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Key Points
Tetralogy of Fallot is a complex congenital cardiac malformation consisting of varying degrees of right ventricular outflow tract obstruction, ventricular septal defect, overriding aorta and right ventricular hypertrophy (although the latter is generally not present in fetal life).
Prenatal diagnosis generally requires careful evaluation of cardiac outflow tracts, including discontinuity between ventricular septum and aortic outflow, as well as a relatively small pulmonary outflow.
Testing for fetal karyotype and 22q11 deletion is recommended.
Infants should be delivered in a controlled setting with ability to provide prostaglandin infusion and prompt pediatric cardiology availability.
While initial palliation with a systemic-to-pulmonary arterial shunt may be required, many centers today perform definitive complete surgical correction within the first 6 months of life.
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Tetralogy of Fallot is a cardiac malformation comprising ventricular septal defect (VSD), right ventricular outflow tract obstruction, aorta overriding the interventricular septum, and right ventricular hypertrophy. This malformation presumably occurs because of unequal division of the conotruncus or incorrect alignment of the ascending aorta during embryogenesis (Romero et al., 1988). A wide spectrum of severity exists for this condition, ranging from mild right ventricular outflow tract obstruction to complete pulmonary atresia, and aortic override ranging from minimal to 75% (Pinsky and Arciniegas, 1990). In addition, the hypoplasia may involve simply the infundibulum of the right ventricle or it may also involve the pulmonary valve or pulmonary arteries. Tetralogy may therefore also include pulmonary stenosis, pulmonary atresia or absent pulmonary valve, with this degree of right ventricular tract obstruction determining the amount of right-to-left shunting and cyanosis in infancy (Bashore, 2007). Approximately 3% to 6% of all cases of tetralogy will present with absent pulmonary valve (Shinebourne et al., 2006). The VSD is most often in a superior or perimembranous location, and it is usually large and nonrestrictive. The diameter of the aortic root is generally inversely proportional to that of the pulmonary artery, so that in cases of pulmonary atresia the aorta is very wide, with more than 50% committed to the right ventricle (Graham and Gutgesell, 1990).
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In general, tetralogy of Fallot does not cause significant intrauterine hemodynamic compromise for the fetus because of similarities in the pressure between the systemic and pulmonary circulations. Right ventricular hypertrophy is therefore usually not seen until after birth. In cases of tetralogy with complete absence of the pulmonary valve, significant regurgitation may cause congestive cardiac failure in utero and ultimately, hydrops (Romero et al., 1988). Following birth, the closure of the ductus arteriosus, together with the narrowed right ventricular outflow tract, results in development of a significant right-to-left shunt. This leads to blood flow bypassing the pulmonary bed, resulting in hypoxemia in the systemic circulation. Because the right ventricular outflowtract obstruction is fixed, the degree of right-to-left shunt is almost entirely dependent on the systemic vascular resistance (...