Tetralogy of Fallot

Keys to the diagnosis of tetralogy of Fallot in our patient include the history - the recognition since infancy of cyanosis made worse by exertion and the physical examination with evidence of right ventricular hypertrophy, a characteristic right ventricular ejection murmur and an inaudible pulmonary component of S2.

Tetralogy of Fallot is a pathologic complex consisting in its classical form of a specific type of large, unrestricted ventricular septal defect; right ventricular infundibular stenosis, anterior, rightward displacement of the aorta, with overriding of the ventricular septum; and right ventricular hypertrophy.

Tetralogy of Fallot is not a single clinical entity, however. It is a spectrum, based upon severity of the right ventricular outflow tract obstruction, as this substantially affects patient age at presentation, type and severity of symptoms and some physical examination findings. A patient with mild obstruction may demonstrate both little or no cyanosis and evidence of a large left-to-right shunt through the ventricular septal defect.

At the other extreme, the most severe, is a patient born with complete obstruction or atresia of the outflow tract. In this case, findings may be limited to severe cyanosis and no murmur. This newborn's survival depends upon presence or establishment of some other source of pulmonary blood supply, such as a patent ductus arteriosus or collateral arteries from the descending aorta running into the pulmonary artery. If dependent only on a patent ductus arteriosus, further survival usually requires a surgical procedure to establish pulmonary arterial blood flow.

We shall now further evaluate our patient's diagnosis. Patients with tetralogy of Fallot typically present with some degree of cyanosis. Cyanosis, indicating systemic arterial desaturation, occurs because of the right-to-left shunt that results as obstruction of flow from the right ventricle into the pulmonary arteries causes systemic venous blood to flow from the right ventricle through the large ventricular septal defect into the overriding aorta. Shunt volume is directly related to the degree of obstruction. These patients also present with a significant systolic murmur due to turbulent blood flow through the obstructed right ventricular outflow tract. No murmur of the VSD occurs, because it is large, resulting in equal pressures in both ventricles and, therefore, no turbulence of flow across it.