THE FONTAN CIRCULATION

Abstract

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 1 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. 2Typically for this circuit, cardiac output is no longer determined by the heart, but rather by transpulmonary flow (itself mainly determined by pulmonary vascular resistance). INDICATIONS FOR A FONTAN CIRCUIT cA univentricular Fontan repair can be considered in cardiac malformations with a single functional ventricle, usually because of the absence of an adequate atrioventricular valve or pumping chamber-for example, tricuspid atresia, pulmonary atresia with intact ventricular septum, double inlet ventricle, hypoplastic left heart syndrome (fig 2).In other very complex malformations with high surgical risk morbidity, or need for ''high maintenance'' (frequent conduit replacement), a Fontan strategy may offer a lower surgical risk and lower incidence of reinterventions for a similar clinical and functional long term result. SELECTION OF PATIENTSIn 1978 Choussat and Fontan 3 described their recommendations for a successful Fontan operation, defined as having a good cardiac output at an acceptable systemic venous pressure.These rules have been refined by many centres, but all reflect that after repair left atrial pressure must be low (determined by good ventricular function), and that the transpulmonary gradient must be low (determined by the pulmonary vasculature).Cardiac requirements nowadays are: unobstructed ventricular inflow (no atrioventricular valve stenosis, no regurgitation), a reasonable ventricular function, and unobstructed outflow (no subaortic stenosis, no arterial hypertension, and no coarctation).Pulmonary requirements include a non-restrictive connection from systemic veins to the pulmonary arteries (Fontan connection), good sized pulmonary arteries without distortion (at repair and later during growth), a well developed distal vascular bed, (near) normal pulmonary vascular resistance , 2.5 U/m 2 , and unobstructed pulmonary venous return.As soon as possible following birth, the pre-Fontan management must aim to reach these goals; some deviations are acceptable, however, with increased operative mortality and increased late morbidity and late mortality.The haemodynamic evaluation just before the Fontan surgery must try to predict how lungs and heart will interact after Fontan completion.This can be very difficult because at the time of Fontan surgery ventricular preload will significantly decrease (and according to Frank-Starling also contractility), and with current 839 www.heartjnl.