Figure 1.

A: Twelve-lead electrocardiogram showed persistent atrial flutter (AFL) with positive P waves in leads II (with a tiny negative initial deflection), III, aVF, and V₁; negative P waves in lead aVR; and almost isoelectric P waves in leads I, aVL, and V₂–V₆. B: Intracardiac electrograms of the AFL recorded from a 20-electrode catheter from the lateral wall of the right atrium (RA) to the distal coronary sinus (CS). The tachycardia cycle length was 270 ms. The activation sequence in the RA was consistent with a counterclockwise direction while the activation in the CS was almost simultaneous. C: Fluoroscopic image. D: Ablation at the cavotricuspid isthmus led to a sudden alteration of atrial activation sequence, although the tachycardia continued. E: Isolation of the right pulmonary veins and linear ablation of the left atrial roof led to termination of the tachycardia and restoration of sinus rhythm. CSd = distal of the coronary sinus; CSp = proximal of the coronary sinus; Halo d = distal of the RA part of the 20-electrode catheter; Halo p = proximal of the RA part of the 20-electrode catheter; LAO = left anterior oblique.