RADIO-FREQUENCY CATHETER ABLATION OF ATRIAL-FLUTTER - FURTHER INSIGHTS INTO THE VARIOUS TYPES OF ISTHMUS BLOCK - APPLICATION TO ABLATION DURING SINUS RHYTHM

Background Radiofrequency ablation of type 1 atrial flutter (AFl) has recently evolved toward an anatomically guided procedure directed to i sthmuses at the lower part of the right atrium (RA). However, differen t types of block at these isthmuses may be observed and potentially co rrelated with different late outcomes. In addition, because the ablati on is anatomically guided, ablation should be possible during sinus rh ythm. Methods and Results Forty-four patients underwent ablation of ty pe 1 AFl performed during ongoing tachycardia (33 patients) or sinus r hythm (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, i ncomplete block mimicking complete block because of intra-atrial condu ction delay but leading to a different low RA activation pattern was i ndividualized. 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 o f 12.1+/-5.5 months, 4 patients, experienced AFl recurrence; all had s hown incomplete or no block. Conclusions Detailed multiple-point low R A mapping is necessary to differentiate incomplete from complete isthm us block. Complete block is the best marker for long-term success of A Fl ablation, although incomplete block may be sufficient to prevent re currence in a significant number of cases. Isthmus block is achievable during sinus rhythm, and AFl induction is not mandatory.