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Figure 3 (A) Typical isthmus-dependent atrial flutter (IDAF) in a patient with ToF (patient 12). The patient has had heart block since the surgical correction. Note the counterclockwise initial activation sequence in the Halo catheter positioned on the tricuspid annulus, with high-to-low activation of the lateral right atrial wall. Pacing performed through the distal ablation catheter (ABLATE-D) located near the ostium of the coronary sinus did not affect the activation sequence, and the postpacing interval was nearly identical to the tachycardia cycle length. HALO-1 = distal; HALO-10 = proximal. (B) Recording obtained during ablation of the isthmus between the tricuspid annulus and the inferior vena cava (IVC) in the same patient. The cycle length of the IDAF is prolonged in comparison with (A) as a result of partial ablation of the isthmus. The IDAF abruptly terminated during the RF energy application and was immediately replaced with an intra-atrial re-entrant tachycardia (IART) of different cycle length and activation sequence (arrows). This was an IART dependent on the region of the atriotomy scar in the lateral right atrium. Successful ablation of the tricuspid valve/IVC isthmus was confirmed after ablation of the IART. The surface electrocardiographic leads are I, L, F and V1.
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