Endovascular therapy has revolutionized the treatment approach for patients with abdominal aortic aneurysm (AAA) disease. For those who meet specific anatomic criteria, endovascular repair of AAA (EVAR) is currently the preferred therapeutic approach. The main reason for this trend is that patients undergoing EVAR have significantly improved periprocedural outcomes compared to those who undergo direct open repair.1-3 This advantage has been shown in multiple studies with respect to decreased 30-day mortality rates, shorter recovery times, and decreased lengths of hospital stay.3

Currently, the majority of patients with AAA disease have neck anatomy that is suitable for endovascular therapy. Since the inception of EVAR technology, the literature is relatively clear that when specific instructions for use (IFU) guidelines are followed, most endografts perform extremely well, as demonstrated by the excellent 5-year performance records of the currently available devices.4,5 Patients who have a proximal aortic neck length < 15 mm, neck diameter > 26 mm diameter, circumferential neck thrombus, reverse taper anatomy, and/or neck angulation > 60° have traditionally been considered to have a hostile neck, which was a contraindication for the currently available endografts.6

However, with the expansion of EVAR experience by most vascular specialists and with the significant improvement of devices during the last 15 years, the boundaries of the IFUs provided by the device manufacturers have been pushed to the limits by highvolume physicians to include patients exhibiting many of the so-called hostile neck properties (Figure 1). Numerous studies have shown reasonable results when these limits have been pushed with adjunctive stenting and other maneuvers to make neck fixation more secure.7,8 A recent review of the collected data from a nationally available EVAR imaging system revealed that 58% of the EVAR procedures being performed in the United States are being done outside of the device-specific IFUs.9 The true long-term durability of results for these patients remains somewhat uncertain. However, based on 15 years of EVAR experience throughout the world, it is evident that if the endograft does not remain fixed in the proximal neck, adverse outcomes are expected, with inevitable rupture of the AAA.10,11

THE ROLE OF FIXATION IN ENDOGRAFT STABILITY

The theoretical role of fixation in endograft technology is based on the fact that, if properly deployed, the mechanism prevents the device from distally migrating from the seal zone over time. Both the constant aortic blood flow and potentially tortuous anatomy make these devices susceptible to caudal migration. Endografts attempt to achieve fixation with multiple features, including active fixation (using barbs or hooks), columnar strength, outward radial force, and fibrotic reaction with prosthetic materials. Some devices may incorporate more than one of these features. The most common form used in modern endografts is active fixation into the aortic wall of the proximal aorta to maintain the endograft position. Columnar strength refers to the vertical stiffness of the graft to hold the superior aspect of the device. Endograft migration may be limited by the frictional forces induced by the outward radial strength of the device. However, numerous longterm reports have shown that this form of fixation is not durable in hostile necks.12,13

There has been much controversy regarding the need and efficacy of fixation in the short- and long-term performance of endografts. Most physicians currently believe that some type of fixation is required for accurate placement and durability of endografts; most of the endograft systems have an integrated active fixation system incorporated into the proximal segment of the endograft. Some devices, such as the Ancure (formerly Guidant Corporation) and Excluder (Gore & Associates, Flagstaff, AZ) devices, have fixation systems that actively engage the proximal neck itself (Figure 2). Certain devices offer suprarenal fixation with the belief that the suprarenal aortic neck is less likely to dilate over time, thus providing more durable fixation (Figure 3). It is not yet clear if the bare-metal stents of these devices with transrenal stents, which span the orifices of the renal and mesenteric arteries, are associated with longterm renal dysfunction, but there have been reports of occlusive processes partially occluding the origins of the renal and mesenteric arteries after suprarenal stent graft implantation (Figure 4).14

EVAR IN HOSTILE NECKS: SUPRARENAL OR INFRARENAL?

Despite the excellent long-term data from the EVT/ Ancure endograft systems utilizing infrarenal fixation techniques,2 many vascular specialists believe that suprarenal fixation is superior to infrarenal fixation for treating patients with short proximal aortic necks. In theory, the active fixation (barbs) would be in the healthy segment of normal aorta and should allow adequate apposition of graft material and aortic wall just below the renal arteries. In 2001, Stanley et al analyzed the Zenith Endovascular Graft Research Database on 238 patients treated with the Zenith (suprarenal fixation) device (Cook Medical, Bloomington, IN). They found a 56% type I endoleak rate in patients with short aortic necks (≤ 10 mm) and concluded that patients with short aortic necks should not be treated with the Zenith device.15

