THE CONTEXT
Tetralogy of Fallot combines pulmonary stenosis, an overriding aorta, a ventricular septal defect and right ventricular hypertrophy.
Cyanosis and cyanotic spells
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Children are usually cyanosed, but neonatal cyanosis may be absent because a large right-to-left shunt develops only when right ventricular pressure equals or exceeds left ventricular pressure.
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A child may suddenly become more cyanosed after feeding or crying and may become apnoeic and unconscious.
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Cyanotic spells are uncommon in older children, but cyanosis becomes more apparent and may be accompanied by stunted growth, digital clubbing and polycythaemia.
Squatting and examination
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Some children obtain relief by squatting after exertion. Squatting increases left-heart afterload and reduces right-to-left shunting; this is called Fallot sign.
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The characteristic examination finding is cyanosis with a loud ejection systolic murmur in the pulmonary area.
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Cyanosis may be absent in newborns or patients with only mild right ventricular outflow obstruction; this is termed acyanotic tetralogy of Fallot.
Anatomical components and natural history
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The four components are pulmonary stenosis, overriding of the ventricular septal defect by the aorta, a ventricular septal defect and right ventricular hypertrophy.
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Before surgical correction became available, the natural history varied, but most patients died in infancy or childhood.