The Fontan circulation.

Correspondence to: Professor Marc Gewillig, Pediatric Cardiology, Gasthuisberg University Hospital, B 3000 Leuven, Belgium; marc.gewillig@ uzleuven.be _________________________ A normal mammal cardiovascular system consists postnatally of a double—pulmonary and systemic—circuit, connected in series, powered by a double pump—the ‘‘right’’ and ‘‘left’’ heart. Many complex cardiac malformations are characterised by the existence of only one functional ventricle. This ‘‘single’’ ventricle then has to maintain both the systemic and the pulmonary blood circulation, which are not connected in series but in parallel (fig 1A, B). Such a circuit has two major disadvantages: arterial desaturation, both at rest and increasing during exercise, and a chronic volume overload to the single ventricle. Chronic volume overload will in time impair ventricular function, causing from the third decade on a gradual attrition due to congestive heart failure, with few survivors beyond the fourth decade. In 1971 Francis Fontan from Bordeaux, France, reported on a new approach to the operative treatment of these malformations, separating the systemic and pulmonary circulations. In a ‘‘Fontan circulation’’ the systemic venous return is connected to the pulmonary arteries without the interposition of an adequate ventricle, and all shunts on the venous, atrial, ventricular and arterial level are interrupted (fig 1C). In such a Fontan circuit the postcapillary energy is no longer ‘‘wasted’’ into the systemic veins, but collected and used to push the blood through the lungs. Advantages of a Fontan circuit include (near) normalisation of the arterial saturation, and abolishment of the chronic volume overload; the cost for such a circulation includes chronic ‘‘hypertension’’ and congestion of the systemic veins, and decreased cardiac output both at rest and during exercise. Typically for this circuit, cardiac output is no longer determined by the heart, but rather by transpulmonary flow (itself mainly determined by pulmonary vascular resistance).