CT CORONARY ANGIOGRAPHY - A NEW TOOL FOR EARLY DIAGNOSIS &
PREVENTION OF HEART DISEASE
Question: ††††††† What
is MSCT coronary angiography?
Answer: †††††††††† Multi
slice CT Coronary Angiography with 64-slice technology is emerging as the
most reliable non-invasive modality for evaluation of heart disease.
Impressive image quality and non-invasive nature of Multi Slice Computed Tomography
(MSCT) angiography makes it a powerful tool in evaluation of heart
disease. CT Angiography (CTA) is an examination that uses x-rays
to visualize blood flow in coronary arteries which supply blood to the
heart. CT combines the use of x-rays with computerized analysis of the
images. Beams of x-rays are passed from a rotating device through the
heart from several different angles to create cross-sectional images,
which then are assembled by computer into a three-dimensional picture of
Speed and sensitivity
of 64 slice CT, now gives physicians a new way to view the heart and
surrounding structures. Coronary CT angiography captures thousands of
images of a beating heart in mere seconds. 3D reconstructed images are
then formatted, allowing physicians and their patients to easily review
and understand findings of the CT scan. Most patients undergo CT angiography without
being admitted to a hospital. The ability of this technology to
non-invasively image the coronary artery lumen and wall constitutes an
attractive addition to currently available diagnostic tools such as
nuclear perfusion imaging or conventional selective coronary angiography,
for patients with suspected CAD.
Question: ††††††† When
is MSCT coronary angiography needed?
Answer: †††††††††† When a doctor needs to diagnose disease in the heart
arteries (i.e. coronary artery disease) especially when ECG, stress tests
or other indicators have revealed a potential cardiac problem, the next
step for the doctor is to get a close look at the arteries of the heart,
to see where there might be blockage. In this case, cardiac catheterization
with conventional coronary angiography is the best tool, in which a cardiologist
inserts a catheter into the circulatory system, advances it to the heart
and injects dye into the coronary arteries. Because the X-ray is a
"shadow" image that is two-dimensional, the doctor has to
interpret a number of different "camera angles" that were shot
to determine the presence and shape of any obstruction to the blood flow.
However a detailed 3D virtual model of patientís heart prepared on MSCT
is a better alternative -- so that the doctor could rotate, zoom and move
through the heart's anatomy at any angle at will, as if it were a video
game & that too without impacting on the patient! In less than 30
minutes, without the invasiveness of a cardiac catheterization, a patient
can have an MSCT done to determine if there are any arterial blockages
that require an intervention, such as an angioplasty or stent.
††††††† Which groups of patients
Answer: †††††††††† 64 slice CT angiography is especially useful for
patients who are asymptomatic but at high risk of having coronary artery
there are no problems, such as chest pain or breathlessness, but heart
disease needs to be ruled out). The main risk factors are dyslipidemia,
diabetes, family h/o CAD, smoking, hypertension, obesity and those with equivocal
or unclear results on exercise tests. People with multiple risk factors (2
or more of the above) are at much higher risk than those with 1 risk
factor. However Diabetes alone is the only risk factor which may warrant
screening for exclusion of heart disease.
All patients who are
at risk and have been found to be having definite coronary artery disease
on other tests should undergo invasive routine angiography, but there are
many patients who are not willing for conventional angiography
considering it to be an invasive procedure. There counseling should be
done for conventional angiography; but if still not willing they can have
coronary CT angiography. The advantages in these patients can be that
they can go with proper planning for revascularization at a later date.
indication of MSCT in the work up of patients with chest pain needs to be
carefully defined. A 64-slice CT is exceedingly well suited for quickly
and non-invasively evaluating patients with equivocal presentation,
non-diagnostic ECG and initially negative serum markers of myocardial
injury. CT scan allows physicians to quickly diagnose whether the patient
is having coronary artery disease, aortic dissection, pulmonary embolism
or no abnormality at all. All these three are life-threatening
conditions; with the same symptom of chest pain.
Question: ††††††† What are the preparations for the procedure?
The patient will be asked not to eat or drink for 2 hours, to avoid
caffeinated drinks & exercise for 6 hours prior to the
procedure. The patient will be asked to complete a safety
questionnaire to identify any allergies to foods, drugs, and
iodine. In certain situations, the patient may need a blood test to
assess kidney functions.
