Inhibition of Atrial Electrical Activity by Ventricular Pacing Mediated by Vagal Stimulation

In the absence of retrograde (VA) conduction, ventricular pacing does not exert any appreciable effect upon atrial electrical activity. We report three patients (2 with complete AV block and 1 with preserved AV conduction) in which, during EP study, no VA conduction was present and, in spite of that, excessive suppression (for more than 15 secs in the first patient) of sinus (atrial) electrical activity during RV pacing was observed. The sinus node suppression was reproducible in two patients. In all patients the suppression phenomenon was not observed after intravenous administration of atropine, which suggests that it was mediated by enhanced vagal tone.