Ultrastructural substrates of dystrophic calcification in porcine bioprosthetic valve failure. Am J Pathol 119:12-21, 1985 (M. Valente, U. Bortolotti, G. Thiene) (IF,2000: 6.971)

Calcific degeneration is the main cause of porcine bioprosthetic valve failure. This dystrophic phenomenon has been studied by transmission electron microscopy in 26 explants; six normally processed unimplanted xenografts and a pig aortic valve from the slaughterhouse served as controls. Loss of endothelial lining and proteoglycans were a regular finding in all the commercially processed valves. In order to detect initial calcifications, we investigated in particular areas apparently devoid of mineralization at x-ray. Three main ultramicroscopic features were found: 1) intracytoplasmic and interstitial calcospherulae in 22 explants, 2) calcified collagen fibrils in 15, and 3) platelike calcium deposits upon amorphous material in 3. X-ray diffraction and energy-dispersive microanalysis identified Ca2+ deposits as crystals of hydroxyapatite. From these findings there is evidence that debris and membrane fragments of the pig cusp cells represent one of the initial nuclei of calcification