A protocol for programmed ventricular stimulation is described in which the effect of increasing stimulation current on ventricular refractoriness and arrhythmia induction was specifically examined. The protocol was evaluated prospectively in 70 patients undergoing electrophysiological study for documented or suspected ventricular arrhythmias. Programmed electrical stimulation was performed at the right ventricular apex and outflow tract using single and double extrastimuli and burst pacing. Stimulation currents of 2, 5, 10, and 20 mA were used in ascending order. The initial (lowest) current was never less than twice diastolic threshold and was maintained during each stimulation run until refractoriness was reached. The current was then increased to the next level to facilitate premature capture until refractoriness was encountered at 20 mA or a sustained arrhythmia occurred. Ventricular arrhythmias were induced in 34 patients, 31 of whom had presented with a sustained ventricular arrhythmia. The incidence of induced arrhythmias was low in those patients who had presented with symptoms alone, a non-sustained arrhythmia, or a sustained arrhythmia in association with a predisposing clinical event. Only one patient with a negative result had further ventricular arrhythmias during the mean follow up period of 15 months. Although each increase in stimulation current caused a decrease in measured ventricular refractoriness, this resulted in only four arrhythmias. Only one arrhythmia was induced above 5 mA. These results suggest that this simple protocol using two extrastimuli and a single stimulation current of 5 mA will reliably identify most patients who have symptomatic ventricular arrhythmias.
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