A 73-year-old man is in the Emergency Department with severe palpitation and dyspnea of 1 1/2 hour duration:

• Supraventricular tachycardia, rate 246/min
• Probably atrial flutter with 1:1 AV conduction

Comment: When atrial flutter is conducted in a 1:1 fashion, it can be difficult to see the flutter waves.  Administration of an AV nodal blocker can slow down the ventricular response and “reveal” the flutter waves

IV Adenosine is administered – This ECG is recorded 12 minutes after ECG 1:

• Atrial flutter with variable AV block. Ventricular rate 118/min