Reducing the variability in durability of heart valve bioprostheses. Key factor for future improvement

Two observations concerning the Meadox unicusp bovine pericardial valve were presented. First, calcification has not been a major problem because of the relatively short implant durations (less than 5 years). The second observation was that thromboembolism was found to be practically nonexistent. The third observation was that the leaflets of certain valves that had been removed showed leaflet stretching, which resulted in excess stress in certain loci of the leaflet. The studies reported here showed that the bovine pericardial sac was distensible to various degrees. Strips from various sections of pericardium had a large spectrum of strain (5-45%), at very small stress levels (less than or equal to 4 g/mm2). Further, within any section the material was anisotropic, with strain differences of 25%. Finally, histologic studies of clinical grade Ionescu-Shiley bovine pericardial valves showed marked discrepancies in structure and staining characteristics, further documenting that this material is not homogeneous. New methods of tissue selection are mandatory and have been designed to improve uniformity and ultimately reduce the viability in performance in the clinical setting. This method can be applied to all pericardial valves.