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Figure 4 Postoperative tachycardia with focal mechanism. (A) Electrograms recorded from a number of endocardial sites before successful focal ablation can be seen. This arrhythmia was rapid (CL 200 ms) and regular at the site of successful ablation (right superior pulmonary vein) in contrast to the irregular but well-formed atrial electrograms at other atrial sites. This was consistent with second-degree conduction block between the focus and more distant atrial sites. (B) Termination of the tachycardia 3 s after the onset of the successful radiofrequency application. (C) and (D) X-ray images showing the position of the successful radiofrequency energy application (arrows).