Mitral Valve Compensation for Annular Dilatation: In Vitro Study into the Mechanisms
of Functional Mitral Regurgitation with an Adjustable Annulus Model
Shengqiu He, Jack D. Lemmon, Jr., Matthew W. Weston, Morten Jensen, Robert A. Levine,
Ajit P. Yoganathan

Mitral annulus dilatation has been identified as an important factor in functional mitral regurgitation (FMR). However, the pathophysiological interaction of annular dilatation and papillary muscle (PM) displacement in FMR is still not well understood. To better understand the competing factors, six excised normal porcine mitral valves were mounted in an in vitro model with a D-shaped adjustable mitral annulus that could be changed from 5.5 cm² to 13.0 cm² during experiments. Papillary muscles were placed in normal position and then displaced apically-posterolaterally to simulate pathological conditions. Results showed that in normal PM position, the mitral regurgitant was consistently at low levels until the annulus was enlarged to 1.75 times the normal size. Papillary muscle apical posterolateral displacement caused the regurgitation to occur earlier (1.5 times the normal annulus size), and with larger volumes. Asymmetric PM displacement created even more regurgitant volume. This in vitro study provides insight into the interaction between annular dilatation and PM displacement on FMR. The resultant effects could help further understand the mechanism of FMR and provide additional information to improve future therapeutic strategies.