Simulation of the Fontan circulation during rest and exercise.

The Fontan palliation was introduced as surgical repair method for tricuspid atresia, creating a univentricular serial circulation. However, it is used as treatment for other life threatening complex congenital heart diseases as well. The variation of underlying pathologies treated with this palliation makes optimization difficult. To assist the optimization process, we adjusted a lumped parameter computational model of the biventricular circulation (CircAdapt) and evaluated the univentricular circulation. The model simulates beat-to-beat dynamics of the two cardiac chambers, the valves, and the systemic and pulmonary circulations. The univentricular circulation in rest and exercise was simulated. Exercise resulted in increased stroke volume, heart rate, pulse pressure, and stressed blood volume. Central venous pressure rose as a result of the constant pulmonary resistance, reducing systemic pressure drop. Reduced systemic pressure drop implies either reduction of systemic flow or further decrease of systemic resistance. Based on our simulation results, we conclude that exercise capacity in Fontan patients is limited due to increase of central venous pressure and the impossibility to reduce systemic resistance further, restricting systemic flow.