What is a Coronary CT angiogram (CTA) ?
It is now possible to obtain pictures of the coronary arteries non-invasively with a CAT scan machine. These scanners are fast and able to freeze the motion of the heart so that clear pictures can be obtained. An intravenous catheter is inserted through which iodinated contrast is administered quickly while pictures are being taken. Patients lay on a table which moves through the CAT scanner. Presently, CT scanners which are fast enough to take these pictures are in limited supply and patients are being scheduled for these test at large medical centers. Some insurance carriers are beginning to pay for these tests.
Why is a Coronary CT Angiogram (CTA) ordered?
Coronary CT angiograms are most commonly ordered to exclude the presence of coronary artery disease in patients with suspicious symptoms such as chest pain. The test is most helpful in excluding the presence of coronary disease as a cause of chest pain in patients who are at low risk of developing coronary disease. This test is also helpful in evaluating those patients for whom a cardiac catheterization is considered too risky.
When is a Coronary CT angiogram not appropriate?
Coronary CT angiography is only moderately accurate in measuring the severity of obstruction in the coronary arteries. Therefore, patients who are believed to be at high risk of having severe coronary artery disease are scheduled for a coronary angiogram. Such patients may have accelerating angina, heart attack or significantly abnormal stress tests.
Patients who have fast heart rates or irregular heart rhythm are currently not suitable for these examinations as current CT technology requires relatively slow and regular heart rates to achieve accurate results. Patients must be able to lay flat and hold their breath for fifteen to thirty seconds.
Other relative contraindications to this procedure are (1) allergy to contrast dye, (2) significantly impaired renal function and (3) severe calcification of the coronary arteries (The CT scanner cannot obtain useful pictures if too much calcium is present in the arterial wall).
What can I expect the day of my test?
You will be asked to keep yourself well hydrated till several hours before the test
You will be asked to avoid caffeine or any stimulants that might speed up your heart rate
Food is usually held 3 hours before the test
Diabetic patients are asked to consult with their physicians regarding diabetic medications and patients receiving metformen (Glucophage) are given special instructions to holdi this medication before and after CTA for several days.
Patients with a history of abnormal kidney function may be asked to take a medication called Mucomist for several days before and after this test and receive supplemental intravenous fluids before and after the test. This helps protect the kidneys.
Patients receiving beta-block drugs (e.g. metoprolol, atenolol, nadolol, carvedilol ) are asked to take their medications as these drugs help slow the heart. Most patients are given additional oral or intravenous beta blocker drugs except for patients intolerant to these drugs (patients with allergies to these drugs or those at risk for significant bronchospasm). Patients in this category may be given calcium channel blocker drugs such as diltiazem or verapamil.
Usually you will be asked to get undressed and place a robe over your body.
An intravenous line is placed by a technician through which contrast dye is administered or medications given
What happens during the CTA Examination?
Coronary CT angiography takes only about fifteen minutes to perform. Getting ready to do the test may take thirty minutes to an hour. Adhesive electrodes placed on the skin as the CT scanner must be accurately synchronized to your heart rate and rhythm. You will be asked to practice breathing rhythmically and hold your breath for fifteen to thirty seconds. You may be asked to place your hands in a specific position to allow better pictures. During the test you may feel a rush of warmth or flushing in your body due to circulation of intravenous contrast. Following the test, the intravenous catheter placed earlier will be removed and you will be able to get dressed.
What happens after the CTA examination?
It usually takes several hours to process and interpret CT angiographic studies. Special computer software is used to reconstruct images that a specially trained cardiologist can interpret. Most often results are available in one to two days.