Improved reclassification of mortality risk by assessment of physical activity in patients referred for exercise testing

Background Inability to meet minimal guidelines on physical activity is associated with poor health outcomes, but quantifying activity can be complex. We studied whether a simple question regarding participation in regular activity improves risk classification for all-cause mortality. Methods Maximal exercise testing was performed in 6962 patients (mean age, 58.9 ± 11 years) for clinical reasons. Subjects also were assessed for participation in regular activity using a simple yes/no response to meeting minimal recommendations on activity. The incremental value of adding a simple physical activity assessment to clinical, demographic, and exercise test information to predict mortality was determined using Cox proportional hazards models, net reclassification improvement, and integrated discrimination index during a mean follow-up of 9.7 ± 4 years. Results Subjects who did not meet the minimal guidelines on activity had a lower exercise capacity (7.4 ± 4.3 vs 9.1 ± 3.6 metabolic equivalents, P <.0001) and a higher annual mortality rate (2.42% vs 1.71%, P <.001). Not meeting activity guidelines was associated with an age-adjusted 36% higher risk of mortality (hazard ratio, 1.36; 95% confidence interval, 1.22-1.51, P <.0001). Among clinical and exercise test variables, fitness had the highest C-index for predicting mortality (0.72, P <.001). The addition of physical activity classification to a model including traditional risk factors resulted in a net reclassification improvement of 22.8% (P <.001); adding fitness to the traditional risk factor model resulted in a net reclassification improvement of 43.5% (P <.001). Conclusions The addition of a simple assessment of physical activity status significantly improves reclassification of risk for all-cause mortality among patients who are referred for exercise testing.