Back to the basics: A case of atrial flutter?

An 87-year-old man with a history of left bundle branch block (LBBB), premature ventricular contractions, and chronic lower back pain presented for routine cardiology care. He was asymptomatic. An electrocardiogram (ECG) was recorded (Figure 1A ). The patient was diagnosed with atrial flutter, and anticoagulation was initiated. Subsequent ambulatory monitoring (Zio XT, iRhythm Technologies, San Francisco, CA; and KardiaMobile, AliveCor, Mountain View, CA) showed sinus rhythm without evidence of a sustained atrial arrhythmia. What does the ECG demonstrate?