Atrial tachycardia masquerading as atrial flutter following ablation of the subeustachian isthmus

Pseudo-Atrial Flutter. We report a case of atrial tachycardia masquerading as atrial flutter in a man who had previously undergone catheter ablation f or atrial flutter. The recurrent arrhythmia was electrocardiographically al most identical to the prior atrial flutter; at repeat electrophysiologic st udy, although bidirectional conduction block was observed in the tricuspid annulus-inferior vena caval isthmus, the atrial arrhythmia was readily init iated. Activation mapping suggested typical atrial flutter, but entrainment techniques demonstrated intra-atrial reentry not involving the ablated ist hmus, This case illustrates the need to apply entrainment techniques even i n cases of apparent "typical" atrial flutter to confirm that putative ablat ion targets are necessary for tachycardia perpetuation.