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
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
Specific causes of low voltage include:
The most important cause is massive pericardial effusion / tamponade, which produces a triad of:
- Low voltage
- Electrical alternans
Massive Pericardial Effusion:
- Note the presence of electrical alternans.
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.
- 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
- Mattu A, Brady W. ECGs for the Emergency Physician 2, BMJ Books 2008.