The clinical significance of polymorphic ventricular tachycardia provoked at electrophysiologic testing

Ventricular tachycardia (VT) induced at electrophysiologic studies is felt to be clinically significant if the morphology of the induced arrhythmia and the spontaneous arrhythmia are similar. Yet many times in referral patients, an adequate 12-lead ECG does not exist to permit determination of the VT morphology. Since the significance of differences in induced and spontaneous arrhythmias has not been clearly established, we reviewed the records of 153 patients and correlated induced VT morphology with the incidence of sudden death. Polymorphic VT was induced in 88 patients (57%) and monomorphic VT was induced in 65 patients (43%). The total mortality and sudden death rates were similar in the two groups in spite of antiarrhythmic therapy, 12% and 7% (polymorphic) versus 10% and 5% (monomorphic). All the sudden deaths occurred in patients who presented with cardiac arrest and hemodynamically symptomatic VT and none in the asymptomatic VT group, regardless of VT morphology (p less than 0.005). The induced VT morphology cannot be used to predict the potential efficacy of antiarrhythmic drugs, since patients with either morphology are as likely to respond to conventional or experimental agents. Thus, induced polymorphic VT can be a useful index of electrical instability in high-risk patients (cardiac arrest and hemodynamically symptomatic VT) and may be of utility in guiding antiarrhythmic therapy.