Kinematics of synthetic flexible leaflet heart valves during accelerated testing

The study aim was to examine the effect of variation of test frequencies on the duration and kinematics of valve leaflets during opening, and at the fully open position.

Trileaflet polyurethane heart valves were tested in a Rowan Ash fatigue accelerator at 5, 10 and 15 Hz. Images of the valves were acquired using a high-speed camera and assessed qualitatively during opening and in the fully open position. The bending strains along the leaflet free edge and leaflet belly were also calculated from these images. Results were compared with those found at 1 Hz in a pulsatile flow simulator. The time duration of each phase of the cycle and the strain time integral when opening were also determined.

In the fully open position, the maximum bending strain found at the commissural regions of the valve was not dependent on the cycle rate. During opening, one leaflet always deformed more than either of the others, but this leaflet was not necessarily the same one each time. The opening characteristics of the valves were dependent on cycle rate: increasing bending was observed in the belly of the leaflet with increasing frequency. The ratio of time of opening of the leaflets to time whilst fully open increased with the cycle rate, and the period of time when the valve was fully open and fully closed reduced markedly with increased cycle rate.

Leaflet kinematics, bending strains, the proportion of time the valve was fully closed or open, and the strain time integral were dependent on cycle rate in accelerated testing. This may influence the relative severity of accelerated testers.