USEFULNESS OF ISOPROTERENOL IN THE INDUCTION OF CLINICAL SUSTAINED VENTRICULAR-TACHYCARDIA DURING ELECTROPHYSIOLOGICAL STUDY

Electrophysiological testing remains the basic procedure in the assess ment of life-threatening sustained ventricular tachycardias (VT). The predictive value of inducible VT depends on the baseline stimulation p rotocol and probably on some other factors, including autonomic balanc e. We report the cases of four patients, with a history of myocardial infarction, who experienced recurrent episodes of syncope; the clinica l aspects of the syncope were suggestive of syncopal VT. With a baseli ne stimulation protocol, electrophysiological testing only allowed the induction of well-tolerated non-sustained VT. Using the same stimulat ion protocol (rapid ventricular pacing or basal ventricular stimulatio n with 2 extra-stimuli), monomorphic sustained VT that had the same EC G morphology, as non-sustained VT, could only be induced while low dos es of isoproterenol (1-2 mu g/min) were being administered. In these c ases, increased sympathetic tone appears to be prerequisite for a sust ained 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 isoprotere nol may facilitate the induction of clinical sustained VT and increase the predictive value of electrophysiological testing. Possible mechan isms of ventricular arrhythmogenesis by isoproterenol are discussed.