The 5-minute EKG was presented by our fan-favorite attending, Dr. Patwari. See EKG below (Answer to follow). You’re handed this EKG from triage.
As always, it is important to approach an EKG in a systematic way including rate, rhythm, axis, intervals, and segments. However, the big takeaway from this EKG is that it is a Regular Narrow-Complex Tachycardia with HR roughly 150. Now we just need to decide which type of Regular Narrow-Complex Tachycardia. This should lead us to a differential including Sinus Tachycardia, SVT (AVNRT vs. AVRT), and Atrial Flutter. You could also consider Atrial Ectopic Tachycardia (more commonly seen in peds), however, it is a rarer diagnosis compared to above.
Drumroll… This is Atrial Flutter. Clues to this are the saw-tooth appearance caused by the flutter waves, HR of roughly 150, and P waves that march out at a rate of roughly 300.
Atrial Flutter Basics
— Type of supraventricular tachycardia caused by re-entry circuit within the right atrium
— Since it originates from the atria, the heart rate will resemble the atrial rate, most often ~150 bpm (though there can be variability person-to-person with average range 130-170)
— The AV node acts as the electrical gateway between the atria and ventricle, and has long refractory period allowing it to “block” excessive depolarizations from the atria
— This most often leads to a 2:1 AV ratio block meaning for every two P waves produced, a QRS will form (as seen above) which often produces a ventricular rate (QRS) of HR roughly 150.
— If there is a higher-degree block (e.g. from medications or underlying heart disease), you can see a 3:1 or 4:1 block, which corresponds to the number of P waves prior to the QRS. This also gives a much better “saw-tooth” appearance which we remember from our Med School rhythm strips seen in FirstAid (as below)
— If we confused the first EKG with SVT, and gave adenosine (AV nodal blocking agent), we would see the continuation of flutter waves, but no QRS depolarizations due to the AV nodal blocking properties of adenosine (seen in EKG below). The good news is that adenosine only lasts 10-15 seconds, and ventricular contractions will continue thereafter. The same is true for vagal maneuvers which may transiently unmask the flutter waves (though more commonly will cause no changes)
Pitfalls of Diagnosing Atrial Flutter
— The rate isn’t always exactly 150. If the rate is slower (e.g. HR 125-140, it can resemble Sinus Tachycardia. Therefore, in any regular narrow-complex tachycardia with HR 130-170, it is important to consider atrial flutter. Also Atrial flutter patients are often stable, and therefore, there is time to work up the EKG
— If the rate is faster (e.g HR 160-175), it can resemble SVT as P waves become buried in the frequent QRS complexes. Of note, SVT typically presents with HR 170-250. You can attempt vagal maneuvers to either convert to NSR or cause unmasking of flutter waves. Adenosine can also unmask the underlying flutter.
Treatment of Atrial Flutter
— Treatment options to be discussed in more detail in a following conference. But briefly, the options include cardioversion, rate-control and +/- anticoagulation. Treatment is very similar to Atrial Fibrillation. Of note, atrial flutter is very sensitive to cardioversion often only requiring 50-100 J.