Coronary CT Angiography (CCTA)

Also Known As Multislice CT Scans

CT Scan
CT Scan. Morsa Images/Getty Images

Attempts have been underway for a number of years to perfect noninvasive tests that could replace cardiac catheterizations in the diagnosis of coronary artery disease (CAD). Coronary CT angiography (CCTA) - also called the multislice CT scan - is one such approach. While CCTA has improved significantly over the years, however, it still has limitations and is not yet suitable for routine screening for CAD.

What Are CCTA Scans?

A computerized tomography (CT) scan is an imaging procedure that uses a series of x-ray images taken from several different angles. These images are digitally processed to create cross-sectional views, or “slices,” of the tissue being scanned.

CCTA scans produce multi-slice views of the coronary arteries, allowing the visualization of blockages that may be present.

CCTA scans are different from another kind of cardiac CT scan - the “calcium scans” used to detect calcium deposits in the coronary arteries. While both types of scans use CT technology, the calcium scans are used only to detect the presence of calcium in the arteries and are not able to give the detailed anatomical information you can get from a CCTA scan.

How Good Are CCTA Scans?

Several studies have been conducted comparing the results of CCTA scans with the “actual” coronary artery anatomy, as defined by cardiac catheterization.

In these studies, any coronary artery plaque that produced more than a 50% blockage was considered to be a significant blockade.

On average, the positive predictive value of CCTA scanning was estimated to be between 91 and 93 percent. This means that if a CCTA scan says you have a significant blockage, there is a little better than a 90 percent chance that you actually do.

The negative predictive value was even higher in these studies - between 95 and 100 percent. So if a CCTA scan says you do not have significant coronary artery blockages, odds are very strong that you really don’t.

So CCTA scans are excellent at ruling out CAD if none is present and quite good (but not perfect) at detecting CAD if it is present.

Comparison to Cardiac MRI

MRI is another technique being applied to the problem of noninvasively visualizing coronary arteries. While MRI shows a lot of promise, because of the complexities of performing MRI on a moving heart the CCTA scan is currently regarded as the superior of the two methods.

Comparison To Stress Testing

The noninvasive test most commonly employed to diagnose coronary artery blockages is the cardiac stress test, generally done along with a nuclear cardiology scan such as a Thallium scan.

A stress test is generally helpful in detecting whether or not a significant blockage is present, and if Thallium testing is done it is often useful in predicting which coronary arteries are involved. But this kind of testing cannot give the detailed anatomical information that one gets, ideally at least, from CCTA scanning.

The PROMISE study compared clinical outcomes for patients with suspected CAD who were evaluated either with stress testing or CCTA testing.

This study showed no difference after 25 months in the composite endpoint (heart attack, death, unstable angina, or major complication). So, while the information obtained with CCTA scans may be more detailed than with stress testing, it is not clear that this additional information makes any difference in clinical results.

Limitations of CCTA Scans

CCTA scanning requires a resting heart rate below 70 beats per minute, and the heart rate also must be regular - so it cannot be used in a person with atrial fibrillation. The patient must also be able to hold his/her breath for at least 15 seconds, and must not have an allergy to contrast dye which is injected during the study.

Also, CCTA scans are poor at visualizing coronary arteries with significant calcium deposits, or which have already been stented.

CCTA scans may not be able to visualize all the coronary arteries. In some studies, only 71% of the important segments of the coronary arteries could be fully evaluated.

CCTA scanning also produces a relatively high exposure to radiation. Radiation doses can be 30 - 50 times higher than with a chest x-ray, 5 - 10 times higher than with simple calcium scans, and approximately the same as with a cardiac catheterization.

The Bottom Line

While the images obtained with CCTA scans have greatly improved in recent years, they are still not sufficient to serve as a replacement for a catheterization procedure. Especially considering its limitations, CCTA scans are not a suitable tool for routinely screening patients for CAD.

Today the test is used mainly in patients who are suspected to have CAD and who are not suitable candidates for stress testing, or who have had equivocal results with stress testing.


Garcia MJ, Lessick J, Hoffmann MHK et al. Accuracy of 16-row multidetector computed tomography for the assessment of coronary artery stenosis. JAMA 2006; 296:403-411.

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Douglas PS, Hoffman U, Patel MR, et al. Outcomes of anatomical versus functional testing for coronary artery disease. N Engl J Med 2015.