Can aspect ratio be used to categorize intra-aneurysmal hemodynamics?—A study of elastase induced aneurysms in rabbit

Abstract

Clinical studies suggest aneurysm aspect ratio (AR) is an important indicator of rupture likelihood. The importance of AR is hypothesized to arise from its influence on intra-aneurysmal hemodynamics. It has been conjectured that the flow in the domes of high AR sacs is slower than in low AR sacs and some aspect and leads to a cascade of enzymatic activities that weaken the aneurysm wall. However, the connection between AR, hemodynamics and wall weakening has never been proven. Animal models of saccular aneurysms provide a venue for evaluating this conjecture. The focus of this work was to evaluate whether a commonly used elastase induced aneurysm model in rabbits is suitable for a study of this kind from a hemodynamic perspective. In particular, to assess whether hemodynamic factors in low and high AR sacs are statistically different. To achieve this objective, saccular aneurysms were created in 51 rabbits and pulsatile computational fluid dynamics (CFD) studies were performed using rabbit specific inflows. Distinct hemodynamics were found in the low AR (AR<1.8, n=25), and high AR (AR>2.2, n=18) models. A single, stable recirculation zone was present in all low AR aneurysms, whereas a second, transient recirculation zone was also found in the superior aspect of the aneurysm dome for all high AR cases. Aneurysms with AR between 1.8 and 2.2 displayed transitional flow patterns. Differences in values and distributions of hemodynamic parameters were found between low and high AR cases including time averaged wall shear stress, oscillatory shear index, relative residence time and non-dimensional inflow rate. This work lays the foundation for future studies of the dependence of growth and remodeling on AR in the rabbit model and provides a motivation for further studies of the coupling between AR and hemodynamics in human aneurysms.

Analysis of Morphologic and Hemodynamic Parameters for Unruptured Posterior Communicating Artery Aneurysms with Oculomotor Nerve Palsy

“…21 A recent study performed on an animal model also proved that high AR appears more deleterious to the aneurysm wall with pathologically low WSS. 22 Above all, in this case series, it inferred that low WSS might play an important role in aneurysm rupture.…”

Morphological and Hemodynamic Analysis of Mirror Posterior Communicating Artery Aneurysms

“…[6], [26], [27] Ujiie et al [27] speculated that the relevance between AR and aneurysm rupture was owing to differences in intra-aneurysmal flow. Zeng et al [28] found differences in values and distributions of hemodynamic parameters between low and high AR cases with rabbit models. Moreover, the geometric and hemodynamic relevance of the rabbit model to human IAs has been previously demonstrated.…”

Optimization of Strut Placement in Flow Diverter Stents for Four Different Aneurysm Configurations

“…However, Liou et al suggested that the characteristics of aneurysmal inflow and outflow areas under steady conditions are consistent with those of pulsatile flow, except for small differences using idealized sidewall aneurysms with an aspect ratio (AR) of 2.0 [30]. In contrast, Zeng et al demonstrated changes in the flow pattem in an aneurysm during pulsation in a realistic, high AR aneurysm [31]. The model we used is an idealized sidewail aneurysm with an AR of 1.6.…”