CORONARY COMPUTED TOMOGRAPHY ANGIOGRAPHY (CORONARY CTA ) – A PATIENT GUIDE
WHAT IS CORONARY COMPUTED TOMOGRAPHY ( CTA ) ?
Heart attacks often occur without warning. A new imaging technology called Coronary Computed Tomography (a specialized type of X-ray test) is used to scan the heart in just minutes. This can detect deposits of cholesterol in the heart arteries that may lead to a heart attack.
In the past, exercise testing was the usual way for screening for heart disease. The only way to directly look at the heart arteries was through a procedure called a Coronary Angiogram, which is invasive (a small tube was passed into the body), and hence associated with a small risk of serious complications.
Coronary CTA provide pictures of the coronary arteries which supply blood to the heart muscle in a non-invasive manner. It enables your Cardiologist to look for narrowings some of which cannot be detected by the more traditional exercise testing. It is estimated that up to 3/4 of heart attacks occur in narrowings that are less than 50% in severity. These narrowings will often be missed by exercise testing and only be picked up by Coronary CTA. When such narrowings are detected, it is important that the person initiates medications that can prevent a heart attack in the future.
HOW IS CORONARY CTA PERFORMED AND WHAT ARE THE RISKS OF THE PROCEDURE ?
Patients undergoing a Coronary CTA scan receive a dye as an IV (intra-venous) solution to ensure the best images possible. A very small needle is placed in the vein of the arm and allows the dye to be given. A medication to temporarily slow the patient’s heart rate for clearer images is sometimes given. During the examination, which usually takes about 10 minutes, X-rays pass through the body and onto a “detector”. The higher the number of detectors, the clearer the final images. The latest generation of scanners can acquire 64 “image slices” of the heart in a minute.
In people allergic to iodine which is found in the dye, pretreatment with medications is necessary to prevent allergic reactions. In people with abnormal kidney function and/or diabetes, the dye may worsen kidney function. Finally, there is radiation exposure which is similar to that of a conventional coronary angiogram. In summary, coronary CTA is a very safe test for most people, but should only be undergone when ordered by a doctor familiar with the patient.
WHO SHOULD CONSIDER CORONARY CTA ?
Despite the high safety profile, Coronary CTA should not be used as a “screening” test for all.
On the basis of currently available information, Coronary CTA may be considered as a reasonable test for persons with:
- In persons who are at high risk of developing coronary artery disease due to risk factors such as smoking, high cholesterol levels, hypertension, diabetes or those with a strong family history.
- Unclear or inconclusive stress-test (treadmill test) results.
- Persons with symptoms that could suggest underlying heart artery narrowing.
HOW ACCURATE IS CORONARY CTA ?
If the Coronary CTA is normal or only mildly abnormal, it makes the likelihood of a severe narrowing/blockage of the coronary arteries extraordinarily small (< 1%).
Conversely, if a narrowing is seen on a coronary CTA, there is a high probability that a narrowing that would compromise heart function is present. In such situations, a coronary angiogram would be needed for further evaluation and possible treatment.
Occasionally, a person with moderate narrowings is found. In such situations, exercise stress testing can be complimentary to the coronary CTA in making a decision on further management.
WHAT TYPE OF CORONARY CTA IS USED AT THE NOVENA HEART CENTRE ?
The Novena Heart Centre uses the latest generation, state-of-the-art multi-slice CT Scanner (Toshiba 64-Slice Coronary CTA scanner) which can simultaneously acquire 64 image slices of the heart in one minute, resulting in highly detailed images of the coronary arteries and the heart.
WHAT PREPARATION IS REQUIRED FOR A CORONARY CTA ?
Coronary CTA is performed as an outpatient procedure and does not require hospitalization. The whole procedure takes approximately 20 to 30 minutes. The following steps are required:
- Do not eat or drink for four hours before the scan. Caffeine (coffee or tea) should be avoided because it may cause irregular heart beats which may compromise the quality of the images.
- An IV line is inserted into the vein in the arm, and is used both to give a medication to slow or stabilize the patient’s heart rate for better imaging and administer an iodine-containing dye.
- Patients are required to hold their breath for 10 to 12 seconds during scanning. This is essential for obtaining high quality images.