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
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
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
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
10-year risk of heart attack or dying of heart
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
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