In 2006, an analysis of the 3,499 patients in the EUROSTAR registry was performed to help predict outcomes after EVAR based on the length of the proximal aortic neck. The patients were divided into three groups: group A had proximal aortic necks > 15 mm (reference group, n = 2,822), group B had necks of 11 to 15 mm (n = 485), and group C had proximal necks < 10 mm (n = 192). Univariate and multivariate analyses were performed and found a significantly higher number of type I endoleaks at 1 month in group C as compared to group A (10.9% vs 2.6%) and within 48 months (11.3% vs 3.4%).8These outcomes were also demonstrated by AbuRahma and colleagues, who examined patients who underwent EVAR with short proximal aortic necks.16 Their study examined 238 patients and subdivided them into three groups: patients with proximal necks ≥ 15 mm (L1, n = 195), patients who had necks of 10 to 14 mm (L2, n = 24), and patients with < 10 mm necks (L3, n = 17). They found that the rates of early type Ia endoleaks occurred in 12%, 42%, and 53% in groups L1, L2, and L3, respectively (P < .001). They also noted that the need for proximal aortic cuffs to achieve adequate seal was 10%, 38%, and 47%, respectively (P < .0001). There was no statistically significant difference in the rate of reintervention or sac regression. The investigators concluded that EVAR can be performed in patients with extremely short aortic necks, although the rate of proximal endoleaks is significantly higher and requires more frequent proximal extension cuffs to achieve adequate seal.

In a recent study that directly compared the midterm performance of two specific types of endograft systems utilizing two different fixation methods (transrenal and infrarenal), it was demonstrated that there were no differences in the rates of migration, AAA sac stability, and other associated complications such as aneurysm-related deaths. The study identified 84 of 1,379 patients with short proximal aortic necks over an 8-year period. Morphology inclusive of a short proximal neck was stratified into two groups: those who underwent EVAR with infrarenal fixation (Excluder device) or those who underwent EVAR with suprarenal fixation (Zenith device).

In this study, patients were selected based on the presence of a proximal aortic neck < 15 mm (12 mm for the infrarenal fixation group and 11.4 mm for the suprarenal fixation group). All of these patients were considered to be high risk for direct open AAA repair. Patients were excluded if the neck angulation was > 60° and had a reverse taper > 5 mm. The primary endpoints for 1- and 2-year periods of the study were (1) the presence of type I endoleaks, (2) graft migration > 5 mm, and (3) change in sac size.17 The midterm results, even in these relatively high-risk EVAR patients, were excellent using both types of devices.

TECHNOLOGICAL ADVANCES

Recent advances in EVAR infrarenal fixation technology have focused on applying fixation after the endograft is already in place to ensure its stability. The HeliFX EndoAnchor system (Aptus Endosystems, Inc., Sunnyvale, CA) delivers anchors from the lumen of the endograft already in place to secure the proximal portion of the graft into the infrarenal neck (Figure 5).18 Some endograft systems employ “fish mouth” configurations with active fixation to the proximal portion to maximize the seal zone.19 The short- and midterm results of these infrarenal systems have also clearly demonstrated that excellent EVAR durability can be achieved with infrarenal fixation alone.

The evidence for durability of active infrarenal fixation is clear in the literature. Even in nonideal EVAR situations when hostile neck features are present, these endograft systems appear to have reasonable migration-free outcomes. The only real issue is whether there are adverse effects of suprarenal fixation. Oberhuber et al20 studied the effects of infrarenal versus suprarenal fixation on aortic neck and proximal aortic stresses. They showed that patients who underwent EVAR with suprarenal devices had a significantly higher rate of neck expansion (31% vs 10%; neck expansion > 2 mm). These results may have been related to excessive oversizing in these suprarenal systems,21 but the influence of the suprarenal stent structure cannot be ignored.11,13,16 There are no biomechanical or clinical studies that have evaluated these metal structures across the suprarenal aorta. In some cases of extreme angulation, these fixation mechanisms may not even function in that capacity due to the lack of aortic apposition (Figure 6) and actually may cause direct trauma to the aortic wall when not apposed to the wall. The infrarenal fixation systems also allow for “reticulation” of the proximal fixation region to allow for increased flexibility (Figure 7).

CONCLUSION

Today, there are multiple infrarenal and suprarenal fixation endograft systems that perform extremely well under most conditions and even in situations of isolated hostile neck anatomy. The mid- and long-term data from these modern endograft systems do not demonstrate superiority of one type of system over another. Neck expansion appears to be higher in suprarenal systems, but this issue has not translated to higher migration rates in reports that have studied these patients. In severely angulated necks, caution must be taken with suprarenal devices due to disengagement of the fixation system in the suprarenal aorta.

The key to successful EVAR is good patient selection and accurate deployment of the device so that the fixation system can engage the aortic wall as intended. Both systems can lose their active fixation advantage when misdeployed (and not allowing the fixation to function properly). As endograft technology has progressed, there has been emphasis on refining deployment accuracy. This is evident by the introduction of the “repositionable” systems.22,23 When endografts are positioned accurately in appropriate patients, the long-term outlook for EVAR durability is extremely promising.

Robert Y. Rhee, MD, is Chief of Vascular and Endovascular Surgery at Maimonides Medical Center in Brooklyn, New York. He has disclosed that he is a paid consultant to Gore & Associates and Medtronic, Inc. Dr. Rhee may be reached at (718) 283-7993; rrhee@maimonidesmed.org.

