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A new test is
available to diagnose coronary artery disease. In the past, noninvasive
functional tests of the heart were used, such as treadmill tests and
nuclear studies, to indirectly assess if there were
blockages in the coronary arteries. The only way to
directly look at the coronary arteries was via a cardiac catheterization
and coronary angiogram.
CT scans have been
used to look at various anatomic regions, but have
not been useful for the heart because the heart is continuously in
 motion.
CT is very effective in looking at "static" areas, such as the brain,
abdominal cavity, and extremities. Most early CT scanners take 1-8
pictures (slices) a minute, much slower than the rate of the
heart. Just as taking a picture of a moving object with a
camera results in a blurry picture, conventional CT scans of the heart
are not helpful. A new generation of CT scanners which can take 64
pictures a minute is now available; with the use of a little medication
to slow the heart rate to less than 64, CT images of the coronary
arteries are now possible.
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This procedure use intravenous dye which contains iodine
and CT scanning to image the coronary arteries. While
the use of catheters is not necessary (thus the term
"noninvasive" test applies to this procedure), there are
still some risks involved. In people allergic to iodine,
pretreatment with medications is necessary to prevent
allergic reactions to the dye. In people with abnormal
kidney function and/or diabetes, the dye may worsen
kidney function. Finally, there is radiation exposure
which is similar to, if not greater than, that received
with a conventional coronary angiogram. Nonetheless,
this is generally a very safe test for most people, but
should only be undergone when ordered by a physician
familiar with the patient and their underlying medical
condition.
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While CT angiography should not be used as a "screening"
test in the general population, it is a major new tool
in the diagnosis of coronary artery disease. In patients
at high risk for developing coronary disease (cigarette
smokers, those with genetic risk, high cholesterol
levels, hypertension, or diabetes), who have unclear
results with treadmill or other testing, or who have
symptoms suspicious of coronary disease, CT angiography
is an excellent next step in the diagnosis. If the CT
scan is normal or only mildly abnormal, it makes the
likelihood of a severe blockage of the coronary arteries
extraordinarily small. Conversely, if the CT scan is
significantly abnormal, cardiac catheterization and
angiography are then indicated, to see if angioplasty,
stenting, or coronary bypass surgery may be indicated.
In people who have had bypass
surgery, CT angiography is very effective at evaluating
the patency of the bypass grafts. In people who have had
coronary stents , it is sometimes difficult to image the
inside of the stent to see if it is narrowed. Due to
these complexities, while CT coronary angiography is an
exciting new modality, it is imperative to discuss with
your physician if this is the correct test for you. As
more experience is obtained, the indications for the
test will become even clearer.
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Coronary CT angiography
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Diagnosis of non-calcified plaques
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Diagnosis and quantification of coronary artery
stenoses
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Follow up after surgical bypass procedures
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Evaluation of myocardial perfusion, scarring and
contractility
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Coronary calcium scoring
Preparation/instructions
When you were referred by your physician for a radiological exam, you
may have been told about certain instructions to be done prior to the
exam, or when you were scheduling your appointment, the scheduler should
have informed you about the preparations that should be done prior to
your exam. If you did not or if you want a recheck, you can refer to the
information listed below.
Keep in
mind that you may have been given some additional or different
instructions, based on your own particular circumstances. If you have
any questions, please call our hotline 16171 or (202) 3336-3310 (Mohandeseen),
(202) 2417 5556 (Heliopolis) or (202) 2528 4888 (Maadi) to speak with a
radiologist or cardiologist if you have any questions. It is best to call between 10
a.m. and 10 p.m., Saturday through Thursday.
Instructions
You should not eat or drink anything
for six hours prior to your scheduled exam.
Your heart rate should not exceed 70
beats/min. It it does you will be asked to take a beta blocker drug to
reduce it to the required rate 30 minutes prior to the examination.
Check with your doctor to see if this
pertains to your exam. If you are diabetic and take insulin, you must
consult with your doctor to adjust your dose. You should not take
insulin if you are fasting for this examination. When making an
appointment for this test, tell the person scheduling the study that you
are diabetic and request an appointment early in the day.
Medications can be taken prior to your
exam. Pills should be taken with only a small amount of water. Bring
with you a list of medications you take.
If you are allergic to any type of food, iodine or X-ray contrast
material (dye) you should notify the responsible radiologist or
technician.
You will be asked by one of our doctors about some information
regarding your medical history. This information helps to structure your
exam.
If you have any heart, asthma, kidney
problems, sickle cell disease, or if you are or could possibly be
pregnant, please let the technologist know before your exam.
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Children under
the age of 18 years need to be accompanied by an adult (parent or
guardian). We strongly advise that CT patients not bring children along
without another responsible supervising adult. We cannot provide
supervision for the children.
The procedure can take between 10-45 minutes depending on the exact
test performed.
You must remove
earrings, glasses, hearing aids and dentures prior to your exam.
You will need to have an IV line so that IV contrast can be given
just before imaging begins. The contrast may make you feel warm all
through your body. Some patients experience a metallic taste during the
injection. These sensations last until the injection is completed.
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After the exam
you can resume your normal activities. If you received IV contrast you
may want to increase your normal fluid intake to help flush this
material from your system. Unless your doctor objects you should
increase your fluid intake over a 24 hour time period.
Results of your
exams will be discussed with you by your doctor.
Please call our hotline
16171 or (202) 3336-3310 (Mohandeseen), (202) 2417 5556 (Heliopolis) or
(202) 2528 4888 (Maadi) to speak with a radiologist if you have any
questions. It is best to call between 10 a.m. and 10 p.m., Saturday
through Thursday.
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