In vitro hydrodynamic characteristics among three bileaflet valves in the mitral position

The non-fully open phenomenon of the advancing standard medical bileaflet h eart valves (the ATS valve) are frequently observed in clinical cases, even though there is no problem with their hemodynamic function. The movement o f the leaflets was affected easily by the transvalvular flow because of the unique open pivot design of the ATS valve. In this paper, a comparative in vitro hydrodynamic test was conducted among 3 different types of bileaflet valves, and the effect of different shapes of downstream conduits, which i nduce different transvalvular flow, on hydrodynamic performance was studied . Three bileaflet valves, the ATS valve, CarboMedics valve (CM), and St. Ju de Medical valve (SJM), with an annulus diameter of 29 mm for the mitral po sition were chosen throughout our experiments. First, pressure drops across the valves under steady flow were measured. Then, the valves were tested a t the mitral position with our pneumatically driven pulsatile pump. In this pulsatile flow study, 2 different conduits (straight shape and abrupt enla rgement shape) were in turn incorporated at the downstream portion of the m itral valve. A high-speed video camera was employed to observe leaflet move ments. In a steady-flow test, the ATS and the SJM produced the same pressur e drop, but the CM recorded a higher value. In the pulsatile study, it was observed that the ATS leaflets did not open fully in the mitral position wh en the downstream conduit with an abrupt enlargement shape was incorporated . However, the CM and the SJM always indicated a fully open movement regard less of the shape of downstream conduits. When the straight downstream cond uit was incorporated, the ATS produced a similar pressure drop to that of t he SJM, which coincided with the steady test results. When the enlargement conduit was incorporated, however, the ATS presented the lowest pressure dr op despite the non-fully open movement. The conduit shape at the valve down stream had a significant influence on the closing volume. These findings in dicate that the conduit shape at the valve outlet can affect the hydrodynam ic characteristics of bileaflet valves.