An electrocardiogram (ECG) is a graphic recording of your heart's electrical activity.

Normally, electrical impulses move unimpeded throughout the heart, and play an important role in causing the heart to beat. An electrocardiogram can give your doctor considerable information about the health and functioning of your heart. Your doctor can learn about your heart rhythm, the chambers of your heart, the functioning of your heart muscle and whether you had a heart attack in the past.

A signal averaged electrocardiogram can tell your doctor if you are at risk for developing potentially lethal heart rhythms .

A signal averaged electrocardiogram is a technique which amplifies low amplitude ECG signals, and reduces random noises surrounding these signals. These signals are called, "late potentials". The ECG is filtered and parts of it are averaged, allowing identification of late potentials.

Late potentials represent delayed conduction through diseased heart muscle. Late potentials may be present in a variety of situations; a few of which are: arrhythmias (irregular heart rhythms), heart chamber abnormalities, syncope (loss of consciousness), and in scar tissue from prior heart attacks.

• Why has my doctor ordered this test for me?
• Are there any risks associated with a signal-averaged electrocardiogram?
• What preparations should I make before the test?
• What happens during the test?
• What happens after the test?
• What will my physician do with this information?

Why has my doctor ordered this test for me?
If you recently had a heart attack or have undergone open heart surgery, your doctor may want to evaluate your heart rhythms to rule out life-threatening arrhythmias.

You may have presented to your doctor with symptoms such as syncope of unknown origin and/or palpitations. The signal-averaged electrocardiogram will help your doctor determine whether further testing (e.g. electrophysiology study), is required.

Are there any risks associated with a signal-averaged electrocardiogram?
This is a safe, painless test. There are no known risks associated with the ECG, and you will not have to sign a consent form.

What preparations should I make before the test?
At the commencement of the test, you will be asked to undress from the waist up. Females should wear two-piece outfits that button or zip in the front.

What happens during the test?
After you have removed your garments, a nurse or technician will place a number of electrodes on your chest and back.

Then the nurse or technician will place the electrodes on your body. and attach the leads to the ECG machine. The electrodes are usually small, thin, gel backed and self-sticking. The gel may feel a little cool at first.

Then you will lie down for a few minutes, while the technician enters information into the ECG computer.

Next, the technician will press a button, and you will be asked to lie still. You will not feel anything. The whole test lasts from 30 to 60 minutes.

What happens after the test?
Sometimes your doctor will examine you immediately after the test. Sometimes you will get dressed and your doctor will discuss the results of the test in her office or at another time.

What will my physician do with this information?
Based on the results of the signal-averaged ECG, your history and physical examination, your doctor will determine if additional testing is necessary. She may prescribe medication for you or decide that no further action is required.