Impact of prolonged storage time on homograft ultrastructures: an attempt to find optimal guidelines for homograft processing.

According to guidelines, total ischemic time for homografts at processing must be kept short to avoid degeneration. Many homografts are discarded due to practical inability to finish all steps from procurement to cryopreservation within the time limit. Although, several studies have shown that homografts with prolonged ischemic time show adequate quality and performance. Twenty aortic and 12 pulmonary homografts were collected and biopsies were retrieved at preparation (day 0) and after 1, 2, 3, 4, 7, 14, 21, 28, and 60 days in antibiotic decontamination at 4 °C. Biopsies were prepared for light microscopy (LM) and transmission electron microscopy (TEM). Assessment generated scores for cells, elastin, and collagen. Relative differences between times were compared with Wilcoxon signed rank test. Bonferroni corrected p value of 0.0056 was considered significant. LM could only reveal decrease in cell count at 60 days in aortic homografts, no other differences was detected. TEM showed affected cell appearance in day 3 and day 4 and beyond for aortic and pulmonary homografts respectively. Elastin appearance was affected at day 60 for aortic and day 21 for pulmonary homografts. Collagen appearance was affected at day 28 for aortic homografts, with no significant differences in pulmonary homografts. Cell degeneration starts early after homograft procurement, but elastic and collagen fibers are more resistant to degeneration. Overall structure integrity as seen in LM was not affected at all, while TEM could reveal small degeneration signs in individual elastic fibers and collagen bundles at 21 and 28 days respectively.