Right, But Not Left, Bundle Branch Block Is Associated With Large Anteroseptal Scar

Objectives This study sought to test the hypothesis that right bundle branch block (RBBB) patients have larger scar size than left bundle branch block (LBBB) patients do. Background A proximal septal perforating branch of the left anterior descending (LAD) coronary artery most commonly perfuses the right bundle branch and left anterior fascicle, but not the left posterior fascicle. Thus, proximal LAD occlusions should cause RBBB, not LBBB. Methods We performed electrocardiograms and magnetic resonance imaging for scar quantification in 233 patients with left ventricular (LV) ejection fraction ≤35% who were receiving primary prevention implantable cardioverter-defibrillators (ICD cohort). Scar size and location were compared among patients with RBBB, LBBB, nonspecific LV conduction delay, and QRS