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American Journal of Pathology, Vol 119, 12-21, Copyright © 1985 by American Society for Investigative Pathology

REGULAR ARTICLES

Ultrastructural substrates of dystrophic calcification in porcine bioprosthetic valve failure

M Valente, U Bortolotti and G Thiene

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.

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