Spontaneous host endothelial growth on bioprostheses: Influence of fixation

Background. Neither homografts nor bioprostheses have previously been seen to acquire a host endothelium. We previously reported a direct relation between aldehyde tanning and bioprosthesis calcification and the absence of calcification in the absence of aldehyde. Methods and Results. Bovine pericardium was 1) treated with 0.625% glutaraldehyde and stored in 4% formaldehyde, 2) treated with 99.5% glycerol, and 3) treated with 99.5% glycerol and stored in formaldehyde (0.25-4%). The treated pericardium was used to construct stentless mitral valve prostheses (of a single pattern) that were implanted in weanling sheep. After the animals were killed, a strip of anterior cusp from annulus to papillary muscle was processed and examined by scanning electron microscopy for the presence of host endothelial growth. Avoidance of aldehyde allowed host endothelial growth in all cases (six of six), and pure aldehyde treatment inhibited growth in five of six animals. Exposure to aldehyde after glycerol treatment interfered with endothelialization significantly; after longer periods of implantation, however, endothelial growth occurred almost invariably in this group (12 of 13 implanted longer than 200 days). For this group, there was a statistically significant difference for duration of implantation between the valves that grew endothelium and those that did not (218.4±61.9 versus 128.5±65.4 days). Conclusions. Aldehyde treatment inhibits endothelial growth. With glycerol treatment, growth is uniformly present. Limited exposure to aldehydes after glycerol treatment inhibits endothelial growth, but this effect was ameliorated by prolonged implantation. The possibility of host endothelium-covered, noncalcifying bioprostheses is now real.