Abstract 10375: Right (Not Left) Bundle Branch Block is Associated with Large Anteroseptal Infarcts
Background: Among patients receiving cardiac resynchronization therapy (CRT), mortality is highest with right bundle branch block (RBBB), intermediate with nonspecific intraventricular conduction delay (IVCD) and lowest with left bundle branch block (LBBB). CRT likely benefits LBBB patients most because RBBB and IVCD patients have normal Purkinje activation of the left ventricle (LV) that is not improved by LV pacing. We hypothesized that RBBB is also associated with poor prognosis because it is most commonly caused by proximal left anterior descending artery (LAD) occlusion leading to large scar size.
Methods: We performed ECG and contrast-enhanced MRI for scar quantification in two cohorts. The first comprised 162 ischemic and nonischemic patients with left ventricular ejection fraction (LVEF) ≤35% receiving implantable defibrillators (ICD cohort). Scar size and location were compared among patients with RBBB, LBBB, non-bundle branch block QRS ≥120 ms and QRS <120 ms. A second cohort of 20 hypertrophic cardiomyopathy (HCM) patients undergoing alcohol septal ablation was studied to determine whether controlled infarction in a proximal LAD septal perforator caused RBBB or LBBB.
Results: In the ICD cohort, there was no difference in LVEF between RBBB and LBBB, however patients with RBBB had significantly larger scar (25% LV) and patients with LBBB had significantly smaller scar (8% LV) (p<0.001). RBBB patients (compared to LBBB) were more likely to have ischemic heart disease (88% vs. 34%, p=0.001) and ischemic heart disease with anteroseptal scar (59% vs. 25%, p=0.03). In the HCM cohort, 15 of 20 patients (75%) developed RBBB, while no patients developed LBBB.
Conclusions: In patients with LVEF ≤35%, RBBB is associated with a significantly greater scar burden than patients with LBBB, which is due to proximal LAD infarcts more commonly causing RBBB than LBBB. In contrast, LBBB is most commonly caused by nonischemic pathologies.
- Magnetic resonance imaging
- Infarct size
- Bi-ventricular pacing
- Heart conduction system
- © 2011 by American Heart Association, Inc.