9.1
Code 9.1 — Minnesota Code 9-1: low QRS amplitude (low voltage). The QRS complexes are unusually small: the peak-to-peak amplitude is 5 mm or less in all limb leads, or 10 mm or less in all precordial leads. Low voltage means that either the heart produces weaker electrical forces, or something between the heart and the electrodes (fluid, air, fat or abnormal tissue) attenuates them.
Causes
| Mechanism | Examples |
|---|---|
| Fluid or tissue around the heart | Pericardial effusion (with fast heart rate — risk of tamponade), pleural effusion, generalised oedema |
| Air or distance | Emphysema/COPD, pneumothorax, obesity |
| Heart muscle replaced or damaged | Cardiac amyloidosis (low voltage despite thick walls), extensive infarction, dilated cardiomyopathy, myocarditis |
| Metabolic | Hypothyroidism (myxoedema) |
| Technical | Incorrect calibration (e.g. 5 mm/mV), electrode problems |
Clinical significance
Low voltage is a non-specific but important finding, especially when it is new. A combination of low voltage with a fast heart rate and breathlessness may indicate a large pericardial effusion. Low voltage together with thick ventricular walls on echocardiography is a classic clue to cardiac amyloidosis. The first steps are to check calibration and to perform echocardiography.
if low voltage is found together with breathlessness, chest pain, fast heart rate, low blood pressure or fainting.
References
- Prineas RJ, Crow RS, Zhang ZM. The Minnesota Code Manual of Electrocardiographic Findings. 2nd ed. London: Springer; 2010. doi:10.1007/978-1-84882-778-3
This article is for general information and does not replace a consultation with a doctor. ECG findings must be interpreted by a physician together with symptoms and other tests.
Published on 14 May 2019