Effect of papillary muscle position on mitral valve function: relationship to homografts.

BACKGROUND: We used a finite element model to determine the effect of papillary muscle position on the stress distribution in the mitral valve.
METHODS: A normal model was modified to move the posteromedial papillary muscle outward by either 2.5 mm or 5.0 mm. Next, the thickness was increased by 20%, simulating diseased tissue. Physiologic loading pressures were applied, and leaflet stress, chordal stress, and coaptation results were analyzed.
RESULTS: Displacement of the posteromedial papillary muscle increased the leaflet stresses and altered the normal stress patterns. The displacement also restricted the leaflets from closing completely, allowing regurgitation. Combining increased thickness with papillary displacement decreased the stresses slightly. However, the amount of leaflet coaptation was further decreased, creating larger gaps for regurgitation. In all models, the stresses in the chordae were increased in the marginal chordae and decreased in the basal chordae, demonstrating a transfer of stress.
CONCLUSIONS: Papillary muscle displacement creates abnormal valve stresses, and the potential for significant regurgitation. Papillary-chordal-leaflet geometry must be maintained in partial or complete mitral homograft replacement.