Effects of mechanical fatigue on the bending properties of the porcine bioprosthetic heart valve

The mechanisms underlying the failure of porcine bioprosthetic aortic heart valves are not well understood. One possible explanation is that delaminat ions of the layered leaflet structure occur through flexion, leading to cal cification and further delaminations, and finally resulting in valve failur e. We investigated the changes in flexural rigidity of the belly of aortic valve cusps subjected to accelerated durability testing. We used three-poin t bending wherein a load was applied to the center of each specimen by a th in stainless steel bar calibrated to a known load-displacement relationship . Ten circumferential and 15 radial specimens from valves fatigued to 0, 50 , 100, and 200 million cycles were flexed both with and against the curvatu re of the cusp. Linear beam theory was applied as a means to compare the re lative bending stiffness between groups. Although specimens aligned to the circumferential direction were stiffer when bent against the cuspal curvatu re, the radial oriented specimens exhibited no bending directional dependen ce. Both the radial and circumferential specimens experienced a significant decrease in the bending stiffness with an increased number of accelerated test cycles. Overall, our results suggest that it is the fibrosa that exper iences the greatest loss of stiffness with mechanically induced fatigue dam age.