Electrocardiogram
(ECG,
EKG, Resting ECG, Resting EKG)
What
is an electrocardiogram?
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 physician's information and further interpretation.
Other
related procedures that may be used to assess
the heart include exercise electrocardiogram (ECG),
Holter monitor, signal-averaged 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 ultrafast CT scan. Please see
these procedures for additional information.
The
heart's electrical conduction system:
The
heart is, in the simplest terms, a pump made up
of muscle tissue. Like all pumps, the heart requires
a source of energy in order to function. The heart's
pumping action comes from an inborn electrical
conduction system.
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 (AV) node, where impulses
are slowed down for a very short period,
then continues 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 both 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 ECG from the normal tracing may indicate
one or more of several heart-related conditions.
Understanding
ECG tracings:
Almost
everyone knows what a basic ECG tracing looks
like. But what does it mean?
The
first short upward notch of the ECG tracing is
called the "P wave." The P wave indicates that
the atria (the two upper chambers of the heart)
are contracting to pump out blood.
The
next part of the tracing is a short downward section
connected to a tall upward section. This next
part is called the "QRS complex." This part indicates
that the ventricles (the two lower chambers of
the heart) are contracting to pump out blood.
The
next short upward segment is called the "ST segment."
The ST segment indicates the amount of time from
the end of the contraction of the ventricles to
the beginning of the rest period before the ventricles
begin to contract for the next beat.
The
next upward curve is called the "T wave." The
T wave indicates the resting period of the ventricles.
When
the physician views an ECG, he/she studies the
size and length of each part of the ECG. Variations
in size and length of the different parts of the
tracing may be significant. The tracing for each
lead of a 12-lead ECG will look different, but
will have the same basic components as described
above. Each lead of the 12-lead ECG is "looking"
at a specific part of the heart, so variations
in a lead may indicate a problem with the part
of the heart associated with a particular lead.
Some
reasons for your physician to request an ECG include,
but are not limited to, the following:
- to determine the cause
of chest pain
- to evaluate other signs
and symptoms which may be heart-related, such
as fatigue, shortness of breath, dizziness,
or fainting
- to identify irregular
heartbeats
- to determine the status
of the heart prior to procedures such as surgery
and/or after treatment for conditions such as
a heart attack (myocardial infarction, or MI),
endocarditis (inflammation or infection of one
or more of the heart valves), or after procedures
such as heart surgery or cardiac catheterization
- to assess the function
of an implanted pacemaker
- to determine the effectiveness
of certain heart medications
- to obtain a baseline
tracing of the heart's function during a physical
examination that may be used as a comparison
with future ECGs, to determine if any changes
have occurred
There
may be other reasons for your physician to recommend
an ECG.
An 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 upon your specific
medical condition. Be sure to discuss any concerns
with your physician 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, intake of
high-carbohydrate meal, and/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 physician 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 physician
of all medications (prescribed and over-the-counter)
and herbal supplements that you are taking.
- Notify your physician
if you have a pacemaker.
- The area(s) where the
electrodes are to be placed may be shaved.
- Based upon your medical
condition, your physician may request other
specific preparation.
An 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 physician’s
practices.
Generally,
an 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, arms,
or legs are 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, arms, and legs.
- 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 ECG will be started.
It will take only a short time for the tracing
to be completed.
- 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 physician instructs you
differently.
Generally,
there is no special care following an ECG.
Notify
your physician if you develop any signs or symptoms
you had prior to the test (e.g., chest pain, shortness
of breath, dizziness, or fainting).
Your
physician may give you additional or alternate
instructions after the procedure, depending on
your particular situation.
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