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Heart Attack Prevention

From the Current Issue

How Useful Are Coronary Calcium Scans?
This simple test can identify atherosclerosis but may not accurately predict heart attack risk.

Most healthy people who are concerned about their risk of a heart attack are familiar with their cholesterol and blood pressure measurements. Now many are asking: Should they also know their calcium scores?

Calcium in the coronary arteries indicates atherosclerosis—the buildup of plaques that can lead to heart attacks. New imaging technologies called electron-beam computed tomography (EBCT) and multidetector computed tomography (MDCT) are now available to measure coronary calcium. This development has led to hospitals and testing clinics advertising EBCT and MDCT scans that may provide a quick, easy, accurate way to assess the presence and severity of coronary atherosclerosis and the risk of a heart attack.

Yet earlier this year, the government’s Preventive Services Task Force recommended that EBCT not be used to screen healthy people unless they have known coronary heart disease (CHD) risk factors or symptoms—and that even then, the usefulness of the test is unclear.

What Are EBCT and MDCT?

EBCT and MDCT, also known as ultra-fast CT, are painless, five- to eight-minute tests. The patient lies face up on an examination table under a CT scanner. An electron beam generates x-rays (four times as strong as a simple chest x-ray) that pass through the patient’s body. Calcium in artery walls appears as whitish spots or streaks on the x-rays.

Technicians identify the calcium deposits in the images, then use a computer program to derive a coronary artery calcium score that reflects the total calcium “load” in the coronary arteries. Scores of 0 to 10 reflect arteries largely free from coronary plaque (minimal coronary calcification). Scores of 11 to 400 indicate mild to moderate plaque buildup; scores above 400 indicate extensive plaque.

What the Score Reveals . . .

Many studies have shown that people with higher calcium scores are at greater risk for heart attacks and strokes and that those with very low scores are at relatively low risk over the next five years. What has been controversial is whether calcium screening with EBCT or MDCT adds useful information beyond that provided by standard risk factors (cholesterol, blood pressure, triglycerides, obesity, smoking, diabetes, age, and family medical history).

A September 2003 study in Radiology showed that calcium screening adds considerable predictive value. Researchers tested more than 10,000 people between the ages of 30 and 85 who were at above-average risk for CHD but had no symptoms. Increased calcium scores were associated with substantially worse survival five years later.

A January 2004 study in the Journal of the American Medical Association (JAMA) revealed similar findings: In testing 1,461 asymptomatic adults with at least one CHD risk factor, a calcium score above 300 was associated with a large increase in the risk of heart attacks (or other CHD-related deaths) compared with risk predicted by the Framingham Risk Score, which uses age, blood pressure, cholesterol levels, and smoking.

. . . And What It Doesn’t

While there is widespread agreement among cardiologists that EBCT and MDCT can correctly identify the presence and extent of atherosclerosis, there is less agreement over what to do with the information and how accurately the results can predict the risk of a heart attack. Increasingly, experts have recognized that a heart attack most commonly occurs when a soft, unstable plaque in the artery wall breaks open and causes the formation of an artery-plugging blood clot. But EBCT and MDCT, as well as other types of imaging studies, can’t reliably distinguish between stable and unstable plaques. In the JAMA study, for example, low calcium scores did not totally preclude heart attack risk. However, it is clear that the more calcified plaque that is present, the more numerous are the softer, noncalcified plaques.

In addition, because EBCT and MDCT are relatively new, researchers are still refining the implications of different calcium scores. Generally, an individual’s score is compared with the average score for someone the same age and gender. But more clinical data are needed to establish standardized risk thresholds and treatment guidelines for specific scores.

What To Do Now

Because no study has examined the outcome of using calcium scores as a guide in determining treatment for asymptomatic individuals, the U.S. Preventive Services Task Force has recommended against routine EBCT and MDCT screening for the general population—arguing that screening may occasionally cause unnecessary further invasive testing and treatment in patients with positive calcium scores.

The American College of Cardiology and the American Heart Association also argue that more data are needed to clearly determine who will benefit from EBCT or MDCT screening and whether the tests are significantly better as screening tools than standard, less expensive, readily available tests with decades of research behind them.

Many experts feel that ECBT and MDCT should not be stand-alone tests—they should be done with your doctor’s supervision and interpretation. And even in a comprehensive clinical setting, scanning doesn’t necessarily provide useful additional information for everyone. For example, most (though not all) patients at low risk according to Framingham scores will also have low calcium scores (unless they have a family history of premature CHD), while high-risk patients should be treated aggressively no matter what a calcium scan would show. In the JAMA study cited above, knowing the calcium scores did not substantially change the predicted risk for patients considered at low risk or high risk according to their Framingham scores.

But for the many adults at intermediate risk—with a Framingham score showing a 10% to 20% risk of a CHD event in the next 10 years—screening can be valuable. Such patients potentially could be candidates for aggressive preventive therapy with aspirin and blood pressure- and cholesterol-lowering medication (if they have a very high calcium score for their age).

Knowledge of calcium scores might also motivate intermediate-risk patients to comply with healthier lifestyle habits and medical therapy, though research into the roles EBCT and MDCT might play in patient compliance has only just begun. Others who could potentially benefit from EBCT and MDCT are people at low risk according to Framingham scores but with other well-established risk factors not utilized by Framingham, such as metabolic syndrome, obesity, or a family history of premature CHD.

Developing a consensus on guidelines concerning the role of EBCT and MDCT in primary heart attack prevention will require a number of carefully conducted trials. The clearest picture yet should emerge from the Multi-Ethnic Study of Atherosclerosis (MESA), an ongoing National Institutes of Health study of various imaging technologies that will include the most rigorously conducted assessment to date of EBCT in 6,700 asymptomatic people with different ethnic and racial backgrounds. Johns Hopkins is one of seven participating research centers, and results from this study are expected in 2008.



The Heart Bulletin is a quarterly publication that presents the latest information available to help you make informed decisions about your cardiac care.
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