Simple Method of Counterclockwise Isthmus Conduction Block by Comparing Double Potentials and Flutter Cycle Length

BACKGROUND AND OBJECTIVES: Local wide split double potentials are used as a parameter to determine complete conduction block during cavotricuspid isthmus ablation in patients with isthmus dependent atrial flutter. However, delayed slow conduction in that region can sometimes be very difficult to differentiate from complete block. Flutter cycle length (FCL) can be used to confirm isthmus conduction block, because FCL is a measure of conduction time around the tricuspid annulus (TA). This study was designed to determine which degree of splitting of the local electrograms is adequate to confirm complete isthmus block, using FCL as a reference. SUBJECTS AND METHODS: Cavotricuspid isthmus (CTI) ablation was performed in fifty consecutive patients. The interval between the pacing stimulus on the lateral side of the CTI and the first component of the double potentials on the block line (SD1) corresponded to the counterclockwise conduction time. The interval between the pacing stimulus and second component (SD2) represented the clockwise conduction time to the contralateral side of the ablation line. SD1 and SD2 were measured before and after complete isthmus block. RESULTS: An SD1+SD2 reaching 90% of the FCL identified the counterclockwise isthmus conduction block with 94% sensitivity and 100% specificity. CONCLUSION: If the sum of SD1 and SD2 following isthmus ablation was close to the FCL, complete conduction block was predicted with high diagnostic accuracy and positive predictive value for at least counterclockwise conduction.