A 15-year-old boy with incessant drug-refractory atrial tachycardia was referred to our department for an ablation procedure. The tachycardia was diagnosed at 13 years of age during routine medical screening for soccer competition. Despite the administration of metoprolol, verapamil, and flecainide, the arrhythmia persisted and ventricular response was not controlled. Physical examination was normal except for a heart rate of 130 bpm; no signs of congestive heart failure were found.

Blood examinations revealed normal thyroid function. Twelve-lead ECG showed a narrow QRS tachycardia with positive P waves in II-III-aVF-V1-V2 leads, negative P waves in I-aVL leads, and a short PR interval (Figure 1), suggesting a left atrial origin. 1, 2 Transthoracic echocardiography showed normal left ventricular size with normal systolic function and normal atrial volumes. During electrophysiological study, the earliest atrial activation during tachycardia was located on the distal bipole of the coronary sinus catheter, confirming a lateral left atrial origin. 1–3 Left atrial access was obtained by transseptal approach with a Brockenbrough needle. Electroanatomic