A woman's fitness level and the time it takes for her
heart to return to normal after exercise are more accurate
predictors of female heart disease risk than electrical
recordings of the heart, according to a national study led
by Johns Hopkins researchers.
Among nearly 3,000 women ages 30 to 80 who underwent
treadmill exercise tests, these fitness measures clearly
identified women at risk for death from heart disease or
any cause. Specifically, peak exercise capacity (obtained
from the length of time women could exercise during a
standard treadmill test) and heart rate recovery or HRR
(peak heart rate minus heart rate two minutes after
exercise) predicted risk of death from heart disease or
other causes.
Results of the study, published in the Sept. 24 issue
of the Journal of the American Medical Association,
also demonstrated that ST-segment depression (a measure of
decreased blood flow) on electrocardiogram readings —
used to diagnose hidden heart disease in men — did
not accurately identify women with hidden heart disease.
Overall, after accounting for many risk factors,
scientists found that women who performed below average in
peak exercise capacity and recovery rate were 3.5 times
more likely to die of heart disease than women who were
above average. Among women with seemingly low risk for
heart disease based on traditional criteria, those who
scored below average on these measures were nearly 13 times
more likely to die of heart disease than those who
performed better on the tests. Death risk increased
gradually with each level of poorer performance, and
researchers noted the difference as early as one year after
the treadmill test.
"There is great public health interest in
cost-effective and readily available tests that can predict
cardiovascular risk in asymptomatic women, since nearly
two-thirds of women who die suddenly have no previous
symptoms," said Roger S. Blumenthal, senior study author
and Hopkins' director of
Preventive Cardiology. The results, he emphasized,
support the potential role of exercise treadmill testing
for further risk analysis in women with low or intermediate
risk scores on the Framingham scale, a method that uses
factors such as age, cholesterol level and smoking status
to tally a person's risk for heart disease within a 10-year
time period.
Blumenthal and colleagues examined data from the
national Lipid Research Clinics Prevalence Study at Hopkins
and nine other medical centers from 1972 to 1976. They
studied death rates and causes among 2,994 seemingly
healthy women who were followed for an average of 20 years
after their exercise test by annual mailed questionnaires
and/or telephone or home visits. Deaths were ascertained by
death certificates, hospital records or speaking with the
participants' family members. Only 3 percent of women were
taking cholesterol-lowering medications at the study's
start.
During the follow-up period, there were 427 deaths, of
which 147, or 34 percent, were due to heart disease. Women
with high levels of exercise capacity and HRR had fewer
deaths during the follow-up period. On average, they were
younger, reported more regular exercise and had more
favorable clinical and exercise tests compared with women
who had lower exercise capacity or HRR.
When the study population was divided into four groups
based on average values for exercise capacity and HRR,
women below average for these two factors were 3.5 times
more likely to die of heart disease than women who were
above average. Death risk increased progressively for women
in each grouping below average.
The researchers then divided the 2,817 women with
low-risk Framingham scores into the following three
categories based on exercise capacity and HRR: above
average in both test variables, above average in one of the
variables, and below average in both. Compared to women who
scored above average in both variables, those who scored
below average in one of the variables were four times more
likely to die of heart disease. Those who scored below
average in both were 13 times more likely to die.
Regular exercise is the best way to combat your risk
factor, researchers say.
Samia Mora, lead study author and a senior clinical
fellow in Hopkins' Division of Cardiology, said, "Our study
suggests that women may benefit from higher fitness levels,
independent of changes in weight, blood pressure or
cholesterol levels. Exercise capacity might be improved by
15 to 30 percent with moderate regular physical
activity."
Blumenthal and Mora cautioned that sedentary women or
those with multiple risk factors should check with their
health care providers before starting a vigorous exercise
program.
The study was supported by the National Heart, Lung
and Blood Institute and by the nonprofit Maryland Athletic
Club and Wellness Center and Shoppers Food Charitable
foundations. Co-authors were A. Richey Sharrett, of Johns
Hopkins; Rita F. Redberg, of the University of California,
San Francisco; and Yadong Cui, Maura K. Whiteman and Jodi
A. Flaws, all of the University of Maryland, Baltimore.