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ECG - Low Voltage Complexes
Related Subjects: |ECG Basics |ECG Axis |ECG Analysis |ECG LAD |ECG RAD |ECG Low voltage |ECG Pathological Q waves |ECG ST/T wave changes |ECG LBBB |ECG RBBB |ECG short PR |ECG Heart Block |ECG Asystole and P wave asystole |ECG QRS complex |ECG ST segment |ECG: QT interval |ECG: LVH |ECG RVH |ECG: Bundle branch blocks |ECG Dominant R wave in V1 |ECG Acute Coronary Syndrome |ECG Crib sheets
📏 Calibration: Standard ECG calibration is 1 mV = 1 cm. ⚠️ If set incorrectly at 2 mV = 1 cm, the voltage will appear falsely halved → always check calibration before interpreting “low voltage.”
📖 Definition
- 👉 Low Voltage QRS:
- QRS height in limb leads < 5 mm
- QRS height in precordial leads < 10 mm
⚠️ Causes of Low Voltage QRS
- 🌬️ Pulmonary: Emphysema, Pneumothorax (↑ distance / insulation from chest wall)
- 💧 Pericardial Effusion (classic cause)
- 🧊 Endocrine/Metabolic: Myxoedema (severe hypothyroidism)
- 🧩 Infiltrative: Amyloidosis, Sarcoidosis, Haemochromatosis
- 🛡️ Pericardial Disease: Constrictive pericarditis, Scleroderma
- ❤️ Global ischaemia / cardiomyopathy
- ⚖️ Severe obesity (signal dampening)
- 📝 Technical error: Incorrect calibration (as above)
💡 Teaching Pearl
Low QRS voltage suggests either electrical signal dampening (fluid, fat, lung hyperinflation) or true myocardial disease (infiltration, ischaemia, cardiomyopathy). 👉 In pericardial effusion, look for the triad: low voltage, tachycardia, and electrical alternans → think impending tamponade!
📚 ECG References
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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