FDA Approval of Medtronic's Endurant AUI Stent Graft System: An Interview With Michel Makaroun, MD

In May, Medtronic announced that it has received US Food and Drug Administration (FDA) approval of its Endurant II Aorto-Uni-Iliac (AUI) Stent Graft System. The Endurant II AUI Stent Graft System is the only FDA-approved AUI device in the United States indicated for the primary endovascular treatment of infrarenal abdominal aortic or aortoiliac aneurysms in patients whose anatomy does not allow for the use of a bifurcated device. Unlike the bifurcated device, the AUI device requires access to only one iliac artery. 

Vascular Disease Management spoke with Michel Makaroun, MD, about the approval of the Endurant AUI system. Dr. Makaroun was principal investigator for the Endurant Stent Graft System US Clinical Study, which studied the AUI system. 

 Q: Could you describe the system and the appropriate settings where it can be used?

A: The Endurant AUI system is very similar to the bifurcated Endurant system, which has been approved for over a year. The AUI device, which is essentially identical to the bifurcated device, does not have a leg intended to go to the opposing side. It has the same construction, which is polyester and nitinol rings with a suprarenal extension. It also has the same deployment system as the bifurcated device, but does not have an additional leg that goes to the opposite side. 

The applicability of such systems has been known for many years because there was an AUI system available years ago, when the Ancure endograft had both a bifurcated and AUI configuration. That Ancure system went off the market in 2001 and since then we have not had an approved AUI system in the United States until this one. We had something we have used as an AUI system which was approved by the FDA for use in salvage of migrated grafts, called the Zenith Renu system from Cook Medical. It resembles the AUI system in the way that it does not have a contralateral leg and it tapers down so it can fit into the limb. It was not approved for the first-line treatment of aneurysms, although it does function in the same way as the Endurant AUI system. 

There are many appropriate anatomic settings where we might believe an AUI would be better than a bifurcated system. When you have a complete occlusion of one iliac system or one system that connects the aorta to the groin on one side, clearly we cannot choose a bifurcated system, and in that situation you have to go with open repair or an AUI system, and that’s where this device now offers us an alternative to open repair. It will expand the indications slightly to patients who have occlusion on one side. 

But it doesn’t stop there, because some patients have severe narrowing and disease in one of the iliac systems which makes it difficult to keep a contralateral leg patent after it is cramped into a small arterial system, so in those situations too it may be easier to use an AUI system. 

As in some patients, when the end of the aorta that is beyond the aneurysm, before the bifurcation, is severely narrowed, it is easier to place one leg that goes to one side rather than two legs that get cramped into that distal aorta. There are ways to deal with this, which include severe ballooning and essentially breaking up the aorta at that level, but clearly that’s less desirable than placing an AUI system on one side. 

An AUI system has also been applied over the years when it’s difficult to cannulate from the other side, such as in severe tortuosity of the iliac or bilateral large iliac aneurysms, it may be beneficial in certain situations to use an AUI system.

Q: Why did the previous stent graft go off the market?

A: The entire Ancure brand went off the market. Guidant Corporation encountered problems in their reporting to the FDA, and after a large fine the company decided to stop manufacturing the device rather than modifying and upgrading it to make it more compatible with other devices. It was not an AUI system problem, it was regulatory issues with the Ancure system in general.   

Q: Could you share some pertinent information data from the clinical trial for the Endurant AUI system? 

A: Initially we were planning to have one trial that included all of the configurations of the Endurant, but the FDA preferred to have two separate trials because they pointed out that they believed the patient population where an AUI is indicated is different than the patient population where a bifurcated graft is indicated. That was born from the Ancure data from years ago that showed a higher complication rate among patients getting an AUI. That was also borne out by the Endurant data: typically we are treating more women, more patients with severe iliac disease, patients with more generally comorbidities having higher underlying problems, and these are the kind of patients for whom an AUI is typically preferred over a bifurcated system. So we ran a separate trial and that was just reported to the FDA and the FDA approved it – it shows a slightly higher complication rate than bifurcated but it’s still excellent with fairly stable results at 1 year without any major downside such as rupture or migration.

Right now we only have data up to 1 year, which is good enough for the FDA to approve it, but in general the data confirmed what we knew ahead of time: the patients who need an AUI device are sicker, are slightly older, are more often female, and have a higher general complication rate. The most important results from the trial show that it’s quite safe and effective to use. 

Q: Were there any surprising results or limitations? 

A: If anything the use of the AUI system is simpler than using a bifurcated system, because it does not require additional steps such as cannulation of the opposing leg, and it can be deposed very quickly. We normally have to add manenuvers such as a fem-fem bypass graft, adding a surgical intervention that is to a certain degree what increases complication rate. But in general it proves what we expected, that it’s fairly safe and effective for treating aneurysms when patients have the kind of anatomies that make the AUI system preferred over a bifurcated system. 

Q: Are these results influential to the development of similar devices? 

A: This is clearly a market issue. The number of patients in general who have aneurysmal disease and have the anatomic substrate that would make them better candidates for AUI is rather small, it’s not really a very large subgroup of patients. I don’t know if other manufacturers would be interested in going through the clinical studies that would be required to develop another AUI device that would be applicable to this other subgroup of patients. 

 Q: What is the most important takeaway message for the vascular specialist?

A: We now have a device that allows us to treat patients who have anatomic issues with the iliac arteries or blocked aorta that make them suitable for an AUI device. It will also enable us to salvage grafts or treat ruptured cases when the AUI device might be preferable. It is not a game changer in terms of replacing other devices, but it expands what is available to use to treat patients with aneurysmal disease.

The configuration of AUI is something that most people know about, the problem was we did not have it available in the United States, and now we do. We had been using the Renu as an alternative to AUI, which did relatively well in some patients, but now we have another one that’s available, which provides us with more options for patients. 

Michel Makaroun, MD,  is professor and chief of the division of vascular surgery at the University of Pittsburgh School of Medicine (UPMC), director of endovascular surgery at UPMC, and director of the vascular lab and the vascular surgery training programs at UPMC. Dr. Makaroun reports consultancy to W.L. Gore, Medtronic, Cordis, and Daiichi Sankyo.