Biomechanical changes to aortic allografts after implantation: implications for function and longevity

Grant Christie, Ph.D.

Green Lane Hospital, Auckland, New Zealand

Aortic allografts have been widely used as substitute heart valves since the 1960s and the overall clinical experience has been very good. The recipient requires no anticoagulation, the haemodynamic performance is excellent and the calcification and infection rates are very low compared to the alternatives. The most common failure mode is increasing central valvar incompetence which generally develops slowly and late, allowing ample time for re-operation.

We investigated freehand allograft failures at Green Lane Hospital by measuring the biomechanical properties of explanted valve leaflets using two-dimensional tensile testing. It was found that the leaflets lose compliance at a steady rate from the time of implant relative to unimplanted controls.

The measured properties were then used in an anatomically based mathematical model of the aortic valve to show how this change in tissue compliance, coupled with aortic root dilatation and valve sizing, is related to the onset of central incompetence.