3 in one (Fig. 1). The distance between the origin of the LCCA and the proximal entry tear was,15 mm in all. TEVAR With Chimney Graft Implantation Carotid and vertebral artery circulations were assessed by CTA or digital subtraction angiography (DSA) before TEVAR; no patient had a dominant left vertebral artery, so no chimney graft or bypass was considered necessary for the LSA in these patients. The primary treatment goal was coverage of the entry tear with a stent-graft, preferentially the Chinese-made Hercules stent-graft

3 J ENDOVASC THER LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR 479 Figure 1 A zone 3 proximal entry tear in the 29-year-old woman (1: the proximal entry tear is close to the LSA; 2: false lumen; 3: true lumen; 4: true lumen). (Microport Medical, Shanghai, PRC). This device has a 20-mm-long scallop-shaped bare stent in the proximal aspect instead of the anchoring barbs common to the Zenith stentgraft (Cook Inc., Bloomington, IN, USA), which was also used. The Hercules also has a longitudinal support strut that helps avoid axial shortening and minimize graft migration. The Relay stent-graft (Bolton Medical SL, Barcelona, Spain), another option, has a scallop-shaped bare stent in the proximal aspect and a spiral support strut without anchoring barbs. Under general anesthesia, the right common femoral artery (CFA) was exposed through a small incision, and appropriate guidewires and catheters were inserted via the CFA puncture. If the right CFA was not suitable due to high flow from the false lumen, the left CFA was chosen as the access site. After angiography and measurement of the aortic lesions, the aortic endograft and chimney graft were selected using 10% to 20% oversizing for the endograft and 10% for the chimney graft. The aortic stent-graft was introduced upward to the thoracic aorta. The LCCA was exposed through a longitudinal neck incision, and an 8-mm-diameter stentgraft [Fluency (C.R. Bard, Inc., Murray Hill, NJ, USA) or Passager (Boston Scientific, Natick, MA, USA)] was advanced retrograde into the LCCA via a CCA puncture; the chimney graft was positioned (but not deployed) precisely with only a very short segment (0.5 1 cm) in the aortic lumen and the distal segment in the LCCA. Under fluoroscopy and reduced systolic pressure (80 90 mmhg), the aortic stent-graft was deployed using standard techniques, covering the entry tear as well as the ostia of the LSA and LCCA. After the aortic endograft

4 480 LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR J ENDOVASC THER TABLE 2 Details for 8 Patients Treated for Non-A Non-B Aortic Dissection Aortic Stent-Graft Model and Size, mm LCCA Chimney Graft and Size, mm Morbidity Follow-up, mo Latest CT Outcome 1 Hercules Fluency Patent 2 Hercules Fluency 8360 Type II endoleak* 15 Patent 3 Hercules Fluency Patent 4 Hercules Fluency 8360 Type II endoleak{ 11 Patent 5 Hercules Passenger Patent 6 Relay Passenger Patent 7 Relay Fluency Patent 8 Zenith Fluency Patent CT: computed tomography. * Disappeared 2 weeks postoperatively. { Disappeared after 11 months. was released, the status of the LCCA origin was assessed again; the chimney graft was then quickly deployed to preserve flow to the overstented LCCA. The chimney graft was dilated with an 8-mm angioplasty balloon to optimize expansion, making sure the chimney graft was dilated adequately. Finally, the CFA and the LCCA access sites were closed with a 5 0 Prolene (Ethicon, Inc, Somerville, NJ, USA) suture after the procedure was finished. All patients were prescribed oral aspirin (100 mg/d) after TEVAR. Follow-up Patients were scheduled for follow-up through the outpatient service with physical examination and CTA at 2 weeks, 3 months, 6 months, and 12 months postoperatively, and annually thereafter. They were also contacted by telephone from time to time. RESULTS The procedures of all 8 patients were technically successful, with 1 main aortic stent-graft deployed and 1 chimney graft used in the LCCA (Table 2). DSA showed complete exclusion of the proximal entry tear (Fig. 2), and the false lumen along the covered section disappeared at once. No type I endoleak was observed, but 2 retrograde type II endoleaks were detected immediately after TEVAR. The endoleaks were left untreated and surveyed Figure 2 (A) A zone 2 proximal entry tear (indicated by the 1 ) between the LSA and the LCCA. (B) DSA documented complete exclusion of the first entry site, and the false lumen in the covered section of the aorta disappeared at once. 2 denotes the chimney graft, and 3 is the aortic stent-graft.

