What is Coronary CT Angiography scan?
CT Angiography is a safe outpatient procedure that uses specially designed x-rays and intravenous contrast to see the detailed anatomy of the blood vessels throughout the body. It is most frequently utilized in the evaluation of arteries in the head, neck, chest, abdomen and legs. Coronary CT angiography refers to the scanning procedure of the arteries of the heart i.e. those involved in ischaemic heart disease like heart attacks.
How safe is Coronary CT Angiography scan?
There are certainly radiation issues with this modality. The effective dose is almost similar to that of an invasive cardiac catheterization (5-8 mSv). Contrast use would entail the risk of allergic reaction in a small proportion of the population. Therefore, not all persons would benefit from this test. Please discuss with your doctor the proper indications and the risk-benefit analysis of performing such a scan.
Who should have a Coronary CT Angiography scan?
Coronary CT Angiography is ordered by your physician if there is a need to establish the presence of significant coronary artery disease. It may be indicated if initial cardiac screening tests e.g. Stress ECG tests or nuclear cardiac scans are abnormal. It is also used for the follow-up of patients after coronary angioplasty and stenting, post coronary bypass grafting surgery.
How is the Coronary CT Angiography done?
Intravenous access need to be obtained. You will be asked to lie down on the CT scanning table. Breath-holding instructions will be given. Often the whole heart can be imaged within 5 heart beats. Contrast injection is necessary and sometimes, you may need a medication to slow down the heart rate.
Following image acquisition, our radiographer and doctor will process and report on the images. The results will be discussed with you.
How can I prepare for a Coronary CT Angiography scan?
You need only to fast for about 4 hours before the scan. Please refrain from caffeinated drinks e.g. coffee or tea on the day of examination.
How long does a Coronary CT Angiography scan take?
Although the actual heart scanning takes only 5-8 seconds, the whole scanning procedure may take about 15-20 minutes from preparation to completion. You would be able to leave immediately after the procedure and would be able to resume with normal activities.
How good is a Coronary CT Angiography?
The most advanced multi-detector CT today is a 128-detector row scanner. By using very fast gantry rotation speed and large volume detector coverage, we are able to obtain detailed visualization of the coronary tree. This is a very promising new technology. The latest data are reporting excellent results.
A recent study, presented in March 2005 at the annual meeting of the American College of Cardiology, compared the capacity of 128-slice cardiac CT versus coronary angiography to detect significant coronary artery stenosis (defined as more than 50 percent lumen diameter reduction). 30 patients with stable angina or acute coronary syndrome were enrolled in the study; individuals unable to hold their breath for less than 15 seconds were excluded from the study. The heart was scanned following intravenous injection of contrast material and analyzed by two observers who were not aware of the results obtained from invasive angiography.
Most patients received a beta blocker before the study, and all coronary arteries were compared between coronary CT and selective angiography. Compared with selective angiography, 128-channel cardiac CT showed a sensitivity of 96 percent and specificity of 89 percent when detecting significant stenosis (narrowing). The authors concluded that 128-channel cardiac CT could reliably detect significant coronary stenoses in patients with stable angina or acute coronary syndrome (Source : Mollet, et. al., presentation #1054-83, ACC ‘05).
A more recent analysis (Hoffman et al., JAMA 2005; 293:2471-2478) showed a MDCT sensitivity of 95% and specificity of 98%.
Is Coronary CT Angiography an alternative to Catheter Angiography?
Cardiac catheterization remains the gold standard for diagnosing coronary artery disease. However, the setback with this approach lies in the fact that it is invasive, requires longer hospital stay and has its complications, e.g., bleeding, pain and it costs more.
Compared to Catheter Angiography, CT Angiography is a less invasive and a more patient-friendly procedure. Although contrast is injected through an artery in Catheter Angiography, CT Angiography contrast is injected into a vein which is technically less difficult and has a very low risk of complication. As a result, the patients typically leave immediately following the procedure and can resume normal activities.
Cardiac CT also offers the advantage of being able to visualise the atherosclerotic plaque composition. Cardiac catheterization only opacifies the arterial lumen.
What does it mean if my scan is positive or equivocal?
Your scan would be able to tell if there is atherosclerotic narrowing of the coronary arteries. It can also estimate the degree of obstruction. Based on these findings, your cardiologist will advise you further on the subsequent management. Sometimes, the presence of excessive calcium or certain stents in the arteries may interfere with the proper interpretation of the scans and hence reduce its accuracy.
Does a negative scan mean that I am free from coronary arterial disease?
Having a normal scan is an excellent result. The negative predictive value of a 128-slice MDCT Coronary Angiography is about 99-100%. This means that if the scan result is normal, the likelihood of this being true is nearly 100%.
Disclaimer: This is only general information. A doctor should be contacted if you need any medical advice or if medical decisions need to be made.