What Is an Electrocardiogram?
An electrocardiogram (e-lek-tro-KAR-de-o-gram), or
EKG, is a simple, painless test that records the hearts electrical
activity. To understand this test, it helps to understand how the heart
works.
With each heartbeat, an electrical signal spreads
from the top of the heart to the bottom. As it travels, the signal causes the
heart to contract and pump blood. The process repeats with each new heartbeat.
The hearts electrical signals set the rhythm of the heartbeat.
For more detailed information, see the Diseases and
Conditions Index article on
How
the Heart Works.
An EKG shows:
- How fast your heart is beating
- Whether the rhythm of your heartbeat is steady or
irregular
- The strength and timing of electrical signals as
they pass through each part of your heart
This test is used to detect and evaluate many heart
problems, such as
heart
attack,
arrhythmia
(ah-RITH-me-ah), and
heart
failure. EKG results also can suggest other disorders that affect heart
function.
EKGs also are used to monitor how the heart is
working. This article focuses on how EKGs are used for testing
purposes.
Other Names for Electrocardiogram
An electrocardiogram also is called EKG or ECG.
Sometimes the test is called a 12-lead EKG or 12-lead ECG because the
electrical activity of the heart is most often recorded from 12 different
places on the body at the same time.
Who Needs an Electrocardiogram?
Your doctor may recommend an electrocardiogram (EKG)
if you have signs or symptoms that suggest a heart problem. Examples of such
signs and symptoms include:
- Chest pain
- Heart pounding, racing, or fluttering, or the
sense that your heart is beating unevenly
- Problems breathing
- Feeling tired and weak
- Unusual heart sounds when your doctor listens to
your heartbeat
You may need to have more than one EKG so your
doctor can diagnose certain heart conditions.
An EKG may be done as part of a routine health exam.
The test can screen for early heart disease that has no symptoms. Your doctor
is more likely to look for early heart disease if your mother, father, brother,
or sister had heart diseaseespecially if it developed early.
You may have an EKG so your doctor can check how
well heart medicine or a medical device, such as a
pacemaker,
is working. The test also may be used for routine screening before major
surgery.
Your doctor may use EKG results to help plan your
treatment for a heart condition.
What To Expect Before an Electrocardiogram
No special preparation is needed for an
electrocardiogram (EKG). Before the test, let your doctor or doctors
office know what medicines youre taking. Some medicines can affect EKG
results.
What Happens During an Electrocardiogram?
An electrocardiogram (EKG) is painless and harmless.
A technician attaches soft, sticky patches called electrodes to the skin of
your chest, arms, and legs. The patches are about the size of a quarter.
Typically, 12 patches are attached to detect your
hearts electrical activity from many angles. To help the patches stick,
the technician may have to shave areas of your skin.
After the patches are placed on your skin, you lie
still on a table while the patches detect your hearts electrical signals.
A machine records these signals on graph paper or displays them on a
screen.
The entire test takes about 10 minutes.
EKG
The illustration shows the standard
setup for an EKG. In figure A, a normal heart rhythm recording shows the
electrical pattern of a regular heartbeat. In figure B, a patient lies in a bed
with EKG electrodes attached to his chest, upper arms, and legs. A nurse
watches the painless procedure.
Special Types of Electrocardiogram
The standard EKG described above, called a resting
12-lead EKG, records only seconds of heart activity at a time. It will show a
heart problem only if the problem is present during the time that the test is
run.
Many heart problems are present all the time, and a
resting 12-lead EKG will detect them. But some heart problems, like those
related to an irregular heartbeat, can come and go. They may occur for only a
few minutes out of the day or only while you exercise.
Special EKGs, such as stress tests and Holter and
event monitors, are used to help diagnose these kinds of problems.
Stress Test
Some heart problems are easier to diagnose when your
heart is working hard and beating fast. During stress testing, you exercise to
make your heart work hard and beat fast while your hearts electrical
activity is recorded. If youre not able to exercise, youre given
medicine to make your heart work hard and beat fast.
