Myocardial
Perfusion Scan, Stress (with Exercise or Pharmacologic)
(Exercise
Thallium, Stress Thallium, Cardiac Nuclear Imaging,
Adenosine Thallium Scan, Cardiolite® Scan)
What
is a stress 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 stress
myocardial perfusion scan is used to assess the
blood flow to the heart muscle (myocardium) when
it is stressed by exercise or medication 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.
There
are two types of stress myocardial perfusion scans,
one that is used in conjunction with exercise
(myocardial perfusion scan with exercise) and
one that is used in conjunction with medication
(pharmacologic myocardial perfusion scan).
- myocardial perfusion
scan with exercise
A myocardial perfusion scan with exercise is
used to determine what areas of the heart muscle
(myocardium) have decreased blood flow during
exercise. This is done by injecting a radionuclide
(thallium or technetium) into a vein in the
arm or hand during exercise. After the radionuclide
has been injected into a vein and has circulated
through the blood stream, a special machine
called a gamma camera takes pictures of the
heart while the person lies still on a table.
This scanning usually lasts about 30 minutes.
Any areas of the myocardium that have blocked
or partially blocked arteries during exercise
will be seen on the scan as "cold spots," or
"defects," because these areas will be unable
to absorb the radionuclide into the myocardium.
A second set of scans is taken some hours later,
at rest. The resting phase is done in order
to compare the results with the exercise phase
to see if areas that do not get adequate blood
flow while exercising are able to absorb the
radionuclide during rest.
- myocardial perfusion
scan with pharmacologic intervention
A pharmacologic myocardial perfusion scan is
used when the physician has determined that
exercise on a treadmill is not an appropriate
choice due to the person’s medical condition.
In this situation, a medication is given that
causes the coronary arteries to dilate. This
dilation of the coronary arteries increases
blood flow and is very similar to the response
of the arteries during exercise. The medication
is injected into a vein in the arm or hand.
After a given period of time, the radionuclide
will be injected into a vein in the arm or hand.
The gamma camera will take pictures of the heart
while the person lies still on a table. A resting
scan will be performed afterwards, just as with
the actual exercise scan.
Other
related procedures that may be used to diagnose
heart disorders include exercise and resting electrocardiograms
(ECG or EKG), 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, 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 myocardial perfusion scan.
Indications
for an exercise or pharmacologic 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
an artery to keep the artery open)
There
may be other reasons for your physician to recommend
a myocardial perfusion scan.
The
exercise portion of the test may have rare instances
of abnormal heart rhythms, chest pain, or heart
attack due to the stress on the heart caused by
the exercise.
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 a myocardial perfusion
scan. Radiation exposure during pregnancy may
lead to birth defects. If you are lactating, or
breastfeeding, you should notify your physician
due to the risk of contaminating breast milk with
the radionuclide.
Patients
who are allergic to or sensitive to medications,
contrast dyes, 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:
- medications containing
theophylline
- 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.
- If you are scheduled
for a pharmacologic myocardial perfusion scan,
you will need to avoid taking any medications
containing theophylline or caffeine. Coffee,
even decaffeinated, is not allowed, as it contains
some caffeine. Medications for asthma may contain
theophylline. If you have asthma, inform your
physician. Theophylline medications should be
stopped 48 hours prior to the test. Medications
that contain caffeine and all food and drink
containing caffeine should be held for 12 to
24 hours. Some over-the-counter medications
that contain caffeine include Anacin®,
Excedrin®, and NoDoz®. Consult your
physician for specific instructions.
- If you are pregnant
or suspect that you may be pregnant, you should
notify your physician.
- Notify your physician
of all medications (prescription and over-the-counter)
and herbal supplements that you are taking.
- Notify your physician
if you have a pacemaker.
- For an exercise scan,
plan to wear loose, comfortable clothing for
the exercise portion of the test, as well as
a pair of comfortable walking shoes.
- Based upon your medical
condition, your physician may request other
specific preparation.
A stress
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 stress myocardial perfusion scan follows this
process:
- You will be asked to
remove any jewelry or other objects that may
interfere with the procedure.
- If you are asked to
remove clothing, you 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.
Exercise
myocardial perfusion scan:
- You will exercise on
a treadmill. The intensity of the exercise will
be gradually increased by increasing the speed
of the treadmill.
- Your heart rate and
blood pressure will be monitored. Once you have
reached your maximal exercise point (determined
by the physician based on your heart rate and
age), the radionuclide will be injected into
your IV line.
- After the radionuclide
has been injected, you will continue to exercise
for one to two minutes.
Pharmacologic
myocardial perfusion scan:
- You will not exercise
on a treadmill. Instead, you will lie on the
table while a medication is injected into your
IV to increase your heart rate.
- Your heart rate and
blood pressure will be monitored.
- Once you have reached
your target heart rate, the radionuclide will
be injected into your IV line.
Procedure
completion, both methods:
- 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.
- You will lie flat on
a table while the images of your heart are obtained.
Approximately 10 to 60 minutes after the radionuclide
is injected, the gamma camera will begin to
take pictures of your heart. In a special kind
of test called SPECT (single photon emission
computed tomography), the scanner will rotate
around you as it takes pictures.
- Your arms will be positioned
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.
- After the scan is completed,
you may be allowed to leave the area, but will
need to return at the appropriate time for a
second set of scans. The second set of scans
will be taken three to six hours after the first
set. During this time, you will not be allowed
to eat, unless specifically instructed to do
so by the technologist, and will be allowed
limited water or decaffeinated/non-caloric liquids.
Your physician may decide to have you return
on another day for the second set of scans.
- The second set of scans
will be similar to the first set - you will
lie on the table as before while the scanner
takes pictures of your heart.
- Once the second set
of scans has been completed, 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 you additional or alternate
instructions after the procedure, depending on
your particular situation.
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