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

Isthmus Block During Atrial Flutter Ablation. Introduction: Complete bidire ctional cavotricuspid isthmus block is the endpoint for ablation of typical atrial flutter, The purpose of this study was to determine whether the ext ent of prolongation of the transisthmus interval after ablation predicts co mplete bidirectional block. Methods and Results: Fifty-seven consecutive patients underwent 60 ablation procedures for isthmus-dependent atrial flutter, The clockwise and counter clockwise transisthmus intervals were determined before and after ablation during pacing from the low lateral right atrium and the coronary sinus. Bid irectional block was achieved with ablation in 55 (96%) of 57 patients. The transisthmus intervals before ablation and after complete transisthmus blo ck were 100.3 +/- 21.1 msec and 195.8 +/- 30.1 msec, respectively, in the c lockwise direction (P < 0.0001), and 98.2 +/- 24.7 msec and 185.7 +/- 33.9 msec, respectively, ih the counterclockwise direction (P < 0.0001). An incr ease in the transisthmus interval by greater than or equal to 50% in both d irections after ablation predicted complete bidirectional block with 100% s ensitivity and 80% specificity. The positive and negative predictive values were 89% and 100%, respectively. The diagnostic accuracy of a greater than or equal to 50% prolongation in the transisthmus interval was 92%. Conclusion: Prolongation of the transisthmus interval by greater than or eq ual to 50% in the clockwise and counterclockwise directions is associated w ith a high degree of diagnostic accuracy and an excellent negative predicti ve value in determining complete bidirectional transisthmus block. This may be a useful and simple adjunctive criterion for assessment of complete tra nsisthmus conduction block.