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 r eport three patients (2 with complete AV block and 1 with preserved AV conduction) in which, during EP study, no VA conduction was present a nd, in spite of that, excessive suppression (for more than 15 sees in the first patient) of sinus (atrial) electrical activity during RV pac ing was observed. The sinus node suppression was reproducible in two p atients. In all patients the suppression phenomenon was not observed a fter intravenous administration of atropine, which suggests that it wa s mediated by enhanced vagal tone.