The successful treatment of infrarenal aortic aneurysms via endovascular repair has been demonstrated, and a number of devices have been approved for this indication. However, the feasibility of this technique is limited in patients with short and/or angulated proximal aortic necks or access site challenges such as severe tortuosity or calcification of the iliac arteries. Unfortunately, patients with high surgical risk who are routinely screened for endovascular aneurysm repair (EVAR) often have this type of complex aortoiliac anatomy that makes the aneurysm unsuitable for endovascular repair. Aneurysms with so-called hostile necks are usually excluded from the endovascular treatment option because they are strongly associated with the risk of proximal type I endoleak. Alternative techniques and new devices have been introduced to overcome these limitations.

NEW TECHNOLOGY
The most significant technical innovation in the endovascular treatment of abdominal aortic aneurysms is reflected in the advent of flexible stent grafts that more readily conform to the patient's native anatomy. This evolution makes the procedure feasible for patients with highly angulated necks. The Endurant Stent Graft (Medtronic, Inc., Minneapolis, MN) exhibits high flexibility due to M-shaped, nitinol stents on the main body of the graft and the absence of a longitudinal connecting bar. Endurant relies on active fixation with suprarenal anchoring pins that provide proximal fixation and reduce the risk of migration even in highly angulated anatomies.

An article describing the performance of the Endurant stent graft, published in 2010,1 reported only one type I endoleak at 30 days (2.2%). Another prospective study that was conducted at our center reported 2- year freedom from type I endoleak at a rate of 97.3%.2

Additionally, we found that the performance of the Endurant Stent Graft in hostile, short, and angulated neck cases was promising. In this series, one-third of aneurysms had a neck length of < 10 mm, and approximately 40% of patients presented with a severely angulated neck (> 60°). Both early (1.3% type I endoleak at 30 days) and midterm outcomes (96.9% freedom from type I/III endoleak at 2 years) were excellent. In this series, it was also found that the key factor in long-term durability was proximal aortic neck length.

ALTERNATIVE TECHNIQUES
Several strategies have been investigated to overcome the current limitations related to very short aortic neck anatomies. Fenestrated grafts have been used with good clinical success, but the procedure is technically demanding and is not feasible in patients with angulated necks. Hybrid open/endovascular repair including bypass surgery of the renal arteries followed by endovascular exclusion of the aneurysm is an option for pararenal aortic aneurysms. However, the reported early mortality for these procedures reflects the complexity of the hybrid technique and highlights the need for an effective alternative treatment.

Prophylactic use of the chimney technique3 or vascular endostapling4,5 have been proposed elsewhere. The chimney technique consists of placing covered stent(s) parallel to the main aortic stent graft to preserve or rescue flow to aortic branch vessels in the stent graft seal zone.

We have adopted the chimney technique at our institution and have used it in more than 26 cases (Figures 1 through 5). Outcomes have demonstrated acute technical success, even in necks shorter than 5 mm. Our preliminary results in 15 patients with juxtarenal aortic aneurysms has recently been published.6 In this series, the acute technical success rate was 100%. A high 6-month patency rate also serves to justify this approach. Only one chimney graft was occluded postoperatively at day 45. The patient underwent open thrombectomy of the left renal artery and iliac-renal bypass. Additionally, one type II early endoleak was detected via retrograde flow from the inferior mesenteric artery and was treated conservatively with surveillance.

In contrast to other groups, we prefer to use balloonexpandable covered stents. We have a high level of experience with the Advanta V12 stent (Atrium Medical Corporation, Hudson, NH) and have used it in more than 64 aneurysms involving the iliac bifurcation7 and more than 45 branched devices for thoracoabdominal aortic aneurysms. This covered stent provides accurate placement, good fluoroscopic visibility, and high radial force. The placement of the Advanta covered stent ensures preservation of flow in the stented-over renal artery and a synchronous extension of the proximal fixation zone of the abdominal aortic stent graft.

