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Difficulty: MediumPediatric Cardiovascular Disorders

During a routine assessment in the newborn nursery, a 2-day-old female infant is found to have central cyanosis that worsens when she cries. She was delivered vaginally at 39 weeks gestation following an uncomplicated pregnancy. Vital signs include a heart rate of 158/min, respiratory rate of 55/min, and blood pressure of 68/40 mm Hg in the right arm. Pulse oximetry indicates an oxygen saturation of 76% on room air. After administration of 100% supplemental oxygen for 10 minutes, her saturation marginally improves to 78%. Physical examination confirms bluish discoloration of the perioral area and mucous membranes. Cardiac auscultation reveals a normal S1, a loud and single S2, and a grade 3/6 holosystolic murmur at the left lower sternal border. An electrocardiogram demonstrates left axis deviation, small R waves in the right precordial leads, and tall P waves in lead II. Chest radiography reveals a normal cardiac size with diminished pulmonary vascular markings. Which of the following is the most likely diagnosis?

  1. A
    Tetralogy of Fallot
  2. B
    Total anomalous pulmonary venous return
  3. Tricuspid atresiaAnswer
  4. D
    Transposition of the great arteries
  5. E
    Ebstein anomaly

Answer

Tricuspid atresia
The correct answer is Tricuspid atresia. Tricuspid atresia is a cyanotic congenital heart defect characterized by the complete absence of a tricuspid valve, resulting in no direct communication between the right atrium and the right ventricle. Because of this, venous blood must flow through an atrial septal defect (or patent foramen ovale) into the left atrium and left ventricle. Pulmonary blood flow typically relies on a ventricular septal defect or a patent ductus arteriosus. The hallmark of tricuspid atresia on a neonatal electrocardiogram is left axis deviation. This occurs because the right ventricle is severely hypoplastic, leaving the left ventricle as the dominant chamber. This contrasts with normal neonates, who have physiologic right ventricular dominance and right axis deviation. The electrocardiogram also shows decreased right ventricular forces (small R waves in V1 and V2) and right atrial enlargement (tall, peaked P waves in lead II) due to atrial volume overload against an imperforate valve. Chest radiography typically reveals decreased pulmonary vascular markings because of restricted blood flow to the lungs. The patient's failed hyperoxia test confirms a right-to-left intracardiac shunt.

Step-by-Step Solution

1
Interpret the hyperoxia test results.
The minimal increase in oxygen saturation (from 76% to 78%) after administering 100% oxygen indicates a failed hyperoxia test.
This confirms the presence of a right-to-left intracardiac or extracardiac shunt, which is typical of cyanotic congenital heart disease rather than a primary pulmonary pathology.
2
Analyze the electrocardiogram (ECG) for the cardiac axis and chamber dominance.
The ECG shows left axis deviation (LAD) and decreased right precordial R waves.
Normal neonates have physiologic right ventricular dominance and right axis deviation; the presence of left axis deviation in a cyanotic newborn strongly points to a hypoplastic right ventricle and a dominant left ventricle.
3
Synthesize the clinical, ECG, and radiographic findings to determine the specific cardiac anomaly.
The combination of a failed hyperoxia test, left axis deviation, and decreased pulmonary vascular markings leads to the diagnosis of tricuspid atresia.
Tricuspid atresia results in an absent right atrioventricular connection, leading to a hypoplastic right ventricle (explaining the left axis deviation) and restricted pulmonary blood flow (explaining the chest radiograph findings).

Key Concept

Tricuspid atresia is a cyanotic congenital heart defect characterized by an absent tricuspid valve and a hypoplastic right ventricle, which uniquely presents with left axis deviation on a neonatal electrocardiogram.
Estimated Time:1m 15s
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Topics

Pediatric Cardiovascular Disorders

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