In vitro pulsatile flow hemodynamics of five mechanical aortic heart valve prostheses.

In vitro measurements of velocity, turbulent shear stress, effective orifice area (EOA), and regurgitant fraction were performed on five new-generation low-profile mechanical aortic heart valve designs under pulsatile flow conditions. These were: Medtronic-Hall tilting disc, St. Jude Medical bileaflet, Björk-Shiley Monostrut tilting disc, Omni-Carbon tilting disc, and Duromedics bileaflet. In general, bileaflet valves have larger EOAs than the tilting disc design, especially in the larger sizes, due to the larger opening angles and lack of obstructive struts. The regurgitant fractions range from 8% for 21-mm valves to 13% for the 29-mm sizes. This increase was largely due to an increase in leakage volume as opposed to closing volume. Furthermore, the leakage volumes increased as the mean aortic pressures increased. The tilting disc valves generally have better regurgitant characteristics compared to the bileaflet valve designs, due to lower leakage volumes and to the smaller opening angle of the occluder providing a more rapid closure of the valve. The velocity and shear stress measurements showed that none of the current valve designs are ideal: all designs create areas of stasis and/or regions of low-velocity reverse flow and regions of elevated turbulent shear stresses capable of causing sublethal and/or lethal damage to the formed elements of blood. It is therefore unlikely that these valve designs will eliminate the problems of hemolysis, thrombosis, and thromboembolic complications.