Fluid-Structure Interaction Simulation of Mitral Valve Structures in a Left Ventricle Model

Simulations of blood flow in patient-specific models of heart ventricles is a rapidly developing field of research, showing promise to improve future treatment of heart diseases. Fluid-structure interaction simulation of the mitral valve, with its complex structure including leaflets, chordae tendineae, and papillary muscles, provides additional prospects as well as challenges to such models. In this study, we combine a patient-specific model of the left ventricle with an idealized unified continuum fluid-structure interaction model of the mitral valve, to simulate the intraventricular diastolic blood flow. To the best of our knowledge, no monolithic fluid-structure interaction model, without the need for remeshing, has ever been used before to simulate the native mitral valve within the left ventricle. The chordae tendineae are simulated as a region of porous medium, to partially hinder the flow. Simulation results from this model are compared to those of a model with the same patient-specific left ventricle, but with the mitral valve simply modeled as a time-variant inflow boundary condition. The blood flow is analyzed with the E-wave propagation index, and by use of the triple decomposition of the velocity gradient tensor, which decomposes the flow into rigid body rotational flow, shearing flow, and irrotational straining flow. The triple decomposition enables analysis of the formation of initially large dominant flow features, such as the E-wave jet and the vortex ring around it, and their subsequent decay into smaller turbulent flow structures. This analysis of the development of flow structures over the duration of diastole appears to be in general agreement with the theory of the stability of rotation, shear, and strain structures. Elevated shear levels are investigated, but are found only in limited amounts that do not indicate significant risks of thrombus formation or other blood damage, which is to be expected in this healthy ventricle. The highest shear levels are localized at the leaflets in the fluid-structure interaction model, and at the ventricle wall in the planar model. The computed E-wave propagation indices are 1.21 for the fluid-structure interaction model and 1.90 for the planar valve model, which indicates proper washout in the apical region with no significant risk of blood stasis that could lead to left ventricular thrombus formation.