For more information, see the Diseases and
Conditions Index article on
Stress
Testing.
Holter and Event Monitors
Holter and event monitors are small, portable
devices. They record your heart’s activity while you do your normal daily
activities. A Holter monitor records the heart’s electrical activity for
a full 24-hour period or longer.
An event monitor only records your heart’s
electrical activity at certain times while you’re wearing it. For many
event monitors, you push a button to start the monitor when you feel symptoms.
Other event monitors start automatically when they sense abnormal heart
rhythms.
For more information, see the Diseases and
Conditions Index article on
Holter
and Event Monitors.
What To Expect After an Electrocardiogram
After an electrocardiogram (EKG), the electrodes
(soft patches) are removed from your skin. You may get a rash or redness where
the EKG patches were attached. This mild rash usually goes away without
treatment.
You usually can go back to your normal daily routine
after an EKG.
What Does an Electrocardiogram Show?
Many heart problems change the hearts
electrical activity in distinct ways. An electrocardiogram (EKG) can help
detect a number of heart problems.
EKG recordings can help doctors diagnose a
heart
attack that’s happening now or has happened in the past. This is
especially true if doctors can compare a current EKG recording to an older
one.
An EKG also can show:
- Lack of blood flow to the heart muscle
- A heart that’s beating too fast, too slow,
or with an irregular rhythm (arrhythmia)
- A heart that doesn’t pump forcefully enough
(heart
failure)
- Heart muscle thats too thick or parts of
the heart that are too big
- Birth defects in the heart (congenital
heart defects)
- Problems with the heart valves (heart
valve disease)
- Inflammation of the sac that surrounds the heart
(pericarditis)
An EKG also can reveal whether the heartbeat starts
at the top right part of the heart like it should. The test shows how long it
takes for the electrical signals to travel through the heart. Delays in signal
travel time may suggest
heart
block or
long
QT syndrome.
What Are the Risks of an Electrocardiogram?
An electrocardiogram (EKG) has no serious risks.
Its a harmless, painless test that detects the hearts electrical
activity. EKGs dont give off electrical charges, such as shocks.
You may have a mild rash where the electrodes (soft
patches) were attached. This rash usually goes away without treatment.
Key Points
- An electrocardiogram (EKG) is a simple, painless
test that records the hearts electrical activity.
- An EKG shows:
- How fast your heart is beating
- Whether the rhythm of your heart is steady or
irregular
- The strength and timing of electrical signals
as they pass through each part of your heart
- EKGs are used to detect and evaluate many heart
problems, such as
heart
attack,
arrhythmia,
and heart
failure.
- Your doctor may recommend an EKG if you have
signs or symptoms that suggest a heart problem. An EKG also may be done as part
of a routine health exam, to check how medicine or a medical device is working,
or for routine screening before major surgery. Your doctor may use EKG results
to help plan your treatment for a heart condition.
- No special preparation is needed for an EKG.
Before the test, let your doctor or doctor’s office know what medicines
you’re taking. Some medicines can affect EKG results.
- For an EKG, soft, sticky patches called
electrodes are attached to the skin of your chest, arms, and legs. You lie
still on a table while the patches detect your heart’s electrical
signals. A machine records these signals on graph paper or displays them on a
screen. The entire test takes about 10 minutes.
- If you have a heart problem that isn’t
present all of the time, you may need a special type of EKG, such as a
stress
test or
Holter
or event monitor.
- You usually can go back to your normal daily
routine after an EKG.
- Many heart problems change the heart’s
electrical activity in distinct ways. An EKG can help detect a number of heart
problems. Results from an EKG can suggest problems such as lack of blood flow
to the heart muscle, problems with heart rhythm or the heart’s pumping
action, birth defects, problems with heart muscle or heart valves, and
inflammation of the heart.
- An EKG has no serious risks. EKGs don’t
give off electrical charges, such as shocks. You may have a mild rash where the
electrodes were attached. This rash usually goes away without treatment.
Links to Other Information About Electrocardiogram
NHLBI Resources
Non-NHLBI Resources
Clinical Trials
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