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What is Cardiac CT?
Cardiac Computed Tomography, or cardiac CT, is a painless test that uses an x-ray machine to take clear, detailed pictures of the heart. This common test is used to look for problems in the heart.
A CT scanner is a special X-ray machine which produces cross-sectional images of the body. You will lie on a couch which will move through a ‘polo’ shaped machine. Multiple images or pictures will be taken. These will be reported by a Cardiologist and or Radiologist. The procedure takes about ten to fifteen minutes.
There’s a small chance that cardiac CT will cause cancer because of the radiation involved. The risk is higher for people younger than 40 years old, especially children.
Cardiac CT is a common test for finding and/or evaluating:
• Calcium build-up in the walls of the coronary arteries. This type of CT scan is called a coronary calcium scan. Calcium in the coronary arteries may be an early sign of coronary artery disease. In
Coronary Heart Disease (CHD), a fatty substance called plaque narrows the coronary (heart) arteries and limits blood flow to the heart.
• CHD. If contrast dye is used during cardiac CT, it helps highlight the coronary arteries on the x-ray pictures. This can show whether the coronary arteries are narrowed or blocked (which may
cause chest pain or a heart attack).
• Problems with the aorta. The aorta is the main artery that carries oxygen-rich blood from the heart to the body.
Cardiac CT can detect two serious problems in the aorta:
• Problems in the pulmonary veins. The pulmonary veins carry blood from the lungs to the heart. Problems with these veins may lead to atrial fibrillation (AF), an irregular heart rhythm. The pictures that cardiac CT creates of the pulmonary veins can help guide procedures used to treat AF.
• Pericardial disease. This is a disease that occurs in the pericardium, the sac around your heart. A cardiac CT takes clear, detailed pictures of the pericardium.
Different types of CT scans may be used for different purposes. For example, multi-detector computed tomography (MDCT) is a fast type of CT scanner. Because the heart is in motion, a fast scanner is able to produce higher quality pictures of the heart. MDCT also may be used to detect calcium in the coronary arteries.
What to expect before Cardiac CT
Your doctor will tell you how to prepare for the cardiac CT scan. People usually are asked to avoid drinks that contain caffeine before the test. Normally, you’re allowed to drink water, but you’re asked not to eat for 4 hours before the scan. If you take medicine for diabetes, talk with your doctor about whether you’ll need to change how you take it on the day of your cardiac CT scan.
Tell your doctor whether you:
• Are pregnant or may be pregnant. Even though cardiac CT uses a low radiation dose, you shouldn’t have the scan if you’re pregnant. The x rays may harm the baby.
• Have asthma or kidney problems or are allergic to any medicines, iodine, and/or shellfish. These problems may increase your chance of having an allergic reaction to the contrast dye that’s sometimes used during cardiac CT.
A member of the Nursing team will ask you to remove your clothes above the waist and wear a hospital gown. You also will be asked to remove any jewellery from around your neck or chest. Taking pictures of the heart can be hard because the heart is always beating (in motion). A slower heart rate will help produce better quality pictures. Therefore, your doctor or nurse may prescribe a medicine to help slow your heart rate prior to your scan. In most cases a medicines called Ivabradine or beta-blockers are used. These medicines both hold a UK licence for the treatment of angina and heart failure although there is strong evidence confirming Ivabradine is the most effective way to slow your heart rate for this scan.
If you are known to have an irregular heart rhythm you may already be on a beta-blocker, in which case this dose may be increased in clinic for the procedure.
What to expect during Cardiac CT
The cardiac CT scan will take place in a hospital or outpatient office. A doctor who has experience with CT scanning will supervise the test. Your doctor may want to use an iodine-based dye (contrast dye) during the cardiac CT scan. If so, a needle connected to an intravenous (IV) line will be put in a vein in your hand or arm. The contrast dye will be injected through the IV during
the scan. You may have a warm feeling when this happens. The dye will highlight your blood vessels on the CT scan pictures.
The Nurse or Radiographer will clean areas of your chest and apply sticky patches called electrodes. The patches are attached to an ECG (electrocardiogram) machine to record your heart’s electrical activity during the scan. You will lie on your back on a sliding table. The table can move up and down, and it goes inside the polo shaped machine.
The table will slowly slide into the opening in the machine. Inside the scanner, an x-ray tube moves around your body to take pictures of different parts of your heart. A computer will put the pictures together to make a three-dimensional (3D) picture of the whole heart. The radiographer controls the CT scanner from the next room. He or she can see you through a glass window and talk to you through a speaker. Moving your body can cause the pictures to blur. You’ll be asked to lie still and hold your breath for short periods, while each picture is taken. A cardiac CT scan usually takes about 15 minutes to complete. However, it can take more than an hour to get ready for the test and for the medicine to slow your heart rate enough.
What to expect after Cardiac CT
After the cardiac CT scan is done, you’ll be able to return to your normal activities. A doctor who has experience with CT will provide your doctor with the results of your scan. Your doctor will discuss the findings with you.
What does cardiac CT show?
Many x-ray pictures are taken during a cardiac CT scan. A computer puts the pictures together to make a three-dimensional (3D) picture of the whole heart. This picture shows the inside of the heart and the structures that surround the heart.
Figure A shows the exterior of the heart. The arrow shows the point of view of the cardiac CT image. The inset image shows the position of the heart in the body. Figure B is a cardiac CT image showing the coronary arteries on the surface of the heart. This is a picture of the whole heart put together by a computer.
What are the risks of Cardiac CT?
There are some risks involved with CT scans as radiation is used. Depending on the body part being scanned, this is equal to the natural radiation we all receive from the atmosphere over a period of between 10 months and 7 years. You should not worry about this radiation, as your doctor feels he needs to investigate a potential problem, and the risk from not having the examination could be greater. Ask the radiographer if you have any concerns If you have an injection, there is a slight risk of an allergic reaction. Staff in the Radiology Department are trained to deal with any complications and again the risk involved is very small. It is possible that a reaction can occur up to a week after, if you develop itching or a skin rash you should contact your GP or the
Emergency Department at the hospital.
Tell the radiographer if you have previously had a reaction to contrast media when having a Kidney X-Ray (IVP/IVU) or CT. You must also inform the radiographer if you are aware that you have, or may have, a kidney disorder. Please use this space to write down any questions you may wish to ask:
Milton Keynes University Hospital 01908 660033
Booking Co-ordinator 01908 997203 (Monday to Friday office hours)
Cardiology Department Nurses 01908 996539 (Monday to Friday office hours)