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- Reviewed by Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing
What is it?
An electrocardiogram (EKG) is a painless process that records the heart's electrical activity. Small metal electrodes are placed on the person's wrists, ankles and chest. The electrical signals travel from the electrodes through wires to the EKG machine, which transforms the signals into patterns or waves. Different waves represent different areas of your heart through which electrical currents flow. The electrical currents stimulate the heart muscles to contract and relax. The P wave represents the current in the upper chambers of the heart (atria); the QRS complex represents current in the lower heart chambers (ventricles); and the T wave represents the heart's brief "rest period" as it recharges electrically (repolarizes) between heartbeats.
EKG waves are recorded on paper as they move through the EKG machine, showing the heart rate and heart rhythm. The appearance of the wave patterns can give important clues about damage to the heart muscle or irritation of the membrane around the heart (pericardium).
In most cases, a basic EKG takes about 5 to 10 minutes. It can be done in a doctor's office, in a laboratory or in a hospital.
What it's used for
An EKG can be used to evaluate someone with chest pain, people who may be having a heart attack, and those suspected of having coronary artery disease or a cardiac arrhythmia. It also can help to diagnose an inflammation of the membrane around the heart (pericarditis), a blood clot blocking blood flow in a lung (pulmonary embolism), abnormal blood levels of potassium or calcium, or overdoses of certain medications.
An EKG sometimes is used as part of a regular physical examination or as a screening test in people at high risk of heart problems, including people with high blood pressure (hypertension), high cholesterol, diabetes, a strong family history of heart problems, and people who smoke. The EKG sometimes will suggest that a person has coronary artery disease even if there are no symptoms.
During surgery, an EKG tracing helps to monitor the functioning of the person's heart.
In most cases, no special preparation is necessary. However, if you are taking any medications, tell the EKG technician about these drugs beforehand. This is because certain medicines have effects on the heart that can influence an EKG.
You will be asked to remove any bracelets and long necklaces during your EKG. Also, it is helpful to wear a shirt that can be unbuttoned easily.
How it's done
You will need to expose the skin above your ankles, wrists and chest. If you need to undress, you will be given a gown. You will lie on an examination table. An EKG technician will clean portions of your arms, legs and chest to remove excess skin oils and sweat. In certain men, a small area of chest hair may need to be shaved.
Next, about 10 small metal electrodes will be attached with sticky pads to various parts of your body, including one on each arm and leg, six across the left side of the chest and, at times, one or more at other sites on the chest, neck and back.
Once the electrodes are attached, you only need to relax as your EKG is recorded. You won't feel anything. Breathe normally, avoid talking and don't make any unnecessary motions. When your EKG is done, the technician will remove the electrodes and you will be allowed to dress. Ask the technician if you need to speak with your doctor before you leave.
Depending on why your doctor ordered the EKG, he or she may ask to see it immediately. If the EKG is part of a routine physical or preoperative evaluation, then ask the technician whether your doctor will notify you of the result, or whether you will need to call the doctor's office.
An EKG is considered a safe, routine diagnostic procedure, with no harmful side effects.
When to call a professional
Because harmful side effects are not expected, people typically need to call their doctors only for EKG results.
National Heart, Lung, and Blood Institute (NHLBI)
American Heart Association (AHA)
About the Reviewer
Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of last review or update on all articles.
No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.
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