Resolution of Left Bundle Branch Block–Induced Cardiomyopathy by Cardiac Resynchronization Therapy

OBJECTIVES: The study sought to describe a specific syndrome characterized by isolated left bundle branch block (LBBB) and a history of progressive left ventricular (LV) dysfunction, successfully treated by cardiac resynchronization therapy (CRT). BACKGROUND: Isolated LBBB in animals causes cardiac remodeling due to mechanical dyssynchrony, reversible by biventricular stimulation. However, the existence of LBBB-induced cardiomyopathy in humans remains uncertain. METHODS: Between 2007 and 2010, 375 candidates for CRT were screened and retrospectively included in this study if they met all criteria of a pre-defined syndrome, including: 1) history of typical LBBB for >5 years; 2) LV ejection fraction (EF) >50%; 3) decrease in LVEF to <40% and development of heart failure (HF) to NYHA functional class II to IV over several years; 4) major mechanical dyssynchrony; 5) no known etiology of cardiomyopathy; and 6) super-response to CRT with LVEF >45% and decrease in NYHA functional class at 1 year. RESULTS: The syndrome was identified in 6 patients (1.6%), 50.5 years of age on average at the time of LBBB diagnosis. HF developed over a mean of 11.6 years. At the time of referral, Doppler echocardiograms showed major mechanical dyssynchrony at left atrioventricular, interventricular, and left intraventricular levels. During CRT, NYHA functional class decreased, LV dimensions normalized and mechanical dyssynchrony was nearly resolved in all patients, and mean LVEF increased from 31 ± 12% to 56 ± 8% (p = 0.027). CONCLUSIONS: These observations support the existence of a specific LBBB-induced cardiomyopathy resolved by CRT. Its prevalence, time course, and risk factors need to be prospectively studied.