Apparent bidirectional conduction block following radiofrequency catheter ablation of typical atrial flutter

Objective: The purpose of this study is to determine the reliability of act ivation sequence mapping in assessing the presence of bidirectional conduct ion block (BCB) in typical atrial flutter (AFL) ablation. Introduction: Radiofrequency ablation (RFA) can cure typical AFL by creatin g BCB across the right atrial isthmus. Effective conduction block across th is region can prevent AFL recurrence, but accurate assessment of isthmus co nduction may be flawed. Methods: BCB was measured before and after RFA by pacing at multiple rates on both sides of the isthmus during sinus rhythm. Pacing was performed from a low lateral tricuspid annulus site (proximal to the isthmus) and a coron ary sinus Os site (distal to the isthmus), while recording simultaneously f rom 8-10 right atrial sites bordering the isthmus (4-5 free wall sites; 4-5 septal sites) as well as from an isthmus site. After ablation reinduction of atrial flutter was attempted from both sides of the block with rapid atr ial pacing after BCB was established in all patients. In some patients line s of conduction block were evident at the isthmus (using the ablation cathe ter to map). Results: Of 65 patients undergoing RFA of AFL, 59 had typical AFL. In all 5 9 patients, BCB was demonstrated at all pacing cycle lengths 30 min after R FA applications. In 6 of these 59, AFL was inducible with atrial pacing des pite apparent BCB. Further RFA resulted in non inducibility in all 6 patien ts. In the remaining 53/59 patients, BCB was associated with noninducibilit y at 30 min. A total of 8 recurrences were seen during a mean 19.3 +/- 8.3 (SD) month follow-up. Conclusion: Apparent BCB as determined by activation sequence mapping outsi de of the isthmus is an excellent marker, but, as measured, may be a mislea ding method of assessing the presence or absence of conduction through the isthmus. It is necessary to attempt reinduction of AFL after apparent succe ss. Elimination of typical AFL does not preclude other AFLs.