"Runaway" in a modern generation pacemaker.

Life-threatening episodes of ventricular tachycardia were documented in a patient with an implanted Omni-Stanicor pacemaker due to episodic pacemaker runaway. The unit generated impulses at rates varying from 73 to 500 per minute. Ventricular capture at high rates was variable, but frequently resulted in heart rates in excess of 200 per minute. These episodes were associated with loss of consciousness secondary to inadequate cardiac output. Although the pacemaker could be inactivated by reprogramming its output to 2 mA, and suppressed by chest wall stimulation with an external pulse generator, no spontaneous rhythm resulted during these maneuvers. Urgent removal of the battery at the bedside and immediate resumption of pacing with an external generator was required to resolve the problem. Although runaway is infrequent with current generation pacemakers, it should be considered in addition to the more common causes of pacemaker malfunction in the patient with appropriate symptoms.