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,
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 Johns Hopkins team reports that 90
percent of men and women with no early signs of coronary
heart disease, or 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 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," said
senior study author and cardiologist Roger S. Blumenthal,
an associate professor and director of the Ciccarone
Preventive Cardiology Center at the School of Medicine and
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 FRS 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
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 Johns 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
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
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
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
"Our best means of preventing coronary heart disease
is to identify those most likely to develop the condition
and intervene before symptoms appear," said the study's
lead author, cardiologist Samia Mora, then a research
fellow at Johns 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.
Other researchers involved were Rita Redberg, of the
University of California, San Francisco; and A. Richey
Sharrett, of Johns Hopkins.