Atrial tachycardia arising from the right atrial inferoseptum masquerading as common atrial flutter.

Radiofrequency catheter ablation was performed in 2 patients with atrial tachycardia (AT). In both cases the AT originated from the inferoseptal portion of the right atrium, and the cycle length was 210 ms. The surface ECG demonstrated common counterclockwise atrial flutter, probably caused by functional block in the clockwise direction at the cavo-tricuspid isthmus and posterior right atrium with rapid activation of the origin. Although rare (2%), AT originating from the inferoseptum of the right atrium should be considered when the surface ECG exhibits common atrial flutter.