Page 21, Developmental Pathophysiology, Develop. Physiol., Dr. D. Penney

Congenital Defects (cont...)

Tetralogy of Fallot:

The complex or condition known as Tetralogy of Fallot ("Blue baby" syndrome) is really a trilogy at first, being a VSD, an aorta overriding the interventricular septum, and varying degrees of pulmonary stenosis (Table 4.20, Figure 4.09). Hypertrophy of the right ventricle develops later.

Tetralogy contributes to about 7% of congenital heart defects. "Tet" was the first congenital heart defect to be treated successfully. This was done in Detroit in 1958 at Ford Hospital and Children's Hospital of Michigan. You might consult the book by the famous heart surgeon, Helen B. Taussig.

The overriding septum results from the unequal division of the truncus arteriosus into a small pulmonary artery and a larger aortic component, resulting in malalignment of the conotruncal septum, producing pulmonic stenosis and a large VSD underlying the aorta. When the VSD is non-restrictive, full equalization of right ventricle and left ventricle pressures occur.

Pulmonary stenosis limits flow to the lungs and determines the amount of shunt flow from right ventricle into the aorta, thus the degree of cyanosis. Shunting can occur in three ways: from right to left atrium, from right to left ventricle, and from left ventricle to pulmonary artery.

The degree of right to left shunt is estimated by aortic oxygen saturation. Cyanosis, and weakness and dyspnea upon exertion are the usual symptoms. The prognosis is early death unless surgical correction is attempted.

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