Article Archive
May/June 2012

Coronary Calcium Test Predicts Heart Attack Risk

By Juliann Schaeffer
Aging Well
Vol. 5 No. 3 P. 32

Coronary calcium scoring can enhance providers’ prediction of a patient’s risk of heart attack, making it particularly useful for patients who may have no other classic indicators.

Cardiovascular disease (CVD) is currently the No. 1 killer of men and women in the United States, and every 34 seconds finds another person added to the list of Americans who have a heart attack. The American Heart Association projects that by 2030, roughly 40% of the US population will have some form of CVD, the most common of which is coronary artery disease, characterized by the narrowing or blockage of the coronary arteries.

While numerous tests exist to aid physicians in diagnosing and treating patients with heart disease, determining which patients will actually have a heart attack is not an exact science. Indeed, many heart attacks occur in individuals with no previous history of heart disease.

However, new research has recently shown coronary calcium scoring to be the best indicator of risk compared with other predictive tests, such as measuring C-reactive protein in the blood and using carotid ultrasound. Experts say it could be used to better determine heart attack risk and help guide physicians’ treatment decisions in a particular patient population.

Predicting Heart Attack Risk
The standard protocol for predicting patients’ heart attack risk is the Framingham Risk Score. “Currently physicians have a pretty broad array of tests at their disposal, but most commonly used and most recommended are what we call the traditional risk factors,” says Diane Bild, MD, associate director of the National Institute of Health Heart, Lung, and Blood Institute’s Program in Prevention and Population Sciences.

These well-known risk factors include blood pressure, blood cholesterol, smoking history, and blood glucose. “These are considered very good predictors, but what is also very valuable about them is that they can be treated,” Bild explains. “So if somebody has high blood pressure, if you lower their blood pressure, you lower their risk.” Age and family history are also calculated into a person’s risk score, though physicians of course can’t directly treat these factors.

Based on these data, physicians can estimate a patient’s risk of having a heart attack, categorizing them as low, intermediate, or high risk.

The trouble is, while these factors present a good place to start and can predict fairly well whether a patient will have a heart attack, this isn’t the case for all patients. “Unfortunately, many patients considered low or intermediate risk by Framingham still have heart attacks,” says Michael Blaha, MD, a clinical and research fellow at the Johns Hopkins Ciccarone Center for the Prevention of Heart Disease, who conducted the recent review of tests. “In fact, a majority of all heart attacks occur in patients not deemed high risk. Framingham was a study of white patients many decades ago before modern drugs, etc, so its accuracy is poor, particularly for women.”

Blaha says patients considered at low or intermediate risk by Framingham standards could benefit the most from coronary calcium scoring.

What Is Coronary Calcium Scoring?
Coronary calcium scoring is a noninvasive, noncontrast CT scan of the heart that predicts heart attack risk by measuring the amount of calcified plaque in the coronary arteries.

“They are done using standard, widely available equipment using the same amount of radiation as a mammogram,” explains Blaha. Generally requiring a patient to hold his breath for roughly 15 seconds, the test takes less than one minute to perform, 10 minutes total, including prep time prior to the scan, says Blaha. He notes that the scan looks for calcium in the coronary arteries, with calcium equating to coronary atherosclerosis.

Whereas predicting risk based on traditional risk factors involves a lot of guesswork, Blaha explains that coronary calcium testing “gives an individualized risk assessment of a patient’s coronary atherosclerosis burden,” adding that coronary calcium is the single best predictor of heart attack. “Nothing beats looking directly at the arteries that cause heart attacks,” he says.

Blaha notes that testing costs roughly $100 in metropolitan areas and is increasingly reimbursed by insurance. While he says usage of coronary calcium scoring varies by hospital, “It is increasingly used and recently received a IIa recommendation [as a reasonable test] from the American Heart Association and American College of Cardiology for risk assessment in asymptomatic patients” at intermediate risk.

He anticipates that it will become more widely utilized in the future but says physician education is necessary to prevent unnecessary testing. “Yes, practitioners are likely to use it more frequently, but we must be sure that it is ordered in the right patients and the results are understood correctly. A high score does not mean that patients require more advanced testing. This is a mistake that we commonly see.”

