Abstract
BACKGROUND: In cardiac implantable electronic device management, confused electrocardiograms are sometimes encountered. CASE SUMMARY: We experienced a case of dizziness and presyncope, which was accompanied by irregular pacing spikes following QRS complexes, pacing failure, sensing failure, or something else. The patient's second active pacemaker in her left chest was functioning normally. However, her old abdominal pacemaker had automatically changed from the OVO to VVI mode because of an elective replacement indicator. As a result, her old and second pacemakers had an interaction. Old invalid pacing spikes induced oversensing of the current pacemaker, which interfered with valid pacing. DISCUSSION: We experienced a rare case of dizziness and presyncope with confused pacing spikes. Physicians should be aware of the unexpected interactions that are possible with devices with automatic mode changes.