Nomogram developed to assess exercise-related mortality risk

Clinicians could use information about a patient’s exercise capacity and age to develop an exercise prescription.

The relationship between exercise capacity and age can be used to predict the risk of mortality in women, and researchers have developed a nomogram to plot this relationship.

Martha Gulati, MD, assistant professor of cardiology and preventive medicine at Northwestern University in Chicago, said exercise capacity evaluations should be a part of all screening visits for women.

“When a patient comes in for screening we do a good job at assessing cholesterol, blood pressure, smoking status and diabetes, but we can also get important prognostic information about exercise capacity beyond a normal or abnormal stress test. Too often, we aren't doing that,” Gulati told Cardiology Today.

The predictive value of exercise capacity has been proven in other studies, but normative values of exercise capacity and age in women had not been established. In an article published in the New England Journal of Medicine, Gulati and colleagues sought to determine a relationship between age, exercise capacity and mortality.

Asymptomatic/symptomatic

Researchers enrolled 5,721 asymptomatic women and performed a symptom-limited maximal stress test. Exercise capacity was measured in metabolic equivalents. Linear regression was used to estimate the mean metabolic equivalent level achieved for age, and a nomogram was established on the basis of age and the exercise capacity achieved.

Similar tests were performed on 4,471 women with cardiovascular symptoms.

Survival data were obtained for both cohorts, and Cox survival analysis was used to estimate the rates of death from any cause and cardiac causes in each group.

The mean age of patients was 52 in the asymptomatic group and 61 in the symptomatic group. Asymptomatic women were more likely to be white (85% vs. 62%); symptomatic women were more likely to be black (28% vs. 9%).

Symptomatic women were more likely to have hypertension than asymptomatic women but were less likely to have a family history of CAD or hypercholesterolemia.

Peak exercise capacity was eight metabolic equivalents among asymptomatic women, with a range of 1.4 metabolic equivalents to 20 metabolic equivalents. The peak exercise capacity was 6.9 metabolic equivalents among symptomatic women, with a range of 1.2 metabolic equivalents to 17.4 metabolic equivalents.

Predictive value

Researchers noted a linear relationship between exercise capacity and age in the asymptomatic cohort, as well as a similar relationship in symptomatic women.

In the asymptomatic cohort, there were 180 deaths overall and 58 deaths from cardiac causes during a mean follow-up of 8.4 years. Women with an exercise capacity that fell below 85% of the age-predicted normative value on the nomogram had a hazard ratio for death from any cause of 2.03 (P<.001) and a hazard ratio for death from cardiovascular disease of 2.44 (P<.001).

In the symptomatic population, there were 537 deaths overall and 45 deaths from cardiac causes during a mean follow-up of 5.3 years. Women whose exercise capacity was <85% of the age-predicted normative value on the nomogram had a hazard ratio of 2.37 (P<.001) of death from any cause and a hazard ratio of 2.02 (P<.001) for death from cardiac causes.

Gulati said clinicians could use this information as plotted on a nomogram to give patients an “exercise prescription.”

“Fitness levels should be screened; there’s a prognostic value to one’s fitness level. … Physicians need to be translating that to patients,” Gulati said. – by Jeremy Moore

For more information:

• Gulati M, Black HR, Shaw LJ, et al. The prognostic value of a nomogram for exercise capacity in women. N Engl J Med. 2005;353:468-475