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Byline: J. Dunmore-Buyze, Derek R. Boughner, Nick Macris, Ivan Vesely Abstract: Lipid droplets have been demonstrated within both explanted porcine bioprostheses and normal porcine aortic valves. Because of the increasing interest in pulmonary valves as an allograft or xenograft aortic valve substitute, we examined the incidence and distribution of such lipid deposits in 50 porcine aortic valves and 50 matched porcine pulmonary valves. All 300 cusps were removed with surgical scissors and, under a dissecting microscope, the ventricularis layer was removed to expose the spongiosal layer. Macroscopic extracellular lipid droplets were exposed. The position and amount of the visible unstained droplets were analyzed by means of a dissecting microscope with an eyepiece grid and stereology point-counting techniques to provide an area-density average spatial probability map for each cusp. Only 8% of porcine aortic valves were free of lipid, with the distribution of the lipids being 52% [+ or -] 14% right coronary cusp, 90% [+ or -] 8% left coronary cusp, and 68% [+ or -] 13% noncoronary cusp. Of the pulmonary valves, 60% were free of lipid, with the incidence of lipids being 26% [+ or -] 12% left cusp, 6% [+ or -] 7% right cusp, and 12% [+ or -] 9% anterior cusp. Subsequently, lipid cluster samples underwent thin-layer chromatography, which showed them to be phospholipids, oleic acid (fatty acid), triglycerides, and unesterified cholesterol. One primary mode of bioprosthetic valve failure is leaflet calcification. The similarity of distribution within the spongiosal layer between leaflet calcification and intrinsic cusp lipids suggests that the observed lipids might act as a nucleation site for calcification. The substantially lower incidence of lipid in pulmonary valves therefore may represent a potential benefit when these valves are considered for use as aortic valve replacements. (J THORAC CARDIOVASC SURG 1995;110:1756-61) Author Affiliation: London, Ontario, Canada Article History: Received 7 February 1995; Accepted 9 May 1995 Article Note: (footnote) [star] From The John P. Robarts Research Institute, a and The Departments of Electrical Engineering, b Medical Biophysics, c and Medicine, d University of Western Ontario, London, Ontario, Canada., [star][star] Supported by a grant-in-aid from the Heart & Stroke Foundation of Ontario. Dr. Vesely is a Research Scholar of the Foundation and Dr. Boughner is a Career Investigator., a Address for reprints: D. R. Boughner, MD, PhD, University Hospital, P.O. Box 5339, 339 Windermere Rd., London, Ontario, Canada N6A 5A5., aa 0022-5223/95 $5.00 + 0, acents 12/1/66221