Low QRS Voltage

Low QRS Voltage Overview

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 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.
  • This ECG also demonstrates biphasic anterior T waves (Wellens syndrome) indicating new critical occlusion of the LAD artery.

Example 3
Pulmonary disease pattern


  • Low voltages in the limb leads is classically seen in patients with emphysema.
  • Other features of emphysema include: rightward axis, peaked P waves (P pulmonale) and clockwise rotation (persistent S wave in V6)

Related Topics


LITFL Further Reading

Advanced Reading




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

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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