Junctional rhythm associated with ventriculoatrial block during slow pathway ablation in atypical atrioventricular nodal re-entrant tachycardia

AIMS: We assessed responses to slow pathway ablation with respect to the appearance of ventriculoatrial (VA) block during junctional rhythm in both typical and atypical types of atrioventricular nodal re-entrant tachycardia (AVNRT). METHODS AND RESULTS: The 31 subjects included 16 patients with slow-fast type of typical AVNRT and 15 patients with atypical AVNRT (9 patients with fast-slow type and 6 patients with slow-slow type). During atypical AVNRT, the HA interval was prolonged (>70 ms) and the earliest atrial activation was located around the coronary sinus (CS) ostium. The difference in atrial activation times at the CS ostium and His-bundle area A(CS-His) during AVNRT was measured. Slow pathway ablation was performed using a classical electro-anatomical approach. In typical AVNRT, A(CS-His) was -21.3 +/- 3.4 ms, and the HA interval was 34 +/- 14 ms. During slow pathway ablation, all patients with typical AVNRT had junctional rhythm with retrograde atrial conduction. In contrast, in patients with atypical AVNRT, A(CS-His) was 12 +/- 19.3 ms and the HA interval was 189 +/- 77 ms. In 13 of the 15 patients with atypical AVNRT, slow pathway ablation induced junctional rhythm, which was not associated with retrograde atrial conduction. After ablation, AVNRT became non-inducible and antegrade atrioventricular (AV) conduction was preserved in all patients. CONCLUSION: In patients with atypical AVNRT, junctional rhythm with VA block during slow pathway ablation is commonly observed and indicates the success of the ablation of retrograde slow pathway conduction, but has no relation to the risk of subsequent AV block. During junctional rhythm, occasional appearance of the sinus beats with intact antegrade AV conduction is essential for safety of ablation.