An Asymptomatic Man With an Abnormal ECG

A 76-year-old man presented for a routine health evaluation. He reported no symptoms and the cardiovascular physical examination was within normal limits. He takes amlodipine for hypertension. He was referred for a cardiology evaluation after the following ECG was performed. Please turn the page to read the diagnosis. The ECG in Figure 1 shows 2 dissociated and independent atrial rhythms, a condition called atrial dissociation. An amplified view of the same ECG is shown in Figure 2, where the 2 rhythms are evident: one is a normal sinus rhythm (green arrows in lead II rhythm strip) at 60 beats/min with a QRS axis of +50 and a PR interval of 140 ms. The other is a rapid atrial rhythm (RAR) with a low-voltage P wave (red arrows in lead V1 rhythm strip) with a constant interval …