![]() Early on surgeons used valves (cavo-atrial, atrioventricular, or atriopulmonary), and created various connections between the right atrium and the pulmonary artery (anterior atriopulmonary connection, with or without inclusion of a small hypoplastic right ventricle, posterior atriopulmonary connection), and with different materials (valved conduits, homografts, patches, direct anastomosis). Since its original description, the Fontan circuit has known numerous modifications. All clinicians involved in the management of these patients have learned that these predictions are, at best, just that-predictions. ![]() 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 treatment strategies pulmonary flow will increase, influencing the transpulmonary gradient. The haemodynamic evaluation just before the Fontan surgery must try to predict how lungs and heart will interact after Fontan completion. 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. 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. 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). 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). In 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. 2 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). 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. 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. 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 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. Ao aorta LA, left atrium LV, left ventricle, RV, right ventricle. In the absence of fenestration, there is no more admixture of systemic and pulmonary venous blood, but the systemic venous pressure is notably elevated. ![]() The volume overload to the single ventricle is now less than expected for body surface area. The right atrium (RA) or systemic veins are connected to the pulmonary artery (PA). The systemic and pulmonary circulations are connected in series. There is complete admixture of systemic and pulmonary venous blood, causing arterial oxygen desaturation. The width of the line reflects the degree of volume load. The systemic and pulmonary circuits are connected in parallel, with a considerable volume overload to the single ventricle (V). ![]() (B) The patient with a univentricular heart. The right ventricle maintains the right atrial pressure lower than the left atrial pressure, and provides enough energy to the blood to pass the pulmonary resistance. The pulmonary circulation (P) is connected in series with the systemic circulation (S). (A) The normal cardiovascular circulation.
0 Comments
Leave a Reply. |