An endovascular aortic repair (EVAR) revolution may be here, Andrew Holden, associate professor of Radiology, Auckland City Hospital, Auckland, New Zealand, told delegates at the CIRSE annual meeting (14–18 September, Barcelona, Spain).
Holden proposed that endovascular aneurysm sealing (EVAS) technology, a procedure that treats the abdominal aortic aneurysm by sealing the aneurysm using a constrained liquid polymer that polymerises into solid material, may represent an advance in the endovascular treatment of abdominal aortic aneurysms.
Holden explained: “There was an expectation that minimally invasive EVAR would result in dramatically reduced morbidity and mortality compared to open abdominal aortic aneurysm repair. However, early registries such as EUROSTAR reported disappointing and disturbing results and sceptics soon appeared.”
Large randomised controlled trials, the British EVAR I trial and the Dutch DREAM (Dutch randomized endovascular aneurysm repair) trial, comparing EVAR and open repair for abdominal aortic aneurysm showed a long-term re-intervention rate for EVAR much higher than open repair, without a mortality benefit. The excessive cost of EVAR compared with open surgery was also confirmed in these trials.
“Re-intervention is really the Achilles’ heel of EVAR; it is seen in both these trials that as time goes on, the incidence of re-intervention goes up. This is not seen in open repair and it is the major contributor to the excess of costs with EVAR,” Holden pointed out.
In the early days, re-interventions were due to stent migration, graft thrombosis and endoleaks of various types. For modern EVAR devices, randomised controlled trial data evaluating these devices are limited. Large industry-sponsored device registries are available. These have shown that the incidence of type I and III endoleak, limb thrombosis and device migration has been significantly reduced, when devices are used within company instructions for use.
“But even in these registries, the incidence of endoleak remains a problem, particularly type II endoleaks. Type II endoleak is the most controversial topic in endoluminal aneurysm treatment. Pragmatists often say that type II endoleaks do not cause problems so should be ignored. However, the fact that patients with a type II endoleak have a significantly higher rate of aneurysm expansion, re-intervention and major complications is beyond debate,” Holden stated.
Unlike most EVAR devices, open repair treats the aneurysm sac directly. The aneurysm sac is ablated and the aortic side branches ligated. There is no risk of endoleak (including type II endoleak), or migration. The procedure is extremely durable with low re-intervention rates.
Holden emphasised that “another limitation of EVAR devices is the inability to treat the majority of abdominal aortic aneurysm morphologies. Infrarenal neck anatomy is the most common limitation because almost all current devices seal the aneurysm by artery wall apposition at the proximal and distal sealing zones.”
“With developments in EVAS technology, if durability can be achieved without significant secondary intervention, the current post-EVAR imaging surveillance protocol can be seriously altered with major cost savings,” he said.
There are currently two devices (Endologix’s Nellix and TriVascular’s Ovation) that can be used to perform EVAS.
The Nellix device seals the entire aneurysm. Balloon-expandable stents are surrounded by endobags; these achieve aneurysm sealing by being filled by a polymer that quickly cures to the consistency of a pencil eraser. The compliant polymer-filled endobags form a cast of the aneurysm blood lumen, which potentially prevent endoleaks and device migration.
The proposed advantages of EVAS with Nellix over EVAR are the ability to treat anatomies adverse for standard EVAR, the absence of endoleaks and absence of secondary interventions with reduced surveillance requirements and cost savings.
With TriVascular’s Ovation device, the EVAS technology is confined to the proximal neck seal and composite junction seal. A 161-patient core laboratory adjudicated IDE trial showed 0% incidence of type IA endoleak at 30 days and at one year.
Holden noted that the procedural simplicity and ability of the device to treat a range of aortic anatomies makes Nellix an ideal mechanism for ruptured abdominal aortic aneurysms. This has been successfully performed at several sites. “The technology shows great promise and has the potential to change EVAR by treating the aneurysm sac directly. However, the potential has to translate into results and this is yet to be proven.”
In Auckland, experience in 54 patients has shown a technical success rate of 100%; aneurysm-related mortality of 0%; 1.8% (1/54) instance of type I or III endoleak. The secondary intervention rate was 1.8% (1/54). A post-market global registry (EVAS-Global) commenced in early October 2013.
Holden also told delegates about work by Arsenal Medical that is developing a foam technology that forms in the space excluded by a conventional endograft. The foam excludes the aneurysm without compression of the graft or branch artery embolization. In this case, a liquid is injected and reacts upon contact with blood to expand and cure. “Most impressively, the foam has a mechanically robust skin on its surface that prevents embolization down aortic branch arteries. This foam has the potential to stabilise an endograft, prevent migration and prevent endoleaks,” Holden reported.