Clinical Meaning of Right Bundle Branch Block Pattern on Surface Electrocardiogram in Pacemaker Patients During Right Ventricular Endocardial Pacing

Introduction: Right bundle branch block (RBBB) pattern is sometimes observed in right ventricular (RV) endocardial pacing. However, the true mechanism and the clinical meaning of this phenomenon are still unknown. Methods and results: Out of 218 consecutive patients with RV apex endocardial pacing, we studied 30 cases with RBBB pattern and 111 cases with left bundle branch block (LBBB) pattern. No significant differences were found between these 2 groups in age, sex, and pacing mode. However, the percentage of cardiomyopathy patients in the RBBB pattern group was significantly higher than in the LBBB pattern group (36.7% versus 1.8%, p < 0.0001). The left ventricular diastolic dimension (52.2 ± 9.3 mm versus 48.0 ± 5.5 mm, p = 0.05) was bigger and left ventricular ejection fraction (56.2 ± 14.7% versus 66.4 ± 11.6%, p = 0.0003) was lower in the RBBB pattern group. In RBBB pattern group, 11 out of 13 patients with low cardiac function (ejection fraction