Randomized study defining the optimum target interlesion distance in ablation index-guided atrial fibrillation ablation

Aims: While the CLOSE protocol proposes a maximally tolerable interlesion distance (ILD) of 6 mm for ablation index ablation index-guided atrial fibrillation (AF) ablation, a target ILD has never been defined. This randomized study sought to establish a target ILD for ablation index-guided AF ablation.

Methods and results: Consecutive patients scheduled for first-time pulmonary vein (PV) isolation (PVI) were randomly assigned to ablation protocols with a target ILD of 5.0-6.0 mm or 3.0-4.0 mm, with the primary endpoint of first-pass PVI. In compliance with the CLOSE protocol, the maximum tolerated ILD was 6.0 mm in both study protocols. A target ablation index of ≥550 (anterior) or ≥400 (posterior) was defined for the '5-6 mm' protocol and ≥500 (anterior) or ≥350 (posterior) for the '3-4 mm' protocol. The study was terminated early for superiority of the '3-4 mm' protocol. Forty-two consecutive patients were randomized and 84 ipsilateral PV pairs encircled according to the study protocol. First-pass PVI was accomplished in 35.0% of the '5-6 mm' group and 90.9% of the '3-4 mm' group (P < 0.0001). Median ILD was 5.2 mm in the '5-6 mm' group and 3.6 mm in the '3-4 mm' group (P < 0.0001). In line with the distinct ablation index targets, median ablation index was lower in the '3-4 mm' group (416 vs. 452, P < 0.0001). While mean procedure time was shorter in the '3-4 mm' group (149 ± 27 vs. 167 ± 33min, P = 0.004), fluoroscopy times did not differ significantly (4.7 ± 2.2 vs. 5.1 ± 1.8 min, P = 0.565).

Conclusion: In ablation index-guided AF ablation, an ILD of 3.0-4.0 mm should be targeted rather than 5.0-6.0 mm. Moreover, the lower target ILD may allow for less extensive ablation at each given point.