Question: ††††††† How to proceed further after
getting the report?
growing number of studies have suggested that 64 slice coronary CT
angiography is highly accurate for the exclusion of significant coronary
artery stenosis with negative predictive values of 98%-100% in comparison
with invasive selective coronary angiography. This means that when
the study is reported to be normal, it will be normal. This makes it a
more accurate test than stress-testing, stress-echocardiography,
stress-thallium and stress-perfusion MRI. Hence MSCT provides a less
invasive and less expensive method of ruling out the need for additional
intervention if no blockages are detected.
significant blockages are found, then the patient is referred for cardiac
catheterization with a probable angioplasty or stenting. If previous
tests show a very high likelihood of patient having significant coronary
artery disease, then MSCT angiography probably is not indicated, because
the patient will no doubt have to go to interventional treatment anyway.
An interesting feature
of CT Angiography scans comes into play if some disease is found, but it
is not advanced enough to require revascularization using angioplasty /
stenting or coronary artery bypass surgery (CABG). Physicians have
reported that when patients see such a clear and understandable picture
of their heart, they are much more motivated to make lifestyle and other
changes to lower their risk factors. Drug therapy is very useful in these
patients to help prevent progression of blockages and heart attacks.
Question: ††††††† What are the main advantages of
Answer: †††††††††† The main advantage is that it is non-invasive, fast,
painless and requires no hospitalization. The patient is fully prepared
for revascularization procedure when he is going for conventional
procedure of coronary angiography. Precious time in cardiac catheterization
laboratory is saved which is currently wasted for performing mere
diagnostic angiograms and can be more cost effectively dedicated to more
patients who require actual intervention.
An inherent advantage
of CT for imaging of the coronary arteries is the cross sectional nature
of this technology. Because of its unsurpassed spatial resolution,
conventional catheter angiography is widely accepted as the gold standard
for detection of CAD. However it only shows the vessel lumen and degree
of luminal narrowing in a cast like manner. It fails to visualize the
coronary artery wall, on the other hand contrast enhanced CT scan
delineates calcified / non-calcified or even non-stenotic lesions within
coronary artery wall itself.
††††††† What are the main disadvantages
/ misconceptions about MSCT angiography?
Answer: †††††††††† Relative contraindications of the procedure are - patients
with hypersensitivity to iodinated contrast agents, renal insufficiency,
congestive heart failure, atrial fibrillation and inability to hold
breath for 10 seconds.
The technique is also
vulnerable to a few drawbacks resulting in inability to diagnose
accurately. These are - extensive calcification obscuring the arteries,
motion artifacts due irregular beating of the heart or inadequate breath
As it is not a dynamic
study so it very difficult to comment whether it is near total occlusion
with antegrade flow or total occlusion with retrograde flow.
There is lot of
misconception about the substantially higher radiation dose for MSCT
angiography in comparison to conventional angiography. In routine
retrospectively gated helical (RGH) MSCT the radiation dose is
approximately 10-15 mSv and for conventional coronary angiography the
approximate dose of 6-8 mSv. However in newer machines MSCT coronary
angiography is performed with prospectively gated transverse coronary
(PGT) technique with approximate radiation dose of only 3-6 mSv.
There is also some
misconception about the contrast media used in this technique. Since
proper opacification is needed only for a couple of seconds, so what
really matters is the ability of the machine to catch the good quality
contrast (Iso- osmolar) at the appropriate time and not the quantity of
the contrast. Study is completed with minimum amount of contrast to the
range of 50 to 60 ml of non-ionic iso-osmolar contrast media which is as
much contrast being used in hundreds of CT examinations done everyday
like in CT Abdomen and Chest.
Question: ††††††† What is the future of MSCT
Answer: †††††††††† The future of MSCT technology
holds great promise for non-invasive diagnosis of heart disease. The
introduction of 64 slice scanners has greatly improved spatial
resolution. It holds the promise of reaping the benefits of diagnosing
heart disease without invasive conventional coronary angiography. This tool
is likely to develop further as a complimentary tool rather than a
replacement to conventional angiography, especially in patients where
heart disease needs to be ruled out.