Cardiovascular · Year 1 · from Cardiovascular
Case 1: Tetralogy of Fallot - Cyanotic Heart Disease with "Tet Spells"
Clinical Image
Source: Wikimedia Commons - Tetralogy of Fallot - CC BY-SA 3.0
Patient Presentation
A 4-month-old male infant is brought to the pediatric emergency department by his parents after an episode of becoming deeply blue, limp, and unresponsive that lasted approximately 3 minutes. The parents report that the baby had been crying vigorously before the episode. This is the third such episode in the past week. The parents note the baby often appears bluish around the lips, especially when feeding or crying, and seems to tire easily.
Demographics
- Age: 4 months
- Sex: Male
- Birth History: Term delivery, prenatal ultrasound showed "heart abnormality"
- Family History: No congenital heart disease
Chief Complaint
Cyanotic spell with unresponsiveness following vigorous crying
Physical Examination
- Heart rate: 150 bpm
- Respiratory rate: 44/min
- Oxygen saturation: 78% on room air
- Weight: 5.2 kg (10th percentile)
- General: Mild central cyanosis, appears mildly tachypneic
- Cardiovascular: Right ventricular heave, single S2, grade 3/6 harsh systolic ejection murmur at left upper sternal border (decreases during spell)
- Extremities: Clubbing not yet present
- Neurological: Alert, appropriate for age
Workup
- Chest X-ray: "Boot-shaped" heart (coeur en sabot), decreased pulmonary vascular markings
- ECG: Right axis deviation, right ventricular hypertrophy
- Echocardiography: Large VSD, overriding aorta, severe right ventricular outflow tract obstruction (infundibular and valvular), right ventricular hypertrophy
- Oxygen saturation: Does not significantly improve with supplemental oxygen (confirms right-to-left shunt)
- Hemoglobin: 18.2 g/dL (compensatory polycythemia)
Diagnosis
Tetralogy of Fallot with Hypercyanotic ("Tet") Spells
Treatment
Acute Management of Tet Spell:
- Knee-chest position (increases systemic vascular resistance)
- Supplemental oxygen
- IV fluids for volume expansion
- Morphine (reduces respiratory drive and agitation)
- Phenylephrine if persistent (increases SVR, reverses shunt)
- IV propranolol (relaxes infundibular spasm)
Definitive Management:
- Complete surgical repair: VSD closure and relief of RVOT obstruction
- Timing: Complete repair typically between 3-6 months of age
- Palliative shunt (Blalock-Taussig shunt) if too small for complete repair
- Long-term follow-up with pediatric cardiology
Physiological Principles Demonstrated
- Shunt physiology: In TOF, the direction and magnitude of shunting depends on the balance between systemic vascular resistance (SVR) and the resistance at the RVOT obstruction. When SVR drops (crying, hypovolemia), more blood shunts right-to-left, worsening cyanosis.
- Hypercyanotic spell mechanism: Infundibular spasm further increases RVOT obstruction, creating a positive feedback loop: more right-to-left shunting leads to hypoxia, which causes catecholamine release, which worsens infundibular spasm.
- Treatment rationale: Increasing SVR (knee-chest position, phenylephrine) favors left-to-right shunting at the VSD level, increasing pulmonary blood flow and improving oxygenation.
- Murmur paradox: During a tet spell, the murmur decreases because less blood is flowing through the obstructed RVOT (more is shunting through the VSD).