Fontan Circulation: How a Model can Hinder or Help to Understand and Manage a Complex Problem

Author(s): Marc Gewillig, Thomas Salaets, Alexander Van de Bruaene, Stephen C Brown

When faced with complex circulatory issues, a model can assist the clinician in understanding, manipulating, and treating the underlying problem. The creation of a Fontan circuit currently consists of connecting the caval veins to the pulmonary arteries without the interposition of a pumping chamber. Complications of this univentricular circulation carry a significant morbidity and mortality and are notoriously difficult to manage. The most obvious and intuitive model places the pulmonary vasculature downstream of the ventricle, impeding the run-off after the systemic capillaries. This implies that the ventricle can overcome the downstream problems, which in clinical practice has been shown to be incorrect. Another possible but less intuitive model for the Fontan circulation is putting the pulmonary circulation upstream of the ventricle, thereby restricting the preload. Here the pulmonary circulation acts like a dam creating upstream congestion and downstream decreased flow inertia. This model allows much better to predict the observed changes in the cardiovascular system over time. Based on this concept, the late ventricular deterioration will not be the result of excessive ventricular afterload but secondary to chronic volume depletion/underloading. A model can be good at one level but inadequate or even incorrect at another level; the choice of the model may hinder or help the understanding of the problem.