Abdominal Aortic Aneurysm Growth Is Associated With Changes in Thrombus Deposition

Abstract

Background: Abdominal aortic aneurysm (AAA) rupture has an associated mortality of 90%. AAAs are repaired when they meet size criteria, become symptomatic, or rupture. Use of aortic diameter as the primary criterion in the decision to intervene fails to take into consideration that AAAs rupture at sizes below operative thresholds or reach extreme size without rupture. We have previously shown that AAAs rupture at sites of low wall shear stress (WSS) where flow recirculation and intraluminal thrombus (ILT) tend to be more abundant. This study examined the fate of ILT deposition in AAA growth. We hypothesized that AAA expansion would be associated with increasing ILT deposition in sites of flow recirculation. Methods: A total of six patients with serial images of AAA growth over three time points were studied. Aortic measurements and sites of ILT deposition were recorded. Three-dimensional AAA geometry was generated from computed tomography angiography images. Predicted aortic blood flow velocity, localized pressure variation, and WSS profiles were correlated with AAA growth and ILT deposition. This study was carried out with biomedical ethics approval. Results: AAA growth was associated with increasing ILT deposition in most cases. The site of maximal ILT deposition strongly correlated with regions of flow recirculation and low WSS but did not correlate with the region of maximal aortic expansion. Interestingly, in some cases, the recirculation zone changed location with AAA growth, and this was associated with similar change in location of ILT deposition. Conclusions: This study has shown that ILT increases with increasing AAA size in most aneurysms and that deposition of ILT occurs at sites with low WSS and flow recirculation. An understanding of the alterations in WSS in pulsatile flow and its effect on vascular endothelium will lead to a better understanding of AAA development and growth and may ultimately lead to better prediction of AAA rupture potential.

Intraluminal thrombus: Innocent bystander or factor in abdominal aortic aneurysm pathogenesis?

“…The location and thickness of the ILT was recorded at each time point. 49 In virtually all cases, the ILT had increased over time and its location coincided with the zones of low WSS and vortex flow. ILT deposition tended to increase in the same location in all but one case.…”

“…Reprinted, with permission, from Boyd et al. 49 Video 2 Computational fluid dynamics modeling of abdominal aortic aneurysm (AAA) blood flow showing recirculation flow. …”

Association of Aneurysm Tissue Neutrophil Mediator Levels with Intraluminal Thrombus Thickness in Patients with Abdominal Aortic Aneurysm

“…ILT deposition is a dynamic process, building increasing ILT at varying AAA regions over time. AAAs with relatively more significant amounts of ILT may reflect a slower aneurysm growth with longer deposition times [ 55 ]. It should also be borne in mind that any AAA wall adjacent to thick thrombus most likely originally adjoined thin ILT, and further thrombus build-up may have covered the original luminal layer of the ILT.…”

Increased matrix metalloproteinase 9 activity correlates with flow-mediated intraluminal thrombus deposition and wall degeneration in human abdominal aortic aneurysm

“…In cases with dense circumferential ILT, flow was more laminar and similar to that in the nonaneurysmal aorta. We have previously examined ILT deposition over time in human AAA 25 and showed that ILT deposition is a dynamic process building increasing ILT in varying regions over time. It is not known why some AAA have relatively greater amounts of ILT but it may reflect a slower AAA growth with longer deposition times.…”