Stress Test Gauges Women's Risk of Death From Heart Disease
This new, more accurate model uses data based on women, not men, study reports
WEDNESDAY, Aug. 3, 2005 (HealthDay News) -- When assessing fitness levels to predict who is most at risk to die of heart disease, doctors have had to rely on standards set by research done only on men, which often meant women were incorrectly diagnosed.
But doctors at Northwestern Memorial Hospital in Chicago have developed a simple chart for women based on new data to more accurately identify those most at risk of mortality based on their fitness level as determined by a treadmill stress test.
The data is based on an analysis of stress tests of more than 10,000 women, both those who were healthy and those at risk for heart disease. The researchers then used this information to determine what could be considered normal exercise capacity and fitness levels for women at different ages.
"We just didn't have guidelines for women -- we knew the ones we had weren't relevant because of our clinical experience. But we now have standards for women for their ages and fitness levels," said study author Dr. Martha Gulati, an assistant professor at Northwestern Memorial Hospital's Bluhm Cardiovascular Institute.
Gulati said the guidelines are important because research has increasingly shown that fitness levels as measured by a standard stress test are an independent predictor of mortality risk, particularly for heart disease.
And while more research is needed to determine whether it's cost-effective for healthy women to undergo stress tests to assess mortality risk as part of a normal physical examination, doctors now have the tools to more accurately identify women at risk, she said.
Men have more exercise capacity than women, a gap that increases as men and women age. This meant that exercise/mortality risk assessments based on studies of men incorrectly identified too many women as at high risk of death, Gulati said.
"If we used the male values, we would identify more women at risk than who really are," she said.
The new guidelines are 15 percent more accurate in identifying those healthy women at risk of death based on their fitness levels than the former, male-based standards. And they are 17 percent more specific in teasing out who is not at risk of death from heart disease, Gulati said.
Results of the research appear in the Aug. 4 issue of the New England Journal of Medicine.
Using the new data, and a chart to track the data called a nomogram, Gulati and her colleagues found that otherwise healthy women whose exercise capacity was less than 85 percent of the age-predicted level had twice the risk of death, compared to women reaching at least 85 percent. The majority of the women did have fitness levels at 85 percent or above. Among the women diagnosed with coronary disease symptoms, those whose exercise capacity was less than 85 percent were 2.4 times more likely to die from cardiovascular disease, the study found.
"This gives us evidence to give these women a reason to start working out," Gulati said.
For the study, Gulati and her colleagues reviewed data from 5,721 healthy women from the St. James Women Take Heart Program in Chicago, and from 4,471 women who were evaluated for suspected coronary disease at six medical centers. All the women had taken standard stress tests on a treadmill that measured their maximal oxygen intake "as expressed in metabolic equivalents (MET)." The researchers then studied the number of deaths in both groups over a five- to eight-year period, starting in 1992.
In the group without heart disease symptoms, there were 180 deaths (3 percent), 58 from cardiac causes over the eight-year period. In the group with symptoms, there were 537 deaths (12 percent), 45 from cardiac causes in a five-year follow-up.
Gulati said the study is dedicated to the late Dr. Arfan Al-Hani, who designed the St. James Women Take Heart Project nearly 15 years ago.
"We are very indebted to him. In 1992, we weren't talking about women and heart disease, and without his foresight, this study would not have been possible," she said.
In an editorial accompanying the study, Drs. William E. Kraus and Pamela S. Douglas of Duke University Medical Center noted that while many doctor/patient consultations about heart disease include questions about cholesterol, diet and tests like electrograms, the importance of exercise is often neglected, despite proof of its strong impact in reducing risk of death.
"We hope that this report will provide a stimulus to reintroduce fitness assessments into the routine clinical environment for both women and men," they wrote.
Dr. Nieca Goldberg, chief of women's cardiac care at New York City's Lenox Hill Hospital, said, "This is a really well-done study and very timely. We had no frame of reference for women, and this gives us a format to assess" the risk of mortality for women.
"This is a terrific study," agreed Dr. Alison Schecter, co-director of Women's CARE in the Cardiovascular Institute at Mount Sinai Medical Center in New York City. "It's important to exercise, but important to know how much exercise to do, and these guidelines will help doctors help patients."
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