In two-thirds of women who die suddenly from heart disease there are no warning signs. But a new study reveals that how long a woman can exercise and how quickly her heart rate returns to normal following a workout may be a better indicator of heart attack risk than an EKG.
An ST segment depression on an electrocardiogram, or EKG, suggests decreased blood flow, which is usually the result of a blocked artery. Studies on men undergoing EKGs have shown the test to be a good predictor of heart disease. In this study, the John’s Hopkins researchers found that ST segment depression on an EKG did not help doctors predict cardiovascular death in women.
The study is published in the September 24th issue of the Journal of the American Medical Association.
In it, lead investigator, Dr. Samia Mora and others write, "Our study underscores the independent value of exercise capacity in predicting cardiovascular and overall risk in asymptomatic women…and suggest that low levels of both HRR (heart rate recovery) and exercise capacity have significantly worse prognosis, even after accounting for age and other risk factors."
The study involved nearly 3000 women, ages 30 to 80, with no apparent symptoms of heart disease. All were given an exercise test to measure the length of time they could run on a treadmill as well as their heart rate recovery, which is the difference between the peak heart rate and the resting heart rate two minutes after completing the exercise.
The researchers took into consideration other risk factors for heart disease using the Framingham risk equation. It estimates the risk of experiencing a coronary event over 10 years based on certain factors such as high blood pressure, obesity, high cholesterol, family history and smoking. Using the Framingham risk scores, 95 percent of the women were at low risk, with four percent at intermediate risk, and one percent at high risk.
After following the study participants for 20 years there were a total of 427 deaths. Of those, 147 were cardiovascular deaths. The women with the lowest fitness levels were 3.5 times more likely to die of heart disease than the women who performed better on the treadmill tests. Study participants with the highest levels of exercise capacity and heart rate recovery had fewer deaths.
When the researchers looked at only those women with low Framingham risk scores, those who scored below average on the exercise measures were almost 13 times more likely to die of heart disease than those with a high fitness level. Death risk increased gradually as the exercise performance level got worse. The researchers noted the difference as early as one year following the treadmill test.
"There has to be a new assessment of how we evaluate heart disease in women," said Dr. Nieca Goldberg, chief of the Women’s Heart Program at Lenox Hill Hospital in Manhattan, who was not involved in the study.
The stress test, or exercise capacity test, has been around for more than 30 years, and Goldberg says overall more men are sent for stress tests than women.
"Initially when the stress test was done they just focused on the changes in the EKG that ST segment depression," Goldberg said, "but in fact it didn’t matter if the EKG changes were present in this particular study, what was really predictive was the length of time that the women spent on the stress test."
The researchers say this study sheds new light on the significance of staying physically fit, and that it’s not only being able to exercise, but that women who can exercise longer are at a lower risk for heart disease.
Goldberg says women who are having symptoms of heart disease should definitely get a stress test. Also, asymptomatic women who have never participated in an exercise program and who are thinking of starting a routine should also be tested. And those women who have multiple risk factors for heart disease such as high blood pressure, diabetes, and smoking should have a stress test prior to beginning an exercise program.