Light and electron microscopy studies on homograft and heterograft heart valves

Light and electron microscopical changes were studied in 23 valvular homografts and six pig aortic heterografts, which had been inserted into patients for lengths of time varying from three days to 54 months. Prior to insertion, eleven of the homografts had been sterilised by beta-propriolactone and freeze-dried, the other twelve had been sterilised by gamma-radiation. The morphological changes in the freeze-dried group were characterised by moderate to severe structural changes including gross vacuolation, fibrinoid degeneration and calcification in the absence of any significant cellular events. It is concluded that the structural changes were due to physico-chemical degradation of the collagen due to improper preservation of the graft, prior to insertion. The morphological changes in the homografts treated with gamma-radiation were fewer and less severe in that there was less vacuolation of the matrix, less fibrinoid degeneration and no examples of calcification. Clear-cut examples of graft regeneration were never observed in either group, but the significance of minor cellular infiltrates in two of the gamma-irradiated grafts is discussed in terms of abortive regeneration. The heterografts showed moderate to intense cellularity, predominantly of macrophages. It is postulated that graft rejection phenomena are responsible for the graft failure in this group.