Inhibition of ventricular output in a dual chamber pacemaker with normal pacing and sensing parameters: What is the mechanism?

A 65-year-old gentleman with dual chamber pacemaker presented with presyncope. The ECG raised concerns of oversensing which was confirmed by magnet response. The device interrogation revealed noise in ventricular channel temporally associated with P wave. The pacing thresholds were normal. Although the ventricular lead impedance was within normal limit the impedance trend suggested 100 Ω decline over last 1 year. RV lead insulation failure was speculated and supported by the bipolar and unipolar intracardiac electrogram. Device was programmed to DOO temporarily. He underwent RV lead replacement uneventfully.