  1. Greenhalgh RM, Brown LC, Kwong GP, et al; for the EVAR trial participants. Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomized controlled trial. Lancet. 2004;364:843-848.
  2. Moore WS, Matsumura JS, Makaroun MS, et al; EVT/Guidant Investigators. Five-year interim comparison of the Guidant bifurcated endograft with open repair of abdominal aortic aneurysm. J Vasc Surg. 2003;38:46-55.
  3. Franks SC, Sutton AJ, Bown MJ, Sayers RD. Systematic review and meta-analysis of 12 years of endovascular abdominal aortic aneurysm repair. Eur J Vasc Endovasc Surg. 2007;33:154-171.
  4. Peterson BG, Matsumura JS, Brewster DC, Makaroun MS; Excluder Bifurcated Endoprosthesis Investigators. Five-year report of a multicenter controlled clinical trial of open versus endovascular treatment of abdominal aortic aneurysms. J Vasc Surg. 2007;45:885-890.
  5. Greenberg RK, Chuter TA, Cambria RP, et al. Zenith abdominal aortic aneurysm endovascular graft. J Vasc Surg. 2008;48:1-9.
  6. Dillavou ED, Muluk SC, Rhee RY, et al. Does hostile neck anatomy preclude successful endovascular aortic aneurysm repair? J Vasc Surg. 2003;38:657-663.
  7. Kim JK, Noll RE Jr, Tonnessen BH, Sternbergh WC 3rd. A technique for increased accuracy in the placement of the “giant” Palmaz stent for treatment of type IA endoleak after endovascular abdominal aneurysm repair. J Vasc Surg. 2008;48:755-757.
  8. Leurs LJ, Kievit J, Dagnelie PC, et al; EUROSTAR Collaborators. Influence of infrarenal neck length on outcome of endovascular abdominal aortic aneurysm repair. J Endovasc Ther. 2006;13:640-648.
  9. Schanzer A, Greenberg RK, Hevelone N, et al. Predictors of abdominal aortic aneurysm sac enlargement after endovascular repair. Circulation. 2011;123:2848-2855.
  10. Brewster DC, Jones JE, Chung TK, et al. Long-term outcomes after endovascular abdominal aortic aneurysm repair: the first decade. Ann Surg. 2006;244:426-438.
  11. Prinsse M, Wever JJ, Mali WP, et al. Concerns for the durability of proximal AAA endograft fixation from a 2-year and 3-year longitudinal CT angiography study. J Vasc Surg. 2001;33:S64-S69.
  12. Conners MS III, Sternbergh WC III, Carter G, et al. Endograft migration 1-4 years after endovascular AAA repair with the AneuRx device: a cautionary note. J Vasc Surg. 2002;36:476-484.
  13. Abbruzzese TA, Kwolek CJ, Brewster DC, et al. Outcomes following endovascular abdominal aortic aneurysm repair (EVAR): an anatomic and device-specific analysis. J Vasc Surg. 2008;48:19-28.
  14. Walsh SR, Tang TY, Boyle JR. Renal consequences of endovascular abdominal aortic aneurysm repair. J Endovasc Ther. 2008;15:73-82.
  15. Stanley BM, Semmens JB, Mai Q, et al. Evaluation of patient selection guidelines for endoluminal AAA repair with the Zenith stent graft: the Australasian experience. J Endovasc Ther. 2001;8:457-464.
  16. AbuRahma AF, Campbell J, Stone PA, et al. The correlation of aortic neck length to early and late outcomes in endovascular aneurysm repair patients. J Vasc Surg. 2009;50:738-748.
  17. Hager ES, Cho JS, Makaroun MS, et al. Endografts with suprarenal fixation do not perform better than those with infrarenal fixation in the treatment of patients with short straight proximal aortic necks. J Vasc Surg. In press.
  18. Deaton DH, Mehta M, Kasirajan K, et al. The phase I multicenter trial (STAPLE-1) of the Aptus endovascular repair system: results at 6 months and 1 year. J Vasc Surg. 2009;49:851-857.
  19. Perdikides T, Georgiadis GS, Avgerinos ED, et al. The Aorfix stent-graft to treat infrarenal abdominal aortic aneurysms with angulated necks and/or tortuous iliac arteries: midterm results. J Endovasc Ther. 2009;16:567-576.
  20. Oberhuber A, Schwarz A, Hoffmann M, et al. Influence of fixation mechanism on changes of the supra- and infrarenal segment of the aorta after endovascular treatment of infrarenal aortic aneurysm. Zentralbl Chir. 2010;135:433-437.
  21. Sternbergh WC III, Money SR, Greenberg RK, Chuter TAM; for the Zenith Investigators. Influence of endograft oversizing on device migration, endoleak, aneurysm shrinkage and aortic neck dilation: results from the Zenith multi-center trial. J Vasc Surg. 2004;39:20-25.
  22. Ridel SG, Geelkerken RH, Prescott RY, et al; The Anaconda AAA stent graft system: 2 year clinical and technical results of multicenter clinical evaluation. Eur J Vasc Endovasc Surg. 2009;38:732-740.
  23. Verhoeven EL, Oikonomou K, Möhner B, et al, European C3 Global Registry Participants. First experience with the new repositionable C3 excluder stent graft. J Cardiovasc Surg. 2011;52:637-642.