Fatigue-induced changes in bioprosthetic heart valve three-dimensional geometry and the relation to tissue damage

In a previous study, we used magnetic resonance (MR) imaging to reconstruct, three-dimensionally, porcine bioprosthetic heart valve (PBHV) cusp geometry. Initial results using three valves indicated that accelerated testing induced changes in cuspal shape, including focal regions of high curvature. Since for thin-walled shell structures, such as the PBHV cusp, curvature changes can affect the stress distribution independently from changes to mechanical properties, shape changes might have adverse effects on PBHV durability.

The MR technique was applied to an expanded valve database to explore more fully shape change with fatigue. The spatial curvature distribution was compared across valves subjected to a range of accelerated test times.

Results confirmed our initial findings that PBHV cusps undergo a continuous, non-recoverable deformation with accelerated testing. This deformation resulted in an increase in the portion of cuspal surface exhibiting high curvature values. In one cusp we mapped structural information obtained by small-angle light scattering back to the three-dimensional cuspal surface using an interpolation technique. Results from the mapped cusp demonstrated a strong spatial correlation between elevated curvatures and structural damage.

The observed changes in cuspal shape accelerate PBHV damage due to an increase in flexural strains induced by an increase in curvature reversal during operation, rather than an increase in tension during closure.