Pitfalls and outcomes from accelerated wear testing of mechanical heart valves

In 1990 Sorin Biomedica introduced a new bileaflet heart valve called the Bicarbon valve. This design was reported to eliminate wear in the hinge mechanism. Clinical quality Sorin Bicarbon, CarboMedics, St. Jude Medical, Duromedics and Jyros valves were obtained to test this claim and to compare the wear in the pivot of this new valve to other available heart valves. The valves were visually inspected then subjected to 4,000 cycles at a physiological beat rate in vitro. The valves were re-inspected then subjected to 400 million cycles in a Reul type accelerated wear tester. Scanning electron microscope photographs were taken of all contact areas at 40, 80, 120, 160, 200, 240, 280 and 400 million cycles. Wear marks on the inflow side of the Sorin, CarboMedics and St. Jude leaflets were measured and compared. Orifice wear was not quantified because of difficulty with measuring inside complex depressions. After 4,000 cycles of testing at a physiological beat rate the CarboFilmTM coating on the Sorin orifice showed signs of erosion. The other valve components only exhibited minor burnishing after 4,000 cycles. Following completion of 400 million cycles in an accelerated wear tester, approximately ten years in vivo, all valves showed significant wear. The inflow face of the pivot on the Sorin Bicarbon leaflets exhibited the deepest wear marks. The CarboFilm coating on the Sorin Bicarbon orifices was removed from most areas of leaflet contact. The transition between the remaining coating and the eroded areas created a rough edge. The tips of the Sorin leaflets contacted the bottom of the orifice pivot, in contrast to the St. Jude Medical and CarboMedics designs, which had minimal contact between the leaflet and the orifice.