Current risk-assessment techniques
in heart disease have one thing in common — they
generally leave the physician no wiser as to whether a
patient at intermediate risk actually needs treatment.
Thankfully, a better predictor of coronary risk may be
just on the horizon. A fast CT scan of calcium in the
coronary arteries performed better than the established
Framingham risk index, reports a study conducted at St
Francis Hospital in New York.
"Increasing the accuracy of risk
stratification through the use of fast CT scanning provides
a very direct benefit to patients," says Dr Alan Guerci,
lead author of the St Francis Heart Study published
July 5 in the Journal of the American College of
Cardiology. "Many patients classified at intermediate
risk with clear signs of underlying disease can get
potentially life-saving treatment, while others with
no signs of disease can be spared an unnecessary and
expensive regimen of medications."
TO
PUT IT BLUNTLY
When it comes to assessing coronary risk, physicians
around the world generally turn to the tried and tested
Framingham criteria — a simple equation that uses
risk factors like obesity and smoking to stratify patients
into high, low and intermediate categories. But the
number of patients in each category is vast, and few
cardiologists are happy with a blunt instrument that
lumps about a quarter of Canadians aged 40-70 into the
intermediate risk category.
The discovery of the role of C-reactive
protein (CRP) allowed some refinement in risk calculation
but made the equation more complicated. The latest study
suggests that CT scanning can more accurately predict
cardiovascular events than even Framingham and CRP combined.
Between 1996 and 1999, the researchers
put 4,903 asymptomatic men and women aged 50-70 through
electron beam CT scanning of the coronary arteries.
After 4.3 years, 119 had sustained at least one atherosclerotic
cardiovascular disease event, such as coronary death,
heart attack or bypass surgery. All these subjects had
higher baseline scores of coronary artery calcium, a
major ingredient of atherosclerotic plaque. A scoring
system that measured calcium in the coronary arteries
and nothing else was able to predict adverse events
more accurately than Framingham alone, or a scoring
system that included CRP. The technique also enabled
researchers to predict which patients were most at risk
within a given Framingham risk category.
NARROWING
THE FIELD
In 50% of cases of coronary artery disease, a heart
attack is the first visible symptom of illness. But
giving drugs to all those potentially at risk is not
only expensive, it's potentially dangerous. Too many
new drugs that were introduced to prevent heart disease
have been found later to have unforeseen ill effects.
The latest study "shows that CT scanning of coronary
arteries can be used to refine the standard risk categories,"
says Dr Guerci. "Our study creates a very strong argument
for scanning all patients at intermediate risk according
to the Framingham criteria."
There is one fly in the ointment.
A companion study tested a combination of vitamins C
and E, low-dose aspirin, and 20mg atorvastatin in the
subjects with the highest calcium scores. The drug regimen
appeared to reduce adverse cardiovascular events by
about a third over the four-year study period. Yet it
didn't retard progression in coronary calcium scores
measured by CT scan. So the technique can't be used
to monitor the effectiveness of lipid treatment. There
is still no explanation for this discrepancy.
J Am Coll Cardiol Jul 5, 2005;46:158-65
|
