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Tetralogy of Fallot

Tetralogy of Fallot is a cardiovascular disorder consisting of the combination of (1) obstruction to right ventricular outflow (pulmonary stenosis), (2) ventricular septal defect (VSD), (3) dextroposition of the aorta with septal override, and (4) right ventricular hypertrophy. Obstruction to pulmonary arterial blood flow is usually at both the right ventricular infundibulum (subpulmonic area) and pulmonary valve. The main pulmonary artery is often smaller than usual, and there may be various degrees.

CLINICAL MANIFESTATIONS

Infants with mild degrees of right ventricular outflow obstruction may initially present with congestive heart failure caused by a Often cyanosis is not present at birth, but with increasing hypertrophy of the right ventricular infundibulum and growth, cyanosis occurs later in the 1st yr of life. It is most prominent in the mucous membranes of In infants with severe degrees of right ventricular obstruction, cyanosis is noted immediately in the neonatal period. In these infants pulmonary blood flow may be dependent on flow through the ductus arteriosus. When the ductus begins to close in the 1st few hours or days of life, severe cyanosis and circulatory collapse may occur. Older children with long-standing cyanosis may have extreme cyanosis, with a dusky blue skin surface, gray sclerae with engorged blood vessels (suggesting mild conjunctivitis), and clubbing of the fingers and toes.

Dyspnea occurs on exertion. Infants and toddlers will play actively for a short time and then sit or lie down. Older children may be able to walk a block or so before stopping to rest.

DIAGNOSIS

Roentgenographically, the typical configuration as seen in the anteroposterior view consists of a narrow base, concavity of the left heart border in the area usually occupied by the pulmonary artery, and normal heart size. The hypertrophied right ventricle causes the rounded apical shadow to be uptilted so that it is situated higher above the diaphragm than normal. The cardiac silhouette has been likened to that of a boot or wooden shoe (coeur en sabot). The hilar areas and lung fields are relatively clear, because of diminished pulmonary blood.

The electrocardiogram demonstrates right axis deviation and evidence of right ventricular hypertrophy.

Selective right ventriculography best demonstrates the anatomy of tetralogy of Fallot. The contrast medium outlines the heavily trabeculated right ventricle. The infundibular stenosis varies in length, width, contour.

PROGNOSIS AND COMPLICATIONS

Patients with tetralogy of Fallot prior to correction are susceptible to several serious complications. Cerebral thromboses, usually occurring in the cerebral veins or dural sinuses and occasionally in the cerebral arteries.

ASSOCIATED CARDIOVASCULAR ANOMALIES

An associated PDA may be present and defects in the atrial septum are occasionally seen. A right aortic arch occurs in approximately 20% of cases of tetralogy of Fallot, and other anomalies of the pulmonary arteries.

Congenital absence of the pulmonary valve produces a distinct syndrome, usually marked by signs.

Absence of a branch pulmonary artery, most often the left, should be suspected.

TREATMENT

The treatment of tetralogy of Fallot depends on the severity of the right ventricular outflow tract obstruction. Those infants with severe tetralogy require medical treatment and surgical intervention in the neonatal period. Therapy is aimed at providing an immediate increase in pulmonary blood flow to prevent the sequelae.

Infants with marked right ventricular outflow tract obstruction may deteriorate rapidly because as the ductus arteriosus begins to close pulmonary blood flow is further compromised. The administration of prostaglandin E1 (0.05-0.20 g/kg/min).

The modified Blalock-Taussig shunt is currently the most common aorto-pulmonary shunt procedure.