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Alternative Techniques to Abdominal Debranching
Abstract
As aortic endograft technology has evolved over the last two decades, several endovascular techniques have been proposed for the treatment of juxtarenal, suprarenal and thoraco-abdominal aneurysms. The purpose of this article is to review these modalities, including abdominal aortic debranching, fenestrated and branched endografts and encroachment techniques. The history, technical aspects and published outcomes of these techniques are described.
VASCULAR DISEASE MANAGEMENT 2010;7(10):E210–E213
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Introduction
Since the introduction of endovascular abdominal aortic aneurysm repair (EVAR) by Parodi and colleagues in 1991,1 this method has become widely accepted for the treatment of infrarenal abdominal aortic aneurysms (AAAs). EVAR has proven to be an equally effective treatment modality that is less invasive and associated with significantly lower rates of perioperative mortality and complications compared with traditional open surgical repair.2,3 Repair of aneurysms involving the perivisceral aorta has an increased risk of perioperative mortality and complications when compared to infrarenal AAAs. The need for suprarenal or supraceliac aortic cross clamping, with resultant visceral organ ischemia, can adversely affect the outcome of conventional open repair.4,5 The treatment of juxtarenal or suprarenal AAAs using endovascular techniques would therefore likely provide an even higher mortality and morbidity benefit than those seen with infrarenal AAAs.
Currently Approved Aortic Endografts
In the United States, there are currently five commercially available stent grafts that are approved by the Food and Drug Administration (FDA) for use in the abdominal aorta. These include: Zenith (Cook Medical, Bloomington, Indiana); Excluder (W.L. Gore & Associates, Flagstaff, Arizona); AneuRx (Medtronic, Inc., Minneapolis, Minnesota); Talent (Medtronic); and Powerlink (Endologix, Irvine, California). Irrespective of the endograft, excellent perioperative and 5-year outcomes can be obtained with each device if employed according to the recommended instructions for use (IFU). All the approved stent grafts have similar anatomic restrictions: need for a proximal aortic neck of ≥ 15 mm (≥ 10 mm for Talent); neck angulation ≤ 60 degrees; and neck diameter ≤ 32 mm. With approved endografts, approximately 40% of patients are not candidates for EVAR due to anatomic limitations mainly associated with the proximal aortic neck.6 The use of EVAR in patients with short and compromised aortic necks (as with juxtarenal AAAs) can lead to an inadequate seal by the stent graft with a resultant high incidence of graft migration and proximal endoleaks.7,8 Furthermore, the origin of visceral and renal vessels from the aneurysm itself in suprarenal aneurysms and thoraco-abdominal aortic aneurysms (TAAAs) prohibits the use of the traditional stent-graft technology. To overcome these limitations, the following treatment modalities have emerged as viable alternatives to standard open repair: 1. Hybrid approach with abdominal debranching followed by endograft placement; 2. Fenestrated endografts; 3. Surgeon-modified fenestrated endografts; 4. Branched endografts; 5. Side-branch stenting by snorkel or chimney encroachment techniques.
Abdominal Aortic Debranching
A hybrid approach of retrograde revascularization of the visceral and renal arteries followed by endografting of the abdominal aorta was first reported in 1999.9 The goal of this approach is to maintain visceral and renal arterial patency while avoiding the morbidity associated with suprarenal or supraceliac cross-clamping. The procedure can be performed during a single operation or in a staged fashion. This technique has been described in the treatment of TAAAs (extent II, III, IV) and pararenal aneurysms. However, the published literature is limited to single-center experiences with small numbers of patients.10–14 A recent systematic review evaluated this technique and included 108 patients from 15 published studies.15 This analysis revealed a 15% mortality rate within 30 days, an 11% renal failure rate and a paraplegia rate of 2.7%. These outcomes are not significantly different than those seen with conventional open surgical repair. Furthermore, despite the limited experience with this technique, it is clear that the debranching operation is by no means a simple procedure to perform, and thus the outcomes are not as good as investigators had hoped. Abdominal debranching, thus, has a limited role for selected patients and further investigation is needed.
