Clinical scenario: Rapid breathing | Hypoxia | Weak pulses | Pulmonary congestion
A 3-day-old term male neonate, born after an uncomplicated pregnancy, is brought to the emergency department because of poor feeding, increasing lethargy, and rapid breathing that began earlier that day. He had been discharged home well on the second day of life. On examination, he appears pale and poorly perfused with a heart rate of 184/min, respiratory rate of 70/min, blood pressure of 54/30 mmHg, capillary refill time of 6 seconds, and oxygen saturation of 89% in the right hand and 87% in the foot while breathing room air. Peripheral pulses are weak in all four limbs, the liver is palpable 4 cm below the costal margin, and no cardiac murmur is heard. Chest radiograph demonstrates cardiomegaly with pulmonary venous congestion, while arterial blood gas reveals severe metabolic acidosis with a lactate of 9.4 mmol/L.
What is the most likely diagnosis?
A. Critical coarctation of the aorta
B. Hypoplastic left heart syndrome
C. Obstructed total anomalous pulmonary venous connection
D. Persistent pulmonary hypertension of the newborn
E. Severe neonatal myocarditis
Correct answer & Explanation:
Answer: B. Hypoplastic left heart syndrome
Explanation: Hypoplastic left heart syndrome
This neonate has duct-dependent systemic circulation caused by hypoplastic left heart syndrome (HLHS).
Clinical reasoning
Several clues must be integrated:
- Well during the first 48 hours of life, followed by sudden cardiovascular collapse as the ductus arteriosus closes.
- Profound shock with severe metabolic acidosis and elevated lactate.
- Weak peripheral pulses due to critically reduced systemic blood flow.
- Hepatomegaly indicating heart failure.
- Single second heart sound.
- No murmur, which is a classic pitfall—many neonates with HLHS have little or no murmur.
- Cardiomegaly with pulmonary venous congestion due to increased pulmonary blood flow and left atrial hypertension.
Why the other options are incorrect
A. Critical coarctation of the aorta
A close differential. However, infants typically have brachial pulses that are stronger than femoral pulses, whereas this case describes generalized poor systemic perfusion. A single loud second heart sound and pulmonary venous congestion are more suggestive of HLHS.
B. Hypoplastic left heart syndrome — Correct
The left ventricle, mitral valve, aortic valve, and ascending aorta are severely underdeveloped. Systemic circulation depends entirely on a patent ductus arteriosus. Closure of the duct results in rapid circulatory collapse.
C. Obstructed total anomalous pulmonary venous connection
Usually presents with profound cyanosis and severe respiratory distress. Chest radiograph typically shows diffuse pulmonary edema rather than isolated cardiomegaly.
D. Severe Ebstein anomaly
Usually presents with marked cyanosis, massive cardiomegaly, and tricuspid regurgitation producing a murmur.
E. Transposition of the great arteries with intact ventricular septum
Typically presents with profound cyanosis that is disproportionate to the degree of respiratory distress. Shock is not the usual initial presentation unless another lesion coexists.
CPSP Pearls
- Any neonate who develops shock between days 2 and 5 of life should be considered to have a duct-dependent systemic congenital heart lesion until proven otherwise.
- Absence of a murmur does not exclude critical congenital heart disease.
- A single second heart sound is a valuable clue to severe left-sided obstructive lesions, including HLHS.
- Prostaglandin E₁ infusion should be started immediately when a duct-dependent systemic lesion is suspected; echocardiography should not delay treatment.
