Pseudo-Right Bundle Branch Block Pattern During Conventional Right Ventricular Lead Pacing: All That Glitters Is Not Gold.

BACKGROUND

Right ventricular (RV) pacing typically produces left bundle branch block (LBBB) morphology. Right bundle branch block (RBBB) patterns during RV lead placement raise concerns for malpositioning.

CASE PRESENTATION: A 67-year-old male with symptomatic atrioventricular dysfunction and bi-fascicular block underwent dual-chamber pacemaker implantation. During RV lead testing, unexpected RBBB morphology was noted despite correct positioning.

RESULTS

Fluoroscopic verification excluded malpositioning. The Pseudo-RBBB pattern most likely resulted from physiological conduction through existing right bundle disease, where impulses travelled preferentially via septal pathways to activate the left ventricle.

CONCLUSION

RBBB morphology during RV pacing requires systematic evaluation to exclude malpositioning but may represent physiological conduction in patients with or without existing conduction disease.