Radiofrequency (RF) ablation of the atrioventricular nodal (AVN) slow pathway (SP) is usually performed during RF delivery in sinus rhythm (SR) while monitoring, as an accepted surrogate of lesion creation, the occurrence of a slow junctional rhythm. This technique is still associated with a low but residual risk of permanent complete AV block (0,5–1%).

To describe a new method for direct visualization of SP conduction suppression during RF delivery by assessing the Atrial-His (AH) interval shortening using high atrial rate pacing.

Consecutive patients (pts) admitted for AVN re-rentrant tachycardia (AVNRT) ablation were included. Atrial pacing at a rate inducing constant antegrade SP conduction from the proximal coronary sinus (CS) was performed during RF delivery (remote magnetic navigation catheter), while monitoring the AH interval on the hissian catheter. The SP potential was identified using conventional electroanatomical methods.

Four pts were included (all men, 59±9 y). Typical AVNRT was induced in all (cycle length 328±52ms). During ablation, CS pacing was performed at 405±80ms. A 30ms AH shortening was observed during the successful RF application in 1 pt (Figure 1). In 3 pts, a transition from 3:2 Wenckebach (maximal AH 240±100ms) periods to a 1:1 conduction (AH 160±15ms) was seen during the successful pulse. A 13±5% of AH interval shortening was measured between baseline AH in SR (86±17ms) and at the end of the procedure (64±15ms). All pts were successfully ablated with complete absence of inducibility, jump nor echo beat after SP ablation, after isoproterenol infusion. After a follow-up of 6 months, no recurrences were noticed.

Fast atrial pacing during RF delivery allows direct visualization of SP conduction disappearance. This new method seems effective and potentially safer than the conventional one.