THE CLOSING BEHAVIOR OF MECHANICAL AORTIC VALVE PROSTHESES

Abstract

Purpose. Mechanical artificial heart valves rely on reverse flow to close their leaflets. This mechanism creates much regurgitation and water-hammer effect that may form cavitations, damage blood cells, and cause thromboembolism. The trileaflet design opens fully outward to create a central flow like physiological valves. Vortices in the aortic sinuses help close the leaflets with minimal back flow and washing effect to prevent thrombosis formation. This study analyzes closing mechanisms of clinically used valves and a new trileaflet valve. Methods. The monoleaflet (Medtronic Hall 27), bileaflet (CarboMedics 29; St. Jude 29; Duromedics 29), and trileaflet valves were tested in a circulatory mock loop including an aortic root with three sinuses. Flow field velocity downstream of the valves was measured via particle image velocimetry (PIV). Leaflet movement was tracked with a high-speed camera CCD at 1000 frames/sec. Results. The three designs all take approximately 40–50 ms to open, but monoleaflet and bileaflet valves close in a much shorter time (<35 ms) than the trileaflet valve (>75 ms). During acceleration phase of systole, the monoleaflet forms a major and minor flow, the bileaflet has three jet flows, and the trileaflet produces a single central flow. In deceleration phase, the laterally approaching vortices from the aortic sinuses hinder monoleaflet and bileaflet valve closure until reverse flows push them rapidly for a hard closure. Conversely, the vortices help close the trileaflet valve leaflets earlier and more softly, causing less damage.