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
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
- 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
- Infiltrative myocardial diseases — i.e. restrictive cardiomyopathy due to amyloidosis, sarcoidosis, haemochromatosis
- Constrictive pericarditis
- Loss of viable myocardium: Previous massive MI; End-stage dilated cardiomyopathy
Massive Pericardial Effusion:
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.
- 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)
- 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)
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
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e