Role of transisthmus conduction intervals in predicting bidirectional block after ablation of typical atrial flutter

Isthmus Block During Atrial Flutter Ablation. Introduction: Complete bidirectional cavotricuspid isthmus block is the endpoint for ablation of typical atrial flutter. The purpose of this study was to determine whether the extent of prolongation of the transisthmus interval after ablation predicts complete bidirectional block. Methods and Results: Fifty-seven consecutive patients underwent 60 ablation procedures for isthmus-dependent atrial flutter. The clockwise and counterclockwise transisthmus intervals were determined before and after ablation during pacing from the low lateral right atrium and the coronary sinus. Bidirectional block was achieved with ablation in 55 (96%) of 57 patients. The transisthmus intervals before ablation and after complete transisthmus block were 100.3 ± 21.1 msec and 195.8 ± 30.1 msec, respectively, in the clockwise direction (P < 0.0001), and 98.2 ± 24.7 msec and 185.7 ± 33.9 msec, respectively, in the counterclockwise direction (P < 0.0001). An increase in the transisthmus interval by ≥50% in both directions after ablation predicted complete bidirectional block with 100% sensitivity and 80% specificity. The positive and negative predictive values were 89% and 100%, respectively. The diagnostic accuracy of a ≥50% prolongation in the transisthmus interval was 92%. Conclusion: Prolongation of the transisthmus interval by ≥50% in the clockwise and counterclockwise directions is associated with a high degree of diagnostic accuracy and an excellent negative predictive value in determining complete bidirectional transisthmus block. This may be a useful and simple adjunctive criterion for assessment of complete transisthmus conduction block.