Effects of preexisting lipids on calcification of porcine bioprosthetic heart valves. A dynamic in vitro model

Calcification is one of the main causes of failure of porcine bioprosthetic heart valves, a problem which has not been satisfactorily solved to date. Previous studies have shown that calcification is decreased in porcine hear t valves that have undergone treatment for lipid extraction. The relation b etween lipid distribution and calcification of seven new commercially avail able porcine bioprosthetic heart valves (St.Jude Medical, Bioimplant) is as sessed by Sudan red III staining to show preexisting lipids. All porcine bi oprosthetic valves contained lipids to different degrees. Five valves were subjected to the pulsatile accelerated calcification process for 4 weeks. D istribution and level of calcification were evaluated by radiography and co mpared to the Sudan red-stained fatty areas. Comparison of the calcificatio ns detected by radiography and the macroscopically detected lipids showed a coincidence of 57-66%. Two porcine bioprosthetic valves were histologicall y prepared and stained with Hematoxylin and von Kossa's stain, respectively . By light microscopy,the von Kossa staining revealed microcalcifications a nd polarizing microscopic investigation showed birefractive substances in a reas with lipid deposits. These preexisting substances in porcine valve tis sue may play a determinative role in the calcification of the tissue. Subst antial studies are necessary to further determine the role of preexisting l ipids in calcification.