Oversensing from electrode 'chatter' in a bipolar pacing lead: a case report.

An 81-year-old man was treated for high degree AV block and syncope with an AV universal (DDD) pacemaker. Bipolar active fixation atrial and ventricular leads were used. Intermittent oversensing from the ventricular lead was detected on Holter monitoring following implantation. This resulted in inappropriate inhibition of ventricular pacing. Ventricular electrogram showed spurious signals between 5 mV and 15 mV in magnitude coincident with ventricular lead inhibition. Treatment consisted of reprogramming the device to the VVT mode. Six weeks after implantation normal pacemaker function in the DDD mode was demonstrated on Holter monitoring and inappropriate pacer inhibition could not be demonstrated. We postulate that electrode 'chatter' between the cathodal ring electrode and the helix of the ventricular lead resulted in artifactual potentials sufficient to inhibit pacing. We hypothesize that fibrosis and fixation of the ventricular lead tip over a period of weeks eliminated these electromechanical artifacts and resulted in the oversensing problem being self-limited. Physicians should be aware of electrode 'chatter' as a cause of pacemaker oversensing.