Cardiac calcium scoring: Using imaging tests to prevent heart disease
March 7, 2016
Physicians always emphasize the importance of patients knowing their risk for heart disease. But how are we to know whether we’re low-risk, high-risk, or in between?
Of course, lifestyle choices (diet, exercise, and tobacco use) play a big part in heart disease risk. But other predictive information can be revealed within the arteries and blood vessels, often before any heart-related symptoms appear.
One such predictor is calcium deposits within the blood vessels, a fairly common malady that can be harnessed to determine the amount of cholesterol plaque buildup in the arteries. Whenever there is calcium in the heart arteries, there is cholesterol plaque buildup — the calcium is at the scene of the crime, but it is not the culprit. But, since we can see calcium on simple CT scans of the heart, we can use this trick to learn more about the amount of cholesterol deposits.
We can use cardiac calcium scoring to detect cholesterol deposits before they become a problem and help patients avoid a heart attack.
What is cardiac calcium scoring?
Cardiac calcium scoring is an imaging test that helps physicians classify asymptomatic people (individuals who have no cardiac symptoms, such as chest pain) as low, intermediate, or high risk for heart attack. A cardiac calcium score is simply a number that represents how much calcium (and thus cholesterol deposit) has accumulated in the coronary arteries (the blood vessels that supply the heart).
Think of these blood vessels as the plumbing in a house. Minerals can build up in the water pipes, and unless your pipes are fully blocked, you would never know. Similarly, you can have cholesterol deposits in your arteries (lumps and bumps in your pipes), but if there are not enough to decrease blood flow to the heart, you would have no symptoms and could even have a normal stress test.
It turns out that a heart attack usually occurs when one of these cholesterol deposits bursts and causes a blood clot in the artery, completely and suddenly blocking blood flow. Most heart attacks occur in minor blockages that aren’t picked up on a stress test.
A cardiac calcium score doesn’t describe a specific blockage of coronary arteries. Rather, it gives an estimate of the total amount of calcium, and thus cholesterol plaque, in the arteries, which is a powerful window to future heart attack risk. For example, imagine I have an identical twin brother. If I have a cardiac calcium score of 0 and my twin has a score of 500, my twin may have a 10 times higher risk for heart attack than I do.
A cardiac calcium score is a highly predictive number that can be valuable to our patients and referring physicians. It allows doctors to deploy personalized heart disease prevention strategies for each individual rather than applying the same general recommendations to everyone – eat a healthy diet, exercise, don’t smoke, and know your numbers, including blood pressure and cholesterol. Coronary calcium scoring helps physicians be more aggressive with treatment and also avoid unnecessary interventions based on the patient’s future risk. The score can help physicians determine the need for medication, lifestyle modification, and other risk-reducing measures.
Often, people to whom we assign a calcium score are not yet heart patients – they are referred to us because their physicians want to be proactive about their patients’ cardiac risks. For some people, the test offers a chance to reclassify their heart attack risk. If a person is concerned because of a family history of heart attack but we can determine through cardiac calcium scoring that his or her blood vessels are free of calcium deposits, we may be able to assign that person as a lower-risk individual than he or she previously thought.
However, a coronary calcium scan is not for everyone. If you have few or no risk factors for heart disease, and don’t have a strong family history of heart disease, it is unlikely that you will have a concerning amount of calcium. Alternatively, if you are at higher risk for heart disease, you will already need an aggressive prevention plan. It is best used for those who are on the fence about treatment, say with cholesterol medications, or for those who have a strong family history where the usual risk factors may not tell the whole story.
While the risks are quite low, coronary calcium scans do have a small amount of radiation, about the equivalent of 10 chest x-rays, so they shouldn’t be done in patients who won’t benefit from the test.
How is cardiac calcium scoring performed?
When people come for a cardiac calcium score, there is no need for an IV line or contrast dye as there may be with other CT scans. It is a quick test – the actual image is taken in a matter of seconds – but patients should plan to spend at least an hour with us because there is some preparation that must be done before the imaging can take place.
Consuming caffeine can make the heart beat faster, which will interfere with the imaging test. Prior to the test, we ask that people avoid caffeinated food or beverages, including:
Medications can be taken as usual with water the day of the test.
At the radiology clinic, we ask patients to change into a gown and remove any potentially X-ray-blocking metal jewelry or accessories from the chest area. Then we ask a few routine questions – for women of reproductive age, this includes asking about pregnancy. After the questions, we proceed to the imaging machine table (a CT scanner).
This is the part that takes only a few seconds. Once patients are on the table, we’ll ask them to hold their breath four or five times, and to lie completely still as the table moves. The breath-hold instructions will come from the technologist or from an automated voice within the gantry (the wide opening of the machine). Because the machine is wide open, the vast majority of patients will not need to worry about feeling claustrophobic.
Having patients lie still while holding their breath enables the machine to take the clearest X-ray images possible. As people breathe, their diaphragm, chest muscles, and heart move up and down. The heart beats all the time, but we can deploy algorithms within the machine to account for that movement. Breathing and other body movements are much more difficult to isolate and form algorithms for. If the X-ray images are blurred, the physician will have a more difficult time determining the person’s cardiac calcium score.
From there, the technologist and physician will review the CT images and look for signs of calcium deposits. The physician will calculate the score based on the Agatston method. Absence of calcium will result in a score of 0. The radiologists will then further calculate and report the patient’s score percentile compared to other individuals with the same age, gender, and ethnicity. The next step will be for the patient to follow up with his or her physician to determine the appropriate preventive strategy or intervention methods.
If you or your physician are concerned about your heart attack risk, cardiac calcium scoring can give you a reliable baseline for your current and potential heart-health options. To determine your personal coronary calcium score, request an appointment with our imaging team. For more information about a how to create a prevention plan based upon your scan results, you can visit with our preventive cardiology team.