What Is Cardiac CT?

Cardiac computed tomography (to-MOG-rah-fee), 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.

During a cardiac CT scan, an x-ray machine will move around your body in a circle. The machine will take a picture of each part of your heart. A computer will put the pictures together to make a three-dimensional (3D) picture of the whole heart.

Sometimes an iodine-based dye (contrast dye) is injected into one of your veins during the scan. The contrast dye travels through your blood vessels, which helps highlight them on the x-ray pictures.

Because an x-ray machine is used, cardiac CT involves radiation. Although the amount of radiation used is considered small, it's similar to the amount of radiation you're naturally exposed to over a 3-year period.

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. However, new cardiac CT methods are available that reduce the amount of radiation used for this test.

Overview

Cardiac CT is a common test for finding and/or evaluating:

• Calcium buildup 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 heart disease (CHD), also called coronary artery disease. In CHD, a fatty substance called plaque (plak) 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 heart function and heart valves. Doctors may recommend cardiac CT instead of echocardiography or cardiac MRI (magnetic resonance imaging) for some people.
• 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:
  • Aneurysm (AN-u-rism). An aneurysm is a diseased area of a blood vessel wall that bulges out. Aneurysms can be life threatening if they burst.
  • Dissection. Dissection can occur if the layers of the aortic artery wall peel away from each other. This condition can cause pain and may be life threatening.
• Blood clots in the lungs. A cardiac CT scan also may be used to find a pulmonary embolism (PE). A PE is a sudden blockage in a lung artery, usually due to a blood clot that traveled to the lungs from one of the legs. This is a serious but treatable condition.
• 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, multidetector 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.

Another type of CT scanner, called electron-beam computed tomography (EBCT), also is used to detect calcium in the coronary arteries.

Outlook

Researchers continue to study new and better ways to use cardiac CT.

Other Names for Cardiac CT

• CAT scan
• Coronary artery scan
• Coronary CT angiography (an-je-OG-ra-fee)
• CT angiography

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 fetus.
• 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 technician will ask you to remove your clothes above the waist and wear a hospital gown. You also will be asked to remove any jewelry 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.

If you don't have asthma, COPD (chronic obstructive pulmonary disease), or heart failure, your doctor may give you a medicine called a beta blocker to help slow your heart rate. The medicine will be given by mouth or injected into a vein.

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 technician who runs the cardiac CT scanner will clean areas of your chest and apply sticky patches called electrodes. The patches are attached to an EKG (electrocardiogram) machine to record your heart's electrical activity during the scan.

The CT scanner is a large machine that has a hollow, circular tube in the middle. You will lie on your back on a sliding table. The table can move up and down, and it goes inside the tunnel-like 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 technician 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. (For more information, see "What To Expect Before Cardiac CT.")

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.

Cardiac CT

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.

Cardiac CT is a common test for finding and/or evaluating:

• Calcium buildup 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 heart disease (CHD). In 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 heart function and heart valves. Doctors may recommend cardiac CT instead of echocardiography or cardiac MRI (magnetic resonance imaging) for some people.
• 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:
  • Aneurysm. An aneurysm is a diseased area of a blood vessel wall that bulges out. Aneurysms can be life threatening if they burst.
  • Dissection. Dissection can occur if the layers of the aortic artery wall peel away from each other. This condition can cause pain and may be life threatening.
• Blood clots in the lungs. A cardiac CT scan also may be used to find a pulmonary embolism (PE). A PE is a sudden blockage in a lung artery, usually due to a blood clot that traveled to the lungs from one of the legs. This is a serious but treatable condition.
• 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.

Cardiac CT also may be used before or after certain heart procedures, such as cardiac resynchronization therapy and coronary artery bypass grafting. A cardiac CT can help your doctor pinpoint the areas of the heart or blood vessels where the procedure should be done. The scan also can help your doctor check your heart after the procedure.

Because the heart is in motion, a fast type of CT scanner, called multidetector computed tomography (MDCT), may be used to take high-quality pictures of the heart. MDCT also may be used to detect calcium in the coronary arteries.

Another type of CT scanner, called electron-beam computed tomography (EBCT), also is used to detect calcium in the coronary arteries.

What Are the Risks of Cardiac CT?

Because an x-ray machine is used, cardiac CT involves radiation. Although the amount of radiation used is considered small, it's similar to the amount of radiation you're naturally exposed to over a 3-year period.

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. However, new cardiac CT methods are available that reduce the amount of radiation used for this test.

Cardiac CT scans are painless. Some people feel side effects from the contrast dye that's sometimes used during the cardiac CT scan. An itchy feeling or a rash may appear after the contrast dye is injected. Neither side effect normally lasts for long, so medicine often isn't needed.

If you do want medicine to relieve the symptoms, your doctor may prescribe an antihistamine. This type of medicine is used to help stop allergic reactions.

Although rare, it's possible to have a serious allergic reaction to the contrast dye that causes breathing problems. Medicines are used to treat serious reactions.

People who have asthma, COPD (chronic obstructive pulmonary disease), or heart failure may have breathing problems during cardiac CT if they're given beta blockers to slow down their heart rates.

Key Points

• Cardiac computed tomography (CT) is a painless test that uses an x-ray machine to take clear, detailed pictures of your heart. This common test is used to look for problems in the heart.
• During a cardiac CT scan, the x-ray machine will move around your body in a circle. The machine will take a picture of each part of your heart. A computer can put the pictures together to make a three-dimensional (3D) picture of the whole heart.
• Because an x-ray machine is used, cardiac CT involves radiation. Although the amount of radiation used is considered small, it's similar to the amount of radiation you're naturally exposed to over a 3-year period.
• 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. However, new cardiac CT methods are available that reduce the amount of radiation used for this test.
• Cardiac CT is a common test for finding and/or evaluating calcium buildup in the walls of the coronary arteries, coronary heart disease (CHD), problems with heart function and heart valves, problems with the aorta, blood clots in the lungs, problems with the pulmonary veins, and pericardial disease.
• Cardiac CT also may be used before or after certain heart procedures. The test can help your doctor prepare for the procedure or check your heart after the procedure.
• 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.
• 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.
• The CT scanner is a large machine that has a hollow, circular tube in the middle. You lie on your back on a sliding table. The table can move up and down, and it goes inside the tunnel-like machine.
• Inside the scanner, an x-ray tube moves around your body to take pictures of different parts of your heart. A computer puts the pictures together to make a 3D picture of the whole heart.
• 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.
• 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 cardiac CT. Your doctor will discuss the findings with you.
• Cardiac CT scans are painless. Some people feel side effects from the contrast dye that's sometimes used during the scan. Serious complications are rare.
• Researchers are studying new ways to use cardiac CT.

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Source: Information published by the National Institute of Health

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