Longitudinal ultrasound-based fluid–structure interaction study on hemodynamics and wall mechanics in abdominal aortic aneurysms

Abdominal aortic aneurysm (AAA) progression and rupture risk, and the role of intraluminal thrombus (ILT) in it, remain poorly understood. Hemodynamic disturbances are thought to initiate ILT formation and significantly influence AAA progression. However, studies have reported conflicting findings on the specific hemodynamic conditions that promote ILT deposition. Additionally, previous research has shown that ILT has a dual impact on wall mechanics: it reduces wall stress, but also weakens the vessel wall. To advance our understanding of ILT accumulation and AAA progression, it is crucial to study wall mechanics and hemodynamics simultaneously using fluid-structure interaction (FSI) simulations over time. This study included 30 patients with and 9 patients without ILT. Time-resolved 3-dimensional ultrasound (3D+t US) acquisitions were taken at three moments in time. These images were utilized to evaluate geometric parameters and to perform FSI simulations, enabling the assessment of AAA wall mechanics and hemodynamics. Significant differences in hemodynamics were observed between patients with and without ILT, with lower time-averaged wall shear stress (TAWSS) and larger oscillatory shear index (OSI), endothelial cell activation potential (ECAP), and relative residence time (RRT) for patients who remained ILT-free. Notably, patients with fast-growing ILT demonstrated reduced TAWSS and elevated ECAP and RRT values compared to the other patients with ILT. Furthermore, vessel volume growth trends differed between patients with and without ILT, with a weaker correlation between vessel diameter and vessel volume growth rate in patients with ILT. This study underscores the complexity of ILT formation and its influence on AAA growth, highlighting the importance of future studies in larger patient cohorts.