Epidemiology

Etiology

Pathophysiology

During fetal development, anterior and superior deviation of the infundibular septum → misaligned VSD with overriding aortic root and subsequent RVOTO

Clinical features

• Tet spells: intermittent hypercyanotic, hypoxic episodes with a peak incidence at 2–4 months after birth
  • Associated with psychological and physical stress (e.g., crying, feeding, defecation)
  • Caused by either an increase in pulmonary vascular resistance (PVR) or a decrease in systemic vascular resistance (SVR) → low SVR:PVR ratio allows the deoxygenated right ventricular output to take the low-resistance route to the systemic circulation, leading to acute hypoxemia ("Tet spell").
  • Spells occur suddenly and are potentially lethal.
• Untreated children tend to squat
  • Squatting → ↑ SVR → ↓ right-to-left shunt → ↑ blood flow to pulmonary circulation → ↓ hypoxemia → relief of symptoms
• Cardiac examination findings
  • Harsh crescendo-decrescendo systolic ejection murmur at the left upper sternal border
    • Caused by pulmonary stenosis, not the associated VSD
      • VSD is so large that no sound
  • Single S2
  • Possible RV heave and systolic thrill

Diagnostics

• Increased hematocrit: secondary polycythemia

Treatment

• Ductal-dependent CHDs: a group of CHDs that require the patent ductus arteriosus (PDA), which supplies either pulmonary or systemic circulation, to sustain life until surgery can be performed
  • PDA supplies systemic circulation in the following:
    • Transposition of the great arteries
    • Hypoplastic left heart syndrome
    • Coarctation of the aorta
  • PDA supplies pulmonary circulation in the following:
    • Tricuspid atresia
  • Treatment: administration of prostaglandin E1 (PGE1) infusion
    • Example: IV alprostadil infusion
    • Mechanism of action: prevents the ductus arteriosus from closing, creating an intentional shunt to allow mixing of deoxygenated with oxygenated blood