Surface morphology of degenerated porcine bioprosthetic valves four to seven years following implantation.

The surface structure of leaflets from two processed but unimplanted porcine bioprosthetic valves and six degenerated porcine bioprosthetic valves that were surgically removed because of valvular dysfunction after approximately 4 to 7 years implantation were studied with the scanning electron microscope. Variable degrees of endothelial denudation with the resultant exposure of corresponding areas of subendothelial fibers was the typical surface characteristic of the processed but unimplanted porcine valve heterograft. Structural alterations demonstrated on the surface of leaflets from the degenerated porcine bioprosthetic valves included loss of endothelial cells, exposure of large areas of basement membrane material, exposure of wide expanses of subendothelial fibers, fibrin formation, the presence of activated leukocytes, adherent single platelets as well as reversible and irreversible platelet aggregates, and focal accumulations of crystalline deposits. Each of these morphologic features may be a potential contributor to the progressive degradative process.