Functional mitral regurgitation in chronic ischemic coronary artery disease: Analysis of geometric alterations of mitral apparatus with magnetic resonance imaging

Illustration of the mitral area and mitral tetrahedron. The mitral tetrahedron was determined by 4 vertices (A, anterior annulus; P, posterior annulus; M, medial papillary root; L, lateral papillary root) and 6 edges (D_AM, distance between the anterior annulus and the root of the medial papillary muscle; D_AL, distance between the anterior annulus and the root of the lateral papillary muscle; D_PM, distance between the posterior annulus and the root of the medial papillary muscle; D_PL, distance between the posterior annulus and the root of the lateral papillary muscle; D_AP, distance between the anterior annulus and the posterior annulus; D_ML, distance between the roots of the medial and lateral papillary muscle.)

Cine MRI acquired in the left ventricular short-axis plane from base to apex. Gating acquisition was performed with prospective ECG R-wave triggers. Images at a temporal resolution of 30 ms and in-plane spatial resolution of approximately 1 × 1 mm² were obtained. Cine images at end-diastole and end-systole are shown in the upper and lower rows, respectively.

Interpolated and reconstructed images from original MRI data. Three-dimensional coordinates of the points of interest were determined on the long-axis planes decided from the lines of intersection on the short-axis plane. Left upper, Anterior annulus (denoted A and indicated with black arrow on the right panel) and posterior annulus (denoted P and indicated with white arrow). Left lower, Roots of the medial papillary muscle and the lateral papillary muscle (indicated with white dots). Right, Ten points along the mitral annulus (indicated with arrowheads). PL, Root of lateral papillary muscle; PM, root of medial papillary muscle.

A, A scatter plot of the left ventricular end-systolic volume (LVESV) to the left ventricular ejection fraction (LVEF). B, Scatter plots of LVESV to each edge of the mitral tetrahedron and to the mitral area. X, Control group; open circle, CAD group; filled circle, CAD+FMR group. Horizontal lines indicate the cutoff values of respective parameters for FMR.

Scatter plots of 2 typical parameters of the ventricular factors (D_ML and D_AM, left panel) and the annular factors (D_AP and MA, right panel) for distinguishing the CAD+FMR group from the other groups. A clear distinction was found by using a D_ML of 32 mm and a D_AM of 64 mm as thresholds.

Illustration of the tethering effect by the structure of the mitral tetrahedron on the pathogenesis of FMR. A, Increased interpapillary muscle distance (D_ML) causes downward tethering of the midpoints of the mitral leaflets, a predisposition toward central leakage. B, When the increased annular-papillary distances are combined with increased anterior-posterior annular distance, the coapting points of the anterior and posterior leaflets (point C) were pulled apart. This causes FMR to happen.