Peak frequency annotation identifies functional ablation targets in cavotricuspid isthmus-dependent atrial flutter

Background Cavotricuspid isthmus(CTI)-dependent atrial flutter (AFL) is a common tachycardia associated with thromboembolic events and heart failure. Linear radiofrequency ablation across the CTI is the standard therapy with high success rates; however, extensive energy delivery may increase procedural invasiveness and carries potential risks. Because the CTI critical pathway is characterized by slow conduction and relatively high voltage, selective targeting of functionally critical regions may achieve block with fewer applications. Peak frequency annotation using the Ensite X™ system has been reported to identify critical regions in left atrial flutter, but its utility in CTI-dependent AFL remains unclear. Purpose This study aimed to evaluate the feasibility of peak frequency-guided ablation (PFGA) in CTI-dependent AFL and to characterize the electrophysiological properties of high peak frequency regions within the CTI. Methods We retrospectively analyzed 41 consecutive patients who underwent CTI ablation between September 2024 and January 2026 at two Japanese centers. 21 patients underwent conventional linear ablation (LA), and 20 underwent PFGA at the operator’s discretion. In the PFGA group, the CTI was divided into three zones: tricuspid valve side, central portion, and inferior vena cava (IVC) side. Peak frequency mapping was performed during coronary sinus ostial pacing in sinus rhythm. In each zone, the site with the highest peak frequency was targeted first. If bidirectional block was not achieved, the next highest frequency site was sequentially ablated regardless of zone until procedural success. A representative case requiring three applications is shown in Figure 1A. In both groups, radiofrequency energy was delivered at 30 W for 30 seconds per application, targeting a contact force of 10-20 g. Procedural success was defined as bidirectional CTI block confirmed by differential pacing and the presence of double potentials. Results The mean age was 68.5 years, and 73.2% were male. Baseline characteristics were comparable between groups. PFGA required significantly fewer applications (LA:11.4 ± 4.7 vs. PFGA:5.1 ± 3.5, P < 0.001), less total delivered energy (LA:11,870 ± 4,998 J vs. PFGA:5,057 ± 2,801 J, P < 0.001), and shorter ablation time (LA: 351 ± 146 s vs. PFGA: 151 ± 87 s, P < 0.001) (Figure 1B). Across all mapping points in the PFGA group, higher peak frequency was significantly associated with higher bipolar voltage and slower conduction velocity (Figure 2A,B). Conclusion PFGA reduced energy delivery and procedural time compared with conventional linear ablation. High peak frequency regions corresponded to areas of slow conduction and preserved voltage, consistent with electrophysiological features of the CTI critical pathway. These findings suggest that peak frequency annotation may serve as a functional marker of the CTI critical pathway and enable a more mechanism-based ablation strategy.