The painless, 10-minute scan identifies calcium deposits in artery walls. Calcium doesn't cause a heart attack, but deposits signal that plaque is present in artery walls, putting a person at risk of heart attack and stroke. The scans can help physicians determine the extent of artery disease.
"Large studies have shown that half of deaths due to heart disease occur in people with no symptoms," says study author George T. Kondos, M.D., associate professor of medicine and associate chief of the cardiology section at the University of Illinois College of Medicine in Chicago. "And a third of people with heart disease don't have any of the traditional risk factors – diabetes, high blood pressure, high cholesterol, family history or peripheral vascular disease. These individuals would go undetected by traditional screening methods."
To find out if the EBCT scan predicted cardiac events in such patients, Kondos and colleagues studied 5,635 men and women with no symptoms of heart disease. They were self-referrals who were tested between January 1993 and December 1995.
The test – an especially fast form of X-ray imaging technology – is a modified, open-air CT scan. While wearing their clothes, patients lie on a couch that slides into a hollow tube-shaped scanner. They hold their breath on two occasions for 30 seconds to one minute as harmless electron beams bounce around and create multiple images of the heart. A computer measures the density of calcium deposits, which look like white specks on the images. A physician confirms the findings by visual examination of the images.
In the 3.5-year period after having the scan, 224 of the volunteers required bypass surgery or angioplasty to open up clogged heart arteries, had a heart attack or died, Kondos reports.
The CT scan detected high amounts of calcium deposits in 95 percent of those who had such an event, compared with low amounts of calcium in 67 percent of those who did not, he says. "The more calcium, the greater the risk and the worse the prognosis."
Participants were divided into quartiles based on their calcium score. Statistical analysis showed that men in the highest quartile were 2.3 times more likely to die or have a heart attack and 10.1 times more likely to need bypass surgery or angioplasty than those with lower scores. Among women, the risk of angioplasty or bypass surgery was 3.8 times higher for those in the highest quartile. No conclusions could be drawn regarding calcium's predictive value for deaths and heart attacks in women due to the small number of women in the highest quartile.
The appropriate patients, he says, are those at intermediate risk – a group that includes all men over 45 and women over 50 with at least one added cardiac risk factor (age is the first risk factor).
There is no value in giving this test to patients known to be at high or low risk of heart disease, he explains. "This study reinforces that the test is best reserved for individuals at intermediate risk in the population," says Robert Bonow, M.D., president of the American Heart Association.
"Its role is to identify individuals at greater risk in whom more intensive preventive strategies might be employed. However, the current evidence does not suggest that a simple test result is sufficient to change behavior. More research is needed to define the role of screening tests like EBCT in risk assessment and modification."
William Weintraub, M.D., who wrote an editorial accompanying the study in the journal, agrees that the procedure can be useful in certain medium-risk patients.
"But the patients need to be selected carefully," he says, noting that "medium risk" is a broad category. "Electron-beam tomography is predictive and has a place in cardiac care," says Weintraub, a professor of medicine, epidemiology and health policy management at Emory University in Atlanta.
Among the specific questions to address, he says, are whether patients who have the procedure actually fare better than those who don't and whether the procedure is cost-effective.
"In the meantime, until we learn more, it won't do any harm and may help, though it does cost money," Weintraub says.
Co-authors are Julie Anne Hoff, Ph.D., R.N.; Alexander Sevrukov, M.D.; Martha L. Daviglus, M.D., Ph.D.; Daniel B. Garside, M.S.; Stephen S. Devries, M.D.; Eva V. Chomka, M.D.; and Kiang Liu, Ph.D.