An electrocardiogram (ECG) is a test that records the electrical activity of the heart.
You will be asked to lie down. The health care provider will clean several areas on your arms, legs, and chest, and then attach small patches called electrodes to the areas. It may be necessary to shave or clip some hair so the patches stick to the skin. The number of patches used may vary.
The patches are connected by wires to a machine that turns the heart's electrical signals into wavy lines, which are often printed on paper. The test results are reviewed by the doctor.
You usually need to remain still during the procedure. The health care provider may also ask you to hold your breath for a few seconds as the test is being done. Any movement, including muscle tremors such as shivering, can alter the results. So it is important to be relaxed and relatively warm during an ECG recording.
Sometimes this test is done while you are exercising or under minimal stress to monitor changes in the heart. This type of ECG is often called a stress test.
Make sure your health care provider knows about all the medications you are taking, as some can interfere with test results.
Exercising or drinking cold water immediately before an ECG may cause false results.
An ECG is painless. No electricity is sent through the body. The electrodes may feel cold when first applied. In rare cases, some people may develop a rash or irritation where the patches were placed.
An ECG is used to measure:
An ECG is usually the first test done to determine whether a person has heart disease. Your doctor may order this test if:
There is no reason for healthy people to have yearly ECG tests.
Abnormal ECG results may be a sign of
Some heart problems that can lead to changes on an ECG test include:
There are no risks. No electricity is sent through the body, so there is no risk of shock.
The accuracy of the ECG depends on the condition being tested. A heart problem may not always show up on the ECG. Some heart conditions never produce any specific ECG changes.
Ganz L. Electrocardiography. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 54.