The Influence of Iliac Coronal Angulation on Pro-Thrombotic Aorto-Iliac Hemodynamics
X.F.E.A. Brörmann (TU Delft - Mechanical Engineering)
S. Pirola – Mentor (TU Delft - Mechanical Engineering)
Simon Overeem – Mentor (Medtronic Trading)
Job van Helvoirt – Mentor (Medtronic)
M.J.B.M. Pourquie – Graduation committee member (TU Delft - Mechanical Engineering)
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Abstract
Endovascular aneurysm repair (EVAR) is widely used for the treatment of abdominal aortic aneurysms, but thrombotic complications such as iliac limb occlusion and intraluminal thrombus formation remain clinically relevant. Previous computational studies have shown that post-EVAR hemodynamics are influenced by aorto-iliac geometry, yet the isolated relation between iliac coronal angulation and prothrombotic near-wall flow indicators remains insufficiently characterised. This thesis addresses this gap using a parametrically controlled idealised aorto-iliac computational fluid dynamics (CFD) model, in which the iliac coronal angle was varied from 15° to 75° while all other parameters were kept constant. Pulsatile, non-Newtonian simulations were performed in ANSYS Fluent, and the near-wall environment was assessed using time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), relative residence time (RRT), and endothelial cell activation potential (ECAP). The idealised sweep was complemented by statistical shape model (SSM)-derived geometries, representing native, non-stented anatomy, to test whether the same tendencies appeared in more realistic shapes.
When the angle was varied in isolation, the adverse hemodynamic area did not grow with angle: the low-TAWSS area decreased from 61.5% to 58.0% of the analysed wall between 15° and 75°, the elevated-RRT area decreased similarly, and the high-OSI and high-ECAP areas increased from a negligible base. In the SSM-derived geometries, by contrast, the low-TAWSS area increased with the measured coronal bifurcation angle, from 86.4% to 94.0%, and showed the strongest fitted trend of any metric (R² = 0.95), while OSI, RRT, and ECAP showed no consistent trend. That the low-TAWSS area moves in opposite directions when angle is varied alone versus together with realistic anatomy is the central finding: the adverse shear response attributed to angulation arises from the combined geometry that accompanies it, not from the angle by itself.
For clinical interpretation, this suggests that iliac angulation is best interpreted not as a stand-alone marker of thrombus-prone conditions, but as one geometric factor to be assessed together with the surrounding anatomy and device. Extending the analysis towards an explicit EVAR stent-graft within realistic geometries is needed before such metrics could support patient-specific risk assessment.