|How does a Chemical or Pharmacologic
Stress Test work?
When is a Regular
Stress Test ordered?
is an Isotope Stress Test performed?
for the test?
How long does it
How safe is it?
What is the reliability of the test?
How quickly will I get the results?
How does an Isotope Stress
Test Work? How does a Chemical Stress Test
work? A chemical or pharmacological stress test combines
an intravenous medication) with an imaging technique
(isotope imaging or echocardiography) to evaluate the
LV. In these cases, the medication serves the purpose
of increasing the heart load instead of using exercise.
Stress causes normal coronary arteries to dilate, while
the blood flow in a blocked coronary artery is reduced.
This reduced blood flow may decrease the movement of
the affected wall (as seen by echo), or have reduced
isotope uptake in a nuclear scan. Agents that are commonly
used in pharmacologic stress testing include dipyridamole,
dobutamine and Adenosine (Trade name).
When is a Chemical
Stress Test Performed? Treadmill stress testing
is the test of choice when a patient is able to exercise
because of the physiologic effect that exercise has
on the blood pressure and heart rate. It also helps
give the physician an idea about the patient's exercise
tolerance and whether or not exertion has any adverse
effects on the patient's symptoms or irregular heart
beats. Additionally, one does not have to contend with
any potential side-effects of chemical stress, even
if they are usually minor.
exercise may not be possible because of physical limitations
like back trouble, joint disease, marked fatigue, unsteady
gait, prior stroke, dizziness, shortness of breath,
etc. In such cases, chemical stress testing is employed.
In other words, pharmacologic or chemical stress test
is performed in situations where patients are unable
to perform more than moderate exercise due to severe
arthritis, prior injury, reduced exercise tolerance
(as a result of debilitating illnesses, etc.), or in
patients who are unable to increase the heart rate (as
in some with heart pacemakers or in the setting of certain
diseases that keep the heart from speeding up).
How is a Chemical Stress
Test performed? The imaging portion of the
test is identical to that used during Stress Echocardiography
or Isotope Stress Testing (depending upon the technique
employed) and is performed either in a cardiologists
office, a satellite lab or the hospital. An intravenous
line is started in the arm, the blood pressure is checked
and an EKG recorded. The EKG is also constantly monitored
on the screen. If Stress Echo is being performed, an
echocardiogram is obtained before and immediately after
administration of the stress producing medication. In
cases of stress isotope testing, the resting images
may be obtained before or approximately two hours after
the stress (depending upon the lab and the employed
isotope). The stress-producing medication is given intravenously,
as per protocol. In cases of dobutamine, drug is given
as a continuous drip with a gradual increase in the
rate (at three minute intervals). The patient's heart
rate accelerates and the isotope is given when 85% of
the target heart rate is achieved. In cases of dipyridamole,
the medication is usually given over four minutes, through
the IV line. A drop in the diastolic (lower number)
blood pressure is generally awaited before administration
of the isotope.
If a patient is able to perform mild exercise, he or
she may be asked you to walk on a treadmill for a minute
or so after the injection of dipyridamole.
for an Isotope Stress Test: The following recommendations
are "generic" for all types of cardiac stress
- Do not eat or drink for three hours prior to the
procedure. This reduces the likelihood of nausea that
may accompany strenuous exercise after a heavy meal.
Diabetics, particularly those who use insulin, will
need special instructions from the physician's office.
- Caution about asthma: The use of dipyridamole is
generally avoided in patients with asthma. Please
be sure to notify your physician if you have a history
of asthma, bronchitis or emphysema.
- Specific heart medicines may need to be stopped
one or two days prior to the test. Such instructions
are generally provided when the test is scheduled.
- Wear comfortable clothing and shoes that are suitable
- An explanation of the test is provided and the patient
is asked to sign a consent form.
How long does the entire
test take? A patient should allow approximately
two to four hours for the entire test, including the
preparation. Dual isotope and technetium stress testing
takes less time than thallium. The first part of the
test generally takes an hour. The second part takes
anywhere from 15 to 30 minutes. Between the two parts
of a thallium test, you will be allowed to leave the
lab and get a light snack or lunch.
How safe is a chemical Stress
Test? The patient is exposed to a very small
amount of radiation and the risk is minimal, if any.
The risk of the chemical stress portion of the test
is very small and similar to what you would expect from
any strenuous form of exercise (jogging in your neighborhood,
running up a flight of stairs, etc.). As noted earlier,
experienced medical staff is in attendance to manage
the rare complications like sustained irregular heart
beats, unrelieved chest pain or even a heart attack.
In such cases, the patient is better off having the
problem in the presence of experienced staff, rather
than have it happen when they are exercising alone.
Also, the stress medicine like Dobutamine can be immediately
stopped if there are problems, The effects of dipyridamole
(which can occasionally cause nausea or a headache can
be reversed by aminophylline (an anti-asthma medication).
Please also see the caution about asthma under the "Preparing..."
the reliability of a Chemical Isotope Stress Test?
If a patient is able to achieve the target heart rate
in cases of dobutamine or an appropriate drop in the
diastolic blood pressure with dipyridamole, and if good
quality images are obtained, an isotope treadmill stress
test is capable of diagnosing important disease in approximately
80% of patients with coronary artery disease. Approximately
10% of patients may have a "false-positive"
test (when the results is falsely abnormal in a patient
without coronary artery disease). Technical problems
can occur when a patient is markedly overweight. Women
may have an abnormality in the front portion of the
heart because of overlying breast tissue. Some men may
demonstrate an inferior wall abnormality because of
a prominent diaphragm (muscular partition that separates
the chest cavity from the abdomen. Patients who have
a left bundle branch block on their EKG may also have
a false abnormal test.
How quickly will I get
the results and what will it mean? The physician
performing the stress test can give you a preliminary
report about the EKG and Echo (if it is used) portion
of your test. However, the official result from the
isotope scans may take a few days to complete. The results
may influence your physician's decision to change your
treatment or recommend additional testing such as cardiac