Unmasking of myopotential oversensing by an integrated bipolar defibrillator lead following AV node ablation.

A 73-year-old man with nonischemic cardiomyopathy underwent catheter ablation of ventricular tachycardia that had resulted in frequent shocks from his implanted cardiac resynchronization therapy defibrillator (CRT-D). Coexisting atrial fibrillation required AV node ablation which rendered the patient pacemaker dependent. During follow-up, recurrent episodes of dizziness occurred caused by inhibition of pacing due to oversensing of pectoral muscle myopotentials. Surgical revision was performed and the intraoperative examination revealed an intact integrated bipolar defibrillator lead with appropriate connections to the CRT-D header. The placement of an additional pace/sense lead completely resolved the patient's symptoms and no further myopotential oversensing was recorded.