5 J ENDOVASC THER LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR 481 Figure 3 CTA showed patency of the aortic stent-graft and the chimney graft (CG), enlargement of the true lumen, compression of the false lumen, and total occlusion of the LSA. A residual false lumen in the distal segment of the aorta existed after TEVAR. closely by CTA in the postoperative course, since they were expected to be thrombosed spontaneously based on our experience with these low-flow post-tevar leaks. There were no instances of puncture site complications, ischemia of the left upper extremity, LSA steal syndrome, stroke, paralysis, or death during the hospital stay. During a mean follow-up of 11.4 months (range 6 15), there were no deaths, and CTA showed all the stent-grafts and chimney grafts to be patent, with enlargement of the true lumen and compression of the false lumen (Fig. 3), which persisted in the distal aorta in 3 cases. There were no instances of renal insufficiency, new late endoleaks, endograft obstruction, migration, fracture, or other stentgraft related complications. One type II endoleak disappeared at 2 weeks postoperatively, while the other endoleak decreased gradually (Fig. 4A) until it had nearly faded away by 11 months postoperatively (Fig. 4B); this patient remains under close surveillance. She was also the only patient who was advised to stop taking aspirin 1 month postoperatively. The patient with Behçet s disease remains

6 482 LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR J ENDOVASC THER Figure 4 (A) A type II endoleak (indicated by the 1 ) decreased gradually at 3 months and was nearly gone (B) by 11 months postoperatively. (C) The chimney graft (indicated by 2 and 3 ) is in good condition. under medical therapy in the rheumatology clinic. DISCUSSION The aortic arch is a challenging site for endovascular repair, which is made more difficult if there is no adequate proximal sealing zone because of lesion proximity to the supra-aortic branches. In these cases, hybrid procedures 11 or more complex endovascular techniques, such as fenestrated/ branched stent-grafts 2 or the chimney technique, would be required for the repair. A hybrid repair would entail total or hemi-arch transpositions and associated endovascular maneuvers. 11 Although effective, this method is traumatic and may be dangerous for some high-risk patients. Fenestrated and branched stent-grafts can preserve vital aortic branches in a minimally invasive manner, 2 but they require considerable manipulation in the aortic arch. Additionally, as custom-made devices, these fenestrated and branched stent-grafts require several weeks to manufacture, which obviously limits their applicability, especially in the emergency setting. The chimney technique, which was called endobranching by Criado, 12 involves deploying a covered or bare metal stent parallel to the aortic endograft, thereby creating a conduit that runs outside the main aortic endograft to retain or restore blood flow into overstented aortic side branches along the sealing zones. Generally, chimney grafts are smaller than the aortic endografts. Smallerdiameter stents provide greater radial force than larger ones in theory, 5 so they can maintain patency of the side branches. Advantageously, the chimney technique uses off-the-shelf instead of custom-made devices, so it can be performed in emergent cases. In our center, the indications for the chimney technique include inadequate landing zones for conventional TEVAR, patient unsuitability for open surgery or hybrid procedures, and an acute AD in need of emergent treatment. Additionally, chimney grafts may be used to emergently salvage one or more vital side branches accidentally overstented during endovascular procedures. 13 The diameter of chimney grafts should be selected carefully because a small diameter stent (covered or bare) is apt to thrombose while an overly large one may increase the risk of endoleak. There have been 4 chimney graft related type I endoleaks documented so far. 6,9,10 Ohrlander et al. 6 reported a proximal type I endoleak 2 days after an innominate chimney graft was successfully implanted;

