Clinical Scenario:
A 2-day-old neonate develops progressively worsening central cyanosis. He was relatively stable immediately after birth, but the cyanosis has become more marked over the last 24 hours. Oxygen saturation is 70% in room air and shows little improvement with supplemental oxygen. He is tachypnoeic but has no significant chest retractions.
On examination, there is a single loud second heart sound and a harsh pansystolic murmur at the lower left sternal border. Peripheral pulses are palpable and equal in all four limbs. There are no clinical features of pulmonary edema.
ECG shows marked left-axis deviation. Chest radiograph demonstrates reduced pulmonary vascular markings with a normal or mildly increased cardiac silhouette.
Which of the following is the most likely diagnosis?
A. Critical pulmonary stenosis
B. D-transposition of the great arteries
C. Tetralogy of Fallot
D. Tricuspid atresia
E. Total anomalous pulmonary venous connection
Correct Answer & Explanation:
Correct answer: D. Tricuspid atresia
Explanation
The combination of early neonatal cyanosis, pulmonary oligemia, a single loud S2, and marked left-axis deviation strongly suggests tricuspid atresia.
In tricuspid atresia, there is no effective passage of blood from the right atrium to the right ventricle. Consequently, systemic venous blood must pass through an atrial-level communication into the left atrium. The right ventricle is hypoplastic, while the left ventricle becomes the dominant ventricle.
The amount of pulmonary blood flow depends largely on the associated anatomy. When there is significant pulmonary outflow obstruction and/or a small VSD, pulmonary blood flow may become duct-dependent. As the ductus arteriosus constricts after birth, pulmonary blood flow falls and cyanosis worsens—explaining why this infant becomes progressively more cyanotic during the first days of life.
Why the clues matter
- Cyanosis in the first days of life: suggests a significant cyanotic congenital heart lesion.
- Minimal response to oxygen: indicates a significant right-to-left/mixing cardiac lesion rather than primary lung disease.
- Single loud S2: characteristic of several cyanotic congenital heart lesions and supports a major outflow/valvular abnormality.
- Left-axis deviation: an especially useful ECG clue for tricuspid atresia.
- Reduced pulmonary vascular markings: indicates reduced pulmonary blood flow, which fits tricuspid atresia with pulmonary outflow obstruction.
- Pansystolic murmur: can result from flow across an associated VSD.
Why the alternatives are less likely
A. Critical pulmonary stenosis — Incorrect
Critical pulmonary stenosis causes severe cyanosis and reduced pulmonary blood flow, but the classic ECG finding is generally right-axis deviation/right ventricular abnormalities, rather than the marked left-axis deviation expected with tricuspid atresia.
B. D-transposition of the great arteries — Incorrect
TGA commonly causes profound neonatal cyanosis with relatively little response to oxygen. However, the classic radiographic and ECG pattern is different, and marked left-axis deviation with pulmonary oligemia points more strongly toward tricuspid atresia.
C. Tetralogy of Fallot — Incorrect
Severe TOF can produce pulmonary oligemia and cyanosis, but the typical ECG shows right ventricular hypertrophy/right-axis deviation, not marked left-axis deviation. Also, severe cyanosis immediately after birth is less typical unless there is critical pulmonary obstruction.
D. Tricuspid atresia — Correct
The combination of cyanosis + pulmonary oligemia + single S2 + marked left-axis deviation is highly characteristic.
E. Total anomalous pulmonary venous connection — Incorrect
TAPVC can cause neonatal cyanosis, particularly when pulmonary venous obstruction is present. Obstructed TAPVC, however, typically produces marked respiratory distress and pulmonary edema, rather than isolated pulmonary oligemia.
Post Graduate Examination Pearl
Cyanotic neonate + pulmonary oligemia + LEFT-axis deviation → think TRICUSPID ATRESIA.
And if the question subsequently asks for management:
Tricuspid atresia + severe pulmonary obstruction → duct-dependent pulmonary blood flow → start PGE₁.
