Bicuspid Aortic Valve (BAV). Q-criterion

Simulating the hemodynamics of a trileaflet aortic heart valve at physiologic conditions requires capturing the complex interaction between blood flow and flexible valve leaflets. In FSI simulations of biological tissues, e.g. heart valve leaflet interaction with blood flow, it is critical to use a relevant and efficient structural model that is able to realistically represent the deformation of the tissue under loads imposed by the pulsatile blood flow. Such undertaking, however, is not a trivial task since the large deformations of the tissue and its underlying geometric non-linearity pose major modelingchallenges. To circumvent these challenges recent studies attempting to simulate FSI of tissue valves chose to either use simplified membrane-like materials or treat the valve leaflets as thick bodies. However, biological tissues of leaflets are normally thin and they exhibit significant bending. Therefore, a shell model for the solid body is a more appropriate choice. Most finite-element (FE) methodologies for handling shells, however, are computationally very demanding as they employ two or three nodal rotations alongside with three nodal translations, i.e. 5 or 6 degree of freedom per node. Note that the efficiency of the FE shell model becomes of paramount concern in FSI simulations of complex problems where the need to couple the fluid and structural solvers together can dramatically increase the computational cost per time step. For that, in this work we adapt and incorporate in the FSI methodology a previously developed nonlinear, rotation-free triangular shell element formulation, which has already been shown to provide accurate and robust solutions of various thin shell FE problems. Such an approach, however, has not been coupled before with a flow solver to simulate FSI problems and it is this coupling that constitutes one of the important contributions of our work.

Understanding the abnormal flow patterns in bicuspid aortic valve compared to trileaflet valves.

Iso-surfaces of the Q-criterion for a bicuspid aortic valve during systolic phase. Linear isotropic Saint-Venant material model was used.

The aortic valve vortex ring grows in complexity rapidly and breaks into turbulence much sooner than for the trileaflet case.

BAV shows significantly different flow patterns that may contribute to aortic wall stress.