Response of functional mitral regurgitation in nonischemic cardiomyopathy to left bundle branch pacing

Functional mitral regurgitation (FMR) in patients with cardiomyopathy is correlated with morbidity and mortality in heart failure. The response of FMR to cardiac resynchronization therapy (CRT) varies.The purpose of this study was to analyze the incidence and severity of FMR in patients with nonischemic cardiomyopathy (NICM) and left bundle branch block (LBBB) and the response to left bundle branch pacing (LBBP).Patients who had undergone LBBP for NICM, LBBB, and FMR between 2019 to 2021 were included retrospectively in the study.A total of 79 patients were identified, of whom 6 were excluded (5 no consistent LBB capture, 1 prosthetic mitral valve). The remaining 73 patients were divided into 2 groups based on the severity of FMR into group I with mild FMR (n = 35 [48%]) and group II with significant FMR (n = 38 [52%]). Mean follow-up duration was comparable in both groups. Group II was characterized by higher N-terminal pro-brain natriuretic peptide levels, New York Heart Association functional class, and larger left ventricular dimensions. LBBP resulted in significant reduction in QRS duration in both group I (113.8 ± 12.7 ms; P <.0001) and group II (117.3 ± 10.3 m s; P <.0001). LBBP resulted in similar percentage reduction in QRS duration (-31% ± 10% vs -33% ± 8%; P = .34), left ventricular (LV) end-diastolic diameter (-8% ± 10% vs -11% ± 12%; P = .25), LV end-diastolic volume (-26% ± 12% vs -31% ± 27%; P = .31), and LV end-systolic volume (-39% ± 16% vs -37% ± 30%; P = .72) in groups I and II, respectively. Percentage change (+59% ± 39% vs +59% ± 41%; P = 1) and absolute change (+19.9% ± 10.4% vs +17% ± 10.04%; P = .22) in LV ejection fraction were similar in both groups. In group II, 31 patients (82%) showed significant reduction in FMR severity during follow-up. No patients in group I showed worsening of FMR.LBBP resulted in excellent electrical resynchronization with significant reduction in FMR severity in the majority of patients with significant FMR and no worsening of FMR from baseline in any patient.