A COMPARISON OF MACROSCOPIC LIPID-CONTENT WITHIN PORCINE PULMONARY AND AORTIC VALVES - IMPLICATIONS FOR BIOPROSTHETIC VALVES

Lipid droplets have been demonstrated within both explanted porcine bi oprostheses and normal porcine aortic valves. Because of the increasin g interest in pulmonary valves as an allograft or xenograft aortic val ve substitute, we examined the incidence and distribution of such lipi d deposits in 50 porcine aortic valves and 50 matched porcine pulmonar y valves, All 300 cusps were removed with surgical scissors and, under a dissecting microscope, the ventricularis layer was removed to expos e the spongiosal layer. Macroscopic extracellular lipid droplets were exposed, The position and amount of the visible unstained droplets wer e analyzed by means of a dissecting microscope with an eyepiece grid a nd stereology point-counting techniques to provide an area-density ave rage spatial probability map for each cusp. Only 8% of porcine aortic valves were free of lipid,,vith the distribution of the lipids being 5 2% +/- 14% right coronary cusp, 90% +/- 8% left coronary cusp, and 68% +/- 13% noncoronary cusp, Of the pulmonary valves, 60% were free of l ipid, with the incidence of lipids being 26% +/- 12% left cusp, 6% +/- 7% right cusp, and 12% +/- 9% anterior cusp. Subsequently, lipid clus ter samples underwent thin-layer chromatography, which showed them to be phospholipids, oleic acid (fatty acid), triglycerides, and unesteri fied cholesterol. One primary mode of bioprosthetic valve failure is l eaflet calcification, The similarity of distribution within the spongi osal layer between leaflet calcification and intrinsic cusp lipids sug gests that the observed lipids might act as a nucleation site for calc ification. The substantially lower incidence of lipid in pulmonary val ves therefore may represent a potential benefit when these valves are considered for use as aortic valve replacements.