The Effect of Mitral Valve Prostheses Design and Orientation on Left Ventricular Flow during Left Ventricular Assist Device Support

Abstract

The mitral valve affects the shape and timing of incoming flow to the left ventricle of the heart, establishing a strong central jet that generates a vortex ring that conserves momentum during the cardiac cycle. When the vortex is disrupted, regions of stasis are introduced that increase blood residence time and the risk of thrombus formation. This risk is increased when multiple medical devices are combined, as occurs in the fraction of patients with mitral valve prostheses that experience heart failure and receive treatment with a left ventricular assist device (LVAD). LVADs are attached directly to the apex of the left ventricle, continuously pumping blood from the heart into the ascending aorta. While LVADs ameliorate the symptoms of heart failure, they are associated with thromboembolic events that result from disrupted blood flow. In this study, six different mitral prosthesis designs/orientations were studied in combination with LVAD support in a mock circulatory loop. Hemodynamics and the intraventricular velocity field were measured and the vortex characteristics determined. The bioprosthetic valve produced the standard flow pattern with a dominant clockwise vortex that circulated within the left ventricle before exiting through the LVAD. The tilting disk valve exhibited skewed inflow that produced a reverse vortex pattern when oriented towards the septum, which greatly increased stasis and residence time. The bileaflet valves split the incoming flow into two streams directed towards the apex but produced weaker vortices than the bioprosthesis. The results inform the surgical planning for LVAD patients with preexisting mitral prostheses, enabling concomitant repair procedures that would decrease the risk of thromboembolic events.