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Coronary tomography angiogram
Computed tomography angiogram (coronary CTA): This heart-imaging test—which generally is used only in specialized hospitals or research centers—helps your doctor determine whether either fatty deposits or calcium deposits have built up in your coronary arteries.
How does it work?
A coronary CTA comes from a special type of X-ray examination. Patients undergoing a coronary CTA scan receive an iodine-containing contrast dye as an IV solution to ensure the best images possible. The same IV in the arm may be used to give a medication to slow or stabilize the patient's heart rate for better imaging results. During the examination, which usually takes about 10 minutes, X-rays pass through the body and are picked up by special detectors in the scanner. Typically, higher numbers (especially 16 or more) of these detectors result in clearer final images. For that reason, coronary CTA often is referred to as "multidetector" or "multislice" CT scanning. The information collected during the coronary CTA examination is used to identify the coronary arteries and, if present, plaques in their walls with the creation of 3-D images on a computer screen.
How is coronary CTA different from other heart tests?
One of the most common heart tests is the coronary angiogram, or cardiac catheterization. This test is more invasive and requires more patient recovery time than coronary CTA. Patients who receive coronary angiograms must have a catheter, or small transport tube, threaded into their coronary arteries, which run along the outside of the heart. The catheter typically is inserted into a blood vessel in the upper thigh and then maneuvered up to the coronary arteries. The catheter then is used to inject the iodine dye needed for the test, which uses X-rays to record "movies" of the interior of the coronary arteries.
Although coronary CTA examinations are growing in use, coronary angiograms remain the gold standard for detecting coronary artery stenosis, which is a significant narrowing of an artery that could require catheter-based intervention (such as stenting) or surgery (such as bypassing). On the other hand, this new technology has consistently shown the ability to rule out significant narrowing of the major coronary arteries and can noninvasively detect "soft plaque," or fatty matter, in their walls that has not yet hardened but that may lead to future problems without lifestyle changes or medical treatment.
Who should consider coronary CTA?
Overall, coronary CTA examinations have tended to help determine a lack of significant narrowing and calcium deposits in the coronary arteries, as well as a presence of fatty deposits. This has been found to be particularly valuable in asymptomatic patients with higher risk for coronary disease, in patients with atypical symptoms but lower risk of coronary disease, or in patients with unclear stress-test results. As a result, many physicians advocate the careful use of coronary CTA for patients who have:
- Intermediate to high-risk profiles for coronary artery disease, but who do not have typical symptoms (especially chest pain, shortness of breath, or fatigue during heavy physical activity.)
- Unusual symptoms for coronary artery disease (such as chest pain unrelated to physical exertion), but low to intermediate risk profiles for coronary artery disease.
- Unclear or inconclusive stress-test (treadmill test) results.
- For these types of patients, coronary CTA can provide important insights to their primary physician into the extent and nature of plaque formation with or without any narrowing of the coronary arteries. Coronary CTA also can noninvasively exclude narrowing of the arteries as the cause of chest discomfort and detect other possible causes of symptoms. But again, initial consultation with their primary physician is key for patients seeking to determine the appropriateness of coronary CTA.
Who should not have coronary CTA?
To date, coronary CTA has not been proven as effective as the coronary angiogram in detecting disease in the smaller heart arteries that branch off the major coronary arteries. For that reason, many physicians do not consider coronary CTA as an adequate substitute for coronary angiography in patients with strong evidence of narrowing of the coronary arteries. Such patients include those with a history of chest pain during heavy physical activity, a history of positive stress-test results, or a known history of coronary artery disease or heart attack. Coronary CTA also is of limited use in patients with extensive areas of old calcified, or hardened, plaque, which is often the case in older patients. Patients who are extremely overweight or who have abnormal heart rhythms also tend not to be suitable candidates for this test because imaging quality is compromised.
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