Long-Term Results of the Viable Cryopreserved Allograft Aortic Valve: Continuing Evidence for Superior Valve Durability

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Abstract
From December 1969 to May 1975, 124 patients underwent aortic valve replacement with an allograft aortic valve sterilized by incubation in a low dose antibiotic solution and stored by refrigeration at 4°C (4°C stored valve group). From June 1975 to December 1987, 231 patients received an allograft aortic valve, sterilized by the same low dose antibiotic solution, but stored by cryopreservation in liquid nitrogen at — 196°C (cryopreserved valve group). The 4°C stored valves were essentially nonviable, whereas the cryopreserved valves were viable at implantation. Of the 355 aortic valve replacements, associated procedures were performed in 127 patients. The 30-day mortality was 8.9% (confidence limits [C.L.] 6.2%...12.3%) (4°C stored) and 4.8% (C.L. 3.3%...6.7%) (cryopreserved). Actuarial survival was similar in both groups, being 71% and 67% at 10 years in the 4°C stored and cryopreserved valve groups, respectively (P = .18). The probability of a thromboembolic event was low, but appeared higher in the 4°C stored valve group (actuarial freedom at 10 years, 90%) than the cryopreserved valve group (actuarial freedom at 10 years, 98%) (P =.01) probably related to associated mitral valve surgery. The actuarial freedom from allograft valve endocarditis at 10 years was 94% and 95% for the 4°C stored and cryopreserved valve groups, respectively (P = .23). Reoperation was undertaken in 34 patients in the 4°C stored group and 12 patients in the cryopreserved valve group for leaflet degeneration, endocarditis, or technical reasons. The actuarial freedom from reoperation was 83% and 89% for the 4°C stored and cryopreserved valve groups, respectively (P = .37). Reoperation for allograft valve degeneration was markedly different (4°C stored, 28 patients; cryopreserved, 2 patients). The actuarial freedom from reoperation for allograft valve degeneration at 10 years was 88% and 99% for the 4°C stored and cryopreserved valve groups, respectively (P = .02). The two patients with cryopreserved valves undergoing reoperation had bioprosthetic mitral valve degeneration as the indication for operation, but aliograft valve degeneration was in evidence macroscopically and histologically. Viability of valve leaflet tissue is an important determinant of valve durability. The clinical results of the viable cryopreserved allograft valve support this contention, however, current methods of donor selection, sterilization, and cryopreservation need to be improved to optimize viability.