Atrial flutter is actually a very interesting rhythm and there is a lot to learn here. Most of this belongs in an ECG course and is beyond the scope of an ACLS review but there are a few salient points that will help you understand and recognize atrial flutter:

Atrial flutter is the first “re-entry” dysrhythmia that we will talk about. All that this means is that there is a short-circuit in the conduction system that allows the impulse to travel around in a circle within the AV nodal region and continue causing myocardial depolarizations.

For anatomical reasons that relate literally to the length of the conduction pathway, the rate of atrial flutter is actually remarkably constant and predictable. Flutter waves usually occur at about 300bpm. The variability in atrial flutter arises from the degree of conduction block between the atria and the ventricles.

To put it simply:

if there is 1:1 conduction, the ventricular rate will be 300bpm;

if there is 2:1 conduction, the ventricular rate is 150bpm.

If there is 3:1 conduction, the ventricular rate is 100bpm.

Etc.

An atrial flutter:

Often has “sawtooth” waves.

Is a narrow-QRS-complex.

Often a tachycardia at approximately 150bpm.

Has regular R-R intervals that distinguish it from atrial fibrillation.