An electrocardiogram (ECG or EKG) is one of the simplest and fastest procedures used to evaluate the heart. Electrodes (small, plastic patches) are placed at certain locations on the chest, arms, and legs. When the electrodes are connected to an ECG machine by lead wires, the electrical activity of the heart is measured, interpreted, and printed out for the doctor's information and further interpretation.
A signal-averaged electrocardiogram is a more detailed type of ECG. During this procedure, multiple ECG tracings are obtained over a period of approximately 20 minutes evaluating several hundred cardiac cycles to detect subtle abnormalities that increase risk for cardiac arrhythmias. These subtle abnormalities are usually not detected on a plain ECG. A computer captures all the electrical signals from the heart and averages them to provide the doctor more detail regarding how the heart’s electrical conduction system is working.
Signal-averaged ECG is one of several procedures used to assess the potential for dysrhythmias or arrhythmias (irregular heart rhythms) in certain medical situations.
Other related procedures that may be used to assess the heart include resting electrocardiogram (ECG), Holter monitor, exercise electrocardiogram (ECG), cardiac catheterization, chest X-ray, computed tomography (CT scan) of the chest, echocardiography, electrophysiological studies, magnetic resonance imaging (MRI) of the heart, myocardial perfusion scans, radionuclide angiography, and cardiac CT scan. Please see these procedures for additional information.
A signal-averaged ECG is a quick, noninvasive method of assessing the heart’s function. Risks associated with ECG are minimal and rare.
Prolonged application of the adhesive electrode patches may cause tissue breakdown or skin irritation at the application site.
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Certain factors or conditions may interfere with or affect the results of the test. These include, but are not limited to, the following:
- Obesity, pregnancy or ascites (accumulation of fluid in the abdomen)
- Anatomical considerations, such as the size of the chest and the location of the heart within the chest
- Movement during the procedure
- Exercise or smoking prior to the procedure
- Certain medications
- Electrolyte abnormalities, such as too much or too little potassium, magnesium, and/or calcium in the blood
- Your doctor or the technician will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure
- Generally, fasting is not required before the test
- Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking
- Notify your doctor if you have a pacemaker
- The area(s) where the electrodes are to be placed may be shaved
- Based on your medical condition, your doctor may request other specific preparation
A signal-averaged ECG may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor’s practices.