Reciprocal Beating Induced by Ventricular Pacing

Ventricular pacing is frequently associated with retrograde ventriculo-atrial conduction. In the absence of atrioventricular (A-V) block, the relatively intact antegrade A-V conduction system supplies the necessary pathway for a re-entry mechanism that may become operative in the presence of delayed retrograde conduction. Two patients with bradycardia and unimpaired antegrade A-V conduction exhibited reciprocal (echo) beating following nodal beats before ventricular pacing was instituted. After the introduction of an artificial ventricular pacemaker, reciprocal beats followed the paced ventricular beats in both patients. These observations suggest that a similar mechanism is involved in the production of reciprocal beats linked to impulses originating from the A-V node and the ventricles. When ventricular pacing is indicated for the treatment of bradycardia in the presence of intact antegrade A-V conduction, a situation which may produce echo beats, demand pacing is considered preferable to fixed-rate pacing as the latter may deliver a stimulus into the vulnerable phase following an echo beat.