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.
The heart is, in the simplest terms, a pump made up of muscle tissue.
The heart's pumping action is regulated by an electrical conduction
system that coordinates the contraction of the various chambers of the
[Illustration of the electrical system of the heart]An electrical
stimulus is generated by the sinus node (also called the sinoatrial
node, or SA node), which is a small mass of specialized tissue located
in the right atrium (right upper chamber) of the heart.
The sinus node generates an electrical stimulus regularly at 60 to 100
times per minute under normal conditions. This electrical stimulus
travels down through the conduction pathways (similar to the way
electricity flows through power lines from the power plant to your
house) and causes the heart's lower chambers to contract and pump out
blood. The right and left atria (the two upper chambers of the heart)
are stimulated first and contract a short period of time before the
right and left ventricles (the two lower chambers of the heart).
The electrical impulse travels from the sinus node to the
atrioventricular node (also called AV node), where impulses are slowed
down for a very short period, then continue down the conduction pathway
via the bundle of His into the ventricles. The bundle of His divides
into right and left pathways to provide electrical stimulation to the
right and left ventricles.
This electrical activity of the heart is measured by an
electrocardiogram. By placing electrodes at specific locations on the
body (chest, arms, and legs), a graphic representation, or tracing, of
the electrical activity can be obtained. Changes in an EKG from the
normal tracing can indicate one or more of several heart-related
Reasons your doctor may request a signal-averaged ECG may include, but
are not limited to, the following:
To assess risk for potentially fatal heart arrhythmias in
patients with known heart disease including coronary artery
disease, heart failure or after a heart attack
To evaluate other signs and symptoms which may be heart-related,
such as fatigue, shortness of breath, dizziness or fainting
To help identify irregularities in heartbeats that can lead to
sudden cardiac death in patients at risk, such as those with
hypertrophic cardiomyopathy (an abnormal thickening of heart
For further evaluation of dysrhythmias or arrhythmias noted on
There may be other reasons for your doctor to recommend a
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
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
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
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.
Generally, a signal-averaged ECG follows this process:
You will be asked to remove any jewelry or other objects that
may interfere with the procedure.
You will be asked to remove clothing from the waist up. The
technician will ensure your privacy by covering you with a sheet
or gown and exposing only the necessary skin.
You will lie flat on a table or bed for the procedure. It will
be important for you to lie still and not talk during the
procedure, so as not to interfere with the tracing.
If your chest is very hairy, the technician may shave small
patches of hair, as needed, so that the electrodes will stick
closely to the skin.
Electrodes will be attached to your chest, abdomen, and back.
The lead wires will be attached to the skin electrodes.
Once the leads are attached, the technician may key in
identifying information about you into the machine's computer.
The EKG will be started. Generally, it will take about 20
minutes to obtain the necessary ECG information.
Once the tracing is completed, the technician will disconnect
the leads and remove the skin electrodes.
You should be able to resume your normal diet and activities, unless
your doctor instructs you differently.
Generally, there is no special care following a signal-averaged ECG.
Notify your doctor if you develop any signs or symptoms you had prior to
the test (for example, chest pain, shortness of breath, dizziness, or
Your doctor may give you additional or alternate instructions after the
procedure, depending on your particular situation.
The content provided here is for informational purposes only, and was
not designed to diagnose or treat a health problem or disease, or
replace the professional medical advice you receive from your physician.
Please consult your physician with any questions or concerns you may
have regarding your condition.
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procedure and related health conditions. We hope you find these sites
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