Left Bundle Branch Pacing: Unexpected Resynchronization Effect of Anodal Capture

Anodal capture can provide a resynchronization effect on biventricular pacing. However, evidence of such an effect remains unclear in left bundle branch pacing (LBBP). We report a patient with a baseline sinus rhythm with complete atrioventricular block and a ventricular escape rhythm with a right bundle branch (RBB) block QRS morphology and left axis deviation who received LBBP for cardiac resynchronization therapy (CRT), and its anodal capture stimulation (ANS) rendered a near-normal QRS morphology. The resolution of the RBB pattern during bipolar pacing in this patient resulted from a fusion of LBBP and right ventricular septal capture from ANS. In conclusion, CRT can be achieved during LBBP by ANS in patients who do not have retrograde RBB activation.