Inappropriate sinus tachycardia or…something else?

We report the case of a 45-year old female patient with a past medical history of rheumatoid arthritis who presented to our cardiology department with a suspicion of inappropriate sinus tachycardia. Echocardiography showed a nondilated left ventricle with a preserved ejection fraction. A careful reinterpretation of her 12-lead ECG reoriented the diagnosis toward an incessant atrial tachycardia. The diagnosis was confirmed by an electrophysiologic study performed with an electro-anatomic mapping system, which identified the origin of the tachycardia at the level of the right atrial appendage. Radiofrequency ablation of the ectopic focus eliminated the tachycardia and improved the patient's symptoms.