Health Encyclopedia

Electrocardiogram

Definition

An electrocardiogram (ECG) is a test that records the electrical activity of the heart.

Alternative Names

ECG; EKG

How the test is performed

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 electrodes stick to the skin.

The number of patches used may vary.

You usually need to remain still, and you may be asked to hold your breath for short periods during the procedure. It is important to be relaxed and relatively warm during ECG recording. Any movement, including muscle tremors such as shivering, can alter the results.

The electrodes are connected by wires to a machine that converts the electrical signals from the heart into wavy lines, which are printed on paper and reviewed by the doctor.

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.

Watch this video about:
Electrocardiogram (ECG) - interactive tool

How to prepare for the 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.

How the test will feel

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.

Why the test is performed

An ECG is used to measure:

Any damage to the heart
How fast your heart is beating and whether it is beating normally
The effects of drugs or devices used to control the heart (such as a pacemaker)
The size and position of your heart chambers

An ECG is a very useful tool for determining whether a person has heart disease. Your doctor may order this test if you have chest pain or palpitations.

An ECG may be included as part of a routine examination in patients over age 40.

Normal Values

Heart rate: 50 to 100 beats per minute
Heart rhythm: consistent and even

What abnormal results mean

Abnormal ECG results may be a sign of

Abnormal heart rhythms (arrhythmias)
Cardiac muscle defect
Congenital heart defect
Coronary artery disease
Ectopic heartbeat
Enlargement of the heart
Faster-than-normal heart rate (tachycardia)
Heart valve disease
Inflammation of the heart (myocarditis)
Changes in the amount of electrolytes (chemicals in the blood)
Past heart attack
Present or impending heart attack
Slower-than-normal heart rate (bradycardia)

Additional conditions under which the test may be performed include the following:

Alcoholic cardiomyopathy
Anorexia nervosa
Aortic dissection
Aortic insufficiency
Aortic stenosis
Atrial fibrillation/flutter
Atrial myxoma
Atrial septal defect
Cardiac tamponade
Coarctation of the aorta
Complicated alcohol abstinence (delirium tremens)
Coronary artery spasm
Digitalis toxicity
Dilated cardiomyopathy
Drug-induced lupus erythematosus
Familial periodic paralysis
Guillain-Barre
Heart failure
Hyperkalemia
Hypertensive heart disease
Hypertrophic cardiomyopathy
Hypoparathyroidism
Idiopathic cardiomyopathy
Infective endocarditis
Insomnia
Ischemic cardiomyopathy
Left-sided heart failure
Lyme disease
Mitral regurgitation; acute
Mitral regurgitation; chronic
Mitral stenosis
Mitral valve prolapse
Multifocal atrial tachycardia
Narcolepsy
Obstructive sleep apnea
Paroxysmal supraventricular tachycardia
Patent ductus arteriosus
Pericarditis
- Bacterial pericarditis
- Constrictive pericarditis
- Post-MI pericarditis
Peripartum cardiomyopathy
Primary amyloid
Primary hyperaldosteronism
Primary hyperparathyroidism
Primary pulmonary hypertension
Pulmonary embolus
Pulmonary valve stenosis
Restrictive cardiomyopathy
Right-sided heart failure
Sick sinus syndrome
Stable angina
Stroke
Systemic lupus erythematosus
Tetralogy of Fallot
Thyrotoxic periodic paralysis
Transient ischemic attack (TIA)
Transposition of the great vessels
Tricuspid regurgitation
Type 1 diabetes
Type 2 diabetes
Unstable angina
Ventricular septal defect
Ventricular tachycardia
Wolff-Parkinson-White syndrome

What the risks are

There are no risks. No electricity is sent through the body, so there is no risk of shock.

Special considerations

The accuracy of the ECG depends on the condition being tested. Some heart conditions are not detectable all the time, and others may never produce any specific ECG changes.

A person who has had a heart attack or who may have heart disease may need more than one ECG. There is no reason for healthy people to have yearly routine testing unless they have a family or person history of specific heart diseases or other medical conditions.

References

Ganz L, Curtiss E. Electrocardiography. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 52.

Review Date:5/2/2009
Reviewed By:David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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