Intraventricular electrogram morphology: effect of increased heart rate with and without accompanying changes in sympathetic tone

The accompanying variations in sympathetic tone on the morphological characteristics of the intracardiac signal was investigated in 25 patients. Electrogram morphology was analyzed using correlation waveform analysis during sinus rhythm and during passages of accelerated heart rate which was maintained either by atrial overdrive pacing or by infusion of epinephrine or isoproterenol. Results indicate that the intraventricular electrogram morphology tends to remain stable during increases in heart rate alone but that heart rate increases caused by α- and/or β-agonism may produce modest morphologic changes. This finding suggests that techniques designed for morphologic signal analysis which have been proposed for future implantable antitachycardia devices may require periodic updating of the sinus rhythm template during deviations in heart rate