Fontan patients can develop veno-venous shunts with time, which are usually closed percutaneously when they reduce oxygen saturation. But the significance of these shunts regarding the type of congenital heart disease or surgical repair and their clinical relevance is not well known.

The purpose of this study was to evaluate the proportion of Fontan patients presenting veno-venous shunt and to evaluate the impact on aerobic capacity.

Twenty-six Fontan patients (mean age 23±9 years) who underwent cardiopulmonary exercise testing with blood gas measurement between January 2016 and January 2018 were included. Twenty patients had total cavopulmonary connection with extracardiac conduit surgery and 6 had atriopulmonary connection. Mean oxygen saturation at rest was 94.9±2.1%. A resting shunt fraction, defined as PaO₂+PaCO₂<120mmHg was found in 100% of patients, with a mean of 96±6mmHg. In the group of patients presenting an important shunt fraction (defined as PaO₂+PaCO₂≤96mmHg), patients reached a lower maximal workload (102±24 versus 121±38 watts, P=0.07 or 58±10 versus 69±15% of predicted value, P=0.04) and had lower maximal oxygen consumption (22±6 versus 27±9mL/kg/min, P=0.06 or 54±9% versus 69±16% of predicted value, P<0.01). There was a small correlation between the importance of shunt fraction and maximal oxygen consumption, r²=0.22.

The importance of shunt fraction in Fontan patients seems correlated to aerobic capacity. Further studies are needed to confirm these results. Whether percutaneous closing of veno-venous shunts in Fontan patients can reduce this shunt fraction and could improve maximal oxygen consumption still remains to be proved.