Numerical Study on Fluid-Structure Interaction in a Patient-Specific Abdominal Aortic Aneurysm for Evaluating Wall Heterogeneity and Material Model Effects on its Rupture

Abdominal Aortic Aneurysm (AAA) is one of the main cardiovascular diseases, which threats human’s health
while it appears, develops and in crucial cases ruptures and leads to hemorrhage. In the current work, we aim
to investigate numerically the transient blood flow in a patient-specific AAA model, while effects of wall
compliance is considered by employing the fluid-structure interaction method. The AAA model is
reconstructed from acquired CT angiographic data of a patient diagnosed with AAA and an intraluminal
thrombus (ILT). For the comparison purposes two different material models, i.e. isotropic and anisotropic are
considered. Additionally, to have a better estimation, wall thickness variability is compared with simpler
uniform wall thickness model. In this study Navier-Stokes equations along with elastodynamics equation are
coupled through Arbitrary Lagrangian-Eulerian formulation method and solved numerically. Findings
demonstrate that the isotropic material model with uniform wall thickness significantly underestimates wall
stresses as compared to the anisotropic material model with variable wall thickness. Indeed, results emphasize
that considering vessel wall as an anisotropic, heterogeneous (variable thickness) structure estimates much
higher wall stresses comparing with isotropic, uniform thickness model. Therefore, given realistic vessel wall
structure and the fact that the anisotropic, variable wall thickness model predicts higher wall stresses, it could
be a more reliable model to give an accurate estimation to physicians to diagnose the stage of a disease and
choosing an appropriate therapeutic procedure.