Which Patients Benefit?
As Blaha explains, even though this test can illustrate coronary artery buildup incredibly well, it is indicated only for a particular subset of the patient population because the test is only a marker of heart attack risk and physicians can’t actually treat the coronary calcium, per se. Instead, the test is used more to guide treatment decisions in patients whose physicians aren’t so sure what their heart attack risk is based on known risk factors.

Bild explains, “The one side of the coin is that coronary artery scoring does improve the ability to predict if somebody will have a heart attack. The other side of the coin, however, is whether it really makes a difference whether you know that additional risk or not. And one reason for that is because, unlike something like blood pressure, coronary calcium is not something that you can treat. It’s a marker, an indicator that you have coronary calcium. In the vast majority of cases, you have it because you have atherosclerosis.”

While the test’s ability to reveal atherosclerosis directly makes it attractive to physicians and patients, Bild says it simply indicates a person is at higher risk of a heart attack. Therefore, it can be useful to guide treatment decisions in patients whose risk score isn’t so certain—those considered at intermediate risk based on the Framingham risk factors.

Consider patient A, a woman in her 30s without symptoms who has normal blood pressure, has normal cholesterol, does not smoke, and has no family history of heart disease. Based on her risk factors, she is considered to be at very low risk for heart attack. “The American Heart Association and the American College of Cardiology would not recommend that a person like that get a coronary calcium score, as they’re so unlikely to have coronary calcium,” says Bild.

By the same token, coronary calcium scoring isn’t indicated for patients at very high risk either. For patient B, a man in his 50s who has very high cholesterol, “You should treat this patient’s cholesterol, regardless of what his coronary calcium is,” explains Bild. “So if there’s a high-risk person, the coronary calcium score likely won’t help you in your decision making of whether you want to go ahead and be more aggressive treating the person to lower their risk.”

It’s the patients who fall somewhere in the middle who can benefit most from this testing: those at intermediate risk. “There’s this intermediate category where this test may be reasonable,” says Bild. “If the person is on the border, where they’re at intermediate risk and the physician isn’t sure whether to treat or not, then the coronary calcium might give a clue to the physician.”

“It is useful if additional risk prediction data is needed,” explains Blaha. For example, for patient C, a 65-year-old woman with normal blood pressure and cholesterol, who doesn’t smoke but has a family history of heart disease, a coronary artery test could provide more details since she has two of the bigger risk factors (age and family history) but no other indicators.

Guiding Decision Making
Based on a patient’s coronary calcium score, “A doctor might consider prescribing aspirin or a statin or other therapies to reduce the risk of heart attack. The results of this test help determine whether the doctor will recommend the therapies or not,” says Blaha.

Specifically, he says this subset of patients typically refers to adults over the age of 40 who are at intermediate risk of heart disease. Patients younger than 40 are unlikely to have developed calcium yet, and physicians already know that patients with known coronary artery disease will have a positive test. “In other words, [for patients whom] we are unable to tell that they are for sure low risk, and we cannot say for sure that they are high risk, coronary calcium can put them into one of these two extreme groups for clinical decision making,” he says.

Blaha has found that an unexpectedly high coronary calcium score can be the catalyst some patients need to make healthy changes in their lives. “We find that patients are motivated by the results. An unexpectedly high score, we find, leads patients to make important lifestyle changes that reduce their risk,” he says, noting that he commonly considers statins and aspirin as treatment for patients with high scores. “It influences both doctors’ decisions and patients’ decisions.”

An important concept to note is that patients whose tests show they have no calcium are likely at very low risk of having a heart attack in the following five to 10 years. According to Blaha, this is most helpful for the following patient population:

• otherwise healthy patients with a family history who want to know whether they are afflicted;

• patients with vague chest symptoms to determine possible heart disease; and

• patients who strongly desire not to be on medication or those in whom side effects are present or likely (such as bleeding with aspirin).

— Juliann Schaeffer is an associate editor at Great Valley Publishing Company.