Hemodynamic Shear Stress Patterns in Abdominal Aortic Aneurysms and Healthy Aortas: A CFD Study

Abdominal aortic aneurysms (AAAs) remain a major cause of mortality, with rupture risk still primarily assessed by maximum diameter. Specialized hemodynamic indices from Computational Fluid Dynamics (CFD) may provide predictive insight into AAA progression.

We performed a comparative CFD study of 10 healthy-control infrarenal aortas and 15 AAAs, utilizing the open source software SimVascular. Blood was modeled as a Newtonian fluid and pulsatile inlet conditions were applied, extracted from multiscale modeling. Three-element Windkessel (RCR) models were imposed at the iliac outlets to capture physiologic flow distribution. Time Averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI) and Relative Residence Time (RRT) surface area coverage exposed to pathological regimes were quantified and compared between healthy and pathological models. Statistical analysis in two separate regions, the proximal neck/aneurysm sac and the iliacs, was conducted.

Pathological-AAA models exhibited significantly bigger surface coverage of low TAWSS and high RRT compared to the healthy aortas in both studied areas. Although the coverage area of OSI was larger in AAAs, it didn't reach statistical significance at the infrarenal part, but only at the iliac region.

The surface area exposed to lower shear and prolonged residence time provides strong evidence of AAA pathology in contrast with OSI, which offers limited information and cannot be a standalone index of pathology. These findings suggest that integrating TAWSS and RRT into clinical assessment may improve the prediction of aneurysm progression and rupture risk beyond diameter-based criteria.