Low QRS Voltage

Diagnostic criteria

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
ECG low QRS voltage
Low voltage QRS: QRS amplitude < 5mm in limb leads

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

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

  • Low voltage
  • Tachycardia
  • Electrical alternans

Patients with this triad need to be immediately assessed for clinical or echocardiographic evidence of tamponade.

Other causes of low voltage include:

ECG Examples
Example 1

Massive Pericardial Effusion:

Example 2
Low voltage in V1-6 due to prior massive anterior MI

Prior Massive Anterior MI:

  • Low QRS voltage in V1-6. This diffuse loss of R wave height suggests extensive myocardial loss from a prior anterior MI.
  • There is also biphasic anterior T waves (Wellens syndrome) indicating new critical occlusion of the LAD artery

Example 3
Pulmonary disease pattern COPD ECG 2


  • Low voltages in the limb leads is classically seen in patients with emphysema.
  • Other assocaited ECG features of emphysema include:
    • Right axis deivation
    • Peaked P waves (P pulmonale)
    • Clockwise rotation (persistent S wave in V6)


Advanced Reading



LITFL Further Reading


Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

One comment

  1. Regarding ECG #2, can we diagnose Wellens when there is q waves and loss of R wave progression?

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