A morphologic overview of the porcine bioprosthetic valve--before and after its degeneration

Patients with valvular heart disease have had their diseased, natural heart valves replaced with the porcine aortic bioprosthetic valve (Hancock type) at Henry Ford Hospital since 1971. This commercially available valvular bioprosthesis is characterized by 1) loss of endothelium from both surfaces of the leaflets, 2) modification in the organization of the fibrous connective tissue of the leaflet, and 3) a reduction in the macromolecular complexes (proteoglycan) of the extracellular matrix. Subendothelial components are therefore exposed to the circulating blood. This bioprosthetic heart valve undergoes degeneration after it is inserted into patients for various lengths of time. Prominent features of the degenerated porcine bioprosthetic valve include 1) penetration of plasma proteins into the interior of the leaflet, 2) adhesion of various types of leukocytes (mononuclear cells and granulocytes) to the surfaces of the leaflets, 3) deposition of single platelets, platelet aggregates and microthrombi onto the leaflet's surface, 4) destruction of collagen fibers, and 5) pathologic deposition of calcium salts. The mechanisms responsible for the degeneration of the porcine aortic bioprosthetic valve are incompletely understood at this time.