Determining the best percent-predicted equation for estimated VO2 peak by a 1-km moderate perceptually-regulated treadmill walk to predict mortality in outpatients with cardiovascular disease.

ABSTRACT

OBJECTIVES: To determine the prognostic ability of established percent-predicted equations of peak oxygen consumption (%PRED) estimated by a moderate submaximal walking test in a large cohort of outpatients with cardiovascular disease (CVD). DESIGN: Population-based prospective study. METHODS: A total of 1442 male patients aged 25-85 years at baseline, underwent a moderate perceptually-regulated (11-13 on the 6-20 Borg scale) treadmill walk (1k-TWT) for peak oxygen consumption estimation (VO2 peak). %PRED was derived from ACSM, Ades et al, Morris et al, and the Wasserman/Hansen equations, and their prognostic performance was assessed. Overall mortality was the end point. Participants were divided into quartiles of %PRED, and mortality risk was estimated using a Cox regression model. RESULTS: During a median 8.2year follow-up, 167 all-cause deaths occurred. The Wasserman/Hansen equation provided the highest prognostic value. Mortality rate was lower across increasing quartiles of %PRED. Compared to the first quartile, after adjustment for confounders, the mortality risk decreased for the second, third, and fourth quartiles, with HRs of 0.75 (95% CI 0.44-1.29, p=0.29), 0.67 (95% CI 0.38-1.18, p=0.17), and 0.37 (95% CI 0.10-0.78, p=0.009), respectively (p for trend <0.0001). Each 1% increase in %PRED conferred a 4% improvement in survival. CONCLUSIONS: The percent-predicted VO2 peak determined by Wasserman/Hansen equations applied to the 1k-TWT is inversely and significantly related to survival in cardiac outpatients. The 1k-TWT is a simple and useful tool for stratifying mortality risk in patients participating in secondary prevention programs.