Impact of Cavotricuspid Isthmus Anatomy on the Ablation Index For Successful First-Pass Typical Atrial Flutter Ablation

Abstract Cavotricuspid isthmus (CTI) linear ablation has been established as the treatment for typical atrial flutter. Recently, ablation index (AI) has emerged as a novel marker for estimating ablation lesions. We investigated the relationship between CTI anatomy and ablation parameters. In addition, we focused on the influence of AI on the procedural results of typical atrial flutter ablation. A total of 107 patients who underwent CTI ablation were retrospectively enrolled in this study. All patients underwent computed tomography before catheter ablation. From the receiver-operating curve, the best cut-off value of CTI depth was < 4.1 mm to predict first-pass success. The patients were divided into two groups according to the CTI depth: the concave group (CG) and straight group (SG). Although the average AI was not different between both groups, the CG required a longer ablation time and showed a lower first-pass success rate (p < 0.01). In addition, the catheter inversion technique was more frequently required in the CG (p < 0.01). The best cut-off values of the weakest AIs at the anterior and posterior lesions for predicting first-pass success were >420 and >386, respectively. Among patients with these cut-off values, the first-pass success rate was 88% in the SG and 50% in the CG (p < 0.01). Although ablation parameters were not significantly different, the first-pass success rate was lower in the CG than in the SG. AI-guided CTI may be useful in straight CTIs, but a modified approach might be required for concave CTIs.