Monday, June 1, 2020

Electrical alternans

Q: Electrical alternans with sinus tachycardia has? (select one)

A) high specificity for pericardial effusion
B) high sensitivity for pericardial effusion

Answer: A

Electrical alternans is well known to be associated with pericardial effusion. It is defined as a cyclical beat-to-beat shift in the QRS axis in the limb and precordial leads due to mechanical swinging of the heart to-and-fro, in a large pericardial effusion. It is usually most apparent in one or more of the precordial leads. Also, it is usually accompanied by sinus tachycardia.

It has a high specificity when other clinical signs support cardiac tamponade. But it is not a sensitive sign. Its absence does not rule out cardiac tamponade.

Electrical alternans can also be observed in ventricular tachycardia, Wolff-Parkinson-White (WPW), accelerated idioventricular rhythm, and supraventricular tachycardia.



1. Goyal M, Woods KM, Atwood JE. Electrical alternans: a sign, not a diagnosis. South. Med. J. 2013 Aug;106(8):485-9. [PubMed]

2. Honasoge AP, Dubbs SB. Rapid Fire: Pericardial Effusion and Tamponade. Emerg. Med. Clin. North Am. 2018 Aug;36(3):557-565

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