Comparison of the oxygen uptake efficiency slope and 6-minute walk test in paediatric and adult Fontan patients

BACKGROUND: Fontan patients experience progressive declines in exercise capacity, highlighting the importance of submaximal exercise parameters for clinical evaluation. OBJECTIVES: To evaluate the oxygen uptake efficiency slope (OUES/kg) compared to 6-minute walk test (6MWT) distance in paediatric and adult Fontan patients. METHODS: peak, OUES, and related variables were recorded. 6MWT was also performed, with distance (m) recorded. RESULTS: < 0.05). OUES/kg discriminated between patients and controls in both age groups (AUCs = 0.724 and 0.848), while 6MWT distance did so only for adults (AUC = 0.809). CONCLUSION: Both OUES/kg and 6MWT distance may serve as valuable indicators of submaximal exercise capacity in Fontan patients, particularly in adults when maximal CPET is not feasible. While OUES/kg demonstrated superior discriminatory ability, the 6MWT remains a simple and clinically useful tool, especially for evaluating functional capacity in adult Fontan patients. These findings emphasise the complementary value of both measures and highlight the importance of age-specific assessments in this population.