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Seven patients with normal specialized conduction system and three patients with the Wolff-Parkinson-White (WPW) syndrome were studied using programmed stimulation of the heart before and after the administration of intravenous disopyramide. The principal effect of this drug was to prolong the effective refractory period of the atria and ventricles, and to prolong the effective refractory period of the anomalous pathway in the WPW syndrome. In addition, it prolonged the conduction time in the anomalous pathway in the WPW syndrome. These findings suggest that disopyramide would be a useful and safe drug in the management of certain atrial and ventricular arrhythmias and in the management of the Wolff-Parkinson-White syndrome with atrial fibrillation.

Two patients with intractable life-threatening ventricular tachycardias have been studied using intracardiac electrograms and programmed electrical stimulation of the heart. Both patients have shown to have an underlying re-entry mechanism in the ventricles as the basis for the tachycardias. Both patients underwent epicardial mapping studies at cardiac surgery, and the site of re-entry was established. In one patient the re-entry front was found to start in the posterobasal region of the left ventricle and in the other patient the re-entry front was found in the anterobasal region of the right ventricle. In both patients surgical interruption of the re-entry front was carried out. Both patients are alive and free from tachycardias at the time of writing.