Identification of a Failure Mode of the Antibiotic Sterilized Aortic Allograft After 10 Years: Implications for Their Long-Term Survival

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Abstract
Freehand aortic allograft valves that had been previously sterilized with antibiotics were recovered at reoperation for biomechanical testing. The elastic extensibility of two leaflets from each explanted allograft stored in modified Hank's solution at 4 degrees C were measured using biaxial testing techniques. It was found that the leaflets had lost a significant amount of the natural, preimplant tissue extensibility. Computer simulation was used to investigate the likely consequences of such a profound change in the biomechanical characteristics of the leaflets on whole valve function. We found that the valve becomes progressively more incompetent as leaflet extensibility is lost and the stress levels at the commissures rise sharply with reduced coaptation. The stress levels in the load-bearing leaflet center are increased in the ventricularis as load is transferred from the fibrosa. The measured change in the radial extensibility of the aortic allograft leaflet needs to be allowed for when sizing the graft at insertion. Inserting the largest possible graft will maximize the time to the onset of central incompetence and improve valvar longevity by lowering the stress during diastole.