Tetralogy of Fallot

Tetralogy of Fallot (TOF) is the most common cause of cyanotic congenital heart disease*. It typically presents at around 1-2 months, although may not be picked up until the baby is 6 months old

TOF is a result of anterior malalignment of the aorticopulmonary septum. The four characteristic features are:

• ventricular septal defect (VSD)
• right ventricular hypertrophy
• right ventricular outflow tract obstruction, pulmonary stenosis
• overriding aorta

The severity of the right ventricular outflow tract obstruction determines the degree of cyanosis and clinical severity.

Other features

• cyanosis
  • unrepaired TOF infants may develop episodic hypercyanotic 'tet' spells due to near occlusion of the right ventricular outflow tract
  • features of tet spells include tachypnoea and severe cyanosis that may occasionally result in loss of consciousness
  • they typically occur when an infant is upset, is in pain or has a fever
• causes a right-to-left shunt
• ejection systolic murmur due to pulmonary stenosis (the VSD doesn't usually cause a murmur)
• a right-sided aortic arch is seen in 25% of patients
• chest x-ray shows a 'boot-shaped' heart, ECG shows right ventricular hypertrophy

Management

• surgical repair is often undertaken in two parts
• cyanotic episodes may be helped by beta-blockers to reduce infundibular spasm