What is the classic ECG appearance of atrial flutter?

• A. Sawtooth flutter waves with variable AV block and atrial activity around 250–350 bpm.
• B. P waves with notching and irregular RR intervals.
• C. Delta waves.
• D. Prolonged QT with T wave inversion.

Answer: (A)

Atrial flutter is a rapid, regular atrial tachycardia produced by a reentrant circuit in the atria. The atrial rate is typically about 250–350 beats per minute, which creates distinctive sawtooth flutter waves. These flutter waves are often best seen as a repeating, organized pattern between the QRS complexes, especially in the inferior leads or V1. The ventricular response depends on how the AV node conducts these impulses and is often described as variable AV block, meaning the ratio of atrial to ventricular beats can change (for example, 2:1, 3:1, etc.), giving a ventricular rhythm that can seem regular yet influenced by conduction. This combination—the sawtooth flutter waves and a high atrial rate with variable conduction—is the hallmark of classic atrial flutter.

Other descriptions don’t fit as well: P waves with notching and irregular RR intervals suggest non-sawtooth atrial activity such as atrial fibrillation or multifocal atrial tachycardia; delta waves point to Wolff-Parkinson-White syndrome; prolonged QT with T wave inversion points to repolarization abnormalities or ischemia.