Geometric determinants of ischemic mitral regurgitation

The precise geometric determinants of ischemic mitral regurgitation (MR) are incompletely understood, although such knowledge is important to improve mitral valve reparative techniques.

The three-dimensional geometry of the mitral apparatus was studied using radiopaque markers in eight closed-chest dogs with acute posterior left ventricular wall ischemia either with (MR) or without (no-MR) MR as assessed by using color Doppler. Using a cylindrical coordinate system (origin at the midpoint between the mitral annulus commissures [anterolateral and posteromedial] and z-axis directed toward the left ventricular apex), we measured the distance to the midpoint (z, in millimeters), radial distance from the z-axis (r, in millimeters), and angle from the intercommissural line (theta) of each marker. A multivariate analysis of variance showed the following differences (P < .005) between the MR and the no-MR groups: 1) markedly increased r of the posterior papillary muscle tip (10.3 versus 6.4 mm, MR versus no-MR, at end-systole) and increased r of the anterior papillary muscle tip; 2) dilation (in the septal-lateral direction) of the midpart of the mitral annulus and near the anterolateral region; 3) increased posterior mitral leaflet r near both commissures (eg, 8.3 versus 6.2 mm on the posteromedial side) and increased z (ie, shifted toward the left ventricular apex) of the posterior leaflet on the anterolateral side (eg, 7.0 versus 6.2 mm), which is analogous to restricted (or type III) leaflet motion.

These findings indicate that the geometric determinants of ischemic MR in dogs are complex and involve many parts of the mitral valve apparatus. This complexity suggests that surgical attention to the entire annulus and excursion of the posterior leaflet may be helpful when annuloplasty alone is inadequate.