Analysis of junctional beats during slow pathway ablation: Illuminating the mechanism of typical and atypical AV nodal re-entrant tachycardia.

Background: Junctional rhythm (JR) frequently occurs during radiofrequency (RF) ablation procedures targeting the slow pathway (SP) for atrioventricular nodal re-entrant tachycardia (AVNRT), signaling successful ablation. Two types of JR have been noticed: typical JR as His activation preceding atrial activation, and atypical JR as atrial activation preceding the His activation. Nevertheless, the origin and characteristics of JR remain incompletely defined.

Objective: This study aimed to investigate whether JR induced by RF ablation at the anatomical SP position could reveal preferential conduction in the antegrade vs the retrograde direction.

Methods: Consecutive RF ablation procedures targeting the SP for AVNRT were performed in 40 patients. Using electroanatomic mapping, the coronary sinus ostium, His bundle, RF sites, and the distances between these sites and the RF sites (n = 216) were analyzed. We compared the H-A and A-H intervals during AVNRT and JR.

Results: In typical AVNRT, the H-A resembled the H-A with an identical atrial activation sequence, supporting JR conduction to the atrium via a fast pathway. The atypical AVNRT group displayed a significantly shorter A-H than the A-H ( .0001) with identical atrial activation. The JR incidence in patients with both typical and atypical AVNRT showed no correlation with the RF site location.

Conclusion: For patients with typical AVNRT, JR induced by SP ablation preferentially followed the fast pathway. In patients with atypical AVNRT and with retrograde SP conduction, a shorter A-H interval during JR, with the same atrial sequence as that observed during atypical AVNRT, implies retrograde conduction from the SP to the atrium.