Six-minute walk distance captures broader patient-reported health than peak oxygen uptake in heart failure

Cardiopulmonary exercise testing (CPET) and the six-minute walk test (6MWT) are both used to characterize functional capacity in heart failure (HF), yet whether they carry equivalent information about patients’ perceived health remains unclear.1 Peak oxygen uptake (peak VO2) reflects maximal integrated cardiopulmonary performance and has established prognostic value,2 whereas the 6MWT is self-paced and submaximal, and may better reflect the demands of daily mobility.3 We compared the independent associations of peak VO2 and percentage-predicted six-minute walk distance (6MWD%) with seven patient-reported domains in a large HF cohort. We screened 1618 assessment records from a tertiary cardiac rehabilitation unit (2016–2024); 896 met record-level eligibility criteria, and selection of one assessment per patient yielded 570 unique patients. HF was a pre-existing diagnosis established by cardiology or cardiovascular surgery specialists according to diagnostic standards in use at the time and was not retrospectively reassigned. New York Heart Association (NYHA) class was available in 543 patients (I, n = 159; II, n = 243; III, n = 117; IV, n = 24). Both functional tests were routinely scheduled for all patients as part of the unit’s standard assessment pathway. A single 6MWT was performed in the morning in a 30-m corridor using standardized encouragement. Symptom-limited CPET followed that afternoon using a locally developed, individualized treadmill protocol, with the protocol level selected according to functional capacity assessed by the preceding 6MWT. Breath-by-breath gas analysis was used; peak VO2 was calculated as the mean of the final 30 s and was available in 558 patients. 6MWD% was calculated using Enright–Sherrill equations.3 Patient-reported domains comprised the Minnesota Living with Heart Failure Questionnaire (MLHFQ),4 Beck Depression Inventory,5 State–Trait Anxiety Inventory,6 Short Form-36 (SF-36) physical and mental component summaries,7 and International Physical Activity Questionnaire.8 Heteroscedasticity-consistent (HC3) robust linear models included standardized peak VO2 and 6MWD% simultaneously, adjusting for age, sex, body mass index, NYHA class, and recorded diagnostic group (e.g. HF not otherwise specified, cardiomyopathy, and ischaemic, valvular, or congenital disease). Medication use and HF duration were unavailable. Complete-case analyses used a false discovery rate correction across 14 focal coefficients. Ethics approval was obtained (2025-4713/25-5T/30); consent was waived. Mean age was 48.4 years (77.2% male); median peak VO2 was 14.0 mL/kg/min and median 6MWD% was 69.3%. Peak VO2 and 6MWD% were moderately correlated (Spearman ρ = 0.46), with no substantial collinearity in adjusted models (both variance inflation factors ≤2.0). Higher 6MWD% remained independently associated with better status across all seven domains (standardized β = 0.14–0.29; all q ≤ 0.047). Peak VO2 retained associations only with MLHFQ (β = 0.16, 95% confidence interval [CI] 0.07–0.26; q = 0.003) and SF-36 physical health (β = 0.12, 95% CI 0.02–0.22; q = 0.030), but not with depression, anxiety, mental health, or physical activity (Figure 1). Replacing 6MWD% with raw 6MWD preserved the direction and significance pattern; corresponding standardized coefficients differed by no more than 0.05. Adjusted standardized associations of peak VO2 and percentage-predicted six-minute walk distance with patient-reported outcomes. Positive coefficients represent better health status or greater physical activity. All models include both functional measures and adjust for age, sex, body mass index, New York Heart Association class, and underlying cardiac diagnosis/clinical group. Error bars indicate 95% confidence intervals. These findings suggest that peak VO2 and 6MWD% are complementary rather than interchangeable. Peak VO2 characterizes maximal cardiopulmonary performance under controlled testing conditions and remains the established test for physiological characterization and prognosis.2 Its selective associations with MLHFQ and SF-36 physical health are consistent with a measure primarily reflecting disease-related physical limitation. The self-paced 6MWT is additionally shaped by symptoms, pacing, confidence, peripheral function, and habitual behaviour,3 which may explain its broader alignment with psychological and behavioural health. Similar signals exist in HF-ACTION: patient-reported health correlated modestly with both peak VO2 and 6MWD, slightly more strongly with 6MWD,9 while depressive symptoms related more closely to 6MWD and NYHA class than to objective severity markers.10 Our findings extend these observations by comparing both measures simultaneously across physical, psychological, and behavioural domains with clinical adjustment and multiplicity control. Clinically, preserved peak VO2 should not reassure clinicians that daily functioning or psychological health is intact. A disproportionately low 6MWD%, or high patient-reported burden despite less impaired peak VO2, should prompt assessment of mood, anxiety, pacing confidence, and habitual activity. The 6MWT does not replace CPET; together with brief patient-reported measures, the tests provide complementary information for individualized rehabilitation planning. Limitations include the retrospective, cross-sectional, single-centre design; a relatively young, predominantly male referral population; inability to classify HF phenotype because left ventricular ejection fraction was available in only 68 patients; unavailable medication use and HF duration; variable outcome availability; and residual confounding. In this large HF cohort, submaximal six-minute walk performance showed broader independent associations with patient-reported health than peak aerobic capacity. Clinicians should interpret the two tests as complementary rather than interchangeable indicators of functional capacity. Ahmet Burak Altay (Conceptualization, Data curation, Methodology, Resources, Visualization, Writing—review & editing [equal], Formal analysis [supporting], Investigation [lead]), Hale Karapolat (Conceptualization, Data curation, Funding acquisition, Investigation, Resources, Supervision [lead], Formal analysis, Methodology, Validation, Writing—original draft, Writing—review & editing [equal]), and Arzu Yağız On (Conceptualization, Investigation, Supervision [equal], Data curation, Formal analysis, Methodology, Validation, Visualization, Writing—original draft, Writing—review & editing [lead], Resources [supporting]) None. De-identified data may be available from the corresponding author on reasonable request, subject to ethics and institutional requirements. AI-assisted tools were used for language editing and text organization. The authors reviewed and take full responsibility for the content. Approved by the Ege University Faculty of Medicine Clinical Research Ethics Committee (20 February 2025; 2025-4713/25-5T/30). Waived (retrospective design, anonymized data).