Questions remaining about the surgical correction of tetralogy of Fallot.

T etralogy of Fallot is the most common cyanotic congenital heart lesion. Its anatomical features were first described by Stenson in 1672. In 1888 Fallot published his clinical observations, linking the four elements he considered to be the main anatomical abnormalities (interventricular septal defect, stenosis of the right ventricular outflow tract, right ventricular hypertrophy and an aorta that straddles the ventricular septum) with the clinical syndrome of progressively increasing cyanosis. Much later, Van Praagh introduced the term tetralogy to describe the incomplete development and hypoplasia of the infundibulum, namely the right ventricular outflow tract. From a pathophysiological point of view, though, the most important elements of tetralogy of Fallot are the existence of a non-restrictive ventricular septal defect and the degree of obstruction of the right ventricular outflow tract. The spectrum of this classical form of the tetralogy is a wide one, with some patients having only mild obstruction (acyanotic tetralogy of Fallot) and occasionally pulmonary hypercirculation, while others have severe hypoplasia of the infundibulum, hypoplasia of the pulmonary annulus and the pulmonary trunk and/or stenosis in the main trunk as well as along the branches of the pulmonary artery. Even though there are often many small collateral vessels leading to the lungs, the existence of major aortopulmonary collateral arteries (MAPCAs) is rather rare in the classical tetralogy with pulmonary stenosis. In a small percentage of patients (3%) a second interventricular shunt is encountered in the muscular ventricular septum, while also in 3% a significant abnormality in the coronary vessels may coexist (usually the anterior descending branch originating from the right coronary artery and crossing the anterior surface of the right ventricular outflow tract). Other forms of tetralogy with different embryology, pathophysiology and quite different surgical treatment are as follows: a. Tetralogy of Fallot with pulmonary atresia and dependence of the pulmonary circulation upon the patent ductus arteriosus. b. Tetralogy of Fallot with pulmonary atresia, hypoplastic pulmonary arteries, pulmonary arterial branching abnormalities and the presence of MAPCAs. c. Tetralogy of Fallot with concomitant complete atrioventricular canal. d. Tetralogy of Fallot with absent pulmonary valve. e. Tetralogy of Fallot with anomalous origin of one pulmonary artery from the aorta (hemitruncus). These subcategories of tetralogy will not be considered in the present article.