Addressing Functional Mitral Regurgitation in Dilated Cardiomyopathy: A Focus on Myocardial Segment Resynchronization Through Cardiac Resynchronization Therapy.

Introduction: Cardiac resynchronization therapy (CRT) has emerged as a pivotal intervention in reducing functional mitral regurgitation (FMR), not only by enhancing global left ventricular (LV) systolic function but also by refining local myocardial synchronization. This study hypothesized that CRT-mediated synchronization of myocardial segments, particularly between papillary muscles, reduces FMR further, independent of the improvement of the LV systolic indices.

Methods: Eighteen patients with dilated cardiomyopathy and biventricular pacing were evaluated. Measurements included the rate of rise in LV systolic pressure (LV dP/dt), asynchrony indices, transmitral pressure differences, mitral regurgitation quantification and diastolic filling times during pacing and with pacemaker interruption. As LV dP/dt decreased while the pacemaker was interrupted, dobutamine infusion was administered to restore LV dP/dt to pacing levels. All parameters were reassessed to evaluate the impact of myocardial resynchronization on FMR, independent of LV systolic performance.  Results: LV dP/dt significantly decreased in 10 patients after pacemaker interruption (838±190 vs 444±72, p<0.01), with no significant change in eight patients (603±134 vs 592±156, p=0.679). Despite similar LV performance indices, biventricular pacing led to a statistically significant reduction in both effective regurgitant orifice area and regurgitant volume across all patients (p<0.001 and p=0.003, respectively).

Conclusion: CRT significantly reduces FMR in dilated cardiomyopathy patients with intraventricular delay independent of improvements in LV systolic performance indicators by resynchronization of the LV segments underlying the papillary muscles. Moreover, it may be the main determinant of the reduction in FMR in CRT, underscoring the need for further research into its mechanisms and therapeutic implications.