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Congenital Cyanotic Heart Diseases: Tetralogy Of Fallot (TOF)

Updated on January 13, 2014

Tetralogy Of Fallot

The essential abnormality in TOF is obstruction to the right ventricular outflow tract associated with ventricular septal defect (VSD).
The essential abnormality in TOF is obstruction to the right ventricular outflow tract associated with ventricular septal defect (VSD). | Source

Clinical Presentation

These are all characterized by cyanosis from birth. The common congenital cyanotic heart diseases are associated with reduced pulmonary flow, the commonest being tetralogy of Fallot (TOF).

In TOF, there is pulmonary stenosis, ventricular septal defect, overriding of the aorta and right ventricular hypertrophy, the aorta and right ventricular hypertrophy. The essential abnormality in TOF is obstruction to the right ventricular outflow tract associated with ventricular septal defect (VSD). The VSD is responsible for the aortic override. Right Ventricular outflow obstruction leads to right ventricular hypertrophy. In two-thirds of the cases, the right ventricular obstruction is caused by infundibular stenosis and in one-third it is caused by pulmonary valvar stenosis. Annular or supravalvular stenosis may coexist in some.

The right ventricular outflow tract (RVOT) obstruction causes reduction in pulmonary blood flow. Arterial desaturation occurs because of right to left shunt across the VSD. Both right and left ventricular blood enter the aorta.

Clinical features

The main symptoms are cyanotic spells, squatting and exertional dyspnea. The age at which the symptoms appear depends upon the severity of right ventricular outflow obstruction. However, tetralogy of fallot seldom presents with cyanosis at birth. Cyanotic spells usually occur after the age of three to six months when the child becomes increasingly active. It is characterized by sudden onset of dyspnea, restlessness and increasing cyanosis. Sometimes such attacks may be fatal. Grown up children adopt the squatting position when they become breathless since they obtain relief in this posture.

Varying grades of central cyanosis and clubbing are detectable easily. Palpation reveals norma;-sized heart without left parasternal heave or pulmonary artery pulsation. This is often referred to as the “silent precordium”. In some cases, a systolic thrill may be felt in the left upper sterna border. Auscultatory findings are the presence of an ejection systolic murmur over the pulmonary area and left sterna border. The second sound is mostly single and is loud. This is the aortic component. In milder cases, the pulmonic component may also be heard as a feeble sound. The murmur is caused by the right ventricular outflow tract obstruction. The length of the murmur bears an inverse relationship with the degree of RVOT obstruction. In some cases, an aortic ejection click may be audible. In cases with severe RVOT obstruction, bronchopulmonary collaterals may develop in an attempt to increase the pulmonary blood flow. These are detectable by the presence of continuous murmurs over the chest as well as along the paraspinal region.

All Anomalies Involved

TOF predisposes to infective endocarditis. Some cases may develop aortic regurgitation due to prolapsed of the aortic cusp into the VSD. In adults with TOF, congestive heart failure may occur.
TOF predisposes to infective endocarditis. Some cases may develop aortic regurgitation due to prolapsed of the aortic cusp into the VSD. In adults with TOF, congestive heart failure may occur. | Source

Course, Prognosis And Treatment

Course and prognosis

This is the commonest cyanotic congenital heart disease which often survives into adolescence and adulthood. In severe cases, frequent cyanotic spells occur in infancy and these may be fatal in some cases. TOF predisposes to infective endocarditis. Some cases may develop aortic regurgitation due to prolapsed of the aortic cusp into the VSD. In adults with TOF, congestive heart failure may occur. Anemia, infective endocarditis, severe aortic regurgitation and hypertension are the associated conditions which tips these patients into heart failure.

Treatment

The treatment consists of surgical correction of the abnormality. The time of surgery depends on the severity of the defect. In severe cases with cyanotic spells palliative surgery is done to increase the blood flow to the pulmonary artery by anastomosing the left subclavian artery to the pulmonary artery (Blalock-Taussing Operation). The more desirable procedure is to undertake total correction and this is done in centers with facilities for open heart surgery. Total correction includes closure of the VSD and relief of RVOT obstruction.

© 2014 Funom Theophilus Makama

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