Makindo Medical Notes

💙 Transposition of the Great Arteries (TGA) is a cyanotic congenital heart defect where: ➡️ The aorta arises from the right ventricle (deoxygenated blood → systemic circulation). ➡️ The pulmonary artery arises from the left ventricle (oxygenated blood → recirculates to lungs). ⛔ Without a natural or created shunt (ASD, VSD, PDA), TGA is incompatible with life because the two circulations run in parallel rather than in series.

📖 About

• Accounts for ~5–7% of all congenital heart disease.
• Leading cause of cyanotic CHD presenting in the neonatal period.
• ❗ Cyanosis typically worsens once the ductus arteriosus starts to close (first days of life).

🧬 Aetiology & Pathophysiology

• Embryological error: failure of the truncus arteriosus to spiral → great arteries arise from wrong ventricles.
• RV → Aorta; LV → Pulmonary artery.
• 🔀 Survival depends on mixing through ASD, VSD, or PDA.

🩺 Clinical Features

• 💙 Severe central cyanosis (day 1–2, especially when duct closes).
• 😮‍💨 Tachypnoea / respiratory distress despite clear lungs.
• 📉 Hypoxaemia not relieved by 100% oxygen (“hyperoxia test” negative).
• 🍼 Feeding difficulty, poor weight gain, lethargy.
• Less cyanotic if large VSD allows mixing (may present slightly later).
• 🫀 Usually no murmur unless VSD or PDA present.
• 👣 Clubbing if untreated long term.

🔎 Investigations

• 🩻 Chest X-ray: Classic “egg-on-its-side” appearance with narrow mediastinum, pulmonary plethora.
• 🫀 Echocardiography: Diagnostic gold standard, defines anatomy and shunts.
• 📉 Pulse oximetry: Persistent low saturations not corrected by oxygen.
• 🧪 Blood gases: Marked hypoxaemia, metabolic acidosis if severe.

🛠️ Management