Biaxial mechanical properties of explanted aortic allograft leaflets,

The leaflets of 33 aortic allograft valves inserted using the freehand method were retrieved at reoperation, and the mechanical properties of the tissue were measured using biaxial testing methodology. Before insertion, the valves had been sterilized for 24 hours in either PSKA or CLPVA antibiotic solutions and then were either wet stored or cryopreserved. The cryopreserved valves were sterilized with CLPVA only, so there were three different treatment types in all. The controls were a set of unimplanted cryopreserved aortic valves. The radial stretch of the valve leaflets was measured and was analyzed as a function of the age of the donor in the case of the controls and the age of the donor plus the duration of implantation for the explanted valves. The biaxial tension test was used to determine the maximum radial stretch of each leaflet because this variable dictates the area of coaptation and, ultimately, valve competency. It was found that the radial stretch of the allograft leaflets after implantation declined faster with time than did the stretch of the native aortic valve leaflet controls. This greater rate of stretch reduction depended mostly on the degree of similarity between the stretch of the donor leaflets and that of the recipient at the time of implantation. No conclusion could be reached about the influence of the preimplantation storage method because of the different time intervals of implantation applicable to each case. After matching for annulus size, matching the ages of donor and recipient is a good graft-selection strategy, but it may be better to use a slightly older donor. This differs from the current strategy, which is to select the youngest donor valve of the correct size.