Effects of a saddle shaped annulus on mitral valve function and chordal force distribution: an in vitro study.

Studies have concluded that the shape of the human mitral valve annulus is a three-dimensional saddle. The objective of this study was to investigate the effects of a saddle shaped annulus on chordal force distribution and mitral valve function. Eleven human mitral valves were studied in a physiological left heart simulator with a variable shaped annulus (flat versus saddle). Cardiac output and transmitral pressure were analyzed to determine mitral regurgitation volume. In six experiments, force transducers were placed on six chordae tendineae to measure chordal force distribution. Valves were tested in normal and pathophysiologic papillary muscle positions. When comparing the flat and saddle shaped configurations, there was no significant difference in mitral regurgitation volume 11.2% +/- 24.7% (p = 0.17). In the saddle shaped configuration, the tension on the anterior strut chord was reduced 18.5% +/- 16.1% (p < 0.02), the tension on the posterior intermediate chord increased 22.3% +/- 17.1% (p < 0.03), and the tension of the commissural chord increased 59.0% +/- 32.2% (p < 0.01). Annular shape also altered the tensions on the remaining chords. Annular shape alone does not significantly affect mitral regurgitation caused by papillary muscle displacement. A saddle shaped annulus redistributes the forces on the chords by altering coaptation geometry, leading to an optimally balanced anatomic/physiologic configuration.