What it is
Atrial flutter is a macro-re-entrant atrial tachycardia, usually circling the cavotricuspid isthmus in the right atrium. The atria depolarise regularly at about 300/min, and the AV node conducts a fraction of these to the ventricles.
ECG features
- Sawtooth "flutter" (F) waves — a continuous undulating baseline, best seen in II, III, aVF
- Atrial rate ~300/min
- Regular ventricular response determined by the conduction ratio:
- 2:1 → ~150/min (the classic, and easily mistaken for sinus tachycardia or SVT)
- 3:1 → ~100/min, 4:1 → ~75/min
- QRS is narrow unless there is aberrancy
The 150 clue
A regular narrow-complex tachycardia at ~150/min is flutter with 2:1 block until proven otherwise. Vagal manoeuvres or adenosine transiently increase AV block, "opening up" the tracing to reveal the flutter waves — diagnostic, even if they don't terminate the rhythm.
Management
- Rate control (beta-blocker, diltiazem/verapamil) and anticoagulation — the same CHA₂DS₂-VASc thresholds as AF
- Cardioversion (electrical or pharmacological) for symptomatic or unstable patients — flutter cardioverts at low energies
- Catheter ablation of the cavotricuspid isthmus is very effective and often curative for typical flutter
See a real 12-lead example
For an annotated tracing of this pattern, see the Atrial Flutter page in the LITFL ECG Library:
ECG image examples are hosted by Life in the Fast Lane (LITFL), whose ECG library is published under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 licence. We link to LITFL rather than reproducing their tracings. The teaching notes above are original and written independently for MedNotes Hub.