The Effects of Class I Drugs on the Cycle Length of Sustained Ventricular Tachycardia and the Signal-Averaged Electrocardiogram

: Evaluation of signal-averaged electrocardiograms (SAECGs) has been reported to be useful for predicting the patients with sustained ventricular tachycardia (SVT) combined with organic heart disease and at high risk for sudden cardiac death. However, the relationship between drug efficacy and SAECGs has not been established. We studied the effects of class I drugs on SVT using SAECGs. The study group consisted of 13 patients with SVT who underwent serial electropharmacologic trials. In 7 trials, SVT could not be induced after administration of class I drugs (group 1). In 17 trials, SVT was still inducible (group 2). Filtered QRS in group 2 were significantly prolonged after administration of class I drugs (p < 0.05). The prolongation of the SVT cycle length was correlated with the prolongation of the original QRS (p < 0.05) and with prolongation of the filtered QRS after administration of class I drugs (p < 0.01). The evaluation of the effects of class I drugs on SAECGs may be useful in predicting the inducibility of SVT and SVT cycle length.