Pacemaker spikes misleading the diagnosis of ventricular fibrillation.

Pacemakers are used more and more in modern cardiology, because of the increasing age of patients and the increasing number of cases of congestive heart failure treated with biventricular stimulation. Twelve lead ECG traces of electro-stimulated patients normally can be interpreted correctly, but in emergency circumstances where only a three lead ECG trace is available (i.e. the usual monitoring setting in the pre-hospital arena or intensive care unit) recognition of the underlying baseline rhythm may be difficult. The case described illustrates how differentiation between true asystole and fine ventricular fibrillation in the presence of some confounding elements (e.g. pacemaker meditated spikes) can be challenging for the physician and life-threatening for the patient. Therefore, after selecting the best diagnostic ECG trace, direct current defibrillation should be used in the presence of a persistent but uncertain cardiac rhythm, even if it may be thought to be asystole or pulse-less electrical activity.