Evaluation of transisthmus conduction interval in predicting bidirectional block after ablation of typical atrial...

To determine whether the extent of prolongation of the transisthmus interval after ablation predicts complete bidirectional block.

Since 1996 to 2002, 30 consecutive patients underwent ablation procedures for isthmus-dependent atrial flutter. There were 23 males and 7 females [mean age (47.85 +/- 9.35) years]. With the use of fluoroscopic view of anatomy, radiofrequency ablation was performed during coronary sinus pacing at a cycle length of 600 ms.

Bidirectional block was achieved with ablation in 29 (97%) of 30 patients. The transisthmus intervals before ablation and after complete transisthmus block were (73.82 +/- 13.01) ms and (140.47 +/- 20.48) ms, respectively, in the clockwise direction (P < 0.0001), and (77.63 +/- 8.36) ms and (138.17 +/- 15.55) ms, respectively, in the counterclockwise direction (P < 0.0001). A period of incomplete isthmus block was observed during 17 (58%) of the 29 ablation procedures. The clockwise transisthmus intervals during incomplete block [(107.65 +/- 21.33) ms] were (45.5 +/- 8.7)% longer than the baseline transisthmus intervals. An increase in the transisthmus interval by > or = 50% in both directions after ablation predicted complete bidirectional block with 100.0% sensitivity and 83.3% specificity. The positive and negative predictive values were 90.6% and 100.0%, respectively. The diagnostic accuracy of a > or = 50% prolongation in the transisthmus interval was 83.3%.

The analysis of transisthmus interval is a valuable method for determining complete bidirectional isthmus block.