Physiological substrate for antidromic reciprocating tachycardia: Prerequisite characteristics of the accessory pathway and atrioventricular conduction system

Background. Although the anatomic ''substrate'' for the occurrence of antidromic reciprocating tachycardia (ART) has been previously examined, the underlying physiological substrate for this unusual arrhythmia in patients with the Wolff-Parkinson-White syndrome has not been thoroughly characterized. Methods and Results. The electrophysiological properties of the accessory pathway and normal ventriculoatrial conduction system in 30 patients with ART and a single accessory pathway were compared with those observed in a control group of 36 patients without this arrhythmia to elucidate the critical physiological substrate essential for the development and maintenance of ART. Inducible ART had a mean cycle length of 286±31 msec. The average retrograde ventriculoatrial conduction system effective refractory period in ART patients was significantly less than that in the control group (244±32 versus 291±46 msec, p=0.0002). All of the ART patients showed retrograde conduction over the normal conduction system at cycle lengths of ≤360 msec; 23 had 1:1 conduction to ≤300 msec, and 16 showed 1:1 propagation at cycle lengths of ≤260 msec. The shortest cycle length accompanied by 1:1 retrograde propagation over the normal conduction system in patients with ART was also significantly less than that observed in the control group (274±39 versus 347±73 msec, p<0.001). The accessory pathway anterograde ERP in ART patients with 1:1 retrograde conduction over the normal ventriculoatrial conduction system at cycle lengths of ≤360 was significantly less than that seen in comparable control patients (247±23 versus 284±56 msec, p=0.001), and the accessory pathway location was significantly further from the atrioventricular node in 21 patients with ART undergoing surgery than that in 22 operated control patients (3.8±0.8 versus 2.9±0.8 mapping units, p=0.0025) who also had retrograde ventriculoatrial conduction to cycle lengths of ≤360 msec. No significant differences in anterograde atrioventricular conduction system properties, retrograde accessory pathway refractoriness, or shortest ventricular pacing cycle lengths maintaining 1:1 conduction via the accessory pathway were observed between groups. Conclusions. This quantitative characterization of the properties of conduction and refractoriness of both the accessory pathway and ventriculoatrial conduction system and the relation between these characteristics and the accessory pathway location in ART patients provides additional insight into the prerequisites for the initiation and maintenance of this rhythm disturbance.