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 VO2max 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 709 children (407 CHD and 302 healthy controls). The association of clinical characteristics with weight-normalized OUES (OUESkg) was studied using a multivariable analysis. The mean OUESkg was significantly lower in CHD than in healthy controls (respectively 38.6±8.5 and 43.9±8.5; P<0.001). The OUESkg was predominantly affected in the most severe CHD. The OUESkg correlated well with VO2max (r=0.85, P<0.001). The decrease of OUESkg 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 VO2max. The OUES has the same clinical determinants as VO2max and therefore may be of interest in submaximal exercise.