Heart scans hold intermediate promise

Published: May, 2007

CT scans for calcium in the heart's arteries only benefit people in the gray zone of heart disease risk.

A debate over whether fast CT scanners should be used to go looking for "silent" heart disease still rages. These machines can detect calcium in the walls of coronary arteries, a sign of atherosclerotic plaque. Proponents claim that scans for coronary calcium save lives. Opponents argue that they do more harm than good by unnecessarily worrying people and leading to stent implantation or even bypass surgery without proven benefit.

Professional groups like the American Heart Association and American College of Cardiology were initially cool to the new technology. The latest guidelines from the two organizations, published in the journal Circulation, offer grudging acceptance for measuring coronary calcium. These guidelines come at an interesting time. A bill before the Texas legislature would widen the use of these machines even as the next generation of CT scanners threatens to make measuring coronary calcium obsolete.

Hardening arteries

It's been known since the 1800s that calcium is part of plaque, the buildup of cholesterol-filled pouches in the walls of arteries. In a sense, calcium is what puts the "hardening" in hardening of the arteries. However, calcium doesn't cause atherosclerosis. Instead, it is an elemental part of the body's response to a continuous cycle of inflammation, damage, and repair — a cycle fueled by high blood pressure, high cholesterol, smoking, and other "insults" to the circulatory system.

Old-fashioned x-rays can detect big buildups of calcium, but because the heart is constantly moving, they can't take clear pictures of the smaller amounts in bouncing, jouncing coronary arteries. It's like trying to use an old, slow camera to take a perfect picture of a single strand of spaghetti in a furiously boiling pot of pasta. Electron beam CT (EBCT) uses beams of electrons to bend x-rays around the body. It does this fast enough to make stop-action pictures of the heart. In 1990, Dr. Arthur Agatston (better known for writing The South Beach Diet) and his colleagues developed a scoring system for coronary calcium based on the amount of calcified plaques and their density. Scores are divided into four categories: under 10 (minimal calcium), 11 to 99 (moderate), 100 to 399 (increased), and 400 and above (extensive). These categories have been related to cardiovascular risk.

Calcium in arteries

Calcium shows up as white patches in EBCT scans. The image on the left shows a coronary artery (white arrows) without calcium; the one on the right shows several patches of it.

Photos courtesy of Dr. Udo Hoffmann

Before anyone had a real understanding of what high and low calcium scores meant, "heart scans" were being advertised directly to the public. Many people, often the so-called worried well, plunked down several hundred dollars — the test isn't covered by Medicare or most private insurers. And some doctors began to use the scans in their practices, even though the benefit of doing so was unproven and the professional cardiology associations warned against their use.

At first glance, it doesn't seem like there could be a downside to measuring coronary calcium. What's not to like about a test that painlessly and almost instantly looks inside the heart and detects whether atherosclerotic plaque is building up inside the vital arteries that nourish the heart muscle? It does have some drawbacks.

"While it is true that few people without calcium have heart attacks, only a small fraction of those with coronary calcium have them," says Dr. Udo Hoffmann, who codirects the cardiac imaging program at Harvard-affiliated Massachusetts General Hospital.

What's more, calcium doesn't necessarily indicate the type of plaque you need to be worried about. Calcium tends to accumulate in tough, scablike patches that may actually seal in plaque and prevent it from breaking open. Such a break is what triggers a heart attack. Vulnerable plaque — the type that is most likely to rupture and spew its contents into the bloodstream — contains little calcium.

One of the biggest drawbacks of the test is the problem of what to do with someone who has a positive test but no symptoms of heart disease. For most people, and this includes doctors, the uncertainty of a high calcium score is unbearable. It almost invariably leads to an exercise stress test or an angiogram. These frequently turn up narrowed arteries (which everyone fears even though most of us have them). Such a finding in turn often leads to bypass surgery or angioplasty, which may be unnecessary.

Refining the rules

The new guidelines from the American Heart Association and American College of Cardiology still warn against checking for coronary artery calcium in people at low risk for heart disease. As a general rule, this means individuals with Framingham risk scores under 5%. The scans aren't useful for people already diagnosed with heart disease or those at high risk (Framingham scores above 20%), since the results won't change their treatment and prevention strategies. The new guidelines say the test might be useful for people with intermediate heart attack risk, corresponding to Framingham scores of 5% to 20% (see "Calcium and intermediate risk"). In this group, a low calcium score could calm worries about having a heart attack, while a high score could ratchet up prevention efforts such as exercising more or taking a statin.

Calcium and intermediate risk

Intermediate Framingham risk scores are a sort of gray zone — too low for very aggressive prevention efforts and too high to do nothing. A report from the Framingham Heart Study shows that in people with intermediate (5%–20%) risk, low calcium scores can be reassuring, while high scores can signal a higher-than-expected risk of having a heart attack.

Coronary artery calcium score




10-year risk of heart attack or dying of heart disease

4% (low)

13% (intermediate)

24% (high)

Not for everyone

The new guidelines on coronary artery calcium don't change our recommendation about it. If your heart disease risk is low or high, don't bother having this test. If your risk is somewhere in between and your doctor recommends getting a calcium score even though you don't have any signs or symptoms of heart disease, it's a reasonable thing to do.

But promise yourself in advance that if the scan turns up anything and you go for an angiogram that shows a narrowed coronary artery, you won't just have a stent popped in. That won't treat the atherosclerosis that is almost certainly elsewhere in your body any more than popping a pimple cures acne. Instead, vow to make changes that will benefit your entire circulatory system, like exercising more, losing weight, and possibly taking medications.

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