Coronary Calcium Scan

A coronary calcium scan is a test that can help show whether a person has coronary artery disease (CAD). In CAD, a fatty material called plaque narrows the coronary (heart) arteries and limits blood flow to the heart. CAD is the most common type of heart disease in both men and women. It can lead to angina, heart attack, heart failure, and arrhythmia.

Other Names

• Calcium scan test
• Cardiac CT for calcium scoring

Sometimes people refer to a coronary calcium scan by the name of the machine used to take pictures of the heart.

• Electron-beam computed tomography (EBCT) or electron-beam tomography (EBT)
• Multidetector computed tomography (MDCT)

Why a Coronary Calcium Scan Is Done

Coronary calcium scanning looks for specks of calcium (called calcifications) in the walls of the coronary arteries. Calcifications are an early sign of heart disease. The test can show, before other signs and symptoms occur, whether there is an increased risk of a heart attack or other heart problems. ^[1]

A coronary calcium scan is most useful for people who are at moderate risk for a heart attack. In order to calculate a person's 10-year risk of having a heart attack, there is a Risk Assessment Tool from the National Cholesterol Education Program. People at moderate risk have a 10%–20% chance of having a heart attack within the next ten years. The coronary calcium scan helps doctors decide who within this group needs treatment. ^[2]

Two machines can show calcium in the coronary arteries—electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT). Both use an x-ray machine to make detailed pictures of the heart. Doctors study the pictures to see whether there is a risk for heart problems in the next two to ten years.

A coronary calcium scan is simple and easy for the patient, who lies quietly in the scanner machine for about ten minutes. Pictures of the heart are taken that show whether the coronary arteries have calcifications.

A coronary artery with calcifications and a coronary calcium scan image. Source: NIH

Figure A shows the position of the heart in the body and the location and angle of the coronary calcium scan image. Figure B is the coronary calcium scan image showing calcification in a coronary artery.

Preparation

No special preparation is needed. Patients are usually asked to avoid caffeine and smoking for four hours before the test. For the scan, the patient will remove his or her clothes above the waist and wear a hospital gown. It is also necessary to remove any jewelry from around the neck or chest.

How a Coronary Calcium Scan Is Done

Coronary calcium scans are done in a hospital or outpatient office. The x-ray machine is called a computed tomography (CT) scanner.

The technician technologist who operates the scanner will clean areas of the chest and apply small sticky patches called electrodes. The electrodes are attached to an EKG (electrocardiogram) monitor. The EKG measures the electrical activity of the heart during the scan. This makes it possible to take pictures of the heart when it’s relaxed, between beats.

The CT scanner is a large machine that has a hollow, circular tube in the center. The patient will lie on his or her back on a sliding table. The table can move up and down and 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 the body to take pictures of the heart. It may be necessary for the patient to hold his or her breath for 10 to 20 seconds while the pictures are taken. This prevents movement in the image.

During the test, the technologist will be in a nearby room with the computer that controls the CT scanner. The technologist can see the patient through a window and talk to them through an intercom system.

Medicine may be given to slow down a fast heart rate. This helps the machine take better pictures of the heart. The medicine will be given by mouth or injected into a vein.

A coronary calcium scan takes about 5 to 10 minutes. During the test, the machine makes clicking and whirring sounds as it takes pictures. It causes no discomfort, but the exam room may be chilly to keep the machine working properly.

Some patients are claustrophobic when placed in an enclosed space and may need to take medicine to stay calm. This isn’t necessary for most people, because the head will remain outside the opening in the machine.

Patients are able to return to their normal activities after the coronary calcium scan is done. A doctor who is trained in reading these scans will discuss the results when they are ready.

What Does the Coronary Calcium Scan Show?

After the coronary calcium scan, patients get a calcium score called an Agatston score. The score is based on the amount of calcium found in the coronary arteries. They may get an Agatston score for each major artery and a total score.

The test is negative if no sign of calcium deposits (calcifications) is found in the arteries. This means the chance of having a heart attack in the next two to five years is low.

The test is positive if calcifications are found in the arteries. Calcifications are a sign of atherosclerosis, a disease in which the arteries harden and narrow due to plaque buildup), and of coronary artery disease. The higher the Agatston score, the greater the amount of atherosclerosis.

This calculator (from the National Heart, Lung, and Blood Institute) can be used determine the score. If it is high, the doctor may prescribe medicines or order more tests.

Risks

Coronary calcium scanning has very few risks. The test isn’t invasive, which means that no surgery is done and no instruments are inserted into the body. Coronary calcium scanning doesn’t require an injection of contrast dye to make the heart or arteries visible on the x-ray images.

Because an x-ray machine is involved, patients are exposed to a small amount of radiation. Electron-beam computed tomography (EBCT) uses less radiation than multidetector computed tomography (MDCT). In either case, the amount of radiation is less than or equal to the amount of radiation people are naturally exposed to in a single year.

Clinical Trials

For a list of American government-sponsored clinical trials involving coronary calcium scans, click here. See also the Multi-Ethnic Study of Atherosclerosis (MESA) study.

Controversy

Calcium scans are being marketed to the general public. People are told that knowing their calcium scores is important and that everyone should have a scan done. It is not even necessary to be sent to a doctor to get a scan. Although these scans may seem like a good way for people to take part in their own health care, the problem is that more research needs to be done on what to do with the information that the test generates. It is unclear whether a high calcium score actually changes the treatment plan that a person would receive if they had not had the scan done. The results of a test may contradict the current risk profile that a person already has, but basing treatment on a low calcium score might not be safe. For example, a person who is at high risk for cardiovascular disease, but who has a low calcium score, still needs to be treated regardless of their score--no test is perfect, and the low calcium score might not be the best way to determine future risk.

References

1. ↑ Rumberger et. al; "Electron Beam Computed Tomographic Coronary Calcium Scanning: A Review and Guidelines for Use in Asymptomatic Persons;" MAYO CLIN PROC. 1999;74:243-252 [Full Text | PDF]
2. ↑ Guerci and Arad; "Predictive Value of EBCT Scanning;" Circulation. 1998;97:2583-2584 Abstract

External Links

• Risk Assessment Tool for Estimating Your 10-Year Risk of Having a Heart Attack (National Cholesterol Education Program)
• Coronary Artery Calcium (CAC) Score Reference Values (Multi-Ethnic Study of Atherosclerosis, or MESA