Six-minute walking distance and decrease in oxygen saturation during the six-minute walk test in pediatric pulmonary arterial hypertension

ObjectiveTo investigate the prognostic value of the 6-minute walking distance (6-MWD), transcutaneous saturation (tcSO2) and heart rate (HR) obtained during the 6-minute walk test (6-MWT) in pediatric pulmonary arterial hypertension (PAH).MethodsThis was an observational study with forty-seven pediatric PAH patients, aged ≥ 7 years, and diagnosed and followed at the national referral center for pediatric PAH in the Netherlands. All patients performed a comprehensive 6-minute walk test (6-MWT), which measures 6-MWD and tcSO2 and HR before (“baseline”), during (“exercise”) and 5 min after (“recovery”) the walk test.ResultsThe 6-MWD expressed either in meters or in sex- and age-corrected z-scores, was associated with transplant-free survival, independently from sex, age, and the presence of a shunt-defect. Shorter 6-MWD correlated with higher WHO-FC and increased NT-pro-BNP. Absolute tcSO2 at exercise and tcSO2-decrease during 6-MWT were associated with transplant-free survival, independent from 6-MWD. Combining tcSO2-decrease with 6-MWD provided the strongest prognostic model. Patients with 6-MWD > 352 m (the median 6-MWD) had a better outcome than those with smaller 6-MWD. A large tcSO2-decrease during 6-MWT (> 19% for patients with and > 5% for patients without a shunt defect) identified patients with worse transplant-free survival both in patients with a 6-MWD above and below the median 6-MWD.ConclusionsThe 6-MWD is an independent predictor of prognosis in pediatric PAH, that reflects disease severity and clinically relevant exercise-tolerance and therefore qualifies as a treatment goal. The magnitude of tcSO2-decrease during 6-MWT, adjusted for the presence of a shunt, indicates an additional risk factor for prognosis in children with PAH.