Usefulness of isoproterenol in the induction of clinical sustained ventricular tachycardia during electrophysiological study

Electrophysiological testing remains the basic procedure in the assessment of life-threatening sustained ventricular tachycardias (VT). The predictive value of inducible VT depends on the baseline stimulation protocol and probably on some other factors, including autonomic balance. We report the cases of four patients, with a history of myocardial infarction, who experienced recurrent episodes of syncope; the clinical aspects of the syncope were suggestive of syncopal VT. With a baseline stimulation protocol, electrophysiological testing only allowed the induction of well-tolerated non-sustained VT. Using the same stimulation protocol (rapid ventricular pacing or basal ventricular stimulation with 2 extra-stimuli), monomorphic sustained VT that had the same ECG morphology, as non-sustained VT, could only be induced while low doses of isoproterenol (1-2 mu g/min) were being administered. In these cases, increased sympathetic tone appears to be prerequisite for a sustained VT reproducing the patients clinical symptoms and discomfort. To conclude, in some patients with recurrent symptoms, including syncope suggesting of ventricular arrhythmia, low-dose infusion of isoproterenol may facilitate the induction of clinical sustained VT and increase the predictive value of electrophysiological testing. Possible mechanisms of ventricular arrhythmogenesis by isoproterenol are discussed.