Prognostic significance of right and left bundle branch block in the general population: findings from a city health study

Background Right (RBBB) and left bundle branch block (LBBB) are established markers of adverse outcomes in patients with cardiovascular disease, yet their prognostic significance in the general population remains uncertain due to inconsistent findings. Purpose This study aimed to (i) determine the prevalence of bundle branch block (BBB) at the population level, (ii) characterize associated clinical and echocardiographic phenotypes, and (iii) evaluate associations between BBB and a composite primary endpoint of incident cardiovascular diseases and all-cause mortality. Methods We recorded 12-lead ECGs in 15,221 participants aged 45-74 years from a City Health Study, enrolled since 2016. BBBs were defined by Minnesota Code criteria as RBBB or LBBB. Participants without BBB served as the reference group. The composite primary endpoint was all-cause mortality and incident cardiovascular diseases (heart failure [HF], myocardial infarction [MI], atrial fibrillation, pulmonary embolism, or stroke). Associations were assessed using Cox proportional hazard models. Results Among 15,221 participants (50.7% male). LBBB was present in 128 (0.8%) and RBBB in 349 (2.3%) individuals. Compared to participants without BBB, those presenting with BBB were older (median age: no BBB 60, LBBB 67, RBBB 68 years). The proportion of males was substantially higher in the RBBB group (80%) compared to both the LBBB (50%) and the no-BBB (49%) group. Hyperlipoproteinemia was more prevalent among participants with LBBB and RBBB (34% and 32%, respectively) than among those without BBB (22.6%). In addition, MI as well as HF were also more prevalent in BBB (MI: 2.9% in controls, 7.5% in RBBB, 8.7% in LBBB; HF: 4.7% in controls, 21.1% in RBBB, 29.7% in LBBB). Echocardiography showed larger right ventricular volumes in RBBB (end-diastolic: median 50.5mL [IQR 22.2] vs 40.1 [IQR 22.5]; end-systolic: median 23.9mL [IQR 11.8] vs 17.6mL [IQR 11.2]) and a thicker interventricular septum (median 10.6 mm [IQR 2.2] vs 9.6 mm [2.0]), compared to controls. LBBB was associated with reduced LVEF (median 54.5% [IQR 5.8] vs 58.2% [IQR 5.5]) and reduced left atrial strain (median 31.5% [IQR 15.5] vs 38.1% [IQR 18.0]). All findings were independent of sex. After a median follow-up duration of almost 5 years LBBB and RBBB were associated with a significantly increased risk of the composite primary endpoint of CV events or death (LBBB: hazard ratio [HR] 2.34, 95% CI 1.46-3.73, p<0.001; RBBB: HR 1.52, 95% CI 1.19-1.94, p<0.001). Conclusions In this population-based study, both LBBB and RBBB were associated with distinct structural and functional echocardiographic abnormalities, higher prevalence of hyperlipoproteinemia, HF, and prior MI, and increased risk of cardiovascular events and total mortality. These findings underscore the potential value of enhanced cardiovascular risk stratification in the otherwise asymptomatic individuals with BBB.Composite primary endpoint