Today, endovascular aneurysm repair (EVAR) is considered the standard treatment option for abdominal aortic aneurysms (AAAs) in appropriate candidates because it is less invasive and carries a perceived lower risk compared to open surgical repair. In 2008, a large number of elective abdominal aortic procedures were carried out via endografting: 78% of 32,382 AAA repairs utilized EVAR within the Medicare population in the United States.1 Based on these numbers, it seems that EVAR has reached maturity and is sustained by evidence from late results of randomized trials showing equivalent survival rates after EVAR and open repair.2,3

New endograft models that have been commercially introduced in the last few years have attempted to address some of the weaknesses of earlier generations. Late fixation failures, material fatigue, and modular component disconnections are rarely reported today as causative factors of reintervention, but concerns remain, particularly for the late incidence of ruptures and aneurysm-related deaths after endografting.4

TARGET AREAS FOR IMPROVEMENT

Deliverability

According to a thorough review of anatomic features of 1,063 patients with AAAs in a 14-year single-center experience, the second most common cause of exclusion for endografting (after short proximal aortic neck length) is the presence of small iliac access.5 Bilateral, small (< 6 mm) iliac lumen is more common in women than in men (47% vs 17%, respectively) and compromises EVAR access.5 Moreover, extensive iliac disease and calcification may increase arterial stiffness and make graft navigation impossible (Figure 1).

The availability of lower-profile devices with better navigation capabilities could increase EVAR suitability. Because most of the space in endograft delivery catheters is filled by the fabric rather than the stent, new, stronger materials with high resistance to friction and very low porosity—but reduced thickness—are being investigated. However, a decrease in device diameter must not compromise graft durability, and no attempt to make EVAR available to more patients should adversely affect late failure risks.

Sealing Stability

Proximal graft fixation and sealing has been identified as the most critical issue in long-term performance of aortic endografts.6 With active fixation methods or suprarenal fixation of modular, tubular aortic segments, clinically significant distal migration of the proximal end of the prosthesis is quite rare in the case of adequate proximal neck anatomy. Due to displacement forces secondary to blood flow vectors, endografts are prone to movement inside the aneurysm sac, and the critical point of fixation is now represented by the distal iliac landing zones. Large aortoiliac aneurysms with short iliac necks, often ectatic, may represent the weak site for late proximal migration of the distal end of the graft. Better fixation of iliac endograft limbs is required in cases of short iliac necks. Solutions to increase iliac sealing length with the aid of bifurcated iliac grafts or improving the resistance to displacement with active iliac fixation modes could be of help.

Type II Endoleak Prevention

Even with supposed reduction of type I endoleak risks in newer-generation endografts, late aneurysm sac growth still occurs in some cases. This finding requires continued surveillance and, at times, follow-up interventions. Type II endoleak is frequently the cause of growth; it is present in 10% to 30% of cases after EVAR and requires treatment in up to 10% of patients.7 In a recent review from the Cleveland Clinic, incidence of sac embolization for type II endoleaks was 7.8% in 809 patients undergoing EVAR during an 11-year period.7 Late results showed secondary procedures were not entirely effective in preventing subsequent growth, with a 5-year freedom from sac expansion rate of 44%; the risk of a repeat embolization procedure was 24%.

Further research is needed to address this issue and prevent formation of type II endoleaks by means of innovative stent graft designs or adjunctive techniques. Sac fillers, with or without endobags inside the aneurysm, may represent a solution that is currently under clinical investigation, whereas other efforts may evaluate the potential of bioactive endografts to locally deliver drugs capable of inducing sac thrombosis or even aneurysm regression or stabilization. These solutions, however, remain unproven, and the body of clinical evidence supporting these novel concepts is still evolving.

LATEST ENDOGRAFT DEVELOPMENTS

In the last few years, all of the major aortic endograft companies have developed renewed models of grafts and/or delivery systems to cope with difficult anatomies and guarantee better delivery, more precise deployment, and improved performance. A true comparison of the results among different models is impossible due to obvious biases in anatomy selection and operator experience at different centers. Moreover, the short follow-up periods available for the newest endograft models may optimistically overestimate the favorable results of EVAR, which can present unpredicted failure modes later after implantation.

By comparison, the Endurant® stent graft (Medtronic, Inc., Minneapolis, MN) is a well-characterized device. The Endurant stent graft has shown high success rates in clinical use in a wide variety of anatomic settings (Figures 2 and 3).8 One-year results in all of the published experiences reported no major migrations, failures, or AAA ruptures, and consistent results have been found across patients treated with Endurant in well-controlled approval trials as well as real-world registries, across both straightforward and complex, challenging anatomies.8-10 In addition, Endurant has demonstrated consistent clinical outcomes between 1 and 2 years, with no incidence of type I endoleaks, migration, conversion to surgery, aneurysm-related mortality, or postoperative ruptures at 2 years.10

A new version of the graft, the Endurant® II, launched commercially in Europe in January 2012 and received FDA approval in May 2012. To facilitate deliverability, the lower-profile Endurant II delivery system in the 28-mm bifurcated device utilizes an extended hydrophilic coating length for enhanced access to tortuous and calcified iliac arteries. The 28-mm-diameter bifurcated segment is now mounted onto an 18-F outer diameter catheter due to the removal of one peak of the suprarenal stent, which is one of a few modifications made to lower the profile of the delivery system. Laboratory testing showed that migration resistance of Endurant II is comparable to that of Endurant, provided that the suprarenal pins engage the aortic wall (Medtronic in vitro bench testing. Data on file.). These innovations render the device very trackable, even in extremely difficult anatomies, and the low profile of Endurant II may also increase the number of women who can undergo minimally invasive endovascular treatment.

The Endurant II device has two new contralateral iliac limb graft lengths (156 and 199 mm) designed to enable more extensive iliac coverage. When possible, the use of fewer pieces to complete infrarenal aortoiliac exclusion may reduce the total costs of the procedure and the risks of modular disconnections. To enhance visibility of the contralateral leg of the bifurcated device, the radiopacity of the distal end of contralateral gate has been improved with the placement of a platinum-iridium markerband. This metallic reference, coupled with a lateral marker positioned on the bifurcated graft, may help in three-dimensional orientation, deployment, and limb cannulation (Figure 4). Even with these new elements, the essential components of the proven Endurant stent graft structure remain unchanged. We expect consistent performance of Endurant II in terms of proven adaptability, known sealing characteristics, and clinical efficacy. We therefore expect that Endurant II will continue to deliver the same consistent clinical performance, trial after trial, as that of the market-leading predecessor Endurant stent graft

Fabio Verzini, MD, PhD, is with the Unit of Vascular and Endovascular Surgery, Hospital S. Maria della Misericordia, University of Perugia, in Perugia, Italy. He has disclosed that he has no financial interests related to this article. Dr. Verzini may be reached at+39 075 5786435; fverzini@unipg.it.

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