LA PATOLOGIA AORTICA NELLA BICUSPIDIA VALVOLARE: MODELLI MATEMATICI AD ELEMENTIFINITI E CORRELAZIONI FLUIDODINAMICHE

Purpose: In bicuspid aortic valve disease (BAV) role of genetic and hemodynamic factors influencing ascending aortic pathology is controversial. To test the effect of BAV geometry on ascending aortic flow, a Finite Element Model analysis was undertaken. Methods: A surface model of the aortic root and ascending aorta was obtained from magnetic resonance images of patients with BAV and tricuspid valve using segmentation facilities of the image processing code Vascular Modelling Toolkit. Analytical models of bicuspid (antero-posterior, AP and latero-lateral, LL) and tricuspid orifices were mathematically defined. Models were then turned into volumetric meshes of linear tetrahedra for computational fluid dynamics simulations. Numerical simulations were performer with the Finite Element code LifeV. Flow velocity fields were assessed ad four levels: aortic annulus, sinuses of Valsalva, sinotubular junction, ascending aorta. Results: Comparison of finite-element analysis of bicuspid and tricuspid aortic valve shows different blood flow velocity pattern. Flow in bicuspid configurations shows asymmetrical distribution of velocity field towards the convexity of mid-ascending aorta, returning symmetrical in distal ascending aorta. On the contrary, tricuspid flow is symmetrical in each aortic segment. Comparing AP-BAV with LL-BAV, more pronounced recirculation zones have been noticed in the latter. Finally, we found that in both BAV configurations maximum wall shear stress is highly localized at the convex portion of mid-ascending aorta. Conclusions: Comparison between models show asymmetrical and higher flow velocity in bicuspid models, in particolar in AP configuration. Wall shear stress is maximum at the aortic level known to be more exposed to aneurysm formation in bicuspid patients. This supports the hypothesis that hemodynamic factors may contribute to ascending aortic pathology in this subset of patients.