Reduced Iliac TAWSS as a Hemodynamic Correlate of Aortic Stent-Graft Partial Thrombus Formation

It was hypothesized that post-endovascular aneurysm repair (EVAR) iliac flow disturbances and geometry variation may predispose to thrombus formation within the aortic stent component.

A retrospective cohort of 52 patients (average age of 72 ± 5.2 years; 88.8% male) treated with infrarenal bifurcated stent graft was analyzed using patient-specific iliac geometry measurement and computational fluid dynamics (CFDs) analysis. Digital computed tomography angiography (CTA) datasets were reconstructed to obtain aortoiliac lumen geometry, and pulsatile flow simulations were performed to compute time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and WSS extremes. Iliac geometric parameters (tortuosity, bifurcation angle) were also quantified. Patients were stratified by presence or absence of aortic in-stent thrombus detected during surveillance CTA.

Iliac WSS metrics differed between groups, with the thrombus cohort demonstrating lower mean TAWSS (0.3 Pa vs. 0.77 Pa, P = 0.006). Conversely, OSI and geometric parameters showed no significant intergroup differences. Spearman analysis revealed strong inverse correlations between TAWSS and OSI (ρ = -0.60 to -0.64, P < 0.001), while tortuosity did not correlate with either WSS metrics. Multivariate analysis adjusting for age and mean hemodynamic parameters did not demonstrate statistically significant associations with aortic thrombus.

Reduced iliac TAWSS magnitude, rather than OSI or iliac tortuosity, appears to characterize post-EVAR hemodynamics in patients who develop aortic in-stent thrombus. These data support a mechanistic role for low-shear outflow conditions in promoting thrombotic complications after EVAR and highlights the potential value of shear-based CFD profiling for risk stratification.