CT scans of the heart may come with trade-offs

CT scans of the heart may come with trade-offs

When my LDL, or "bad," cholesterol rose alarmingly (and for no apparent reason), I tried changing my diet. When that didn't work, the obvious answer was the cholesterol-lowering drugs called statins. But first, several people urged me to have a CT scan of my coronary arteries.

After all, they said, a scan takes only 10 minutes, it is noninvasive and it delivers no more radiation than a chest X-ray. If it showed that my arteries were clean, there would be no reason to take a drug; if it showed they were clogged, I'd have reason enough to take a statin.

Their suggestion prompted me first to take a hard look at what these scans are all about: whether they are safe, whether they really help people avoid heart attacks and whether a positive finding on a scan prompts people to make lifestyle changes to protect their hearts.

Coronary CT scans are being sold directly to the public, and they have found a market in health-conscious people who can afford them. But screening exams can have downsides. They can cause needless worry, and they sometimes reveal other potential conditions that require invasive procedures like biopsies to diagnose.

The older a person is, the higher the incidence of such incidental findings, studies have shown. In one study, they turned up in 40 percent of older people undergoing coronary CT scans. About a third of the findings were considered clinically significant. And there are as yet no data showing that these incidental findings are saving lives.

I soon learned that among the strongest proponents of CT scans of coronary arteries were physicians with financial ties to drug companies that make statins and others connected to imaging centers that would profit directly from widespread CT screenings. What, I wanted to know, do researchers with no such interests have to say about these scans?

What the Scans Show

CT scans of coronary arteries are most often used to screen seemingly healthy people for indirect evidence of atherosclerosis that may someday result in a heart attack or sudden cardiac death. The most frequently used test, electron beam tomography, typically costs $300 to $400 and is rarely covered by insurance. It can reveal calcium deposits that, experts say, reflect the extent of atherosclerosis in the arteries.

Most heart attacks result not from hard calcified plaque in the arteries, but from a chunk of soft plaque that breaks loose and blocks blood flow to the heart. Still, autopsy studies suggest there is a strong correlation between the amount of calcium and soft plaque in coronary arteries.

To visualize soft plaque directly, a procedure called CT angiography is done. It requires injecting a dye, and the scan that follows involves 3 to 10 times the radiation of electron beam tomography to detect calcification.

Last year the American Heart Association published in its journal Circulation a 30-page scientific assessment of the status of cardiac CT scanning.

The 12-member expert panel concluded that "it may be reasonable" to measure atherosclerosis using a CT scan in selected individuals who, based on known risk factors for heart disease, are at "intermediate risk" of a heart attack or sudden cardiac death within the next 10 years.

For someone whose risk factors are low, the experts reasoned, there is little to gain from a CT scan. Their chances of suffering a heart attack in the next decade are less than 10 percent. And for someone known to be at high risk, with more than 20 percent chance of a heart attack within 10 years, the results of a scan would not change the course of medical treatment. They must be treated aggressively, scan or no scan.

But for those in the middle, with a 10-year heart attack risk of 10 to 20 percent, learning that their arteries are clogged could change the course of medical treatment and perhaps foster changes in their habits. The factors considered in estimating risk are gender, age, cholesterol levels, smoking status and systolic blood pressure (the larger number) with and without treatment.

Each factor is assigned a point score. A 50-year-old man (6 points) who smokes (3 points) and has a total cholesterol of 200 to 239 milligrams per deciliter (3 points), an HDL level less than 40 (2 points) and a systolic blood pressure under 120 (no points) would rack up 14 points, giving him a 16 percent chance of a major cardiac event before he turns 60. (A woman at a comparable level of risk would have a point score of 21 or 22.) Based on currently available evidence, this man would be considered a good candidate for a CT scan.

Lowering the Risk

But lowering his risk should entail more than medication to improve his cholesterol readings. He should also quit smoking, change his diet and start exercising to help raise his HDL, the "good" cholesterol that protects the heart. Without intensive intervention to foster such lifestyle changes, according to a well-designed study by Dr. Patrick G. O'Malley and colleagues at Walter Reed Army Medical Center, there was no change in risk level a year after CT screening. And even intensive intervention had minimal effect.

Since even a heart attack does not always stop people from smoking or overindulging, some experts say artery scans are likely to benefit only the most highly motivated.

Nathan Wong, an epidemiologist at the University of California, Irvine, who had previously observed beneficial changes in risk following CT scans, is now conducting a more scientifically designed study of how people respond to the findings of a scan.

In an interview, Wong explained that while the results of a CT coronary artery scan did predict a person's chances of a major cardiac event in the next 10 years, it was not yet known whether the value of screening exceeded that of other tests for heart disease. No randomized trials to assess the benefits of CT coronary scanning have been conducted. Such trials are the only way to know for sure.

Dr. Michael Lauer of the National Heart, Lung and Blood Institute noted in the September issue of The Cleveland Clinic Journal of Medicine that screening individuals for evidence of arterial disease would have far less of an effect on the incidence of heart disease — the nation's leading killer — than a population-based approach to reduce cardiac risk factors.

As for me, a rough calculation of my risk factors showed that I was not at "intermediate risk" for heart disease, and therefore not a good candidate for a CT scan. So I decided to go the statin route, encouraged by recent evidence that statins, or their effect on cholesterol, protect not only against heart disease but may also help prevent dementia. I'll have another cholesterol test in a month or so.