CHICAGO – Clinically significant aortic neck dilation occurs in one-quarter of patients after endovascular abdominal aortic aneurysm repair and is associated with sharply increased risk for type Ia endoleak, stent migration at the proximal seal zone, continued aneurysmal sack enlargement, and even aneurysm rupture, , said at a symposium on vascular surgery sponsored by Northwestern University.
He cited what he considers to be the best-quality systematic review of the literature regarding proximal neck dilation after endovascular aneurysm repair (EVAR), which was conducted by investigators at Paracelsus Medical University in Nuremberg, Germany. The data, he said, speak to the importance of trying to minimize the chances of aortic neck dilation (AND).
The review, which included 26 published studies through 2015 and nearly 10,000 EVAR patients, concluded that AND occurred in 24.6% of these patients. The investigators defined AND as more than 3 mm of dilation, which with an average neck diameter of about 30 mm in all comers, would represent a 10% aortic neck-diameter expansion. The incidence of the composite adverse outcome of type I endoleak, stent migration, and reintervention during a maximum of 9 years of follow-up was 29-fold greater in the AND group than in AND-free patients ().
Continuing controversy exists regarding the extent to which post-EVAR AND is a manifestation of the underlying aneurysmal process as opposed to an adverse effect caused by the outward radial force applied by the stent. That being said, there are several factors related to AND that are potentially within the vascular interventionalist’s control. Topping the list is aggressive oversizing of self-expanding stent grafts in an effort to obtain an excellent seal, according to Dr. Lee, a professor of surgery at Stanford (Calif.) University.
“The data from multiple series definitely suggests that more than 20% oversizing is correlated with a higher incidence of AND. So maybe the answer is oversizing by more like 10%-15%,” the vascular surgeon said.
Another factor contributing to AND is the overwhelming popularity of self-expanding aortic stent grafts, now utilized in 95% of all EVARS done in the United States. Balloon-expandable stent grafts require much less oversizing – less than 5% – to maintain their diameter post deployment, but they are rarely used. Indeed, the only commercially available balloon-expandable device in the United States is the TriVascular Ovation stent system, which seals the stent graft to the wall of the aorta via polyethylene glycol rather than by radial force.
Intriguingly, Italian investigators have reported that, in a multicenter series of 161 patients who underwent EVAR with the Ovation endograft, no AND occurred at CT scanning done after a minimum of 24 months of follow-up ().
Previous studies of the implications of AND after EVAR have been limited to comparisons of early-generation devices, so Dr. Lee and his coinvestigators conducted a retrospective review of a prospective Stanford database that included 86 patients who underwent elective, uncomplicated infrarenal endovascular abdominal aortic aneurysm repairs using a variety of contemporary stent grafts. Eighty-six percent of patients experienced AND during a median radiologic follow-up of 21.9 months, with a mean 1.3-mm increase at 30 days and 3.3 mm at most recent follow-up. The degree of AND correlated with the amount of oversizing. However, AND didn’t vary significantly by device type, which included the Cook Zenith, Gore Excluder, Medtronic Endurant, and Endologix Powerlink self-expanding stent grafts ().
Aortic anatomy also plays a role in AND. Shorter necks with severe angulation have been found to pose a higher risk. Open repair, which entails much less AND than does EVAR, may make more sense in that challenging anatomic situation, according to Dr. Lee.
He reported current research funding from Cook, Gore, and Medtronic.