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ECG Findings

  • Regular narrow-complex tachycardia.

  • Flutter waves appear in a rapid sine wave or “sawtooth” pattern, usually in the inferior leads (II, III, aVF).

  • Atrial activity in lead V1 often appears as rapid P waves at a rate approximating 300 bpm.


  1. The AV node’s refractory period usually prevents 1:1 conduction to the ventricles. Usually, conduction is blocked at a ratio of 1:2 to 1:4. The QRS complexes should appear with regular periodicity. However, AV conduction may be variable from beat to beat, creating irregular R-to-R intervals.

  2. A conduction ratio of 2:1 is usually difficult to discern, because the two flutter peaks between QRS complexes may look like normal P and T waves. A ventricular rate of 140 to 160 bpm should prompt consideration of the possibility of atrial flutter with 2:1 block.

  3. Atrial flutter tends to be more refractory to chemical cardioversion and more susceptible to electrical cardioversion when compared to atrial fibrillation.


Atrial Flutter. (ECG contributor: James V. Ritchie, MD.)


Atrial flutter with 4:1 block. The flutter waves (arrows marking every other flutter wave) may be mistaken for P and T waves.


The “sawtooth” pattern is most apparent in the inferior leads.

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