Electrical conduction disturbance effects on dynamic changes of functional mitral regurgitation.

Objectives: The aim of this study was to investigate the relationship between dynamics of functional mitral regurgitation (MR) and the degree of electrical conduction disturbance, and to evaluate the impact of cardiac resynchronization therapy (CRT) on MR severity and its phasic pattern.

Background: Mechanisms of phasic changes of functional MR, which may be determined by annulus dilation and tethering of the leaflet, remain unclear.

Methods: Transthoracic two-dimensional echocardiography was performed in 60 patients with functional MR. A biventricular pacemaker was implanted in 19 patients. The mitral annulus area (MAA) and the tenting area (TA) were measured from apical views. The MR volume and fraction were assessed by the quantitative pulsed Doppler method. Instantaneous regurgitation flow rate was measured by proximal flow convergence method. A dynamic change in MR flow rate was evaluated by frame-by-frame analysis throughout systole.

Results: A phasic pattern with two peaks at early- and late-systole and decrease in mid-systole was noticed in 57 patients. The early-systolic peak of MR was larger than the late-systolic peak (128.4 +/- 64.3 ml/s vs. 73.9 +/- 55.1 ml/s, p < 0.001). The ratio of flow rate at these two peaks correlated with QRS duration (r = 0.55, p < 0.001). Early-systolic flow rate reduced after CRT (143.9 +/- 60.8 ml/s to 90.7 +/- 54.1 ml/s, p < 0.05), but late-systolic flow rate did not (61.5 +/- 55.0 ml/s to 51.2 +/- 40.9 ml/s, p = NS). A similar pattern was observed for TA, whereas MAA did not change after CRT.

Conclusions: Biphasic pattern was found in functional MR, and the ratio of flow rate at two peaks correlated with QRS duration. The CRT decreased regurgitation flow volume by reducing early-systolic MR but not late-systolic MR, resulting in the change in phasic pattern of functional MR.