Electrocardiogram

Test Overview

An electrocardiogram (EKG or ECG) is a test that checks for problems with the electrical activity of your heart. An EKG shows the heart's electrical activity as line tracings on paper. The spikes and dips in the tracings are called waves.

The heart is a muscular pump made up of four chambers. The two upper chambers are called atria. The two lower chambers are called ventricles. A natural electrical system causes the heart muscle to contract. This pumps blood through the heart to the lungs and the rest of the body.

Why It Is Done

An EKG is done to:

Check the heart's electrical activity.
Find the cause of unexplained chest pain or pressure. This could be caused by a heart attack, inflammation of the sac surrounding the heart (pericarditis), or angina.
Find the cause of symptoms of heart disease. Symptoms include shortness of breath, dizziness, fainting, and heartbeats that are rapid and irregular (palpitations).
Find out if the walls of the heart chambers are too thick.
Check how well medicines are working and see if they are causing side effects that affect the heart.
Check how well mechanical devices that are implanted in the heart, such as pacemakers, are working. These devices help to control the heartbeat.
Check the health of the heart when other diseases or conditions are present. These include high blood pressure, high cholesterol, cigarette smoking, diabetes, and a family history of early heart disease.

How To Prepare

Be sure to tell your doctor about all the medicines you take, even over-the-counter ones. Many medicines can change the results of this test.

Remove all jewellery from your neck, arms, and wrists. Men are usually bare-chested during the test. Women may often wear a bra, T-shirt, or gown. You will be given a cloth or paper covering to use during the test.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .

How It Is Done

You may get an EKG at your health professional's office or during a series of tests at a hospital or clinic. EKG equipment is often portable. This means the test can be done almost anywhere. If you are in the hospital, your heart may be constantly monitored by an EKG system.

During an EKG:

You will lie on a bed or table. Certain areas of your arms, legs, and chest will be cleaned and may be shaved. This provides a clean, smooth surface to attach the electrodes.
Several electrodes are attached to the skin on each arm and leg and on your chest. These are hooked to a machine that traces your heart activity onto a paper. If an older machine is used, the electrodes may be moved at different times during the test. This measures your heart's electrical activity from different places on your chest.
You will be asked to lie very still and breathe normally during the test. Sometimes you may be asked to hold your breath. You should not talk during the test.
After the test, the electrode paste is wiped off.

The test usually takes 5 to 10 minutes.

How It Feels

The electrodes may feel cool when they are put on your chest. If you have a lot of hair on your chest, a small area may need to be shaved to put the electrodes on. When the electrodes are taken off, they may pull your skin a little.

Risks

An EKG is a completely safe test. In most cases, there is no reason why you should not be able to get an EKG.

The electrodes are used to transfer an image of your heart's electrical activity to the tracing on paper. No electricity passes through your body from the machine, and there is no danger of electrical shock.

Results

Your doctor will look at the pattern of spikes and dips on your EKG to check the electrical activity in different parts of your heart. The spikes and dips are grouped into different sections that show how your heart is working.

Electrocardiogram (EKG or ECG) results
Normal:	The heart beats in a regular rhythm, usually between 60 and 100 beats per minute.
	The tracing looks normal.
Abnormal:	The heart beats too slow (such as less than 60 beats per minute). The heart beats too fast (such as more than 100 beats per minute). The heart rhythm is not regular.
	The tracing does not look normal.

Sometimes your EKG may look normal even when you have heart disease. For this reason, the EKG should always be looked at along with your symptoms, past health, and a physical examination.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if:

The electrodes are not securely attached to your skin.
You move or talk during the test.
You exercise before the test.
You are anxious or breathe very deeply or rapidly during the test.

What To Think About

An EKG cannot predict whether you will have a heart attack.
At first, an EKG done during a heart attack may look normal or unchanged from a previous EKG. So the EKG may be repeated over several hours and days to look for changes. These are called serial EKGs.
Sometimes abnormal EKG results can be seen only during exercise or while you have symptoms. To check for these changes in the heartbeat, an ambulatory EKG or stress EKG may be done.
- An ambulatory EKG is a type of portable, continuous EKG monitor. To learn more, see the topic Ambulatory Electrocardiogram.
- A stress EKG is a type of EKG done during exercise. A resting EKG is always done before an exercise EKG test. Results of the resting EKG are compared to the results of the exercise EKG. A resting EKG may also show a heart problem that would make an exercise EKG unsafe. To learn more, see the topic Exercise Electrocardiogram.
EKGs are not usually recommended for people who are healthy and have no symptoms of heart disease.
If your doctor recommends a test, ask what it is for and why you need it. You can help decide if a test is right for you. Talk with your doctor to make that decision. To learn more, see Heart Tests: When Do You Need Them?

References

Other Works Consulted

Chernecky CC, Berger BJ (2013). Laboratory Tests and Diagnostic Procedures, 6th ed. St. Louis: Saunders.

Chou R, et al. (2011). Screening asymptomatic adults with resting or exercise electrocardiography: A review of the evidence for the U.S. Preventive Services Task Force. Annals of Internal Medicine, 155(6): 375–385.

Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.

U.S. Preventive Services Task Force (2012). Screening for coronary heart disease with electrocardiography: Recommendation statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf/uspsacad.htm.

Credits

Current as of: August 31, 2020

Author: Healthwise Staff
Medical Review: Rakesh K. Pai MD, FACC - Cardiology, Electrophysiology
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine
George Philippides MD - Cardiology