Cardio-pulmonary exercise test (CPET) provides accurate evaluation of physical capacity and disease severity in children with congenital heart disease (CHD). However, in clinical practice, full participation to obtain optimal measure of VO2_max may be difficult. As an alternative, the oxygen uptake efficiency slope (OUES) is a reproducible and reliable parameter measured during CPET, which does not require a maximal exercise to be interpretable. This study aimed to evaluate the OUES of a large cohort of children with CHD, and to compare the results with those of healthy controls. We also intended to identify, in this specific population, the clinical and CPET variables associated with the OUES.

This cross-sectional multicenter study enrolled 709children (407CHD and 302healthy controls). The association of clinical characteristics with weight-normalized OUES (OUES_kg) was studied using a multivariable analysis. The mean OUES_kg was significantly lower in CHD than in healthy controls (respectively 38.6±8.5 and 43.9±8.5; P<0.001). The OUES_kg was predominantly affected in the most severe CHD. The OUES_kg correlated well with VO2_max(r=0.85, P<0.001). The decrease of OUES_kg was associated with increased age, increased BMI, number of cardiac catheter or surgical procedures, female gender and decreased FVC (Z-score).

The OUES is significantly impaired in children with CHD and strongly correlates with VO2_max. The OUES has the same clinical determinants as VO2max and therefore may be of interest in submaximal exercise.