Prognostic comparison of the FRIEND and Wasserman/Hansen peak VO2 equations applied to a submaximal walking test in outpatients with cardiovascular disease.

AIMS: The aim of this study was to determine the ability to predict all-cause mortality using established per cent-predicted (%PRED) equations for peak oxygen consumption (VO2peak) estimated by a submaximal walk test in outpatients with cardiovascular disease. METHODS: Male patients (N = 1491) aged 62 ± 10 years at baseline underwent a moderate and perceptually regulated (11-13 on the 6-20 Borg scale) 1-km treadmill-walking test to estimate VO2peak. %PRED was derived from the Fitness Registry and the Importance of Exercise: A National Data Base (FRIEND) and the Wasserman/Hansen equations. RESULTS: There were 215 deaths during a median 9.4-year follow-up. The FRIEND prediction equation provided better prognostic information with receiver operating curve analysis showing significantly different areas under the curve (0.72 and 0.69 for the FRIEND and the Wasserman/Hansen equations respectively, p = 0.001). Overall mortality rate was higher across decreasing tertiles of %PRED using FRIEND, with 26%, 11% and 5% for the least fit, intermediate and high fit tertiles, respectively (p for trend < 0.0001). Compared with the least fit tertile, the adjusted hazard ratios for the second and third tertiles were 0.54 (95% confidence interval 0.34-0.87, p = 0.01) and 0.45 (95% confidence interval 0.25-0.81, p = 0.008), respectively. Each 1% increase in %PRED conferred a 3% improvement in survival (p = 0.0004). CONCLUSION: Low %PRED VO2peak in cardiac outpatients determined by the FRIEND equation was associated with a high mortality rate independent of traditional cardiovascular risk factors and clinical history. The FRIEND equation may provide a suitable normal standard when applied to clinically stable outpatients with cardiovascular disease.

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.

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.