A case report of a rare and distinctive pacing pattern during left bundle branch pacing in a child with third-degree atrioventricular block following ventricular septal defect repair.

After repair of a ventricular septal defect (VSD), atrioventricular conduction block frequently occurs, often requiring pacemaker implantation. Left bundle branch pacing (LBBP) is a physiological pacing modality and has become the preferred pacing approach in pacemaker-dependent children. Conventional right ventricular septal pacing typically produces a left bundle branch block (LBBB) pattern on the electrocardiogram (ECG). Herein, we report the case of a 3-year-old child who developed third-degree atrioventricular block complicated by right bundle branch block (RBBB) after VSD repair. The child subsequently received LBBP. During the procedure, the pacing lead only made superficial contact with the right ventricular septal myocardium without deep septal fixation, yielding an RBBB pattern on ECG. No relevant similar cases have been identified in the current literature, rendering this phenomenon rare in clinical practice.