Fallot’s tetralogy

Fallot's tetralogy is a combination of the following:

• Subvalvular and/or valvular pulmonary stenosis
• Large, subaortic ventricular septal defect in a high location
• Dextroposition of the aorta with overriding of the septal defect  
• Hypertrophy of the right ventricle

If an atrial septal defect is present in addition, this is called Fallot's pentalogy.

The incidence is reported as 11 % of all heart defects. Fallot’s tetralogy is thus the most common cyanotic heart defect. Untreated, the average life expectancy is about 12 years.

With high-grade pulmonary stenosis or pulmonary atresia, lung perfusion may be dependent on aortopulmonary collateral arteries (MAPCAs).

The severity of the disease depends on the degree of pulmonary stenosis. In severe cases, the infants develop obvious cyanosis a few weeks after birth. Later, hypoxaemic attacks with loss of consciousness are observed. The children attempt to improve the peripheral vascular resistance and thus the perfusion of the lung by the characteristic “squatting position“. However, there are also anatomically favourable forms, in which there is practically no right-to-left shunt and therefore no cyanosis (“pink Fallot’s“).

If the pulmonary arteries are well developed, primary correction is possible in infancy. It is performed using extracorporeal circulation and consists of closing the ventricular septal defect and widening the right ventricular outflow tract. In the case of severe pulmonary stenosis, implantation of a transannular patch can be necessary.

When the central pulmonary arteries are underdeveloped, especially if aortopulmonary collaterals are present, lung perfusion is improved by placing a modified Blalock-Taussig shunt. The collaterals should be ligated and connected to the central pulmonary blood stream. The aim of this unifocalisation is creation of normal blood flow through the lungs. Actual correction of the defect is carried out at a later time.