Tetralogy of Fallot

Definition
The most common cyanotic congenital heart disease beyond infancy. It consists of 4 defects (Mnemonic: PROVe):

1. Pulmonary Stenosis (RV outflow tract obstruction - infundibular or valvular).
2. Right Ventricular Hypertrophy (RVH).
3. Overriding of the Aorta.
4. VSD (Ventricular Septal Defect) - large, malaligned.

Originates from Deviated outlet septum (Monology of Stenson)

1. Hemodynamics

• Severity: Depends on the degree of RVOT obstruction.
• Shunt: Large VSD allows pressure equalization between ventricles.
• If RV obstruction is severe $\to$ Right-to-Left shunt $\to$ Cyanosis.
• If RV obstruction is mild $\to$ Left-to-Right shunt $\to$ "Pink Tet".

2. Clinical Features

• Symptoms: Cyanosis (often appears later as infundibular stenosis worsens), Dyspnea on exertion, Failure to thrive.
• Squatting: Child squats after play to increase SVR (kinking femoral arteries) $\to$ reduces R-L shunt $\to$ improves oxygenation.
• Tet Spells (Cyanotic Spells):
• most common in the morning
  • Triggers: Crying, feeding, defecation (morning).
  • Mechanism: Spasm of infundibulum $\uparrow$ RVOT obstruction $\to$ $\uparrow$ R-L shunt $\to$ $\downarrow$ $p{O}_2$ $\to$ Metabolic acidosis $\to$ $\uparrow$ Respiratory drive $\to$ More negative intrathoracic pressure $\to$ More venous return $\to$ Cycle continues.

3. Physical Examination

• Inspection: Central Cyanosis, Clubbing.
• Auscultation:
  • S2: Single (P2 is soft/absent due to stenosis).
  • Murmur: Harsh Ejection Systolic Murmur (ESM) at left sternal border.
  • Note: The murmur is due to pulmonary stenosis, not the VSD. During a severe Tet spell, the murmur may disappear (no flow across PA).

4. Diagnosis

• CXR: "Boot-shaped heart" (Coeur en sabot) due to uplifted apex (RVH) and concave pulmonary bay. Pulmonary oligemia.
• ECG: Right Axis Deviation, RVH. (RsR' in v1, v2 and prominent Q wave in inferior leads)
• Echo: Diagnostic.
• Cardiac Chattelization : Equalization of pressure in RV and LV. PT pressure decreased than normal

5. Management

A. Management of Tet Spell (Medical Emergency)

1. Calm the child.
2. Knee-Chest Position: Increases SVR, promotes venous return.
3. Oxygen: 100% flow.
4. Morphine (SC/IV): Suppresses respiratory center, reduces anxiety.
5. IV Fluids: Volume expansion.
6. Vasoconstrictors: Phenylephrine or Ketamine (increases SVR to reverse shunt).
7. Sodium Bicarbonate: To correct acidosis.
8. Betablockers: Proponalol/esmolol to relieve outflow obstruction

B. Surgical Management

• Palliative: Modified Blalock-Taussig (BT) Shunt (Subclavian artery to Pulmonary artery). Done if baby is too small for total repair.
• Definitive: Intracardiac Repair (usually at 6-12 months).
  1. Patch closure of VSD.
  2. Resection of infundibular muscle / Pulmonary valvotomy (RVOT relief).

6. Complication

• Cerebral thrombosis
• Brain abscess
• Infective endocarditis