Complete subeustachian isthmus (isthmus) block created with radiofrequency (RF) linear lesion eliminates type I. atrial flutter (AFL). The end-point of the procedure is measurable. Patients and method: Ninety patients (21 F) aged 57.6 ± 12.5 years underwent RF catheter ablation for AFL. Twenty patients had significant structural heart disease (SHD). Atrial fibrillation (AF) was previously documented in 34 (37.8 %) patients. Complete isthmus block served as the end-point of the procedure. Results: Following the first ablation procedure complete isthmus block was achieved in 81 (90 %) patients and incomplete isthmus block in 7 (7.8 %) patients. First procedure failed in 2 (2.2 %) patients. AFL recurred in 6 (6.8 %) patients, in 4 (4.9 %) out of 81 patients with complete isthmus block and in 2 (28.5 %) out of 7 patients with incomplete isthmus block. After repeated successful ablation and creation of complete isthmus block in these 6 patients and in 1 patient with previous ablation failure, complete isthmus block was achieved in 84 (93.3 %) patients, incomplete isthmus block in 5 (5.6 %) patients and ablation was unsuccessful in 1 patient. During 21 ± 10.6 (6 - 45) month follow-up since the last ablation AFL did not recur in any of 89 (98.9 %) patients with complete or advanced incomplete isthmus block. AF occurred in 39 (43.3 %) patients. Incidence of AF was significantly higher in patients without SHD and with AF previously docu- mented or induced (group 2) (25/43; 58.1 %) compared to patients without SHD and no AF docu- mented or induced (group 1) (6/27; 22.2 %) (p < 0,01). AF occurred in 40 % patients with SHD (group 3), which did not significantly differ from any of the former two groups of patients. In this group AF occurred in 10 out of 12 (83,3 %) patients with AF documented prior to ablation, which was significantly more compared to 1 (12,5 %) patient out of 8 without documented AF (p < 0,01). Conclusion: Complete conduction block over the subeustachian isthmus during catheter ablation has a clearly measurable end-point and represents effective method in permanent cure of AFL. Clinical benefit is reduced by AF, particularly in patients, in whom the arrhythmia was documented prior to ablation. In these patients catheter ablation of AFL can be considered a first step to combined treatment with previously ineffective antiarrhythmic drugs and with other ablation strategies.

        Key words: Subeustachian isthmus block - Catheter ablation - Atrial flutter - Atrial fibrillation