Low QRS Voltage

Definition

The QRS is said to be low voltage when:

• The amplitudes of all the QRS complexes in the limb leads are < 5 mm; or
• The amplitudes of all the QRS complexes in the precordial leads are  < 10 mm

Mechanisms

Low voltage is produced by:

• The “damping” effect of increased layers of fluid, fat or air between the heart and the recording electrode
• Loss of viable myocardium
• Diffuse infiltration or myxoedematous involvement of the heart

Causes

Specific causes of low voltage include:

• Pericardial effusion
• Pleural effusion
• Obesity
• Emphysema
• Pneumothorax
• Contrictive pericarditidis
• Previous massive MI
• End-stage dilated cardiomyopathy
• Infiltrative myocardial diseases — i.e. restrictive cardiomyopathy due to amyloidosis, sarcoidosis, haemochromatosis
• Scleroderma
• Myxoedema

The most important cause is massive pericardial effusion / tamponade, which produces a triad of:

• Low voltage
• Tachycardia
• Electrical alternans

ECG Examples

Example 1

Massive Pericardial Effusion:

• Note the presence of electrical alternans.

 

Example 2

Prior Massive Anterior MI:

• Low QRS voltage in V1-6.
• This ECG also demonstrates biphasic anterior T waves (Wellen’s syndrome) indicating acute anterior ischaemia.

 

Related Topics

• Pericardial tamponade
• Hypothyroidism

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 Exam Template — a framework for the FACEM part 2 exam.
• ECG Reference Sites on the WEB — the best of the rest

Author Credits

References

• Mattu A, Brady W. ECGs for the Emergency Physician 2, BMJ Books 2008.