Low Voltage


Low voltage can be due to an intrinsic decrease in the myocardium responsible for generating the electrical energy making up the ECG or due to fluid or air in between the heart and the electrodes. Intrinsic problems will not be acute but due to chronic processes such as infiltrative processes including amyloid heart disease, any cardiomyopathy (including hypo or hyperthyroidism, beriberi heart disease, alcoholic and ischemic), obesity or cardiac transplant rejection. Decreased voltage due to hyper-inflation of the lungs or pneumothorax can be acute or chronic due to COPD. Increased fluid can be due to pleural effusion or pericardial effusion. Decreased voltage is frequently seen after open-heart surgery.


Low Voltage a new finding: If the low voltage is an acute change the first step is to correlate with the patients symptoms and check the systolic blood pressure. Check for pulsus paradoxus and a narrow pulse pressure. If the systolic blood pressure is low (< 100 mmHg) consider cardiac tamponade which could require emergency treatment with pericardiocentesis. An acute drop in QRS voltage could also be due to an exacerbation of COPD requiring intensive therapy. It can be a normal finding after open-heart surgery.

Low Voltage present on prior ECGs: While physical examination can help distinguish the causes of a chronic decrease in voltage usually an echocardiogram will be more definitive and is indicated. Thyroid and pulmonary function testing should be considered.

View an ECG Example