INTEGRITY AND VIABILITY OF HOMOGRAFT VALVES

Since it has been suggested that the leaflet tissue viability influenc es durability after homologous valve replacement, we compared differen t harvest and preservation techniques in order to examine the quality and smoothness of homograft conservation. We analyzed human aortic and pulmonary valve leaflets obtained from 'heart-beating donors' (HBD) d uring heart transplantation and from 'non-heart-beating donors' (NHBD) during coroner's autopsies. Valves were either cryopreserved in liqui d nitrogen or stored at 4-degrees-C in nutrient medium similar to the procedure reported in our protocols of the homograft bank system. All grafts from NHBD had been antibiotically sterilized for 3 days beforeh and. Morphological observations were made using light and electron mic roscopy and, in order to characterize the endothelial cell viability, a non-radioactive cell proliferation assay was used. The PGI2 secretio n of the remaining endothelium was defined as the 6-keto-prostaglandin Fl a metabolite by an enzyme immunoassay. Observations in the scannin g electron microscope revealed that, after cryopreservation, homograft s show an almost confluent endothelium when processed within 24 h afte r harvest from HBD, but lack endothelial cells when obtained from NHBD . Cryopreserved grafts from NHBD exhibited an altered tissue structure with edema and vacuolization within the spongiosa of the leaflets as well as irreversible cell damage when examined under the light and tra nsmission electron microscope. That the metabolic activity of HBD homo grafts was maintained was confirmed by proven PGI2 secretion (6150+/-1 200 pg/3 ml M199 after cryopreservation), whereas specimens from NHBD showed a reduced (1950+/-730 pg/3 ml M199) and, after cryopreservation , almost no release (P < 0.0001). Homografts from HBD stored for 1 wee k at 4-degrees-C in nutrient medium displayed the highest endothelial cell viability compared to all remaining groups. It can therefore be s uggested that even after cryopreservation homograft valves from HBD sh ow a high tissue viability and.integrity. Nevertheless, due to the imm unological potential of these cells, endothelial cell viability of HBD homografts should be considered carefully when used for cardiac valve replacement. It remains to be seen to what extent the immunological r esponse to allografts influences long-term tissue durability.