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Heart scans hold intermediate promise

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.

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. 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. 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.

At first glance, it doesn’t seem like there could be a downside to measuring coronary calcium. But 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. 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. 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. 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

0–99

100–399

400+

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. Instead, vow to make changes that will benefit your entire circulatory system, like exercising more, losing weight, and possibly taking medications.

August 2007 update

Help prevent coronary artery disease with this heart health report
Click to enlarge

Beating Heart Disease

If you follow the news about heart disease closely, it’s easy to be overwhelmed or confused about what puts you at risk and how you can protect yourself. This report helps you identify the risk factors you can control, which range from medical conditions such as high blood pressure to lifestyle choices such as an unhealthy diet or lack of exercise. Read more

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