To determine the prevalence, predictors of newly acquired, and the prognostic value of right bundle branch block (RBBB) and incomplete RBBB (IRBBB) on a resting 12-lead electrocardiogram in men and women from the general population.

We followed 18 441 participants included in the Copenhagen City Heart Study examined in 1976–2003 free from previous myocardial infarction (MI), chronic heart failure, and left bundle branch block through registry linkage until 2009 for all-cause mortality and cardiovascular outcomes. The prevalence of RBBB/IRBBB was higher in men (1.4%/4.7% in men vs. 0.5%/2.3% in women, P < 0.001). Significant predictors of newly acquired RBBB were male gender, increasing age, high systolic blood pressure, and presence of IRBBB, whereas predictors of newly acquired IRBBB were male gender, increasing age, and low BMI. Right bundle branch block was associated with significantly increased all-cause and cardiovascular mortality in both genders with age-adjusted hazard ratios (HR) of 1.31 [95% confidence interval (CI), 1.11–1.54] and 1.87 (95% CI, 1.48–2.36) in the gender pooled analysis with little attenuation after multiple adjustment. Right bundle branch block was associated with increased risk of MI with an HR of 1.67 (95% CI, 1.16–2.42) and pacemaker insertion with an HR of 2.17 (95% CI, 1.22–3.86), but not with chronic heart failure (HR 1.37; 95% CI, 0.96–1.94), atrial fibrillation (HR 1.10; 95% CI, 0.73–1.67), or chronic obstructive pulmonary disease (HR 0.99; 95% CI, 0.60–1.62). The presence of IRBBB was not associated with any adverse outcome.

In this cohort study, RBBB and IRBBB were two to three times more common among men than women. Right bundle branch block was associated with increased cardiovascular risk and all-cause mortality, whereas IRBBB was not. Contrary to common perception, RBBB in asymptomatic individuals should alert clinicians to cardiovascular risk.