Useful Are Coronary Calcium Scans?
This simple test can identify atherosclerosis
but may not accurately predict heart attack risk.
Most healthy people who are concerned about their risk of a
heart attack are familiar with their cholesterol and blood pressure
measurements. Now many are asking: Should they also know their
Calcium in the coronary arteries indicates atherosclerosis—the
buildup of plaques that can lead to heart attacks. New imaging
technologies called electron-beam computed tomography (EBCT)
and multidetector computed tomography (MDCT) are now available
to measure coronary calcium. This development has led to hospitals
and testing clinics advertising EBCT and MDCT scans that may
provide a quick, easy, accurate way to assess the presence and
severity of coronary atherosclerosis and the risk of a heart
Yet earlier this year, the government’s Preventive Services
Task Force recommended that EBCT not be used to screen healthy
people unless they have known coronary heart disease (CHD) risk
factors or symptoms—and that even then, the usefulness
of the test is unclear.
What Are EBCT and MDCT?
EBCT and MDCT, also known as ultra-fast CT, are painless, five-
to eight-minute tests. The patient lies face up on an examination
table under a CT scanner. An electron beam generates x-rays (four
times as strong as a simple chest x-ray) that pass through the
patient’s body. Calcium in artery walls appears as whitish
spots or streaks on the x-rays.
Technicians identify the calcium deposits in the images, then
use a computer program to derive a coronary artery calcium score
that reflects the total calcium “load” in the coronary
arteries. Scores of 0 to 10 reflect arteries largely free from
coronary plaque (minimal coronary calcification). Scores of 11
to 400 indicate mild to moderate plaque buildup; scores above
400 indicate extensive plaque.
What the Score Reveals . . .
Many studies have shown that people with higher calcium scores
are at greater risk for heart attacks and strokes and that those
with very low scores are at relatively low risk over the next
five years. What has been controversial is whether calcium screening
with EBCT or MDCT adds useful information beyond that provided
by standard risk factors (cholesterol, blood pressure, triglycerides,
obesity, smoking, diabetes, age, and family medical history).
A September 2003 study in Radiology showed that calcium
screening adds considerable predictive value. Researchers tested
more than 10,000 people between the ages of 30 and 85 who were
at above-average risk for CHD but had no symptoms. Increased
calcium scores were associated with substantially worse survival
five years later.
A January 2004 study in the Journal of the American Medical
Association (JAMA) revealed similar findings: In testing
1,461 asymptomatic adults with at least one CHD risk factor,
a calcium score above 300 was associated with a large increase
in the risk of heart attacks (or other CHD-related deaths)
compared with risk predicted by the Framingham Risk Score,
which uses age, blood pressure, cholesterol levels, and smoking.
. . . And What It Doesn’t
While there is widespread agreement among cardiologists that
EBCT and MDCT can correctly identify the presence and extent
of atherosclerosis, there is less agreement over what to do with
the information and how accurately the results can predict the
risk of a heart attack. Increasingly, experts have recognized
that a heart attack most commonly occurs when a soft, unstable
plaque in the artery wall breaks open and causes the formation
of an artery-plugging blood clot. But EBCT and MDCT, as well
as other types of imaging studies, can’t reliably distinguish
between stable and unstable plaques. In the JAMA study,
for example, low calcium scores did not totally preclude heart
attack risk. However, it is clear that the more calcified plaque
that is present, the more numerous are the softer, noncalcified
In addition, because EBCT and MDCT are relatively new, researchers
are still refining the implications of different calcium scores.
Generally, an individual’s score is compared with the average
score for someone the same age and gender. But more clinical
data are needed to establish standardized risk thresholds and
treatment guidelines for specific scores.
What To Do Now
Because no study has examined the outcome of using calcium scores
as a guide in determining treatment for asymptomatic individuals,
the U.S. Preventive Services Task Force has recommended against
routine EBCT and MDCT screening for the general population—arguing
that screening may occasionally cause unnecessary further invasive
testing and treatment in patients with positive calcium scores.
The American College of Cardiology and the American Heart Association
also argue that more data are needed to clearly determine who
will benefit from EBCT or MDCT screening and whether the tests
are significantly better as screening tools than standard, less
expensive, readily available tests with decades of research behind
Many experts feel that ECBT and MDCT should not be stand-alone
tests—they should be done with your doctor’s supervision
and interpretation. And even in a comprehensive clinical setting,
scanning doesn’t necessarily provide useful additional
information for everyone. For example, most (though not all)
patients at low risk according to Framingham scores will also
have low calcium scores (unless they have a family history of
premature CHD), while high-risk patients should be treated aggressively
no matter what a calcium scan would show. In the JAMA study
cited above, knowing the calcium scores did not substantially
change the predicted risk for patients considered at low risk
or high risk according to their Framingham scores.
But for the many adults at intermediate risk—with a Framingham
score showing a 10% to 20% risk of a CHD event in the next 10
years—screening can be valuable. Such patients potentially
could be candidates for aggressive preventive therapy with aspirin
and blood pressure- and cholesterol-lowering medication (if they
have a very high calcium score for their age).
Knowledge of calcium scores might also motivate intermediate-risk
patients to comply with healthier lifestyle habits and medical
therapy, though research into the roles EBCT and MDCT might play
in patient compliance has only just begun. Others who could potentially
benefit from EBCT and MDCT are people at low risk according to
Framingham scores but with other well-established risk factors
not utilized by Framingham, such as metabolic syndrome, obesity,
or a family history of premature CHD.
Developing a consensus on guidelines concerning the role of
EBCT and MDCT in primary heart attack prevention will require
a number of carefully conducted trials. The clearest picture
yet should emerge from the Multi-Ethnic Study of Atherosclerosis
(MESA), an ongoing National Institutes of Health study of various
imaging technologies that will include the most rigorously conducted
assessment to date of EBCT in 6,700 asymptomatic people with
different ethnic and racial backgrounds. Johns Hopkins is one
of seven participating research centers, and results from this
study are expected in 2008.