6-minute walk test, exercise testing provide similar prognostic value in patients with chronic heart failure

The 6-minute walk test performed similarly to cardiopulmonary exercise testing in patients with heart failure, according to a new study.

Data from the HF-ACTION (Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training) trial were used to compare the prognostic efficacy of both tests in outpatients who had chronic systolic heart failure and were in stable condition (New York Heart Association class II and III, ejection fraction ≤35%). Study end points were all-cause mortality or hospitalization and all-cause mortality alone over 2.5 years of mean follow-up as predicted by distance on the 6-minute walk test or cardiopulmonary exercise testing (peak oxygen consumption [VO₂] and ventilatory equivalents for exhaled carbon dioxide [VE/VCO₂] slope). The study results were published online Nov. 21 by the Journal of the American College of Cardiology.

Overall, 2,054 patients had exercise testing and performed the 6-minute walk test at baseline. Patients' median age was 59 years, and most (71%) were men. Sixty-four percent had class II heart failure and 36% had class III/IV heart failure.

C-indices for distance on the 6-minute walk test were 0.58 and 0.65 in unadjusted models and 0.62 and 0.72 in adjusted models for predicting all-cause mortality or hospitalization and all-cause mortality alone, respectively. Corresponding C-indices for peak VO₂ were 0.61 and 0.68 in unadjusted models and 0.63 and 0.73 in adjusted models, while C-indices for VE/VCO₂ slope were 0.56 and 0.65 in unadjusted models and 0.61 and 0.71 in adjusted models. C-indices did not change appreciably when both exercise testing variables were combined. In adjusted models, 6-minute walk distance and exercise testing variables were found to have similar prognostic value.

The authors noted that HF-ACTION was an exercise training trial and that its exercise intervention may have affected their findings, among other limitations. However, they concluded that both the 6-minute walk test and cardiopulmonary exercise testing had similar value in predicting all-cause hospitalization and mortality and all-cause mortality alone in outpatients with stable heart failure.

They did note that each test's results had only a modest prognostic effect when added to prediction models that use other major demographic and clinical covariates. Nevertheless, they wrote, “these data suggest that a [6-minute walk] test may be substituted for [cardiopulmonary exercise] testing as an inexpensive, practical clinical tool to help gauge prognosis in the large and growing [heart failure] population.”

The author of an accompanying editorial noted that according to the study results, the 6-minute walk test may be preferred for clinical research studies on heart failure and can help clinicians diagnose the cause of patients' dyspnea or fatigue. It may also be useful for determining progress of therapy or clinical course in some patients with heart failure or pulmonary arterial hypertension, he observed.

“However,” the editorialist wrote, “predicting adverse events in heart failure … largely rests on clinical and demographic variables.” The current study, he concluded, “demonstrate[s] that prediction of prognosis was little enhanced by adding the results of either the [6-minute walk] or the [cardiopulmonary exercise] test.”