Improved endothelial viability of heart valves cryopreserved by a new technique

The aim of this study was to compare different techniques of aorticvalve cryopreservation by studying the viability of the endothelial cells.Viability was assessed by measuring their in vitro prostacyclin (PGI2)production under basal and stimulated conditions. Fresh and cryopreservedporcine valves were incubated at 37 degrees C in tissue culture medium andPGI2 content in the medium was measured every 15 min up to 300 min.Cryopreservation by the older procedure A included 5% fetal calf serum(FCS) in the preservation medium, a plastic box inside a freezing plasticbag, a cooling schedule approximating -2 degrees C/min, a long thawing timeand few dilution steps of the cryoprotectant dimethylsulphoxide (DMSO). Thenewer procedure B differed from A in packaging, freezing and thawing ratesand DMSO dilution. Procedure C was similar to B with the exception that FCSwas omitted. Leaflets preserved by procedure A produced significantly lessprostacyclin as compared to those treated according to procedures B or C.We conclude that minor differences in the cryopreservation method canbecome critical to endothelial functional viability.