Atrial Flutter

Atrial flutter is a reentrant tachycardia that typically originates in the right atrium and has a fairly predictable atrial rate around 300bpm. The ectopic pacemaker site is usually between the IVC and tricuspid isthmus. Because of this, the main variable to the rate and rhythm for atrial flutter is the AV conduction. Atrial flutter typically has between a 1:1 to a 4:1 conduction through the AV node. A 2:1 conduction, for example, is where the atria have 2 depolarizations, though only 1 is passed through the AV node to the ventricles. The AV node can also display variable conduction, causing the atrial flutter to provide an irregularly irregular rhythm. The AV node cannot usually allow conduction via a 1:1, which would indicate an accessory pathway. A 1:1 conduction is extremely dangerous and patients are often unstable as ventricular rates around 300bpm do not allow for adequate ventricular filling. Because of these factors, the rate of atrial flutter (with the exception of variable conduction) is minimally variable. One can watch the monitor for atrial flutter with 2:1 conduction with minimal variation, often differentiating it from a sinus rhythm with 2:1 conduction. The ventricular rate for 2:1 conduction is usually 130-170bpm because of this as well. The ventricular rate for 3:1 conduction is about 100bpm. 

The P waves of atrial flutter should be differentiated from those of the sinus node. One should look at the inferior leads (primarily II) and V1 to evaluate the morphology of the P waves. They should be inverted in the inferior leads (upright in sinus rhythm) and positive in V1 (usually inverted or biphasic in sinus rhythm). The classic sawtooth pattern is only seen with AV conduction at least as slow as 2:1, though often requires 3:1 or slower. It is also important to remember that there are P waves often hidden within the QRS complex or ST segment, causing some deviations from the normal in these areas (may mimic ST depression or elevation). This is particular true with 2:1 conduction, which is often misdiagnosed as sinus tachycardia (however, can be differentiated by evaluating P wave morphology already mentioned). If there is diagnostic uncertainty, one can perform vagal maneuvers or administer adenosine to provide temporary AV blocking effect that will reveal the sawtooth pattern P waves with atrial flutter.

There are multiple potential variants, though that is an in depth discussion that is not necessary for the ED provider. Atrial flutter will typically produce a narrow complex tachycardia unless there is an underlying bundle branch block, though can produce wide complexes with aberrancy otherwise (ie hyperkalemia).

Examples:

Further Reading:

https://litfl.com/atrial-flutter-ecg-library/

https://hqmeded-ecg.blogspot.com/search/label/atrial%20flutter

https://hqmeded-ecg.blogspot.com/search/label/Atrial%20Flutter%20that%20is%20Very%20Slow