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Aims The safety of Ablation Index (AI)-guided 50 W ablation for atrial fibrillation (AF) remains uncertain, and mid-term clinical outcomes have not been described. The interplay between AI and its components at 50 W has not been reported. Methods and results Eighty-eight consecutive AF patients (44% paroxysmal) underwent AI-guided 50 W ablation. Procedural and 12-month clinical outcomes were compared with 93 consecutive controls (65% paroxysmal) who underwent AI-guided ablation using 35–40 W. Posterior wall isolation (PWI) was performed in 44 (50%) and 23 (25%) patients in the 50 and 35–40 W groups, respectively, P 7 Ω (54.6% vs. 45.5%, P 600 anteriorly, >500 posteriorly) was more frequent in the 50 W group (9.7% vs. 4.3%, P Conclusion Ablation Index-guided 50 W AF ablation is as safe and effective as lower powers and results in reduced ablation and procedure times. Radiofrequency lesions are more likely to be therapeutic, but there is a higher risk of delivering excessive ablation.

Funding Acknowledgements Type of funding sources: None. Background The safety of Ablation Index (AI)-guided 50W ablation of atrial fibrillation (AF) remains uncertain, and the effects of this high power on other ablation parameters have not been described. We aimed to compare the safety profile of AF ablation using 50W and 35-40W. Methods 59 patients undergoing AI-guided Pulmonary Vein Isolation were enrolled including 31 with 50W and 28 with 35-40W. A contact force (CF)-sensing ablation catheter (Thermocool SmartTouch) was used to deliver point-by-point ablation according to the CLOSE protocol targeting AI values of 550-600 on the left atrial (LA) anterior wall and 400-450 on the LA posterior wall. The generator impedance graph was monitored in real-time for each lesion application. All VisiTags (n = 3766) across both groups were analysed retrospectively. Excessive ablation was defined as AI >600 on the anterior wall and >500 on the posterior wall. Results The mean AI was significantly higher in patients receiving 50W ablation (512 [±61] vs. 500 [±63] with 35-40W ablation, p Scatterplots showing the relationships between contact force (CF) and ablation time for the anterior and posterior segments of the LA for both groups are shown in the Figure. For the anterior wall, the slope of the regression line for the 50W group was -1.0 and for the 35/40W group was -0.5. Overall, there was moderate correlation between the variables CF and time in both groups (50W group: r -0.490, p In the 50W group, high CF was an important predictor of excessive AI. The AUCs for anterior and posterior wall 50W ablations were 0.844 (95% CI, 0.774-0.914; p Conclusion Use of 50W ablation appears to be safe. but may lead to AI overshoot. Our study suggests that operators should strive to limit CF to 15g on the anterior wall and 10g on the posterior wall. Abstract Figure. Relationship between CF and abl time

Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Groupe de Rythmologie de la Société Française de Rythmologie Background Posterior Wall Isolation (PWI) is increasingly performed for Atrial Fibrillation (AF). The use of Ablation Index (AI)-guided 50W ablation for PWI has not been described, nor the interplay between ablation parameters at this power when compared to lower powers. Methods 40 consecutive AF patients (26 males, 65.5 ± 10.0 years. 95% non-paroxysmal AF) underwent PWI following pulmonary vein isolation. A roof line and floor line were created with point-by-point ablation, targeting a contact force (CF) of 10-30g, AI 550-600 on the roof and 400-450 on the floor, and inter-tag distance of Results PWI was successful in 19(95%) of the 35-40W group and in all 20 patients in the 50W group, with FPI seen in 8(40%) and 10(50%) respectively, p = 0.53. The mean CF and number of RF applications on the roof. floor and inside the box were similar between the two groups. Ablation time per lesion (10.4 [8.8-12.5]sec) and total ablation time per patient (3.84[3.34-4.66] min) were shorter in the 50W group as compared to 35-40W (13.0 [11.6-16.2] sec and 5.86 [4.23-7.73] min respectively), p Conclusion Ablation Index guided 50W ablation has a very high success rate for posterior wall isolation with shorter ablation times and higher impedance drop compared to conventional powers. Steam pops may be avoidable by targeting CF

Purpose Treatment of typical atrial flutter (AFL) with cavo-tricuspid isthmus (CTI) ablation is associated with a high occurrence rate of new onset atrial fibrillation (AF) during follow-up. There are data to support the addition of pulmonary vein isolation (PVI) to CTI ablation in patients with both AF and AFL, but the role of cryoballoon PVI only, with no CTI ablation, in AFL patients with no prior documentation of AF has not been studied. Methods CRAFT is an international, prospective, randomised, open with blinded assessment, multicentre superiority study comparing radiofrequency CTI ablation and cryoballoon PVI in patients with typical AFL. Participants with typical AFL are randomised in a 1:1 ratio to either treatment arm, with patients randomised to PVI not receiving CTI ablation. Post-procedural cardiac monitoring is performed using an implantable loop recorder. The primary endpoint is time to first recurrence of sustained symptomatic atrial arrhythmia. Key secondary endpoints include (1) total arrhythmia burden at 12 months, (2) time to first episode of AF lasting ≥ 2 min, (3) time to recurrence of AFL or AT and (4) procedural and fluoroscopy times. The primary safety endpoint is the composite of death, stroke/transient ischaemic attack, cardiac tamponade requiring drainage, atrio-oesophageal fistula, requirement for a permanent pacemaker, serious vascular complications requiring intervention or delaying discharge and persistent phrenic nerve palsy lasting > 24 h. Conclusion This study compares the outcomes of 2 different approaches to typical AFL—the conventional ‘substrate’-based strategy of radiofrequency CTI ablation versus a novel ‘trigger’-based strategy of cryoballoon PVI. Trial registration (ClinicalTrials.gov ID: NCT03401099)