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Atrial Flutter (1:1)

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

Atrial flutter in which the AV node conducts every wave: a regular, narrow rhythm at about 200 per minute, with the sawtooth hidden in the QRS and T.

Updated

What to look for

  1. A very fast, regular rate. About 200 per minute. Every R-R interval is the same.
  2. One flutter wave for each QRS. Every wave conducts, so there is no gap between the beats for the sawtooth to show. It is hidden in the QRS and T.
  3. No P waves. Nothing before each QRS looks like a P wave.
  4. A narrow QRS. At this rate it can widen, and the rhythm then looks like ventricular tachycardia.

The strip

Thirty seconds of atrial flutter with 1:1 conduction in lead II. Find the rate, then look for any flat baseline between the beats.

Look-alikes

Atrioventricular Nodal Re-entrant Tachycardia (AVNRT)

Also fast, regular and narrow. Only a change in the ratio, for example after adenosine, shows the flutter waves.

Monomorphic Ventricular Tachycardia

If the QRS widens at this rate, 1:1 flutter looks like VT. Treat a wide, fast, regular rhythm as VT until proved otherwise.

Why it matters

This is an emergency. At 200 per minute the heart cannot fill, and the patient can collapse. It is most often caused by a drug that slows the flutter (flecainide) without one that slows the AV node, or by exercise.

Next: the 12-leadAtrial flutter with 1:1 conduction, 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