Congenital heart surgery principles

🧬 Core principles - The Heart's Blueprint

• Shunt Physiology:
  • Left-to-Right (L→R): Acyanotic. ↑ Pulmonary blood flow. Examples: VSD, ASD, PDA.
  • Right-to-Left (R→L): Cyanotic. Deoxygenated blood bypasses lungs.
  • 📌 5 T's of Cyanotic CHD: Tetralogy of Fallot, Transposition, Tricuspid atresia, Truncus arteriosus, TAPVR.
• Surgical Goals:
  • Palliative: Temporizing procedures to optimize physiology (e.g., Blalock-Taussig shunt).
  • Corrective: Definitive anatomical repair (e.g., VSD patch closure).
• Key Metric: Pulmonary-to-Systemic Flow Ratio ($Q_p/Q_s$). Ideal is 1:1.

⭐ Eisenmenger Syndrome: A severe form of pulmonary hypertension from a chronic, large L→R shunt. The shunt reverses to R→L, causing late-onset cyanosis and making corrective surgery contraindicated.

💨 Pathophysiology - Shunts & Swirls

• Shunt: Abnormal blood flow between cardiac chambers/vessels, driven by pressure gradients.
• Left-to-Right (L→R) Shunt (Acyanotic)
  • Pathophysiology: Oxygenated blood from high-pressure left heart shunts to low-pressure right heart.
  • Result: ↑ Pulmonary Blood Flow (PBF) → Pulmonary HTN → RV Hypertrophy → heart failure.
  • Examples: VSD, ASD, PDA. Acyanotic at birth.
• Right-to-Left (R→L) Shunt (Cyanotic)
  • Pathophysiology: Deoxygenated blood bypasses lungs into systemic circulation.
  • Result: Systemic hypoxemia, causing early cyanosis ("blue babies").
  • Examples: Tetralogy of Fallot (TOF), Transposition of Great Arteries (TGA).
  • 📌 5 T's: TOF, TGA, Truncus arteriosus, Tricuspid atresia, TAPVR.

⭐ Eisenmenger Syndrome: Chronic L→R shunt causes severe pulmonary HTN, reversing flow to R→L. Results in late-onset cyanosis, making the defect inoperable.

• Quantifying Shunts (Qp:Qs Ratio):
  • Normal: Qp:Qs ≈ 1:1
  • L→R Shunt: Qp:Qs > 1.5 (significant)
  • R→L Shunt: Qp:Qs < 1

🩺 The Surgical Toolkit

• Palliative Procedures: Temporize until definitive repair.

  • Systemic-to-Pulmonary Shunt: ↑ Pulmonary Blood Flow (PBF) in cyanotic defects (e.g., ToF, Tricuspid Atresia).
    • 📌 Blalock-Taussig-Thomas (BTT): Subclavian artery to pulmonary artery.
  • Pulmonary Artery (PA) Banding: ↓ PBF to protect lungs from pulmonary HTN in large L→R shunts (e.g., VSD).

• Corrective Procedures: Definitive anatomical repair.

  • Patch Closure: For ASD, VSD.
  • Arterial Switch (Jatene): For D-TGA.
  • Rastelli Procedure: For TGA with VSD & LVOTO.

⭐ The Fontan circulation is a passive system where systemic venous return bypasses the ventricle, flowing directly to the pulmonary arteries. Success is critically dependent on low pulmonary vascular resistance (PVR).

⚠️ Complications - Post-Op Perils

• Low Cardiac Output Syndrome (LCOS): Most common cause of early mortality. Features: hypotension, oliguria, ↑lactate. Treat with inotropes (e.g., milrinone).
• Cardiac Tamponade: Sudden ↓ chest tube output with ↑CVP & hypotension (Beck's triad). Requires emergent sternotomy.
• Pulmonary: Atelectasis, pleural effusions, chylothorax (thoracic duct injury → milky fluid, ↑triglycerides).
• Neurologic/Renal: Stroke from cardiopulmonary bypass (CPB) emboli; Acute Kidney Injury (AKI) from hypoperfusion.

⭐ Junctional Ectopic Tachycardia (JET) is a high-risk, narrow-complex tachycardia, especially after VSD repair. Key sign: AV dissociation.

⚡ Biggest Takeaways

• L→R shunts (VSD, ASD, PDA) are acyanotic but risk Eisenmenger syndrome (shunt reversal, late cyanosis) from chronic pulmonary overcirculation.
• R→L shunts (e.g., Tetralogy of Fallot, TGA) cause early cyanosis by shunting deoxygenated blood systemically.
• Prostaglandin E1 (PGE1) is a critical pre-op bridge to maintain a patent ductus arteriosus (PDA) in ductal-dependent lesions.
• Palliative shunts (e.g., Blalock-Taussig) temporarily increase pulmonary blood flow in cyanotic defects.
• Cardiopulmonary bypass (CPB) is required for most definitive intracardiac repairs.