Electrical Alternans (Massive Pericardial Effusion)

• Electrical alternans is when consecutive QRS complexes alternate in height.
• The most important cause is massive pericardial effusion, in which the alternating QRS voltage is produced by the heart swinging backwards and forwards within a large fluid-filled pericardium.

Massive pericardial effusion (tamponade) produces a triad of:

• Low voltage
• Tachycardia
• Electrical alternans

• Electrical alternans secondary to massive pericardial effusion

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits

References

• Chan TC, Brady WJ, Harrigan RA, Ornato JP and Rosen PR. ECG in Emergency Medicine and Acute Care. Elsevier 2005
• Mattu A, Brady W. ECGs for the Emergency Physician 2, BMJ Books 2008.