Table 4.20 - Characteristics of Tetralogy of Fallot.

Not initially a tetrad!!
Unequal division of the truncus arteriosus into a small pulmonary and large aortic component, resulting malalignment of the conotruncal septum, producing pulmonary stenosis and a large VSD underlying the large aorta.
VSD is non-restrictive, allowing full equalization of LV & RV pressures; pulmonary stenosis limits flow to lungs and is determined by degree of stenosis.
A RV outflow obstruction which offers more afterload than the afterload on the LV produced by the systemic circuit, produces a R ---> L shunt, resulting in cyanosis.
Shunting can occur in three ways: RA ---> LA, RV ---> LV, LV --->PA.
Large subaortic VSD, overriding aorta, and pulmonary stenosis is seen with echo.
Equalized ventricular pressures can be seen with catheterization.
Degree of R ---> L shunt is estimated by aortic O₂ saturation.