Radiofrequency Catheter Ablation of Atrial Flutter

Background Radiofrequency ablation of type 1 atrial flutter (AFl) has recently evolved toward an anatomically guided procedure directed to isthmuses at the lower part of the right atrium (RA). However, different types of block at these isthmuses may be observed and potentially correlated with different late outcomes. In addition, because the ablation is anatomically guided, ablation should be possible during sinus rhythm. Methods and Results Forty-four patients underwent ablation of type 1 AFl performed during ongoing tachycardia (33 patients) or sinus rhythm (11 patients). Evidence of inferior vena cava–tricuspid annulus isthmus block was assessed by changes in RA impulse propagation while pacing from both sides of the ablation site. Apparent complete isthmus block was achieved in 43 of 44 patients with 9±7 pulses. However, incomplete block mimicking complete block because of intra-atrial conduction delay but leading to a different low RA activation pattern was individualized. At the end of the procedure, isthmus block was complete in 35 patients and incomplete in 8, but since AFl reinduction was no longer possible, patients were discharged. During a follow-up period of 12.1±5.5 months, 4 patients experienced AFl recurrence; all had shown incomplete or no block. Conclusions Detailed multiple-point low RA mapping is necessary to differentiate incomplete from complete isthmus block. Complete block is the best marker for long-term success of AFl ablation, although incomplete block may be sufficient to prevent recurrence in a significant number of cases. Isthmus block is achievable during sinus rhythm, and AFl induction is not mandatory.