OBJECTIVES: This study was aimed at delineating the reentrant circuit of right atrial (RA) upper loop re-entry using noncontact three-dimensional mapping. BACKGROUND: Various forms of atypical atrial flutter including lower loop re-entry and left atrial flutter have been demonstrated. However, little is known about upper loop re-entry in the RA. METHODS: The study population consisted of eight patients (65 ± 12 years, seven men) with atypical atrial flutter. Right atrial activation during atrial flutter was visualized using a noncontact mapping system (EnSite-3000 with Clarity Software, St. Paul, Minnesota) for a three-dimensional reconstruction of the endocardial depolarization. The narrowest parr of the re-entrant circuit was targeted using radiofrequency catheter ablation. RESULTS: Noncontact mapping showed macro-re-entry confined to the RA free wall with RA activation time accounting for 100% of the cycle length (214 ± 21 ms) in all eight patients. Two patients had counterclockwise activation, and six patients had clockwise activation around the central obstacle, which was composed of the crista terminalis, the area of functional block, and superior vena cava. The lower turn-around points were located at the conduction gap in the crista terminalis. Radiofrequency linear ablation of the conduction gap in the crista terminalis was performed and eliminated atrial flutter in six patients without recurrence during a follow-up of 3.2 ± 1.1 months. CONCLUSIONS: Atypical atrial flutter could arise from upper loop re-entry in the RA with conduction through the gap in the crista terminalis. Radiofrequency linear ablation of the conduction gap was effective in eliminating this atrial arrhythmia.
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