PATHOLOGY OF EXPLANTED CRYOPRESERVED ALLOGRAFT HEART-VALVES - COMPARISON WITH AORTIC VALVES FROM ORTHOTOPIC HEART-TRANSPLANTS

Objective: We sought to determine the morphology, mechanisms of deteri oration, cellular viability, extracellular matrix integrity, and the r ole of immune responses in the dysfunction of cryopreserved aortic and pulmonic valve allografts, Methods: We studied 33 explanted left-side d (n = 20) or right-sided (n = 13) cryopreserved human allograft heart valves explanted several hours to 9 years after operation, 14 nonimpl anted allografts, and 16 aortic valves removed from transplanted allog raft hearts 2 days to 4 years after operation, Analysis included gross inspection, radiography, light microscopy, electron microscopy, and i mmunohistochemical studies, Results: Allografts implanted for more tha n 1 day had progressive collagen hyalinization and loss of normal stru ctural complexity and cellularity, including endothelium and deep conn ective tissue cells, Inflammatory cells were generally minimal or abse nt in the allografts, Transmission electron microscopy of long-term cr yopreserved allograft valves revealed no viable cells, focal calcifica tion centered around dead cell remnants, and distorted but preserved c ollagen, In contrast, aortic valves from transplanted hearts showed re markable structural preservation, including endothelium and abundant d eep connective tissue cells; inflammatory infiltrates were generally m ild and of no apparent deleterious consequence, including valves from patients who died of fatal rejection, Conclusions: Cryopreserved allog rafts are morphologically nonviable; their collagen is flattened but l argely preserved, They are unlikely to grow remodel, or exhibit active metabolic functions, and their usual degeneration cannot be attribute d to immunologic responses, In contrast, aortic valves of transplanted hearts maintain near-normal overall architecture and cellularity and do not show apparent immunologic injury, even in the setting of fatal myocardial parenchymal rejection or graft arteriosclerosis.