Teratogy of Fallot - The Most Common Cyanotic Heart Disease in Children

By Funom Makama

Tetratogy of Fallot is the most common cyanotic heart disease in children. The anatomic definition includes four defects:

1. Ventricular septal defect,

2. Pulmonic stenosis

3. an aorta that overrides the ventricular septal defect

4. Right ventricular hypertrophy

The first three defects are congenital, and the fourth is acquired as a result of the increased pressure within the right ventricle.

Embryonic development

The development of the defects in tetralogy of Fallot is the result of abnormal embryologic development of the ventricular septum, which results in infundibular hypertrophy, and in the division of the truncus arteriosus, which results in a smaller pulmonary artery and a larger aorta.

Altered hemodynamics

Shunting of blood through the ventricular septal defect is in the direction of right to left because the pulmonic stenosis, which impedes the flow of blood to the lungs, causes an increased resistance to pulmonary flow and thus increased pressure in the right ventricle. Un-oxygenated blood is then forced through the septal defect to the left ventricle. The increased workload on the right ventricle causes hypertrophy. The decreased flow of blood to the lungs compound the amount of un-oxygenated blood reaching the systemic circulation.

Alone, the associated defects of pulmonic stenosis and ventricular septal defect produce cyanosis. In addition, the aorta overrides the septal defect and accepts un-oxygenated blood directly from the right ventricle. The body attempts to compensate for the chronic hypoxia through polycythemia. However, the resultant viscosity of the blood increases the risk of complications such as emboli and cerebrovascular disease.

Clinical manifestation

Newborns usually do not demonstrate cyanosis because of a patent ductus arteriosus that shunts blood to the lungs, bypassing the pulmonic stenosis. Anoxic spells become evident when the infant's oxygen requirements exceed the blood supply, usually during crying of after feeding. The acute severe episodes of cyanosis and hypoxia, often called "blue" or "tet" spells, are thought pulmonary infundibular spasm which abruptly includes all blood flow to the lungs. The infant characteristically assumes a hypotonic extended position.

As the child grows older, he learns to limit his activity in accordance with the physical disability. He also learns that squatting helps relieve the chronic hypoxia. He usually prefers this position to standing, sitting or lying. When reclining he may assume a knee-chest position rather than an extended positions, Since such posturing is unusual in children, it should always be suspicious of the tetralogy. Children with less severe cyanosis may assume squatting position only after exertion. The child also demonstrates clubbing of the fingers and markedly delayed physical growth development. Auscultatory findings reveal:

• A pansystolic murmur is usually heard at the middle to lower left sternal border

• It is associated with a thrill, which may be felt along the lower left sternal border.