Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android

ECG Findings

  • Sinus tachycardia

  • Low voltage of QRS complex (QRS averaging < 5 mm height in limb leads or < 10 mm height in precordial leads)

  • Electrical alternans (beat-to-beat change in electrical axis and/or amplitude of the QRS complex)


  1. A physiologically significant pericardial effusion compresses the heart and affects the ability of the heart to fill properly. This causes pressure on the heart, which decreases its preload and thereby cardiac output.

  2. Pericardial effusion may be caused by pericarditis, malignancy, uremia, trauma, iatrogenic injury, aortic dissection with retrograde involvement of the pericardium, and free wall rupture after an MI.

  3. Initial treatment of physiologically significant pericardial effusion is with intravenous fluid bolus to increase preload. Emergent pericardiocentesis should be reserved for hemodynamically unstable patients. Surgical pericardial window may be considered.

  4. Electrical alternans, although “classic,” is present in less than one-third of cases. Pericardial effusion should be suspected in the setting of a sinus tachycardia and low voltage with or without electrical alternans.


Pericardial Effusion with Electrical Alternans. (ECG contributor: Kevin E. Zawacki, MD.)


Low voltage, sinus tachycardia, and electrical alternans (arrowheads) demonstrate beat-to-beat alternating QRS electrical axis and/or amplitude. Electrical alternans is often best seen in the anterior precordial leads V3 and V4.

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.