In 14,212 adults aged 45–74 from the Hamburg City Health Study, complete left bundle branch block (cLBBB) carried a hazard ratio of 2.71 for total cardiovascular outcomes — encompassing all-cause mortality, heart failure, myocardial infarction, atrial fibrillation, pulmonary embolism, and stroke — while complete right bundle branch block (cRBBB) carried an HR of 1.52. Prevalence was 0.8% for cLBBB and 2.3% for cRBBB. Echocardiographically, both patterns showed reduced left ventricular ejection fraction, septal thickening, and left atrial enlargement, but cRBBB additionally showed right ventricular dilation while cLBBB showed markedly impaired left atrial strain and elevated NT-proBNP. Critically, the two blocks diverged on specific outcomes: cLBBB independently predicted all-cause mortality, whereas cRBBB distinctly predicted incident stroke.
These findings reframe bundle branch blocks — often treated as incidental ECG findings in asymptomatic patients — as high-risk phenotypes warranting proactive management. The stroke association with cRBBB is particularly underappreciated clinically and may reflect shared pathophysiology with atrial or right-sided remodeling. The large community-based cohort and multivariable adjustment strengthen confidence in the associations, though causality cannot be established from this observational design. Elastic net regularization for feature selection is methodologically sound but adds complexity to interpretation. As this is a preprint not yet peer-reviewed, findings require independent replication before influencing clinical guidelines. Still, the data make a compelling case that routine ECG-detected conduction disease in middle-aged adults should trigger structured cardiac risk stratification rather than watchful waiting.
