Effects of focal thickening on leaflet stresses in a closed bioprosthetic valve: Computations based upon a 3-D linear model

Abstract

A 3-D stress analysis of a porcine bioprosthetic valve leaflet was carried out using the finite element method. Irregularities of leaflet thickness, which can occur with degeneration of such valves, were modeled by introducing increased thickening at a selected site. The tissue was assumed to be isotropic with a Poisson's ratio of 0.3 and a Young's modulus of 5000 kPa. The geometry of the leaflet was approximated as one-half of an elliptic-paraboloid. The stresses were first determined in a normal leaflet with a constant thickness of 0.6 mm and then in a leaflet with a focal thickening of 1.2 mm. The maximal principal stresses predicted for a normal leaflet, 480 kPa, and the focally thickened leaflet, 520 kPa, were of the same order of magnitude and occurred at the aortic surface. Stresses across the thickness were nearly constant and tensile in nature for the uniformly thick leaflet. However, focal thickening markedly altered the stress distribution across the thickness. In the region of focal thickening, compressive stresses occurred at the ventricular surface and tensile stresses developed at the aortic surface. This resulted in a flexure-type deformation. Such a change in the distribution of stress across the leaflet thickness may contribute to further structural deterioration.