Right and Left Bundle Branch Block in the General Population: Structural Heart Findings, Clinical and Prognostic Implications: Insights from the Hamburg City Health Study

Background: This study aimed to determine the prevalence of BBB, characterize associated clinical and echocardiographic phenotypes, and evaluate associations with incident cardiovascular diseases and all-cause mortality in the general population. Methods: We analyzed 12-lead electrocardiograms from 14,212 subjects from the Hamburg City Health Study (45-74 years). BBBs were defined using Minnesota Code criteria. We applied elastic net regularization to identify clinical associations, and multivariable Cox models for outcome analyses. The total cardiovascular outcome included all-cause mortality, incident heart failure, myocardial infarction, atrial fibrillation, pulmonary embolism, and stroke. Results: Complete left (cLBBB) and right (cRBBB) bundle branch blocks were prevalent in 0.8% and 2.3% of subjects, respectively. Subjects with complete BBB were generally older with a higher burden of cardiovascular risk factors and comorbidities, cLBBB additionally showed higher N-terminal pro-hormone of brain natriuretic peptide levels. The main predictor of BBB was age. Male sex was an additional predictor for cRBBB, while hypertension, hypercholesterolemia, and reduced left ventricular ejection fraction predicted cLBBB. Both, cLBBB and cRBBB were associated with a reduced left ventricular ejection fraction, increased septal wall thickness, and left atrial enlargement. cRBBB demonstrated right ventricular dilation, whereas cLBBB showed markedly impaired left atrial strain. In adjusted analyses, both BBBs were associated with the total cardiovascular outcome (cLBBB: hazard ratio [HR], 2.71; 95% confidence interval [CI], 1.68-4.39; p<0.001; cRBBB: HR, 1.52; 95% CI, 1.09-2.12; p=0.01). Although both were significantly associated with incident heart failure, myocardial infarction, and atrial fibrillation, cLBBB uniquely was associated with all-cause mortality, whereas cRBBB distinctly was associated with incident stroke. Conclusion: In the general population, BBB is a high-risk phenotype characterized by subclinical cardiac alterations and a markedly worse long-term outcome. These findings underscore the importance of early risk stratification. Proactive clinical management in otherwise asymptomatic individuals presenting with these conduction disturbances should be considered.