Cool-down Phenomenon in Differentiating Supraventricular Tachycardias

A 63-year-old male patient with a history of hypertension, type 2 diabetes mellitus, prostate cancer and class two obesity was admitted for altered mental status and hypertensive emergency. During his hospital stay he developed narrow complex tachycardia and it was difficult to definitively diagnose the underlying arrhythmia. Observation of the cool down phenomenon on electrocardiogram allowed us to make the diagnosis of atrial tachycardia and elegantly ruled out other causes on the differential. We report this interesting case of narrow complex tachycardia.