<prompt> A 62-year-old male with underlying COPD develops a viral upper respiratory infection and begins taking an over-the-counter decongestant. Shortly thereafter he experiences palpitations and presents to the emergency room, where the following rhythm strip is obtained, demonstratingNormal sinus rhythmJunctional rhythmAtrial flutter with 4:1 atrioventricular blockParoxysmal atrial tachycardia with 2:1 atrioventricular block  <response>: c Source: Braunwald, 15e, p 1297. The rhythm strip in the question reveals atrial flutter with 4:1 atrioventricular AV block. Atrial flutter is characterized by an atrial rate of 250 to 350min; the electrocardiogram typically reveals a sawtooth baseline configuration due to the flutter waves. In the strip, every fourth atrial depolarization is conducted through the AV node, resulting in a ventricular rate of 75min although 2:1 conduction is more commonly seen. 