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Atrial Flutter (4:1)

caution
Lead II
25 mm/s10 mm/mV
HR72bpm
RR833msQT—
Type

Atrial flutter in which the AV node conducts every fourth wave: a regular rhythm at 75 per minute, with the sawtooth in plain view between the beats.

Updated

What to look for

  1. A regular rate of 75. Every R-R interval is the same, 800 ms.
  2. A sawtooth between the beats. Three flutter waves are in plain view between each pair of QRS complexes. The fourth is in the QRS.
  3. No P waves. The flutter waves are regular, one every 200 ms, and they do not stop for the QRS.
  4. A narrow QRS. Under 120 ms.

The strip

Thirty seconds of atrial flutter with 4:1 block in lead II. Count the flutter waves between two QRS complexes.

Look-alikes

Normal Sinus Rhythm

A flutter wave can look like a P wave. But sinus rhythm has one P wave for each QRS, with a flat line between them.

Focal Atrial Tachycardia

Discrete P waves with a flat baseline between them. The flutter baseline is never flat.

Why it matters

A slow, regular rate in flutter usually means a drug is slowing the AV node. The rate is controlled, but the flutter continues, and so does the risk of stroke.

Next: the 12-leadAtrial flutter with 4:1 block, on the 12-leadThe same heart on all twelve leads, with why it happens, what it means and how it is treated.

References

  1. Typical Atrial Flutter: A Practical Review — Journal of Cardiovascular Electrophysiology, 2025
  2. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia — European Heart Journal, 2020