Cause of the "power-on reset" phenomenon other than electric magnetic interference in a patient with a pacemaker

A 67-year old male with a dual-chamber pacemaker visited for a regular check-up. An unfamiliar message emerged on the display just after placing the programmer wand. We could recognize that the pacemaker had already been in the safe back-up mode of DDI, and the programmer prompted a re-initialization request. We are so surprised because there was no indication of device malfunction the day before in daily monitoring and a 12-lead electrocardiogram revealed normally working in the DDD mode just before checking the device. The pacemaker was immediately re-programmed to the former setting. This phenomenon has not recurred for 12 months.