7 J ENDOVASC THER LEFT CAROTID CHIMNEY TECHNIQUE IN TEVAR 483 they believed that the large diameter (12 mm) of the chimney graft was the main reason. In our series, we used 8-mm-diameter chimney grafts and had no type I endoleak. When it comes to choosing between bare or covered stents for the chimney, there is no consensus as yet, but covered stents are supposed to lessen the risk of endoleak. In theory, type Ia endoleak is the weak point of the chimney technique. When a chimney graft creates a route through the proximal aortic lumen to the overstented side branch, it also presents a potential avenue for proximal endoleak between the aortic wall and the aortic stent-graft. 14 Moreover, the space between the chimney graft and the aortic endograft is like a cul-de-sac, where thrombus could form and be a source of cerebral emboli; a covered stent might reduce this risk. 5 According to the literature, both bare 4,5,15,16 and covered 6,7,9,13.17,18 stents have been used in this technique. The trend may be toward covered stents, although Criado (personal communication) still prefers to use bare stents, so more evidence is needed. In selecting the model and dimensions of a chimney graft, we based our choice on our clinical experience with the devices and the anatomy of each patient. Among 15 cases of abdominal chimney graft deployment reported by Donas et al., 7 1 renal artery chimney graft became occluded 45 days postoperatively. The chimney graft is usually of small diameter and must withstand great mechanical pressure from the aortic endograft. Thus, the possibility of chimney graft obstruction exists and may result in a fatal outcome. To help avoid thrombotic stent occlusion, Criado 4 suggested patients take clopidogrel (75 mg/d) for a month and aspirin (325 mg/d) indefinitely; Baldwin and colleagues 5 suggested only clopidogrel. Although the supra-aortic branches are high flow, we routinely prescribed aspirin to avoid obstruction of the chimney graft and thrombus formation around the cul-de-sac, which may result in stroke. We observed continued chimney graft patency in our mean 11-month follow-up. On the other hand, a perfused false lumen may sometimes remain in the distal aorta after TEVAR; while this is expected to thrombose over time, it may on occasion be prudent to limit antiplatelet treatment in AD patients. For example, we advised our female patient with a minor type II endoleak to stop taking aspirin while maintaining strict control of her hypertension. After 11 months, the endoleak had nearly disappeared and the chimney graft was patent. As regards flow to the supra-aortic side branches, the innominate artery and LCCA obviously must be preserved in any setting, but the need to revascularize the LSA is controversial. To be sure, when the LSA contributes to the coronary circulation, or the right vertebral artery is stenotic, or LSA coverage results in symptoms, it is strongly recommended that the LSA be perfused by a chimney graft or bypass. A chimney graft should be deployed via retrograde catheterization of the LSA from a left brachial artery approach. In our 8 patients, however, a thorough imaging examination of the cerebral vasculature documented a non-dominant left vertebral, so only the LCCA was preserved by a chimney graft. No ischemic events related to coverage of the LSA were encountered. This report involves only chimney grafts in the LCCA located at the proximal landing site for the aortic endografts; we have not used this technique for the innominate artery or abdominal side branches. However, chimney grafts have been successfully used in all the supraaortic and abdominal aortic branches overstented intentionally or accidentally 3 10,12 22 and even at the distal end of the main endograft to preserve flow to the internal iliac arteries. 23 Multiple chimney grafts can be used 22 ;Lachat et al. 17 deployed 4 in a single patient to endovascularly revascularize all 4 major renovisceral arteries. Conclusion Aortic dissection that involves the aortic arch can be successfully treated using off-the-shelf stent-grafts and the chimney technique with acceptable short-term durability. The chimney technique provides an encouraging alternative to more invasive surgical treatment, expanding the indications of endovascular repair to more complex aortic pathologies. Long-term durability of chimney grafts, however, remains to be investigated in larger patient cohorts before being widely adopted.

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