Tetralogy of Fallot and Eisenmenger Syndrome
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Direct answer
Tetralogy of Fallot is a common cyanotic congenital heart lesion combining a large subaortic VSD, an overriding aorta, right ventricular outflow obstruction and right ventricular hypertrophy. The chest film shows a boot-shaped heart with oligaemic lung fields, and hypercyanotic spells in infancy are first treated with knee-chest positioning. Eisenmenger syndrome is the late complication in which long-standing left-to-right shunting reverses into right-to-left flow.
What you must remember
- Four features: a large perimembranous VSD, an overriding aorta, right ventricular outflow obstruction and right ventricular hypertrophy.
- Chest film: a boot-shaped heart with an upturned apex, a concave pulmonary artery segment and oligaemic lung fields.
- ECG: right axis deviation and right ventricular hypertrophy.
- Hypercyanotic spell: sudden cyanosis and hyperpnoea, often in the morning, after crying, feeding or defecation; managed with knee-chest position, oxygen, morphine and propranolol.
- Surgery: complete repair in infancy with VSD closure and relief of outflow obstruction; a palliative systemic-to-pulmonary shunt when pulmonary arteries are too small.
- Eisenmenger physiology: pulmonary resistance at or above systemic levels reverses the shunt, causing cyanosis, polycythaemia, clubbing and a loud P2 with no murmur.
- Complications: paradoxical embolism, brain abscess, haemoptysis, gout and sudden death.
- Eisenmenger therapy: pulmonary arterial hypertension drugs such as endothelin receptor antagonists, PDE-5 inhibitors and prostanoids; closure is contraindicated, and pregnancy carries a very high maternal risk.
A morning spell in a three-month-old
A three-month-old girl becomes blue, breathes fast and stops feeding after a morning cry, and settles only when held with her knees drawn to her chest. Recognising a hypercyanotic spell is an emergency, because infundibular spasm increases outflow obstruction, reduces pulmonary blood flow and worsens right-to-left shunting.
- Knee-chest position: This raises systemic vascular resistance and reduces the right-to-left shunt, so it is the first step.
- Oxygen and calm handling: Oxygen is given and the child is handled gently.
- Morphine: If she is still distressed, morphine calms her and may ease the spasm.
- Propranolol and correction: Propranolol reduces the infundibular spasm, and acidosis and volume status are corrected in severe cases.
- Definitive repair: Elective surgery in infancy closes the VSD and enlarges the outflow tract. A palliative shunt is used when the pulmonary arteries are too small for complete repair.
Eisenmenger syndrome does not usually complicate tetralogy, because the outflow obstruction protects the lungs from high pressure. It follows an unrepaired large VSD, ASD or PDA, in which pulmonary resistance rises over years and the shunt reverses. The timeline is the contrast: spells occur in tetralogy during infancy, while Eisenmenger appears years to decades after an unrepaired defect.
Where the examiner tests the direction of shunting
Shunt direction and the spell are the two discriminators examiners test.
- Trap: treating tetralogy and Eisenmenger as the same right-to-left shunt from birth. Correct: tetralogy shunts right-to-left because outflow obstruction pushes blood across the VSD, whereas Eisenmenger is a shunt reversed after pulmonary hypertension develops.
- Trap: expecting a harsh murmur in an adult with Eisenmenger physiology. Correct: tetralogy has a harsh ejection systolic murmur from outflow obstruction, but in Eisenmenger the murmur fades because flow across the defect is reduced.
- Trap: mistaking sudden cyanosis after crying for a seizure or pneumonia. Correct: it is a hypercyanotic spell, and knee-chest positioning comes before any drug is given.
A cyanotic infant with a boot-shaped heart is tetralogy, whereas a cyanotic adult with a long-standing VSD, a loud P2 and no murmur is Eisenmenger.
Frequently asked questions
What are the four components of tetralogy of Fallot?
Tetralogy of Fallot comprises a large subaortic ventricular septal defect, an overriding aorta, right ventricular outflow tract obstruction and right ventricular hypertrophy. Together these produce right-to-left shunting and cyanosis.
What is the boot-shaped heart on chest X-ray?
The boot-shaped heart is a radiograph appearance from an upturned right ventricular apex and a concave pulmonary artery segment. It is seen in tetralogy of Fallot together with oligaemic lung fields.
How is a hypercyanotic spell in tetralogy of Fallot treated?
Hypercyanotic spells are first managed with knee-chest positioning and oxygen. Morphine, propranolol, fluid and correction of acidosis follow if the spell persists, because prolonged hypoxia can cause seizures or stroke.
What is Eisenmenger syndrome?
Eisenmenger syndrome is the late reversal of a left-to-right shunt into right-to-left flow, caused by pulmonary vascular disease. It produces cyanosis, polycythaemia, clubbing and a loud P2.
Why is pregnancy dangerous in Eisenmenger syndrome?
Pregnancy increases preload and lowers systemic vascular resistance, which can worsen pulmonary hypertension and right heart failure. The maternal mortality risk is very high, so pregnancy is generally counselled against.