Vorticity-based analysis in computational hemodynamics models of carotid bifurcation pre and post carotid endarterectomy

Atherosclerosis is one of the most diffuse pathological conditions of the arterial system. It is characterized by the thickening, hardening, and loss of elasticity of arterial walls, which restricts blood flow. This occurs as cholesterol, fats, and cellular debris accumulate between the intima and media layers of the artery wall, forming plaques. Carotid bifurcations are a common site for the development of atherosclerotic plaques. The constriction of the carotid artery results in the reduction of blood flow, which, in the worst case, could lead to a stroke. The most used surgical procedure to remove atherosclerotic plaques in carotid bifurcations is carotid endarterectomy (CEA). Restenosis after CEA is an important complication affecting patients' outcomes, leading to the development of cerebral symptoms or even carotid occlusion and stroke. In this scenario, it is important to predict the long-term restenosis risk. The role played by hemodynamics in the local onset and progression of atherosclerotic disease is well recognized. Recently, it has been demonstrated the ability of peculiar features of the Wall Shear Stress on the luminal surface to identify flow features promoting the development of atherosclerosis. In this context, this thesis aims to understand if, in addition to Wall Shear Stress, vorticity and its related parameters can improve and extend the current understanding of the association between local hemodynamics and the onset of the plaque. To do that, a cohort of 8 asymptomatic patients submitted to CEA interventions (4 treated with a patch and 4 without a patch) was adopted. Computational fluid dynamics simulations (CFD) were performed on 8 carotid models pre-CEA and at 1 month after CEA. From CDF data, a vorticity-based analysis was performed. In particular, the temporal average of vorticity magnitude, Q-criterion, Swirling strength, Stretching, and Local Normalized Helicity were computed. To compare the results between the models, a quantitative analysis was performed by calculating helicity (h1, h2, h3 indices). In addition, geometry parameters (curvature, torsion, and flare) were also estimated to verify potential correlations between arterial geometry and the vorticity-based parameters, and consequently, the possible risk of restenosis. The study concluded with a correlation matrix representing the relationships among the vorticity-based and geometric parameters with Intima-media thickness measured at 60 months after CEA (clinical indicator to detect the presence of long-term restenosis). The results of this study suggest that vortex dynamics and vorticity composition may contribute to a deeper understanding of the mechanistic link between the organization of intravascular blood flow patterns and the development of carotid restenosis after CEA (and, by extension, of atherosclerosis).