NEW ORLEANS — Finally, someone has developed a nomogram devised just for women that calculates exercise capacity as a percentage of normal for age.
Until now, the only nomogram available for assessing exercise capacity as the percentage of normal for age was based on observations in men. But gender is one of the key factors that defines normal exercise capacity, which means that exercise capacity in women has been erroneously assessed, Martha Gulati, M.D., said at the annual scientific sessions of the American Heart Association.
The exercise-capacity nomogram for men is currently recommended for use in both sexes in the joint guidelines of the American College of Cardiology and American Heart Association.
Although these two equations differ by just a small multiplicative factor (a difference of 0.02 metabolic equivalents [METs]), when the difference is multiplied by age, it creates a substantial difference.
For example, a 50-year-old woman will have a normal exercise capacity 1.0 METs less than what is calculated for a man—a major difference, given that normal exercise capacity for a 50-year-old woman is 8.2 METs, said Dr. Gulati, a cardiologist at Rush University Medical Center in Chicago. (See box.)
One MET is the amount of oxygen a person consumes while at rest. The new formula for calculating normal exercise capacity in METs in women is 14.7–0.13 (age), and in men, 14.7–0.11(age).
This difference means that when women were held to the male standard for exercise capacity, they were expected to have a greater capacity than they should have. As a result, an excess of women were diagnosed with impaired exercise capacity, Dr. Gulati said.
The new nomogram was derived from exercise data collected from 5,721 women from the Chicago area who were asymptomatic for coronary disease, older than 35 years, and participants in the St. James Women Take Heart Project.
The women's nomogram was then validated using another set of exercise test results that had been collected from 4,471 women with coronary disease symptoms who participated in the Economics of Noninvasive Diagnosis study.
Follow-up survival data were collected for both groups of women for an average period of about 5 years. Survival data from the asymptomatic women showed that those whose exercise capacity was less than 85% of normal for age were twice as likely to die from cardiac causes as women with an exercise capacity of 85% or greater. Follow-up of the symptomatic women showed that baseline exercise capacity of less than 85% of normal was linked with a 2.4-fold increased risk of death from cardiac causes, Dr. Gulati reported.
Source: Dr. Goldberg