MODELING SURGICAL INTERVENTIONS IN THE MITRAL VALVE WITH THE FINITE ELEMENT METHOD

The behavior of mitral valve tissue is very complex because of its material composition, geometric layout and loading environment. Due to recent advances in the constitutive modeling of mitral valve material, particularly in the area of incorporating the collagen fibers with the continuum tissue matrix, we are able to now simulate the behavior of the mitral valve under various loading and surgical conditions. Further, advance in FEM computational formulation also enables us to accurately simulate the nature of the incompressible material as representative of the mitral valve tissue which was a difficult proposition only a few years ago.In this thesis, we first implemented a constitutive relation specifically developed for mitral valve tissue into a commercial finite element software - LSDYNA. The geometry of the mitral valve and it's chordae were modeled via previously published anatomical measurements and our observations during animal experiments. We first simulated the motion of a porcine mitral valve under normal conditions that enabled us to make inferences about the state of stress of the mitral valve, i.e. we indentified sites of high stress and consequently locations of high failure possibility. Having modeled a healthy mitral valve we then modeled a prolapsed leaflet by removing chordae attached to the anterior leaflet of the valve. Further we proceeded to simulate a novel surgical procedure used to repair prolapse. The effects of surgical repair in term of the stresses the valve were quantified in comparison to its natural state.In our constitutive equations we included the material fiber direction, i.e. the direction of the collagen fibers in the mitral valve tissue. In accordance with stress modulated growth laws, we assumed that the fiber direction will tend to align with the maximum principal direction of stress as the tissue remodels under the influence of new external forces after surgical alteration. This study shows the change in principal stress directions due to surgical alteration, and therefore is an indicator of remodeling to follow. Thus, the ability, as demonstrated by this study, to predict these alteration may be one way to devise a strategy for minimizing fiber reorientation and thereby prolong the effects of surgical intervention or even avoid future re-intervention