High-density characterization of a localized reentry circuit occurred after AF ablation.

We present the case of a localized reentry circuit that developed 24 h after radiofrequency ablation of atrial fibrillation (AF). The circuit was of interest because it overlapped with sites of previous defragmentation during AF. The circuit presented a small funnel that measured only 1.4 mm at its narrowest segment. Fractionated signals, which codify for slow conduction zones, corresponded to the isthmus site. Ablation at this site interrupted the atrial tachycardia.