Published February 2021
Maranda Herner, MD
Expert review – pending
Objectives
Identify the key ECG findings for ectopic atrial tachycardia (AT) and use three key features to distinguish it from other supraventricular tachycardias (SVTs).
Teaching Instructions
Plan to spend 5-15 minutes familiarizing yourself with the ECG and relevant background information. Have the image pulled up on the presenting screen or monitor. Have one learner provide a systematic interpretation of the ECG. If they do not do so on their own, prompt them to point out the distinguishing characteristics (abrupt, ectopic P wave) of this SVT. Then ask them to commit to a specific diagnosis. Advance through the animations to highlight the abnormalities and final diagnosis.
Official ECG Read: Atrial tachycardia, originating at an ectopic focus that is near the SA node (note the upright p axis in II but not III compared to the native sinus p wave earlier and how the ectopic p wave of AT begins before the T wave has finished)
Clinical Diagnosis: Associated with atrial scarring (post-procedural), high catecholamine load, digoxin toxicity, congenital abnormalities, and idiopathic
Teaching: Atrial tachycardia (AT) is due to increased automaticity at an ectopic atrial focus other than the SA node. AT may be difficult to differentiate from ST/flutter/AVRT/AVNRT at high HRs, but can be distinguished by the abrupt onset and non-sinus p wave that precedes the QRS. The closer the ectopic focus is to the SA node, the more it looks like the native p wave, so an abrupt, rather than gradual, onset is key to differentiating the two.
ECG
Take Home Point
- Atrial tachycardia (AT) is due to increased automaticity at an ectopic atrial focus other than the SA node
- AT can be differentiated from ST/flutter/AVRT/AVNRT by the abrupt onset of a non-sinus p wave before the QRS.
- The closer the ectopic focus is to the SA node, the more it looks like the native sinus p wave, so abrupt onset is key to differentiating the two.
References
Goldberger, A. L., Shvilkin, A., Goldberger, Z. D. (2017). Clinical Electrocardiography: A Simplified Approach E-Book. United States: Elsevier Health Sciences.
