Critical Care Trauma Centre


Question of the Week: January 21, 2000

Describe the significant finding on the following arterial pressure waveform?



Electrical Alternans.


  • Regular ECG rhythm.
  • Alternating QRS complexes have decreased voltage or flipped axis.
  • Alternating QRSs can be evident in one or multiple leads.
Generally caused by severe left ventricular failure or pericardial effusion.  The electrical equivalent of pulsus alternans.

Triad of Percardial Effusion

  • ST elevation
  • pulsus alternans
  • low voltage QRS


Marriott, H. (1977).  Practical Electrocardiography (7th Ed.)  Williams and Wilkins: Toronto. p. 465, 471-2.

Brenda Morgan
Clinical Educator, CCTC
January 21, 2000
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