Tetralogy of Fallot is a type of heart defect present at birth (congenital) consisting of four different abnormalities. It usually results in insufficiently oxygenated blood being pumped to the body causing cyanosis (bluish discoloration of the skin). The classic form of Tetralogy includes 4 defects within the heart structures: Ventricular septal defect (hole between the right and left ventricles). Narrowing of the pulmonic outflow tract (tube that connects the heart with the lungs). An aorta (tube that carries oxygenated blood to the body) that arises from both ventricles, rather than exclusively from the left ventricle. A thickened muscular wall of the right ventricle (right ventricular hypertrophy).
Occurs in less than 1 in 2000 live births. Nonetheless, Tetralogy of Fallot is the most common cyanotic congenital heart defect.
The aetiology (origins) of congenital heart defects is not understood but several factors are known to be associated:(1) Maternal drug abuse, alcohol abuse and radiation exposure.(2) Maternal infection during pregnancy (particularly rubella.)(3) Genetic abnormalities.(4) Chromosomal abnormalities (septal defects are common with Trisomy 21- Down's syndrome.)
As the aorta overlies the VSD, it receives blood from the right ventricle and the left ventricle. This causes circulation of deoxygenated blood and central cyanosis (bluish discoloration). The high right ventricular pressure, caused by the outflow obstruction, facilitate this. Because less blood goes through the pulmonary circulation, cyanosis is independant of pulmonary hypertension (in contrast to Eisenmenger's syndrome).
Chest x-ray: a large right ventricle and small pulmonary arteries may be present. ECG: shows evidence of right ventricular hypertrophy (large right heart).Full Blood Picture: haemoglobin, haematocrit, and red blood cell count are usually elevated, depending on the degree of arterial oxygen desaturation.
With the advancement of surgical technology and increased medical management, the prognosis for Tetrlogy of Fallot is quite good. Over 95% of patients with simple Tetralogy of Fallot go on to live beyond 20 years of age.
Complete surgical correction of the Tetralogy is possible and is mandatory for long-term survival of these patients. Beta blocker medication can be used to help with hypoxic spells while the patient awaits definitive surgical intervention. To the right is an image of the afflicted area post operative:
[1] Anderson et al. Paediatric Cardiology. Churchill Livingstone 1987.[2] Behrman, Kliegman, Jenson. Nelson Textbook of Paediatrics 17th Ed. Saunders 2004.[3] Hurst's The Heart 8th Edition, McGRAW-HILL 1994.[4] Kumar and Clark, Clinical Medicine 4th Edition, W.B SAUNDERS 1998.[5] Robinson MJ., Roberton DM. Practical Paediatrics 4th Edition. Churchill Livingstone 1999.[6] Rudolph et al. Rudolphs's Paediatrics (21st edition). McGraw-Hill 2003.
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