Role of Mitral Annulus Diastolic Geometry on Intraventricular Filling Dynamics

Abstract

The mitral valve (MV) is a bileaflet valve positioned between the left atrium and ventricle of the heart. The annulus of the MV has been observed to undergo geometric changes during the cardiac cycle, transforming from a saddle Dshape during systole to a flat (and less eccentric) Dshape during diastole. Prosthetic MV devices, including heart valves and annuloplasty rings, are designed based on these two configurations, with the circular design of some prosthetic heart valves (PHVs) being an approximation of the less eccentric, flat Dshape. Characterizing the effects of these geometrical variations on the filling efficiency of the left ventricle (LV) is required to understand why the flat Dshaped annulus is observed in the native MV during diastole in addition to optimizing the design of prosthetic devices. We hypothesize that the Dshaped annulus reduces energy loss during ventricular filling. An experimental left heart simulator (LHS) consisting of a flexiblewalled LV physical model was used to characterize the filling efficiency of the two mitral annular geometries. The strength of the dominant vortical structure formed and the energy dissipation rate (EDR) of the measured fields, during the diastolic period of the cardiac cycle, were used as metrics to quantify the filling efficiency. Our results indicated that the Oshaped annulus generates a stronger (25% relative to the Dshaped annulus) vortical structure than that of the Dshaped annulus. It was also found that the Oshaped annulus resulted in higher EDR values throughout the diastolic period of the cardiac cycle. The results support the hypothesis that a Dshaped mitral annulus reduces dissipative energy losses in ventricular filling during diastole and in turn suggests that a symmetric stent design does not provide lower filling efficiency than an equivalent asymmetric design.