How do I tell atrial flutter from AFib?

Flutter shows organized sawtooth F waves at a regular atrial rate (~300/min); AFib has a chaotic fibrillatory baseline with no organized atrial activity and an irregularly irregular ventricular response. When unsure, a 12-lead and your clinician settle it.

Why is a rate of 150 a clue?

2:1 flutter conducts an atrial rate of ~300 down to a ventricular rate of ~150. A regular narrow tachycardia sitting right at 150 is classic for 2:1 flutter until proven otherwise.

Does flutter carry stroke risk like AFib?

Atrial flutter carries thromboembolic risk and anticoagulation implications similar to AFib. Those decisions belong to the clinical team — RN PocketPal does not make them.

Atrial flutter — an educational nurse reference.

The sawtooth flutter waves, why conduction ratios matter, and how to tell flutter from AFib on a strip.

Recognizing this rhythm at the bedside means matching pattern, intervals, and clinical context. This page covers the educational pattern; calipers and your clinical judgment carry it across the line.

What RN PocketPal does

Identifying traits

Atrial rate: ~250–350/min (classically ~300), organized.
Flutter (F) waves: sawtooth baseline, best seen in II, III, aVF.
Ventricular rate: depends on conduction ratio (2:1 ≈ 150, 3:1 ≈ 100, 4:1 ≈ 75).
Rhythm: regular when the conduction ratio is fixed; irregular when variable.
QRS: usually narrow unless aberrancy.

Verify with

Look for the sawtooth pattern along the baseline — flutter waves march through the QRS.
A regular narrow-complex tach at exactly ~150 should make you look hard for 2:1 flutter.
12-lead and the clinical team for rate/rhythm decisions and anticoagulation.

Who it’s for

For Nurses and nursing students learning rhythm interpretation.

Frequently asked questions

How do I tell atrial flutter from AFib?: Flutter shows organized sawtooth F waves at a regular atrial rate (~300/min); AFib has a chaotic fibrillatory baseline with no organized atrial activity and an irregularly irregular ventricular response. When unsure, a 12-lead and your clinician settle it.
Why is a rate of 150 a clue?: 2:1 flutter conducts an atrial rate of ~300 down to a ventricular rate of ~150. A regular narrow tachycardia sitting right at 150 is classic for 2:1 flutter until proven otherwise.
Does flutter carry stroke risk like AFib?: Atrial flutter carries thromboembolic risk and anticoagulation implications similar to AFib. Those decisions belong to the clinical team — RN PocketPal does not make them.

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Reviewed by RN PocketPal Clinical Team, RN. Last reviewed June 4, 2026.