What is a CT coronary angiogram?
A new test is available to diagnose coronary artery disease. In the past, noninvasive functional tests of the heart were used, such as treadmill tests and nuclear studies, to indirectly assess if there were blockages in the coronary arteries. The only way to directly look at the coronary arteries was via a cardiac catheterization and coronary angiogram.
CT scans have been used to look at various anatomic regions, but have not been useful for the heart because the heart is continuously in motion. CT is very effective in looking at "static" areas, such as the brain, abdominal cavity, and extremities. Most early CT scanners take 1-8 pictures (slices) a minute, much slower than the rate of the heart. Just as taking a picture of a moving object with a camera results in a blurry picture, conventional CT scans of the heart are not helpful. A new generation of CT scanners which can take 64 pictures a minute is now available; with the use of a little medication to slow the heart rate to less than 64, CT images of the coronary arteries are now possible.
How is CT coronary angiogram performed and what are the risks of the procedure?
This procedure use intravenous dye which contains iodine and CT scanning to image the coronary arteries. While the use of catheters is not necessary (thus the term "noninvasive" test applies to this procedure), there are still some risks involved. In people allergic to iodine, pretreatment with medications is necessary to prevent allergic reactions to the dye. In people with abnormal kidney function and/or diabetes, the dye may worsen kidney function. Finally, there is radiation exposure which is similar to, if not greater than, that received with a conventional coronary angiogram. Nonetheless, this is generally a very safe test for most people, but should only be undergone when ordered by a physician familiar with the patient and their underlying medical condition.
Who should get a CT coronary angiogram?
While CT angiography should not be used as a "screening" test in the general population, it is a major new tool in the diagnosis of coronary artery disease. In patients at high risk for developing coronary disease (cigarette smokers, those with genetic risk, high cholesterol levels, hypertension, or diabetes), who have unclear results with treadmill or other testing, or who have symptoms suspicious of coronary disease, CT angiography is an excellent next step in the diagnosis. If the CT scan is normal or only mildly abnormal, it makes the likelihood of a severe blockage of the coronary arteries extraordinarily small. Conversely, if the CT scan is significantly abnormal, cardiac catheterization and angiography are then indicated, to see if angioplasty, stenting, or coronary bypass surgery may be indicated.
In people who have had bypass surgery, CT angiography is very effective at evaluating the patency of the bypass grafts. In people who have had coronary stents , it is sometimes difficult to image the inside of the stent to see if it is narrowed. Due to these complexities, while CT coronary angiography is an exciting new modality, it is imperative to discuss with your physician if this is the correct test for you. As more experience is obtained, the indications for the test will become even clearer.