Suppression of demand mechanism by inactive myocardial electrodes

A 14 year old girl, at age 8, had had a bipolar pulse generator implanted with myocardial leads. Because one of the myocardial leads fractured near the electrode, a second pair of myocardial leads were implanted. Thus, the patient had two pairs of myocardial leads and one demand pulse generator implanted. When the patient was readmitted to the hospital because of light-headedness, the ECG monitor revealed frequent suppression of pulse generator pulses when hand pressure was exerted over the pulse generator site. Converting the pulse generator into the asynchronous mode with a magnet prevented inhibition. The pacemaker pocket was reopened. The pulse generator could not be inhibited either by pulling on the active myocardial leads or by moving the pulse generator, but the pulse generator could be inhibited by manipulation of the inactive leads which produced electrical signals having amplitudes and frequencies which were in the bandwidth of the sensing circuit. The probable cause of the electrical signals was the irregular contact of the terminals of the inactive leads with the patient's abdominal muscles. Replacement of the demand pulse generator by an asynchronous type resulted in cessation of the patient's light-headedness.