Newswise — Performing cardiac
stress tests that measure exercise capacity and heart rate recovery
can improve dramatically on existing techniques that predict who is
most likely to suffer a heart attack or die from coronary heart
disease (CHD), the leading cause of death in the United States, a
team of cardiologists at Johns Hopkins reports.
In the Sept. 13 edition of the
journal Circulation, the Hopkins team reports that 90 percent
of men and women with no early signs of CHD who, nevertheless, died
from it had had below average results from their cardiac stress
tests conducted 10 to 20 years earlier.
The team’s analysis showed these
asymptomatic people were two to four times more likely to die from
CHD within 10 to 20 years than people with average or
better-than-average stress test results, even though traditional
scoring for major risk factors for the disease, such as such as age,
blood pressure, blood cholesterol levels and smoking status, had
determined the asymptomatic people to be at low or intermediate risk
of having heart problems.
According to the cardiologists,
these exercise stress tests are easy to perform, lasting less than
20 minutes and requiring only that a person walk on a treadmill at
progressively higher speeds and inclines every three minutes until
they become markedly fatigued. During the test, people are hooked up
to a heart monitor.
“This is the strongest evidence to
date that selective use of cardiac stress testing improves
prediction of who is really at high risk of suffering a fatal heart
attack when traditional risk assessment suggests they are not at
high risk of a heart attack within the next 10 years,” says senior
study author and cardiologist Roger S. Blumenthal, M.D., an
associate professor and director of the Ciccarone Preventive
Cardiology Center at The Johns Hopkins University School of Medicine
and its Heart Institute.
The traditional risk factors
combine to give a score called the Framingham Risk Score, or FRS,
that was developed in the last 20 years. Considered the gold
standard, the score is based on a summary estimate of the major risk
factors for heart disease: age, blood pressure, blood cholesterol
levels and smoking status. It consists of a percentage range of how
likely a person is to suffer a fatal or nonfatal heart attack within
10 years.
However, Blumenthal says that many
people, especially women, with cardiovascular problems go undetected
despite use of the Framingham score, which does not factor in a
person’s family history, weight or exercise habits. Blumenthal is
also a spokesman for the American Heart Association, which estimates
that 656,000 Americans died from CHD in 2002, the last year for
which statistics are available.
More than 6,100 people took part
in the study, conducted from 1972 to 1995, and part of a larger
project known as the Lipid Research Clinics Prevalence Study. All
participants in this smaller Hopkins study were age 30 to 70. None
had early signs of heart disease, but every participant did have at
least one major risk factor for it.
At 10 medical centers across the
United States, study participants were given a physical examination,
had blood tests performed and were scored on the FRS. Each
participant also underwent cardiac stress testing, which included
stress testing for exercise capacity and heart rate recovery, plus
any changes in the heart’s electrical signaling that are typical of
decreased blood flow to the heart muscle.
Those with a Framingham score of
less than 10 percent were gauged to be at low risk for future CHD,
while participants with a score between 10 percent and 20 percent
were ranked at intermediate risk for future CHD, and those with a
score higher than 20 percent were judged to be at high risk of CHD.
Once participants were ranked by
Framingham score, the researchers monitored their health every six
months until death or the end of the study to find out who did or
did not die from a heart attack or CHD.
Cardiac stress testing is used to
gauge how well the heart works when it has to pump harder and use
more oxygen, for example, while walking on a treadmill. The
exercise, sustained for five to 10 minutes, mimics the strain placed
on the heart when arteries are blocked or narrowed.
The researchers goal, however, was
to determine if more accurate prediction of whether or not a person
will die from a heart attack could be made by adding exercise
capacity and heart rate recovery to current assessment techniques
that relied mostly on monitoring the heart’s electrical signaling.
During stress testing, a person’s
breathing, blood pressure and heart rate are monitored while the
intensity of their exercising is slowly increased to see how their
heart responds. The amount, in number of beats per minute that the
heart rate drops two minutes after exercise stops, is also recorded
to determine heart rate recovery.
Using tables that take into
account a person’s age, gender and weight, the results can be
compared against average scores to see if a person is below, at or
above the norm. There is very little risk of harm associated with
the testing because participants are closely monitored.
The researchers report that 246
participants died from CHD even though they had initially been
categorized by their FRS as at either low or intermediate risk of
the disease. However, 225 of those who died also had below average
test scores for exercise capacity and heart rate recovery.
“Our best means of preventing
coronary heart disease is to identify those most likely to develop
the condition and intervene before symptoms appear,” says the
study’s lead author, cardiologist Samia Mora, M.D., M.H.S., then a
research fellow at Hopkins.
“Cardiac stress testing could
significantly improve our abilities to find and aggressively treat
these people so that they are much less likely to suffer a heart
attack.”
According to the researchers,
these latest results support conclusions from earlier this year that
traditional risk assessment with the FRS can be improved with
selective use of cardiac CT scans to measure calcium scores in
individuals with more than one risk factor, such as obesity,
smoking, sedentary lifestyle or a family history of heart disease.
Funding for the study was provided
by the Maryland Athletic Club Charitable Foundation in Lutherville,
Md.
Other researchers involved were
Rita Redberg, M.D., M.Sc., from the University of California in San
Francisco; and A. Richey Sharrett, M.D., Dr.P.H., from Hopkins.
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