Electrogram polarity and cavotricuspid isthmus block during ablation of typical atrial flutter

Introduction: The atrial activation sequence around the tricuspid annulus h as been used to assess whether complete block has been achieved across the cavotricuspid isthmus during radiofrequency ablation of typical atrial flut ter, However, sometimes the atrial activation sequence does not clearly est ablish the presence or absence of complete block. The purpose of this study was to determine whether a change in the polarity of atrial electrograms r ecorded near the ablation line is an accurate indicator of complete isthmus block. Methods and Results: Radiofrequency ablation was performed in 34 men and 10 women (age 60 +/- 13 years [mean +/- SD]) with isthmus-dependent, counterc lockwise atrial flutter, Electrograms were recorded around the tricuspid an nulus using a duodecapolar halo catheter, Electrograms recorded from two di stal electrode pairs (E1 and E2) positioned just anterior to the ablation l ine were analyzed during atrial flutter and during coronary sinus pacing, b efore and after ablation, Complete isthmus block was verified by the presen ce of widely split double electrograms along the entire ablation line, Comp lete bidirectional isthmus block was achieved in 39 (89%) of 34 patients. B efore ablation, the initial polarity of E1 and E2 was predominantly negativ e during atrial flutter and predominantly positive during coronary sinus pa cing. During incomplete isthmus block, the electrogram polarity became reve rsed either only at E2, or at neither E1 nor E2, In every patient, the pola rity of E1 and E2 became negative during coronary sinus pacing only after c omplete isthmus block was achieved. In 4 patients (10%), the atrial activat ion sequence recorded with the halo catheter was consistent with complete i sthmus block, but the presence of incomplete block was accurately detected by inspection of the polarity of E1 and E2, Conclusion: Reversal of polarity in bipolar electrograms recorded just ante rior to the line of isthmus block during coronary sinus pacing after ablati on of atrial flutter is a simple, quick, and accurate indicator of complete isthmus block.