Myocardial
Perfusion Scan, Resting
(Resting
Thallium Scan, Cardiac Nuclear Imaging, Cardiolite®
Scan, Sestamibi Scan)
What
is a resting myocardial perfusion scan?
A myocardial
perfusion scan is a type of nuclear medicine procedure.
This means that a tiny amount of a radioactive
substance, called a radionuclide (radiopharmaceutical
or radioactive tracer), is used during the procedure
to assist in the examination of the tissue under
study. Specifically, the myocardial perfusion
scan evaluates the heart’s function and
blood flow.
A radionuclide
is a radioactive substance used as a "tracer,"
which means it travels through the blood stream
and is taken up (absorbed) by the healthy heart
muscle tissue. On the scan, the areas where the
radionuclide has been absorbed will show up differently
than the areas that do not absorb it (due to decreased
blood flow to the area or possible damage to the
tissue from decreased or blocked blood flow).
A resting
myocardial perfusion scan is used to assess the
blood flow to the heart muscle (myocardium) and
to determine what areas of the myocardium have
decreased blood flow. This is done by injecting
a radionuclide (thallium or technetium) into a
vein in the arm or hand.
There
are different types of radionuclides. When one
type of radionuclide is used, areas of the myocardium
that have blocked or partially blocked arteries
will be seen on the scan as "cold spots," or "defects,"
because these areas will be unable to take in
the radionuclide into the myocardium. Another
type of radionuclide binds to the calcium that
is released when a heart attack occurs, so it
will accumulate in area(s) of injured heart tissue
as a “hot spot” on the scan.
Other
related procedures that may be used to diagnose
heart disorders include resting and exercise electrocardiogram
(ECG or EKG), Holter monitor, signal-averaged
ECG, cardiac catheterization, chest x-ray, magnetic
resonance imaging (MRI) of the heart, myocardial
perfusion scan (stress), computed tomography (CT
scan) of the chest, echocardiography, electrophysiological
studies, radionuclide angiography, and ultrafast
CT scan. Please see these procedures for additional
information.
Coronary
artery disease:
Coronary
artery disease (CAD) is the narrowing of the
coronary arteries (the blood vessels that supply
oxygen and nutrients to the heart muscle), caused
by a buildup of fatty material within the walls
of the arteries. This buildup causes the inside
of the arteries to become rough and narrowed,
limiting the supply of oxygen-rich blood to the
heart muscle.
To better
understand how coronary artery disease affects
the heart, a review of basic heart anatomy and
function follows.
The
heart is basically a pump. The heart is made up
of specialized muscle tissue, called the myocardium.
The heart's primary function is to pump blood
throughout the body, so that the body's tissues
can receive oxygen and nutrients and have waste
substances taken away.
Like
any pump, the heart requires fuel in order to
work. The myocardium requires oxygen and nutrients,
just like any other tissue in the body. However,
the blood that passes through the heart's chambers
is only passing through on its trip through the
body - this blood does not give oxygen and nutrients
to the myocardium. The myocardium receives its
oxygen and nutrients from the coronary arteries,
which lie on the outside of the heart.
When
the heart tissue does not receive an adequate
blood supply, it cannot function as well as it
should. If the myocardium's blood supply is decreased
for a length of time, a condition called ischemia
may develop. Ischemia can decrease the heart's
pumping ability, because the heart muscle is weakened
due to a lack of food and oxygen.
Fortunately,
the technology is available to restore blood flow
to heart tissue when coronary artery blockages
are diagnosed. One of several diagnostic procedures
used to diagnose and evaluate coronary artery
disease is the resting myocardial perfusion scan.
Possible
indications for a resting myocardial perfusion
scan may include, but are not limited to, the
following:
- chest pain, either
new onset or occurring over a period of days
or longer
- following a heart attack
(myocardial infarction, or MI)
- to assess blood flow
to areas of the myocardium that have been reperfused
(coronary artery blood flow restored) by bypass
surgery, angioplasty (the opening of a coronary
artery using a balloon or other method), or
stent (a tiny expandable metal coil placed inside
the artery to keep the artery open
The
injection of the radionuclide may cause some slight
discomfort. Allergic reactions to the radionuclide
are rare.
If you
are pregnant or suspect that you may be pregnant,
you should notify your physician due to the risk
of injury to the fetus from myocardial perfusion
scan. If you are lactating, breastfeeding, you
should notify your physician due to the risk of
contaminating breast milk with radionuclide. Radiation
exposure during pregnancy may lead to birth defects.
Patients
who are allergic to or sensitive to medications,
contrast dye, iodine, shellfish, tape, or latex
should notify their physician.
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:
- caffeine within 24
hours of the procedure
- digitalis, quinidine,
or nitrate medications
- Your physician will
explain the procedure to you and offer you the
opportunity to ask any questions that you might
have about the procedure.
- You will be asked to
sign a consent form that gives your permission
to do the test. Read the form carefully and
ask questions if something is not clear.
- Notify your physician
if you are allergic to or sensitive to medications,
local anesthesia, contrast dyes, iodine, shellfish,
tape, or latex.
- Fasting may be required
before the procedure. Your physician will give
you instructions as to how long you should withhold
food and/or liquids. You should refrain from
eating or drinking anything that contains caffeine
for at least 24 hours prior to the procedure.
Some prescription and over-the-counter medications
contain caffeine and should be avoided. Some
over-the-counter medications that contain caffeine
include Anacin®, Excedrin®, and NoDoz®.
- Notify your physician
of all medications (prescription and over-the-counter)
and herbal supplements that you are taking.
- If you are pregnant
or suspect that you may be pregnant, you should
notify your physician.
- Notify your physician
if you have a pacemaker.
- Based upon your medical
condition, your physician may request other
specific preparation.
A resting
myocardial perfusion scan 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,
a resting myocardial perfusion scan 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 and will be given a gown to
wear.
- An intravenous (IV)
line will be started in your hand or arm.
- You will be connected
to an ECG machine with leads and a blood pressure
cuff will be placed on your arm.
- You will lie flat on
a table in the procedure room.
- The radionuclide will
be injected into a vein in your arm or hand.
- After the medication
has circulated through your body (10 to 60 minutes
depending upon the radioactive tracer being
used), the scanner will begin to take pictures
of your heart. In a special kind of imaging
test, called SPECT (single photon emission computed
tomography), the scanner will rotate around
you as it takes pictures.
- You will be lying flat
on a table while the images of your heart are
obtained. Your arms will be positioned on a
pillow above your head. It will be necessary
for you to lie very still while the images are
being taken, as movement can adversely affect
the quality of the images.
- If you experience any
symptoms such as dizziness, chest pain, extreme
shortness of breath, or severe fatigue at any
point during the procedure, let the physician
or technologist know.
- After the scan is complete,
the IV line will be discontinued, and you will
be allowed to leave, unless your physician instructs
you differently.
You
should move slowly when getting up from the scanner
table to avoid any dizziness or lightheadedness
from lying flat for the length of the procedure.
You
will be instructed to drink plenty of fluids and
empty your bladder frequently for 24 to 48 hours
after the test to help flush the remaining radionuclide
from your body.
The
IV site will be checked for any signs of redness
or swelling. If you notice any pain, redness,
and/or swelling at the IV site after you return
home following your procedure, you should notify
your physician as this may indicate an infection
or other type of reaction.
Your
physician may give your additional or alternate
instructions after the procedure, depending on
your particular situation.
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