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Difficulty: MediumPediatric Cardiovascular Disorders

A 1-day-old male neonate is evaluated in the nursery for persistent central cyanosis. He was born at 39 weeks gestation via uncomplicated vaginal delivery to a 28-year-old primigravida. His mother had limited prenatal care but reports taking no medications during pregnancy. On examination, the infant appears comfortable but is notably cyanotic. Vital signs show a heart rate of 155/min, respiratory rate of 55/min, and oxygen saturation of 74% on room air. The cyanosis does not improve with the administration of 100% oxygen via hood. Cardiovascular examination reveals a loud, single second heart sound (S2) and a grade 3/6 holosystolic murmur at the left lower sternal border. Lungs are clear to auscultation. An electrocardiogram (ECG) demonstrates left axis deviation and tall, peaked P waves, with absent R waves in the right precordial leads. Chest radiography shows decreased pulmonary vascular markings and a normal heart size. Which of the following is the most likely diagnosis?

  1. Tricuspid atresiaAnswer
  2. B
    Transposition of the great arteries
  3. C
    Tetralogy of Fallot
  4. D
    Truncus arteriosus
  5. E
    Total anomalous pulmonary venous return

Answer

Tricuspid atresia
The correct answer is tricuspid atresia. This patient presents with cyanosis that does not correct with 100% oxygen (a failed hyperoxia test), which strongly indicates a right-to-left cardiac shunt. Tricuspid atresia is characterized by the absence of communication between the right atrium and right ventricle, leading to a hypoplastic right ventricle. The pathognomonic finding that distinguishes tricuspid atresia from other cyanotic congenital heart defects is left axis deviation on the electrocardiogram (ECG) in a neonate. Normally, neonates have right axis deviation due to physiologic right ventricular dominance in utero. The absent R waves in the right precordial leads further reflect this hypoplastic right ventricle. The single S2 occurs because the pulmonary valve closure sound is absent or obscured by the aortic valve closure, and the holosystolic murmur is typically due to a ventricular septal defect (VSD), which is necessary for pulmonary blood flow. Chest radiography typically shows decreased pulmonary vascular markings due to restricted pulmonary blood flow.

Step-by-Step Solution

1
Interpret the clinical presentation and hyperoxia test.
The infant has central cyanosis that fails to improve with 100% oxygen.
A failed hyperoxia test indicates a right-to-left intracardiac shunt, narrowing the differential to cyanotic congenital heart diseases.
2
Analyze the electrocardiogram (ECG) findings.
The ECG demonstrates left axis deviation and absent R waves in the right precordial leads.
Normal neonates have right axis deviation due to physiologic right ventricular dominance. Left axis deviation in a cyanotic newborn is highly specific for a hypoplastic right ventricle, which is the hallmark of tricuspid atresia.
3
Correlate with chest radiography and auscultation.
Decreased pulmonary markings and a single S2 with a holosystolic murmur are present.
These findings support restricted pulmonary blood flow and the presence of a ventricular septal defect, confirming the clinical picture of tricuspid atresia.

Key Concept

Tricuspid atresia presents with cyanosis, a single S2, decreased pulmonary markings, and uniquely features left axis deviation on an electrocardiogram among the major cyanotic congenital heart defects.
Estimated Time:1m 0s
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Topics

Pediatric Cardiovascular Disorders

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