Cardiac CT Angiography and Calcium Scoring
Cardiac Computed Tomography (cardiac CT) is a painless, non-invasive test that allows high-resolution, three-dimensional visualization of the heart coronary arteries and other adjacent structures.
The two main types of cardiac CT are coronary artery calcium scoring and coronary CT angiography.
Coronary calcium scoring
In this test, which does not use X-ray contrast, pictures are taken of the heart to look for the presence of calcium deposits in the blood vessels of the heart or coronary arteries. Calcium deposits are a very specific sign of coronary artery disease, as is cholesterol and scar tissue buildup in the arteries. While the amount of calcium in the arteries increases with age, patients who have significantly elevated amounts of calcium deposits are at increased risk to have heart attacks or heart complications. This is true for patients of all age groups, for both men and women, and across ethnic groups. In patients who have a strong family history of premature heart disease or in patients at intermediate risk of heart disease based on their age and risk factors, calcium scoring can help better assess their risk of heart disease and can help tailor medical therapy.
Cardiac CT angiography (Cardiac CTA
In this test, a small amount (3 oz) of X-ray contrast is injected through a vein in the arm. As the contrast is circulated through the heart, the CT scanner takes high-resolution images of the heart and heart arteries. This allows for three-dimensional imaging of the heart chambers, coronary arteries and pulmonary veins.
Cardiac CTA is very useful in the evaluation of patients with atypical chest pain–to exclude blockages in the coronary arteries, or rule out abnormal coronary artery anatomy (congenital coronary anomalies). This is particularly true in patients who have a strong family history of early-onset heart disease or in patients who have had equivocal stress tests. Patients who are at high risk of having blockages in the arteries usually will go for a heart catheterization. However, in patients who have a low to intermediate chance of having significant blockages in the arteries, CTA has the advantages of being faster, less invasive and lower risk than an invasive catheterization. Moreover, CTA has the ability to detect the earliest signs of coronary artery disease that cannot be seen by stress tests or on heart catheterization, but that may be useful to tailor medical therapy and affect lifestyle changes in patients.
Cardiac CTA is also used to evaluate the pulmonary veins in patients undergoing certain procedures to treat atrial fibrillation, to image patients with congenital heart disease and to look for abnormal enlargement or aneurysm of the aorta—the major blood vessel in the body.
Cardiac CT scanning requires specialized CT scanners, known as multi-slice CT. These scanners have the ability to take at least 64 pictures of the heart at the same time.
For calcium scoring (see above), no IV access is needed, and no contrast is given. Patients lie flat on a movable table in front of the CT scanner and are placed on a heart rhythm monitor for the scan. They are asked to hold their breath and stay completely still for about 10-15 seconds as the table is advanced through the scanner. The actual CT scanner, or gantry, is doughnut shaped and only about 2 feet thick, so claustrophobia is seldom an issue. The patient’s head and face are not covered for any part of the scan. The entire scanning process usually takes less than 15 minutes.
For cardiac CT angiography, patients do need an IV placed in the forearm near the elbow. They also lie on a movable table in front of the scanner and are placed on a heart rhythm monitor for the scan. Usually, patients are given medications through the IV to slow the heart rate down to 50-60 beats per minute. This makes the arteries easier to see on the scan. Several quick X-rays are performed to help plan the scan, and then contrast is injected rapidly into the arm, and the patient is asked to hold his/her breath, as the table is advanced though the scanner gantry, and pictures are taken. The actual imaging takes 10-15 seconds, although the entire procedure takes approximately 90 minutes. Patients need no sedation and can drive themselves home after the procedure.
The main side effects and complications of CTA are related to contrast reactions and radiation exposure. X-ray contrast can sometimes cause allergic reactions and can worsen kidney function. It is critical to tell your doctor if you have underlying kidney disease, especially if you are diabetic, or if you have allergies to X-ray contrast or iodine. All patients who receive contrast need to have blood work done within 30 days to ensure that kidney function can tolerate the contrast. Diabetic patients taking the medication metformin (Glucophage) need to stop this medication for 48 hours after the scan. Rarely, the IVs can malfunction, and the contrast can infiltrate in the arm tissue. While painful, this usually does not cause long-term problems.
The radiation exposure from a calcium score is negligible. However, the exposure from a CTA is about 3 times the background radiation that one gets living each year in North Carolina. While a single scan poses minimal risk to middle-aged and older patients, younger patients and women—who are more sensitive to the harmful effects of radiation—may be better served with an alternative test. In addition, patients who have had multiple prior CT scans or nuclear medicine studies may be better suited for alternative studies, as the risks of radiation exposure are thought to be cumulative.