False inhibition of a demand pacemaker by inactive myocardial electrodes

A 14-year-old girl has been implanted a cardiac pacemaker with a myocardial electrode since 8 years old. As the first myocardial electrode fractured near its tip, the second one was added. Thus, patient had two pairs of myocardial electrode systems with one demand pacemaker implanted. When she was readmitted to hospital because of light-headedness, ECG monitor revealed the frequent suppression of pacemaker emission on transcutaneous waving of pacemaker unit. Application of the magnet over the generator resulted in no inhibition even on moving the unit. The pacemaker pocket was reopened. Waving the active myocardial electrode or pacemaker unit did not inhibit the demand pacemaker, but manipulation of the inactive lead induced suppression of pacemaker emission. Such manipulation produced high interference waves, which were created probably by motion of the cut end of inactive leads against patient's abdominal muscle. The exchange of the demand pulse generator to a fixed mode was followed by complete disappearance of light-headedness in this case.