Tissue Damage and Calcification may be Independent Mechanisms of Bioprosthetic Heart Valve Failure
Ivan Vesely, J.Edward Barber, Norman B. Ratliff

It has been suggested that calcification stiffens porcine bioprosthetic valve cusps, leading to secondary collagen fiber breakage and leaflet tearing. This thesis was tested in 60 explanted porcine bioprostheses. Valves were examined grossly and histologically, and samples of intact cusps were subjected to materials testing. Cusp tissue from explanted valves was less extensible and weaker, but its stiffness was unchanged relative to controls. Calcification was mild and diffuse in most of the examined samples. Breaks in collagen fiber bundles and tears were found in areas without calcific deposits. These results do not support the thesis that calcification stiffens glutaraldehyde-fixed porcine bioprostheses, unless the entire cusp is transformed into a solid mass of mineral. Instead, leaflet tears may develop as a result of accumulated mechanical damage that is independent of calcification.