Loss of capture late after right ventricular pacing lead revision: what is the mechanism?

A 75-year-old woman was referred to our hospital because of dizziness and presumed pacemaker dysfunction (Fig. 1).Eight weeks earlier, the patient had underwent implantation of a single chamber pacemaker (Sensia, Medtronic, USA) with a tined, steroid-eluting bipolar right ventricular (RV) lead (4074 CapSure Sense, Medtronic, USA) for chronic atrial fibrillation and symptomatic bradyarrhythmia.Two weeks post-implantation surgical revision had been necessary due to RV lead dislocation.Device interrogation prior to hospital discharge had been inconspicuous with a RV pacing threshold less than 1.0 V at 0.4 ms during unipolar stimulation (Fig. 2), a pacing impedance of 612 Ohms and an R wave amplitude sensing of [22 mV.Chest X-ray suggested a regular lead position in the RV apex.At presentation, the patient reported episodic dizziness and intermittent sharp left pectoral pain that was present since approximately 1 week.Intrinsic heart rate at rest was 50-60 bpm and blood pressure 130/85 mmHg.The surface Electrocardiogram (ECG) showed unipolar pacing spikes without capture (Fig. 1).Device interrogation revealed a RV pacing threshold that had increased to [6 V at 1 ms during unipolar stimulation, with a pacing impedance of 521 Ohms and an R wave amplitude sensing of [22 mV.During bipolar stimulation, a pacing threshold of 2.25 V at