Isoproterenol to evaluate resumption of conduction after right atrial isthmus ablation in type I atrial flutter

Background-After radiofrequency (RF) ablation of atrial flutter (AFL), the demonstration of bidirectional isthmus conduction (BIC) block is considered the hallmark of a successful procedure. The purpose of our study was to te st the persistence of BIC block after isoproterenol administration and to e valuate the importance of this finding with regard to AFL recurrences. Methods and Results-RF ablation of AFL was performed in 44 consecutive pati ents with type I AFL by linear ablation of the posterior isthmus (n=29 pati ents), septal isthmus (n=4 patients), or both right atrial (RA) isthmi (n=1 1 patients). The procedural end point was complete BIC block and noninducib ility of AFL. In case of noninducibility and apparent BIC block, the pacing protocol was repeated under isoproterenol infusion (1 to 3 mu g/min). Reve rsal of apparent BIC block occurred in 7 (15.9%) of 44 patients. Six patien ts had bidirectional and 1 had unidirectional resumption of isthmus conduct ion. Counterclockwise AFL could be reinduced in 4 of these patients. Two to 24 (median, 4) additional RF applications were required to achieve permane nt BIC block. At a mean follow-up of 7.3+/-7.6 months (range, 2 to 31 month s), 2 (4.5%) of 44 patients had AFL recurrences. Conclusions-Partial linear RF ablation could possibly aggravate preexisting nonuniform anisotropic conduction in the RA isthmus, resulting in profound conduction slowing and apparent BIC block. Isoproterenol can unmask appare nt BIC block, thus providing an opportunity to assess the possibility of re versal of BIC block and completeness of isthmus ablation during the same pr ocedure. The low incidence (4.5%) of AFL recurrences at follow-up suggests that noninducibility and BIC block under isoproterenol infusion may be a be tter end point for successful AFL ablation.