3-DIMENSIONAL CHANGES IN LEFT AND RIGHT-VENTRICULAR GEOMETRY IN CHRONIC MITRAL REGURGITATION

Regional three-dimensional (3-D) right (RV) and left ventricular (LV) geometry was studied in eight dogs before and 5-6 mo after induction o f mitral regurgitation (MR). Ventricular shape changes were quantified with a 3-D finite-element model fitted to chamber contours traced on cardiac magnetic resonance images. MR increased LV end-diastolic volum e (LVEDV; 99 vs. 57 ml; P < 0.001) and LV stroke volume (LVSV; 55 vs. 26 ml; P < 0.001). In contrast, RVEDV decreased (45 vs. 55 ml; P < 0.0 1), whereas SV was maintained. LV mass (free wall plus septum) increas ed (115 vs. 94 g; P < 0.05), whereas RV free-wall mass was relatively unchanged. Shape changes due to MR were characterized by a marked (7.4 -mm) rightward shift of the septum relative to the lateral LV free wal l at end diastole. In contrast, the distance from the RV free wall to the lateral LV free wall was relatively unchanged (2.7 mm). The distan ce between the LV lateral free wall and septum increased more than the distance between the anterior and posterior LV walls (22 vs. 15%; P = 0.04). During systole, the displacement of the septum into the LV inc reased significantly (7.3 vs. 2.9 mm; P < 0.01). Consistent with the e nd-diastolic dimension changes, LV endocardial circumferential curvatu re was decreased at end diastole to a greater extent in the anterior a nd posterior walls than in the septal and lateral walls (P < 0.01). Th us chronic MR produced an asymmetric LV dilatation with regional varia tion in geometry. The septum increased its contribution to the LVSV at the expense of RVEDV. RVSV was maintained, possibly by ventricular in teraction.