Fitness level and heart rate recovery time after exercise are more accurate predictors of heart disease risk in women than electrocardiograms, according to an article in the September 24th issue of the Journal of the American Medical Association.

American researchers assessed data from nearly 3,000 women ages 30 to 80 years at baseline who had participated in an earlier study that involved treadmill exercise testing. Of possible measures of risk, peak exercise capacity and heart rate recovery time (peak heart rate minus heart rate two minutes after exercise) best predicted risk of death from heart disease or other causes.

The researchers also demonstrated that ST-segment depression on an electrocardiogram did not accurately identify women with hidden heart disease.
Overall, after adjustment for many risk factors, 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 in those measures.

Among women with seemingly low risk for heart disease based on traditional criteria, those who scored below average on the 2 test measures were nearly 13 times more likely to die of heart disease than those who performed better. Risk for death increased gradually with each level of poorer performance, with researchers noting the difference death rates as early as 1 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, M.D., senior study author. He emphasized that the study findings support the potential role of exercise treadmill testing for further risk analysis in women with low or intermediate risk scores on the Framingham scale, the commonly used method that uses factors such as age, cholesterol level, and smoking status to estimate a person's risk for heart disease within a 10-year time period.

Blumenthal and colleagues evaluated data from the national Lipid Research Clinics Prevalence Study, a multicenter U.S. trial conducted from 1972 to 1976. They studied death rates and causes of death among 2,994 seemingly healthy women who were followed for an average of 20 years after their exercise test by annual mailed questionnaires, telephone interviews, 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 (34 percent) were due to heart disease. Women with high levels of exercise capacity and heart rate recovery 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 poorer heart rate recovery times.

When the study population was divided into four groups based on average values for exercise capacity and heart rate recovery, women below average for both 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 3 categories based on exercise capacity and heart rate recovery: above average in both test variables, above average in 1 variable, and below average in both. Compared with women who scored above average in both variables, those who scored below average in 1 variable were 4 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 intervene against other risk factors, according to the authors. "Our study suggests that women may benefit from higher fitness levels, independent of changes in weight, blood pressure or cholesterol levels," said Samia Mora, M.D., M.H.S., lead study author. "Exercise capacity might be improved by 15 to 30 percent with moderate, regular physical activity."