Effect of atrioventricular sequential pacing in patients with no ventriculoatrial conduction

Candidates for the dual chamber "universal" (DDD) pacemaker are frequently tested for the presence of intact ventriculoatrial (VA) conduction to identify those at risk for developing endless loop tachycardia. However, recent reports have cited instances where clinical endless loop tachycardia has occurred even when no VA conduction could be demonstrated during ventricular pacing. A pacing protocol was designed to assess the effect of atrioventricular (AV) sequential pacing on VA conduction in 13 patients who showed no evidence of VA conduction during routine electrophysiologic testing. The absence of VA conduction was inferred by pacing the ventricle at several cycle lengths without obtaining a retrograde atrial capture. With the AV sequential method, which consisted of an AV sequential drive with a programmed AV interval of 100 to 160 ms, the presence or absence of VA conduction was tested utilizing a premature ventricular stimulus (V2) over a wide range of coupling intervals. During the AV sequential method, the V2 effectively propagated to the atria in 5 of 13 patients with V2A2 intervals ranging from 200 to 460 ms (mean 304 +/- 97). It is concluded that in patients showing absent VA conduction during routine testing, the ability of a paced ventricular impulse to propagate retrogradely can be demonstrated in a significant number of cases with AV sequential pacing. Although the exact mechanism could not be determined, it is postulated that as compared with ventricular pacing alone, a longer input into the AV node (first anterogradely during the AV sequential drive and then retrogradely with V2) may be partly responsible for the facilitative effect of the AV sequential method.