Association of Hemodynamics and Morphology With Rupture Risk of Small Abdominal Aortic Aneurysm

Abstract

Objectives:

Decision to operate on abdominal aortic aneurysms (AAAs) is primarily on the basis of aneurysm diameter. However, some patients experience rupture before reaching operative thresholds. This study aimed to determine the influence of morphology and hemodynamic force on the rupture of small AAAs.

Methods:

This was an age and sex matched case control study. Forty infrarenal AAAs (20 ruptured, 20 nonruptured controls) were retrospectively analyzed. Morphological variables (maximum diameter, complex neck, morphology classification, etc) were recorded. Hemodynamic parameters (peak and average flow velocity, wall shear stress [WSS], and aneurysm pressure drop [∆pressure], etc) were derived from computational fluid dynamics (CFD) analyses. Univariable and Multivariable regression was used to determine independent AAA rupture risk factors.

Results:

Mean AAA diameters were similar for control vs rupture groups (40.91 ± 6.16 vs 41.00 ± 9.79 mm; P = .543). Aneurysm morphology (saccular vs fusiform) differed markedly: 14/20 (70%) ruptured AAAs were saccular vs 2/20 (10%) in controls (P = .005). Peak WSS tended to be higher in ruptured AAAs (P = .042). WSS and flow velocity was significantly lower at the site of rupture (P < .05). Only saccular morphology was found to be independent risk factor for rupture (OR = 3.36 [1.67, 17.10]).

Conclusion:

Saccular morphology was associated with a significantly increased rupture risk of small AAAs. AAAs rupture tended to occur in areas of low WSS and low flow velocity. These findings suggest that integrating aneurysm morphology could aid in the identification of small AAAs with a high rupture risk.

Clinical Impact

This study provides an improvement of management strategies of small AAAs based on morphological and hemodynamic analysis. The study presents saccular aneurysms with high overall peak WSS and localized low flow loading have higher risk. The combination of morphological and hemodynamic analysis helps to better predict rupture of small AAAs, even if the diameter is within the conventional safety range.