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Aortic valve mechanics and valve thrombosis

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Calcific aortic stenosis (CAS) is the most common cardiac valve pathology in developed countries, with mortality of more than 50% in 2 years for patients with symptomatic disease, unless valve replacement is performed. Surgical aortic valve replacement (SAVR) is the gold-standard treatment for patients with severe symptomatic aortic stenosis while transcatheter aortic valve implantation (TAVI) is a minimally invasive intervention where bioprosthetic valve mounted on a stent is delivered through blood vessels and deployed on the stenotic valve. Reduced leaflet motion as a result of hypoattenuated leaflet thickening (HALT) in bioprosthetic aortic valves, both in surgical and TAVI, was recently diagnosed by high-resolution CT scans. The highest occurrence of leaflets thrombosis was reported for valve-in-valve (ViV) placement, a TAVI inside a degenerated bioprosthetic valve. Subclinical leaflet thrombosis was suggested as the reason for the reduced leaflet motion. The hemodynamic factors involved with low blood flow rate and regions of flow stagnation near the valve, has been suggested as one of the causes for thrombosis formation. This research aims to compare the hemodynamics of a native aortic valve to surgical valve and ViV, and to assess the effect of each prosthetic valve on the mechanical processes that lead to HALT. The hemodynamics of a native aortic valve will be compared with a post-procedural surgical bioprosthetic aortic valve (Sorin Mitroflow) and with ViV of the latest TAVI devices (Medtronic Evolut PRO, Edwards Sepian 3) using numerical FSI method. The dry modeling of the surgical and TAVI procedures were simulated by finite element analysis (FEA). Hemodynamics models will be created from the native valve model and from the post-procedural configurations. The FSI of the flow through each valve model will be employed with Lagrangian particle tracking to identify flow stagnation regions based on vortices location. The leaflets regions near the stagnating flow will be identified as having a higher risk for stiffening.

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