Ultrastructural pathology of bioprosthetic heart valves with infectious endocarditis

Abstract

Aim. To study the ultrastructure of mitral bioprosthetic heart valves (BHVs) which failed due to infective endocarditis.Materials and Methods. Here we examined 7 ethylene glycol diglycidyl ether-treated xenopericardial BHVs excised during repeated BHV replacement because of prosthetic endocarditis. After being fixed in formalin and postfixed in osmium tetroxide, BHVs were dehydrated and stained in uranyl acetate with the subsequent embedding into epoxy resin, grinding, polishing, and lead citrate counterstaining. Upon the sputter coating with carbon, we visualised the BHV microanatomy by means of backscattered scanning electron microscopy at 15 kV voltage.Results. The extracellular matrix underwent degradation and disintegration resulting in loosening, fragmentation, and reduction in the electron density of collagen and elastin fibers. We observed a number of recipient cells (macrophages, multinucleated giant cells, neutrophils, endothelial cells and smooth muscle cells) within the BHVs. The highest number of cells was localized on the valve surfaces. The localization of the recipient cells on the ventricular and atrial surfaces was different. The central part of the valves was abundantly populated by macrophages.Conclusion. Prosthetic endocarditis is accompanied by the migration of recipient cells into the BHV structure, which is the consequence of surface and extracellular matrix disintegration.