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 D-shape during systole to a flat (and less eccentric) D-shape 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 D-shape. Characterizing the effects of these geometrical variations on the filling efficiency of the left ventricle (LV) is required to understand why the flat D-shaped annulus is observed in the native MV during diastole in addition to optimizing the design of prosthetic devices. We hypothesize that the D-shaped annulus reduces energy loss during ventricular filling. An experimental left heart simulator (LHS) consisting of a flexible-walled 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 O-shaped annulus generates a stronger (25% relative to the D-shaped annulus) vortical structure than that of the D-shaped annulus. It was also found that the O-shaped annulus resulted in higher EDR values throughout the diastolic period of the cardiac cycle. The results support the hypothesis that a D-shaped 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.

On the Significance of Systolic Flow Waveform on Aortic Valve Energy Loss

“…Also, energy dissipation rate per unit volume over the experimentally measured flow domain is calculated following the methodology of Okafor et al 21 . The equation used is as follows integrated over the flow domain: italicEDR=μtrue[false(∂Vx∂xfalse)2+false(∂Vy∂yfalse)2+0.5true(false(∂Vx∂yfalse)+false(∂Vy∂xfalse)true)2true]…”

The hemodynamic effects of acute aortic regurgitation into a stiffened left ventricle resulting from chronic aortic stenosis

“…Left heart simulator. The LV models and AV were integrated into a validated physiologic left heart simulator (LHS) (26,27). In summary the LHS consists of a rigid atrium, a compliant LV, and a rigid aorta.…”

“…We demonstrated that the LVDS of a patient should be taken into consideration to gain insight on the patient's ability to tolerate AR post-TAVR. In this study, AR severity and LVDS were varied in an extensively validated, physiological left heart simulator (26,27). The use of this fully controllable experimental environment allowed for the study to be performed in the absence of other confounding factors that exist in vivo.…”

Heart Valve Biomechanics: The Frontiers of Modeling Modalities and the Expansive Capabilities of Ex Vivo Heart Simulation

“…Many of these publications have changed the understandings of key interactions, particularly those of MV annulus dynamics and the downstream effects on MR and annuloplasty repair. In a series of studies, researchers decoupled the effects of the mitral annulus and leaflet geometry, demonstrating that the D-shaped annulus allows for more efficient LV filling by minimizing energy dissipation ( 58 , 61 , 79 , 80 ). Extrapolating further, a recent publication focused on creating a dynamically contracting mitral annulus to recapitulate the natural annular changes.…”