Fenestrated Endografts
In cases where the proximal aortic neck is too short to allow for a proximal seal between the endograft and the aortic wall, proximal side-openings in the endograft fabric (fenestrations) can accommodate the visceral arteries and therefore extend the sealing zone to the aorta above the renal origins. The first published clinical experience with custom-made fenestrated endografts came from Australia in 2001. The report included 13 aneurysms that were treated using fenestrated devices based on the Zenith system (William A. Cook Australia Pty. Ltd., Brisbane, Australia) with promising results.16 Custom-made fenestrated endografts are currently commercially available outside the United States. In the United States, the Zenith Fenestrated AAA Endovascular Graft (Cook Medical) is undergoing a prospective, multicenter trial and is available only at the participating institutions. When fenestrated endografts are utilized, a preoperative high-resolution computed tomographic (CT) angiogram is used to generate multiplanar reconstructions. The locations of the visceral arteries are then used for precise graft design. The renal and superior mesenteric arteries are accommodated by means of fenestrations or scallops. The endograft is modular in design, with a proximal fenestrated tubular component, a distal bifurcated main body device and a contralateral iliac extension. Radiopaque gold markers localize the fenestrations and help with device orientation. After the initial aortogram, the renal arteries and the superior mesenteric artery (SMA) are selected, and wires are used to mark their locations. The proximal component is then partially deployed and the fenestrations are aligned with the visceral arteries. Guiding catheters and sheaths are then used to select these branches again, but this time from within the graft and through the fenestrations. The graft deployment is then completed by removing the restraining wire and releasing the top cap. Stents are then deployed across the origins of the visceral arteries, leaving 2–4 mm of the stent inside the aorta (endograft), where they are flared using a balloon. These stents maintain vessel patency, provide seal and correct any misalignment between the fenestration and the origin of the target vessel. The distal bifurcated component is then deployed, followed by the iliac extensions in a manner similar to conventional EVAR using the Zenith device. A completion angiogram is always performed to rule out endoleaks and to ensure target-vessel patency. Greenberg et al published the 24-month outcomes of the Zenith Fenestrated AAA Endograft multicenter trial for treating juxtarenal aneurysms.17 The experience included 30 patients from five medical centers. Seventy-seven visceral arteries were accommodated by fenestrations. They reported a 100% technical success rate, no aneurysm-related deaths, ruptures, or conversions and no type I or type III endoleaks. Late renal artery in-stent stenosis occurred in 4 patients, and late renal artery occlusion occurred in 2 patients. No renal failure was reported. The largest published cohort of fenestrated EVAR using the same device came from France and included 134 patients with juxtarenal (74%), suprarenal (20%) and type IV thoraco-abdominal (6%) aneurysms. The median follow-up period was 15 months. The 30-day mortality rate was 2%, and permanent renal failure occurred in 1%. No aneurysms ruptured or required open conversion during the follow-up period. Target-vessel patency was 99% at procedure completion. Pre-discharge imaging identified 16 (12%) endoleaks: 3 type I, 12 type II and 1 type III. Secondary endoleaks were diagnosed in 9 cases during follow-up: 7 type II, 1 type I and 1 type III. Late renal artery occlusion occurred in 4 patients (3%). There was a 9% reintervention rate for endoleaks or to protect threatened visceral branches.18 Very similar results have been quoted in other studies.19–21
Surgeon-Modified Fenestrated Endografts
As mentioned above, the custom-made fenestrated Zenith AAA endograft is not commercially available in the United States. To treat patients unfit for open repairs, some surgeons may elect to construct their own customized fenestrated endografts. The first fenestrated home-made device was described by Park et al in 199622 followed by Faruqi et al in 1999.23 Surgeon-modified devices can also be valuable in the high-risk symptomatic patient who cannot wait the 6–8 weeks currently needed to prepare the fenestrated Zenith endograft. The modified fenestrated stent graft can be customized using the commercially available Cook Zenith or TX2 platform (Cook Medical). The preoperative CTA should be reviewed to ensure that the proximal landing zone is not compromised and includes at least a 20 mm length of noncalcified, parallel aortic wall. Three-dimensional reconstructions and centerline flow analysis are used for measurement of the distances between each one of the target vessels and to locate the origin of each vessel from the aorta in relation to its clock position. Device modification is performed in the operating room under sterile technique. The endograft is partially unsheathed, and the fenestrations and scallops are made coinciding with the clock dial position previously defined. The fenestrations may be small (6 mm x 8 mm) or large (8 mm x 10 mm). Scallops are created between the top stent struts. The edges of the fenestrations are marked with longitudinal and transverse gold markers for fluoroscopic orientation. The stent graft is then resheathed. Deployment is then performed as previously described.24,25 The Mayo Clinic group compared their results using surgeon-modified fenestrated-branched stent grafts (30 patients) with abdominal aortic debranching (16 patients) in the treatment of high-risk patients with complex AAAs or TAAAs. The technical success for branch artery stenting was 98%. The modified fenestrated-branched stent-graft patients had higher fluoroscopy time and contrast use, but significantly less blood loss and total operative time. The 30-day mortality rate was 3.3% (1 patient) in the fenestrated-branched group and 19% (3 patients) after abdominal debranching. The incidence of complications with fenestrated stent grafts was 37% compared with 73% for debranching. Primary branch or target vessel patency at 1 year was 97% for branched stent grafts and 98% for debranching procedures. Freedom from endoleak was 88% and 74% at the same interval, respectively. There were no patients with sac enlargement, rupture or conversion in the fenestrated group.26