For the chimney technique, we prefer a flexible stent graft for the abdominal aorta to achieve suitable apposition of the two components. Up until now, this technique has shown acceptable periprocedural outcomes, although long-term effectiveness has yet to be established.

OVERCOMING LIMITATIONS
Besides hostile proximal neck anatomy, difficulties in gaining access also pose a risk to EVAR success. Many patients are considered ineligible for endovascular treatment because of small vessel size, excessive tortuosity, and/or calcification of the iliac axis. For the graft to pass safely through the vasculature, the diameter and trackability of the delivery system is generally considered the main factor. Several strategies have been reported to overcome unfavorable access situations in high-risk patients. Iliac conduits, brachiofemoral through-and-through wires, arterial reconstructions, “paving and cracking” techniques, and direct aortic access are used to facilitate EVAR and prevent access-related issues. However, some of these techniques make EVAR fundamentally more invasive.

The hypothesis that low-profile delivery systems are associated with lower complication rates has been proven. Their benefit may be significant in female patients because their vessels are generally smaller. The use of highly flexible, lowprofile stent grafts increases the applicability of EVAR, especially in challenging-access anatomies. These attributes also allow for treatment without the need for a conduit.

To this end, Endurant has an improved delivery system with a hydrophilic coating and tip capture to allow for smooth, accurate deployment. Its low profile allows safe access and tracking through small iliac arteries. In our experience, the low outer diameter of the Endurant Delivery System leads to favorable patient outcomes with the option of total percutaneous access. No iliac damage has been noted during the insertion or manipulation of the graft. At 30 days, we have noted only one graft thrombosis (2.2%),1 which is similar to rates demonstrated with other commercially available stent grafts.

CONCLUSION
Our preliminary experience shows that the application of the new Endurant Stent Graft appears to be feasible and safe in the endovascular exclusion of abdominal aortic aneurysms in patients with hostile anatomy of the proximal aortic neck and iliac arteries. New technologies and techniques allow a broader group of patients to be treated with EVAR, even though further studies are needed to evaluate their long-term outcomes.

Giovanni Torsello, MD, PhD, is Professor and Chief of the Department of Vascular Surgery, St. Franziskus-Hospital and Head of the Center of Vascular and Endovascular Surgery, Münster University Hospital in Münster, Germany. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Prof. Torsello may be reached at +48 251 935 3933; giovanni.torsello@sfh-muenster.de.

Konstantinos Donas, MD, PhD, is from the Department of Vascular Surgery, Münster University Hospital in Münster, Germany. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein.

  1. Torsello G, Troisi N, Tessarek J, et al. Endovascular aortic aneurysm repair with the Endurant stent-graft: early and 1-year results from a European multicenter experience. J Vasc Interv Radiol. 2010;21:73-80.
  2. Troisi N, Torsello G, Donas KP, Austermann M. Endurant stent-graft: a 2-year, single-center experience with a new commercially available device for the treatment of abdominal aortic aneurysms. J Endovasc Ther. 2010;17:439-448.
  3. Ohrlander T, Sonesson B, Ivancev K, et al. The chimney graft: a technique for preserving or rescuing aortic branch vessels in stent-graft sealing zones. J Endovasc Ther. 2008;15:427-432.
  4. Criado FJ. A percutaneous technique for preservation of arch branch patency during thoracic endovascular aortic repair (TEVAR): retrograde catheterization and stenting. J Endovasc Ther. 2007;14:54-58.
  5. Donas KP, Torsello G. Midterm results of the Anson Refix endostapling fixation system for aortic stent-grafts. J Endovasc Ther. 2010;17:320-323.
  6. Donas KP, Torsello G, Austermann M, et al. Use of abdominal chimney grafts is feasible and safe: short-term results. J Endovasc Ther. 2010;17:589-593.
  7. Donas KP, Torsello G, Pitoulias GA, et al. Surgical vs endovascular repair by iliac branch device of aneurysms involving the iliac bifurcation. J Vasc Surg 2010. In press.