Low QRS Voltage

Diagnostic criteria

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

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:

• Fluid: Pericardial effusion; Pleural effusion
• Fat: Obesity
• Air: Emphysema; Pneumothorax
• Infiltrative / Connective Tissue Disorders
  • Myxoedema
  • Infiltrative myocardial diseases — i.e. restrictive cardiomyopathy due to amyloidosis, sarcoidosis, haemochromatosis
  • Constrictive pericarditis
  • Scleroderma
• Loss of viable myocardium:
  • Previous massive MI
  • End-stage dilated cardiomyopathy

ECG Examples

Example 1

Massive Pericardial Effusion:

• Characteristc triad of tachycardia, low voltage QRS and electrical alternans

Example 2

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

Emphysema:

• 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)

Related Topics

• Pericardial tamponade
• Hypothyroidism

References

• Ultrasound Podcast – How to diagnose pericardial tamponade on bedside echo, Part 1 and Part 2 (video lessons)
• Dr Smith’s ECG Blog – Differential diagnosis of low QRS voltage (case discussion)

Advanced Reading

Online

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
• Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
• Hampton J, Adlam D. The ECG Made Practical 7e, 2019
• Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
• Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
• Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
• Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004

LITFL Further Reading

• ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
• ECG A to Z by diagnosis – ECG interpretation in clinical context
• ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
• 100 ECG Quiz – Self-assessment tool for examination practice
• ECG Reference SITES and BOOKS – the best of the rest