Association of Uncomplicated Electrocardiographic Conduction Blocks with Subsequent Cardiac Morbidity in a Community-based Population (Olmsted County, Minnesota)

Ventricular conduction blocks (VCBs) identified on a 12-lead electrocardiogram (ECG) are associated with poor outcomes in patients with known cardiac disease. The prognostic implications of uncomplicated VCB (right or left bundle branch block [RBBB or LBBB], left anterior hemiblock) in patients without cardiac diagnoses, however, need to be reevaluated in the current therapeutic era. The purpose of this study was to determine long-term cardiac morbidity and mortality in a community-based population with electrocardiographically-identified VCB, documented normal left ventricular ejection fraction, and no diagnoses of cardiac disease at the time of the index ECG. A retrospective observational cohort study was undertaken of patients in Olmsted County, Minnesota, evaluated from 1975 to 1999. Kaplan-Meier survival analysis post-index electrocardiography was performed with median follow-up of 9.0 years; 706 patients (mean age 64 +/- 16 [SE] years) were identified. Of those, 12% had LBBB with left-axis deviation (LAD); 20% had LBBB without LAD; 26% had left anterior hemiblock; and 42% had RBBB. Kaplan-Meier analysis indicated a significant difference in cardiovascular morbidity risk among the VCB groups (p = 0.017) with left anterior hemiblock and LBBB with LAD, and these were associated with the highest 10-year cardiovascular morbidity risk (58% and 68%, respectively). The incidence of dilated cardiomyopathy was 3% in patients with LBBB with LAD compared with 0.85% in the overall cohort. Significant mortality differences were also demonstrated between LBBB with LAD compared with LBBB without LAD (p = 0.048), left anterior hemiblock compared with LBBB without LAD (p <0.0001), and left anterior hemiblock compared with RBBB (p = 0.0007). In conclusion, the identification of uncomplicated VCB with LAD is associated with increased long-term cardiac morbidity/mortality risk, including the development of dilated and ischemic cardiomyopathy. Isolated VCB is an early marker of cardiac co-morbidities and potentially identifies a high-risk group of patients who warrant preventive intervention.