Focused Interventions Aimed at Increasing Sac Shrinkage Rates After Endovascular Aneurysm Repair: Awaiting a Cohesive Analysis

To the Editors

We were interested to note this article by Antoniou et al ¹ focusing on aneurysm sac shrinkage as a prognosticator for positive outcomes after endovascular aneurysm repair (EVAR), particularly in terms of reduction of rates of reintervention, late aneurysm rupture, other late complications—all considered to be the drawbacks of EVAR—and even death. This would suggest a need to look for particular adjuncts/interventions that might increase the incidence of post-EVAR sac shrinkage, and this aspect has not really been touched upon. This is particularly important given the low rate of sac shrinkage described in most studies, with the best figures (depending on variable shrinkage measurement criteria) hovering around 50% or so, with a suggestion that sac shrinkage occurs less with anatomical criteria such as larger necks^2,3 and more in younger patients with longer necks. ² From an interesting pharmacological standpoint, calcium channel blockers have been implicated in increased sac shrinkage in an isolated study. ⁴ Similarly, other factors such as hypercholesterolemia, smoking, statin therapy, diabetic status have been analyzed regarding their links to sac shrinkage.^5,6

A query whether sac shrinkage is device-specific opens the scope for further comparative analysis with newer generation devices.^7-9 This also raises the question of whether the proximal seal at the aortic neck itself needs to be a more focused target in this context, as this is currently achieved either by stent-graft apposition typical of most devices, or by applying polymer sealing technologies employed by devices such as the Ovation iX (Endologix, Santa Rosa, USA) which also achieves reasonably high sac shrinkage rates.^10,11 Studies that have looked at the use of Heli-FX EndoAnchor System (Medtronic Ltd., Minneapolis, USA), at EVAR have indicated a high rate of sac shrinkage. Hypothetically, endostapling may reduce subtle endograft surface movement, which has been implicated in the development of endoleaks, ¹² possibly reduce neck-related complications (including particularly in large necks) by stable fixation at the proximal landing zone,^13,14 and may be linked to the higher incidence of sac shrinkage (>65%) as noted in several studies.^3,13,14 The authors seem to have not examined results on sac shrinkage from this angle, and this may represent a missed opportunity in looking at whether available tools such as EndoAnchors—which may actually positively influence sac shrinkage rates—might be underused.

Whether this merits further studies comparing sac shrinkage rates—and the implications thereof as highlighted above—between “standard” EVAR and other approaches remains a worthwhile issue to consider given the preexisting pointers ³ ; it would certainly have been interesting to see a Forest plot in their article in this context. It may well be that primary endostapling, or adaptation of a polymer-sealing approach, would possibly represent a proactive intervention, rather than the somewhat more reactive one of intensified surveillance as the authors suggest.

Other approaches to then consider also include active interventions to close off potential sources of type 2 endoleaks^15,16—for example, the inferior mesenteric artery—though the added hypothetical benefit of earlier sac thrombosis does not seem to translate to sac shrinkage; such adjunct techniques at the time of EVAR have not been completely able to prevent all type 2 endoleaks either.

Therefore, if there is a body of evidence that suggests sac shrinkage after EVAR improves long-term prognosis in patients, we should be looking at finding ways of augmenting the current therapeutic strategy around EVAR in order to make this happen, which may well be multifactorial, including patient selection, device selection, and adjunct selection (both mechanical and pharmacological). Sac shrinkage of course does not prevent late failure entirely either. ² At the moment though, we only have data coming through in bits and pieces, and much like the story of the “Six Blind Men and the Elephant,” a more complete assessment is needed.