Targeting slow conduction areas in the cavo-tricuspid isthmus to reduce ablation burden in typical atrial flutter: a multicentre randomized trial

Background During typical atrial flutter (AFL) the cavo-tricuspid isthmus (CTI) exhibits conduction delay, which enables the perpetuation of the reentrant circuit. A new ablation strategy targeting only slow conduction areas has achieved CTI block in 92% of patients, suggesting these regions as preferential targets. Our objective was to compare such strategy to other functional approaches, and to the gold standard of linear ablation. Methods Prospective multicentre randomized trial involving patients undergoing CTI ablation for AFL. Population was divided into four different stepwise strategies, all of them with an eventual linear ablation as the last step: ablation of only slow conduction areas, ablation of only high voltage areas, ablation of confluent areas with both slow conduction and high voltage, and direct linear ablation. Results A total of 124 patients were randomized to any strategy, with no differences among groups. The efficacy to obtain CTI block with the first step of ablation of slow conduction areas, high voltage areas and confluent areas was 81.5%, 48% (p<0,01) and 54% (p=0,04), respectively. The final efficacy of the entire population was 100%, and 86% of procedures were performed in a fluoroscopy-free modality, without differences among strategies. At 6-month follow-up, AFL recurrences were observed in 0%, 21% (p=0,1), 10%, and 0% of patients with slow conduction, high voltage, confluent areas and linear ablation, respectively. Furthermore, atrial fibrillation (AF) episodes were observed at 12 months in 0%, 37% (p = 0.0049), 6% and 6%(p=1), respectively. No other variable other than the strategy was associated to either AFL recurrence nor to AF incidence. In procedures targeting slow conduction zones total procedure time was reduced: 63±16 min versus 76±23 min (p <0.01) compared to high voltage areas, and versus 76±29 min (p = 0.03) compared to linear ablation. The RF time was also shorter with the slow conduction ablation compared to high voltage ablation and linear ablation (237±127 sec vs 271±260 sec, p=0.05, and 366±205 sec, p=0.01, respectively). Conclusions Ablation of only slow conduction areas in the CTI is feasible and shorten the procedure duration and the ablation burden compared to linear ablation, reaching the CTI block in more than 80% of patients. Long-term AFL recurrences with only slow conduction ablation resembles linear ablation but less AF relapses are observed.