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6-Minute Walk Test Provides Prognostic Utility Comparable to Cardiopulmonary Exercise Testing in Ambulatory Outpatients With Systolic Heart Failure
Study Questions:
What is the prognostic efficacy of the 6-minute walk (6MW) and cardiopulmonary exercise (CPX) tests in stable outpatients with chronic heart failure (HF)?
Methods:
Stable New York Heart Association (NYHA) functional class II and III systolic HF patients (ejection fraction 35%) from the HF-ACTION (Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training) trial were studied. 6MW distance (6MWD) and CPX indices (peak oxygen consumption [VO2] and ventilatory equivalents for exhaled carbon dioxide [VE/VCO2] slope) were compared as predictors of all-cause mortality/hospitalization and all-cause mortality over 2.5 years of mean follow-up.
Results:
A total of 2,054 HF-ACTION participants underwent both CPX and 6MW tests at baseline (median age 59 years; 71% male; 64% NYHA functional class II and 36% NYHA functional class III/IV). In unadjusted models and in models that included key clinical and demographic covariates, C-indices of 6MWD were 0.58 and 0.65 (unadjusted) and 0.62 and 0.72 (adjusted) in predicting all-cause mortality/hospitalization and all-cause mortality, respectively. C-indices for peak VO2 were 0.61 and 0.68 (unadjusted) and 0.63 and 0.73 (adjusted). C-indices for VE/VCO2 slope were 0.56 and 0.65 (unadjusted) and 0.61 and 0.71 (adjusted); combining peak VO2 and VE/VCO2 slope did not improve the C-indices. Overlapping 95% confidence intervals and modest integrated discrimination improvement values confirmed similar prognostic discrimination by 6MWD and CPX indices within adjusted models.
Conclusions:
The authors concluded that in systolic HF outpatients, 6MWD and CPX indices demonstrated similar utility as univariate predictors for all-cause hospitalization/mortality and all-cause mortality.
Perspective:
This study reports that a 6MW test provides useful prognostic information for both the composite outcome of all-cause hospitalization/mortality as well as the outcome of all-cause mortality in NYHA functional class II and III HF outpatients. The prognostic information provided was similar to that for peak VO2 and VE/VCO2 slope attained by using CPX testing. It appears that that a 6MW test may be substituted for CPX testing as an inexpensive, easy to use clinical tool to help determine prognosis in the HF population. It should be noted that although 6MWD and peak VO2 both demonstrated utility as predictors in unadjusted prognostic models for all-cause hospitalization/mortality and all-cause mortality, both measures added only modest prognostic discrimination to models that included important demographic and clinical covariates.
Keywords: Heart Diseases, Prognosis, Walking, Carbon Dioxide, Follow-Up Studies, Oxygen Consumption, Cardiology, Heart Failure, New York, Systole, Exercise Test
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