Branched Endografts
Branched endografts are used when the visceral arteries branch off an aneurysmal region of the aorta, which generates a gap between the wall of the endograft and the orifice of the artery that needs to be bridged to prevent endoleak. This is the case with suprarenal and TAAAs. Branched endografting can be performed using one of two stent-graft designs: fenestrated-branched or cuffed-branched endografts.27–29a. Fenestrated-branched endografts. These are endografts that have fenestrations identical in design to the fenestrated endografts. It is also deployed in a similar manner. A 20 mm proximal landing zone is required in a healthy aorta. After deploying the proximal fenestrated endograft component, the visceral arteries, already accessed with wires and sheaths, are stented with balloon-expandable stent-grafts. These stent grafts seal the gap between main body and aneurysm wall. The branch artery stent grafts are flared proximally with a balloon prior to completing the repair with the conventional distal bifurcated device. b. Cuffed-branched endografts. These use cuffs instead of fenestrations as directional branches. The cuffs provide a seal between the branch artery stent grafts and the main body endograft, as opposed to flaring a stent inside the fenestration. Self-expanding stent grafts are used in the visceral branches, and are inserted via a brachial approach due to the caudal direction of the cuffs. These devices are custom made and investigational in the United States. Since the first report of a successful implantation of a branched endovascular endograft for a TAAA by Chuter et al in 2001,30 several series have shown encouraging results with perioperative mortality rates ranging 0–9.1%.31–34 The largest published series with branched endografts is from the Cleveland Clinic. This included 73 patients with TAAA (including 45 patients with type IV) treated with fenestrated and cuffed-branched endografts. There were no conversions to open surgery or ruptures post treatment. Technical success was achieved in 93% of patients. The 30-day mortality was 5.5%. The incidence of paraplegia was 3%, new onset of dialysis 1%, prolonged ventilator support 7%, myocardial infarction 6% and minor hemorrhagic stroke 1%. The incidence of endoleak was 11%.35 The Cleveland Clinic group also compared endovascular and open repair in their patients with TAAAs and descending thoracic aneurysms. No difference in perioperative mortality or spinal cord ischemia was found.36 In general, the results from the published series with branched endografts for TAAA repair are encouraging. They seem to be better than the results of open TAAA repairs from a nationwide discharge database representing 20% of the U.S. hospitals and including 1,542 patients published by Cowan in 2003 (postoperative mortality of 22%).37 More experience and prospective studies are still necessary to assess the role of these new devices.
The Snorkel or Chimney Encroachment Techniques
The encroachment techniques involve advancing the proximal margin of the endograft across the visceral branch vessels. The snorkel technique involves deploying a branch-artery stent that maintains patency of the partially or totally covered branch vessel to extend the proximal landing zone of the endograft. Hiramoto et al published the largest experience with this technique. This report included 29 patients who underwent renal artery stenting during EVAR using the encroachment (n = 23) and the snorkel (n = 8) methods. The procedure was planned in 18 patients (proximal neck length 15 mm). Three type I endoleaks resolved spontaneously in 1 month. The primary assisted patency of renal artery stents was 100% at a median follow-up period of 12.5 months. There were no late type I endoleaks (> 1 month postoperatively) or stent graft migrations.38 The chimney technique, on the other hand, involves deploying a branch-artery stent graft, usually a self-expanding endograft that runs outside and parallel to the aortic endograft, preserving flow in the vessel while extending the proximal landing zone of the endograft. The chimney technique was initially described to preserve flow in the aortic arch branches and to extend the proximal landing zone during TEVAR.39–42 Ohrlander et al described the use of this technique in the endovascular treatment of juxtarenal aneurysms with chimney grafts placed in the SMA and renal arteries.43 These techniques may be particularly useful for patients with juxtarenal AAAs who do not have access to fenestrated endografts. They may also be used as part of a recovery maneuver when a visceral artery is inadvertently covered. More data are necessary concerning these techniques, as there is a significant concern of mid-term endograft proximal attachment failure.
Conclusion
The above modalities were developed as alternatives for the exclusion of aneurysms in the visceral aorta in high-risk patients. In particular, the fenestrated and branched endografts have gained wide acceptance outside the United States. Until these are commercially available in the United States, the other methods remain viable alternatives. Long-term results of all these techniques are still necessary to evaluate specific complications such as migration, material fatigue and component separation that can result in loss of visceral branches.
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From the Section of Vascular Surgery, Department of Surgery, Washington University School of Medicine, Saint Louis, Missouri. Manuscript submitted April 12, 2010, provisional acceptance given April 12, 2010, final version accepted June 15, 2010. Dr. Sanchez discloses that he is a paid consultant to: Aptus, Cook Medical, Medtronic, Trivascular, and W.L. Gore & Associates. The other authors have no disclosures to make concerning the content herein. Address for correspondence: Prof. Luis Sanchez, Department of Vascular Surgery, Campus Box 8109, 660 South Euclid Avenue, St. Louis, MO 63108. E-mail: sanchezl@wustl.edu
