Effects of storage temperature on viable bioprosthetic heart valves

Long-term in vivo success of bioprosthetic allografts is dependent upon retention of cellular functions, such as protein synthesis. The purpose of the experiments presented in this report was to determine the storage conditions necessary for retention of protein synthetic functions in human allograft heart valve leaflets. Tissue viability was assessed by measurement of tritiated-glycine incorporation into proteins. Comparison of short-term (less than 3 month)- and long-term (1 and 2 years)-cryopreserved heart valve leaflet storage in a liquid nitrogen freezer below -135 degrees C demonstrated preservation of fibroblast protein synthesis. In contrast, storage in a mechanical freezer at -80 degrees C resulted in a time-dependent loss of fibroblast protein synthesis. There was no statistically significant effect on protein synthesis in leaflets stored for 1 week at 4 degrees C compared to control cryopreserved liquid nitrogen-stored leaflets. After 2 weeks of 4 degrees C storage leaflet protein synthesis declined significantly to 15% that of cryopreserved controls. These results demonstrate that liquid nitrogen storage of valve bioprostheses is required for long-term preservation of cellular functions.