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September 23, 2003
MEDIA CONTACT: Karen Blum
Exercise Measures Identify Heart Disease in Seemingly Healthy Women
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," says Roger S. Blumenthal, M.D., senior study author and Hopkins' director of preventive cardiology. The results, he emphasizes, 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.
"Our study suggests that women may benefit from higher fitness levels, independent of changes in weight, blood pressure or cholesterol levels," adds Samia Mora, M.D., M.H.S., lead study author and a senior clinical fellow in Hopkins' Division of Cardiology. "Exercise capacity might be improved by 15 to 30 percent with moderate, regular physical activity."
Blumenthal and Mora caution 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, M.D., Dr.P.H., of Johns Hopkins; Rita F. Redberg, M.D., of the University of California-San Francisco; and Yadong Cui, M.D., Ph.D., Maura K. Whiteman, Ph.D., and Jodi A. Flaws, Ph.D., of the University of Maryland-Baltimore.
Mora, Samia et al, "Ability of Exercise Testing to Predict Cardiovascular and All-Cause Death in Asymptomatic Women," JAMA, Sept. 24, 2003, Vol. 290, No. 12.
Johns Hopkins' Division of Cardiology
The Journal of the American Medical Association