Left Bundle Branch Block as a Risk Factor for Heart Failure.

Importance: Left bundle branch block (LBBB) might play a causative role in the progression to heart failure (HF), but the association of LBBB with HF in asymptomatic individuals with structurally normal hearts has not yet been investigated. Objectives: To examine the association of LBBB with the risk of HF in community-dwelling individuals. Design, Setting, and Participants: This longitudinal cohort study used data from 4 US sites participating in the Cardiovascular Health Study (1989-1990), collected from 1989 to 2013. Adults aged 65 years and older with a normal left ventricular ejection fraction (LVEF) and no history of HF at baseline were included. Data were analyzed from February 2018 to October 2024. Exposure: The presence of LBBB as confirmed by 12-lead electrocardiograms obtained on all participants at baseline. Main Outcomes and Measures: Multivariable Cox proportional hazards models were used to estimate the associations of LBBB with the risk of incident HF, hospital admission for HF with reduced EF or HF with preserved EF, 5-year LVEF decline, and death. Results: Among 4541 individuals (mean [SD] age, 72.6 [5.5] years; 2697 female [59.4%]), 44 (1.0%) exhibited LBBB at baseline, and 1321 (29.1%) received a diagnosis of HF over a median (IQR) follow-up of 14.6 (8.4-18.3) years. In the adjusted model, those with baseline LBBB had an increased risk of incident HF (hazard ratio, 4.98; 95% CI, 2.18-11.39; P < .001) and greater odds of 5-year LVEF decline (odds ratio, 4.73; 95% CI, 1.70-13.70; P = .003), but no statistically significant increased risk of death was observed (hazard ratio, 1.39; 95% CI, 0.99-1.94; P = .05). Conclusions and Relevance: In this cohort study of individuals with structurally normal hearts, LBBB was associated with an increased risk of HF and a decrease in LVEF, suggesting that LBBB could be a potential target for early interventions to prevent deterioration of cardiac function and, ultimately, progression to HF.