Cardio-pulmonary exercise test (CPET) is becoming a key examination to assess physical capacity and disease severity in paediatric cardiology. The VE/VCO₂ slope has been increasingly used as a surrogate marker for morbidity and mortality in adult heart failure, pulmonary arterial hypertension and for adult patients with CHD. Nevertheless, the use of the VE/VCO₂ slope in children remains limited in the absence of reference values and clearly identified clinical determinants. This study aimed to compare the VE/VCO₂ slope in a paediatric cohort with CHD to that of age- and gender-adjusted healthy controls. We also intended to identify the clinical and CPET variables associated with VE/VCO₂ slope in this population.

This cross-sectional study was carried out between November 2010 and September 2015 in two tertiary care paediatric cardiology reference centres.

A total of 700 children were enrolled (399 CHD and 301 healthy controls). The mean VE/VCO₂ slope was significantly higher in CHD than in healthy subjects (31.6±4.8 vs. 29.3±4.8; P<0.001). When considering CHD sub-groups, the VE/VCO₂ slope was impaired in single ventricle, complex anomalies of ventriculo-arterial connections, anomalies of the atrioventricular junctions and valves. The VE/VCO₂ slope according to the CHD physiological status was illustrated in the Fig. 1, it was higher in children with significant pulmonary regurgitation, tricuspid regurgitation, right ventricular hypertension and right ventricle outflow tract (RVOT) obstacle. In the CHD group, VE/VCO₂ slope increase was associated with BMI, the presence of a RVOT obstacle, the number of cardiac catheter procedures, as well as low age, FVC, tidal volume, and PetCO2 (Fig. 1).

Increased VE/VCO₂ slope was predominantly in children with single ventricle and/or residual right heart abnormalities suggesting that maldistribution of pulmonary blood flow during exercise is an important CHD-unique determinant of VE/VCO₂ slope.