Mechanisms of reduction of mitral regurgitation by cardiac resynchronization therapy

OBJECTIVES: We sought to investigate the effects of improved left ventricular (LV) synchrony on secondary mitral regurgitation in patients receiving cardiac resynchronization therapy for severe heart failure. METHODS: A total of 22 patients, aged 63 +/- 8 years, were studied during sinus rhythm (unpaced), during LV pacing, and during biventricular pacing. Echocardiography was used to assess LV shape, mitral valve morphology and function, and global systolic and diastolic function. Mechanical ventricular synchrony was calculated from regional systolic timings and velocities, using tissue Doppler. RESULTS: Synchronicity index of LV longitudinal function improved from 36 +/- 19 to 14 +/- 8 milliseconds with LV pacing, and from 31 +/- 17 to 12 +/- 7 milliseconds with biventricular pacing (both P < .01). Heterogeneity of myocardial velocities decreased and mean systolic longitudinal velocity increased. Long-axis and short-axis systolic dimensions decreased, and the LV became less spherical. Apical displacement of coaptation from the plane of the mitral annulus, and annular diameter, were reduced. The severity of mitral regurgitation decreased: vena contracta diameter decreased from 5.3 +/- 1.7 to 4.1 +/- 1.5 mm with LV pacing, and from 5.2 +/- 1.7 to 4.0 +/- 1.7 mm with biventricular pacing (both P < .05), correlating with the increase in mean systolic longitudinal velocity (r = -0.49 for LV pacing and r = -0.67 for biventricular pacing, both P < .05). CONCLUSIONS: Cardiac resynchronization reduces mitral regurgitation by improving LV mechanical synchrony, which leads to an increase in LV longitudinal function and a reduction in subvalvar traction