Function of ventricular pacemakers during resuscitation.

The reciprocal effects of resuscitation and permanent, ventricular-inhibited pacemakers were examined in four, well-documented cases of witnessed out-of-hospital arrest. The resulting observations provide useful insight in the treatment of cardiac arrest in the large number of patients with permanent pacemakers. Transient sensing malfunctions occurred in the two patients in whom direct current countershocks were not required and were probably related to the severely deranged state of the myocardium. In spite of periods of asynchronous pacing in this critically unstable setting, no arrhythmias were precipitated. In the two patients who required defibrillation, transient malfunctions of pacing, capture and sensing occurred in spite of protective electronics in the pacing system, the left-sided location of the generator and, in one patient, the bipolar configuration. The pacemaker appeared to intermittently sense coarse ventricular fibrillatory waves. The malfunctions in the two latter cases were probably the result of the combined effects of the countershock and the abnormal state of the myocardium. All four patients succumbed, three in the emergency room and one on the eighth hospital day. Outcome was predominantly determined by the patient's response to therapeutic interventions. The observed pacemaker malfunctions, although potentially life-threatening, had no obvious, adverse effect on outcome in these four cases, mainly because of the transient nature of the abnormalities. Indeed, in one case, the presence of pacemaker activity was pivotal in identifying the native rhythm, illustrating the diagnostic potential of this analytical approach.