Recently we have observed many young people dying due to heart attack. The cause of death may be multifactorial. One of them could be severe and sudden blockage of coronary arteries. CT coronary angiography is a technique to visualize and evaluate coronary arteries, which supply the heart muscles. Blockage in coronary arteries can lead to heart attack (in medical terminology, it is called myocardial infarction). CT coronary angiography uses a powerful CT scan machine to produce images of the heart and its blood vessels.
What is CT coronary angiography?
CT coronary angiography is a non-invasive tool for the evaluation of coronary arteries (arteries supplying the heart) on CT scan after injecting iodinated contrast.
How is it different from conventional or catheter angiography?
In catheter angiography, a catheter is inserted in artery and contrast is injected directly into coronary arteries. In CT coronary angiography, contrast is injected in peripheral vein and bolus tracking is done. When the contrast reaches in aorta, scan is performed. CT angiography is only for diagnostic purpose and catheter angiography is for diagnostic and therapeutic purpose.
Does it require hospitalization?
No. It is a very routine scan performed on CT scan and hospitalization is not required. It is performed just like other CT scans with some additional preparations.
Who can undergo CT coronary angiography?
Any person wants to know the status of coronary arteries.
Asymptomatic person with family history of cardiac disease.
Person with on and off chest pain without changes of ECG.
Rule out significant luminal stenosis in known case of coronary artery disease
Assessment of patency of stents and coronary bypass grafts
Who should not undergo CT coronary angiography?
Person with severe acute chest pain
Person with on & off chest pain and positive ECG changes
What are the pre-requisites for CT coronary angiography?
There are few pre-requisites for CT coronary angiography.
- Heart rate preferably less than 65 / min and stable.
- Normal S. creatinine level
- NBM (Nil by mouth) for solid food and tea / coffee at least for 3-4 hours. Plain water, any juice or liquids should be taken to keep the kidneys hydrated.
Any accompanying person is required?
Yes, an accompanying adult is required to give content. The person could be family member, neighbour, friend or colleague.
Which type of CT scan machine is required?
64 or higher slice (128 slice, 256 slice) CT scan machine is required.
Why heart rate should be stable and preferably less than 65?
Because CT scan machine is going to scan the beating heart, it is better to have a lower and stable heart rate for optimum visualization of coronary arteries.
What if heart rate is higher than requirement, before the scan?
If heart rate is higher than required, then it can be lower down by specific medicines like beta blockers under supervision of an anesthetist. The dose of medicine depends on the heart rate. Higher the heart rate, higher does required to bring it down.
Why S. Creatinine blood report is required?
Because, the injected contrast is excreted through the kidneys, s. creatinine level should be within normal limits. S. creatinine report reflects function of kidney.
How much time does it take to complete the scan?
The actual scan time is less than 5 min. But the pre-scan preparation time might be longer, depending upon person’s heart rate.
What are the steps of CT coronary angiography?
Following are the steps of CT coronary angiography:
1. First of all, person is given supine position on CT scan table and ECG leads are connected with monitoring of ECG.
2. Calcium scoring is done and it is calculated.
3. If calcium score is within normal limits, then intravenous contrast (dye) is given and angiography is performed. The angiography scan requires roughly 5 heart beats to get it completed.
What is calcium score?
Calcium score is evaluation of amount of calcified atheromatous plaque in coronary (heart) arteries, which indicates risk of a heart attack.
Why calcium scoring is done?
If the calcium score is more than the normal limits then CT coronary angiography can be avoided to prevent overestimation of the stenosis.
What is the cut-off value of calcium score?
The cut-off value of calcium score is 400. It also depends upon site of deposition in coronary arteries.
What is the meaning of high NPV of CT coronary angiography?
NPV means Negative Predictive Value. CT coronary angiography has very high (nearly 99%) NPV. It means, if CT coronary angiography shows normal appearance of coronary arteries without significant plaque of stenosis, then it is 99% accurate.
Can we get any additional findings other than coronary angiography?
Yes. We can also know the status of adjacent structures to the heart, like trachea, bronchus, mediastinum and inner aspect of both lungs. Sometimes incidentally detected infection or tumour are seen on CT coronary angiography.
What are post-scan instructions?
Plenty of liquid should be take to help flush the dye from body. A person can resume daily activities just after the scan. No restrictions in physical activities or food are required.
What are the limitations of CT coronary angiography?
it is only diagnostic angiography and not therapeutic. So if any symptomatic person is found to have coronary artery stenosis (=narrowing), then catheter angiography is performed to evaluate the status of coronary artery and stenting is done.