Objective To assess the relationship between 6-min walk test (6MWT) distance and variables of cardiopulmonary exercise testing (CPET) in children with pulmonary arterial hypertension (PAH).

Design Retrospective study.

Setting Tertiary hospital.

Patients Children with PAH.

Interventions CPETs and 6MWTs.

Main outcome measures Correlations between variables of CPET and 6MWT distance.

Results 41 exercise studies were included: 15 in children with idiopathic PAH (mean age 13.0±3.0 years; 9 female), 18 in children with PAH associated with congenital heart disease (age 14.8±2.8 years; 7 female) and 8 in children with Eisenmenger syndrome (age 11.8±2.9 years; 4 female). All underwent a CPET and 6MWT. Peak oxygen consumption (pVO₂) and 6MWT distance were reduced to 31.5±12.2% and 47.7±16.7% of the predicted value, respectively (p<0.0001 for both). pVO₂ and oxygen consumption at anaerobic threshold showed correlation with 6MWT distance (r=0.49; p=0.001 and r=0.40, p=0.01, respectively), while an inverse correlation was found between measures of ventilatory efficiency (eg, VE/VCO₂) at anaerobic threshold and 6MWT distance (r=−0.43; p=0.005). There was a significant linear relationship between pVO₂ and 6MWT up to a distance of 300 m, with the 6MWT distance accounting for 71% of the variation in pVO₂ but there was hardly any association when the 6MWT distance was >300 m.

Conclusions The 6MWT reflects maximal exercise capacity in patients with a 6MWT distance below 300 m. A CPET should therefore be considered as a complimentary test in children with an exercise tolerance above this threshold. These findings may have implications for assessing response to drug therapy and for consideration as an end point in future PAH trials.