Morphologic Study of Homograft Valves before and after Cryopreservation and after Short-Term Implantation in Patients

Cryopreserved heart valve homografts have been implanted in patients for the past 15 years, but controversies still exist on the survival of donor cells, matrix maintenance, and possible rejection by the host. Therefore a full morphologic study (histology, immunohistochemistry, transmission electron microscopy, and cuprolinic blue-TEM for glycosaminoglycans [GAG]) of short-term implanted uninfected grafts was done using unimplanted valves as the reference. Unimplanted tissues consisted of 5 fresh and 11 cryopreserved valves. Eight implants were recovered at reoperation [4] or autopsy [4], 4 from the right and 4 from the left ventricular outflow tract. The implantation time was 2 hours to 30 days. For unimplanted valves we found a partial preservation of the endothelium, the presence of dendritic Langerhans cells (Lc) and macrophages, and no significant damage to fibroblasts, collagen framework, and GAG pattern, except when the tissues had been ischemic for a long time. Explanted cusps exhibited (i) early disappearance of endothelium and Lc; (ii) nonspecific low-grade inflammatory cell infiltration, mostly of monocytoid type; (iii) viable degree of devitalization of fibroblasts with persistence of viable cells in some areas in most cusps; and (iv) fair preservation of collagen framework and GAGs. It is likely that, in view of the good graft preservation at implantation, humoral rejection is responsible for the earlier destruction of the endothelium and dendritic cells and the delayed devitalization of the fibroblasts and that preservation of the collagen framework and other intercellular matrix components (glycosaminoglycans) should guarantee longterm graft function.