Structural alterations of the porcine heterograft after various durations of implantation.

Morphologic changes in six glutaraldehyde-fixed porcine heterografts recovered from five patients were studied with light and scanning electron microscopy. Light microscopy showed minimal changes in the valves recovered after 2 months of implantation. Fibrin deposits, red blood cell trapping, disruption of the valve matrix and interstitial edema were noted in heterografts 2 months and 2 years after implantation. In valves examined with scanning electron microscopy, 6 hours after implantation the surface changes varied from normal to patchy disruptions. Two months after inplantation, subendothelial fibers were conspicuous and the geometry of endothelial cells was changed. In valves examined after 6 months in place, many nuclei were burst and fibrin strands were seen over the surfaces. Bacterial infection was observed in two cases. The endothelial cells in the valve implanted for 2 years were completely obscured and some areas were densely covered with fibrillar material where blood cells were trapped in the mesh.