Left arm twitching caused by failure of pacemaker lead insulation

An 89-year-old woman with dementia was referred to our neurology clinic after presenting to her family physician with progressively worsening involuntary movements over 1 month.She had undergone permanent pacemaker implantation for complete atrioventricular block 14 years earlier, with generator replacement 3 years before presentation.Routine device follow-up had not been performed after she moved into a long-term care facility.On examination, we observed intermittent left arm twitching at approximately 1 Hz (Appendix 1, Video 1, available at www.cmaj.ca/lookup/doi/10.1503/cmaj.260045/tab-related-content).We considered myoclonus, fasciculation, and tremor, but these were inconsistent with the regular, coarse, low-frequency movements.The movements were simultaneous with pacing on mon itor electrocardiography, suggesting pacemaker involvement.Chest radiography revealed an abnormal configuration of the atrial pacing lead (Figure 1).We diagnosed pacemaker lead malfunction caused by insulation failure.Reprogramming the pacemaker mode from dual-chamber (DDD) to ventricular (VVI) pacing