Glenn then Fontan Circulation Simplified: Understanding Single-Ventricle Palliation

🫀 1. The “Single-Ventricle” Problem

Some babies are born with only one functional ventricle (either LV or RV can’t support circulation).Examples:

• Tricuspid atresia
• Hypoplastic left heart syndrome (HLHS)
• Double-inlet ventricle
• Pulmonary atresia with intact septum

Because of this, the heart cannot pump blood separately to lungs and body like a normal two-ventricle system.

So we create a Fontan circulation, where systemic venous blood flows passively to the lungs (no ventricle) — and the single ventricle only pumps oxygenated blood to the body.

🔶 Stepwise Fontan Pathway (Staged Palliation)

🧭 Stage-by-Stage Explanation

Stage 1 — Initial Palliation

Purpose: To stabilize neonate and balance systemic vs pulmonary blood flow.

• If pulmonary flow is too low → add a BT shunt (subclavian → pulmonary artery).
• If pulmonary flow is too high (e.g., large VSD) → pulmonary artery banding to reduce it.

This keeps baby alive until pulmonary vascular resistance (PVR) drops naturally.

Stage 2 — Bidirectional Glenn (BDG)

Timing: ~4–6 months, when PVR is low enough.

Procedure:

• Connect SVC → right pulmonary artery (and via RPA to LPA = bidirectional).
• Disconnect SVC from RA.

Effect:

• Deoxygenated blood from the upper body goes passively to lungs.
• Reduces volume load on the single ventricle.

🔍 Why we do cath before Glenn:

• To ensure PVR < 2 Wood units·m²
• Mean PA pressure < 15 mmHg
• Good ventricular function
• No AV valve regurgitation
• Good-sized pulmonary arteries

If PA pressure too high → Glenn will fail (SVC congestion).

Stage 3 — Fontan Completion (Total Cavopulmonary Connection, TCPC)

Timing: ~2–4 years, once child is bigger and pulmonary bed is mature.

Procedure:

• Connect IVC → pulmonary arteries (via extracardiac conduit or lateral tunnel).
• Now all venous blood bypasses the heart and flows passively to lungs.

Ventricle pumps only systemic blood (fully oxygenated).This completes the Fontan circulation.

🔍 Cath before Fontan ensures:

• Low PA pressure
• Good ventricular function
• No obstruction in Glenn
• No PA distortion or collaterals

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⚙️ Why This Stepwise Approach?

• Neonate lungs have high PVR → immediate Fontan would fail.
• Gradual adaptation allows lungs and venous system to develop.
• Reduces risk of high venous pressure, pleural effusion, and Fontan failure.

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💡 Why We Create a “Fontan Summary for GP”

A general practitioner (GP) or primary care physician often sees the child between surgeries.They must understand the staged plan to monitor, refer, and prevent complications.

Key reasons:

1. Continuity of care:GP needs to know what stage the child is in (e.g., post-Glenn vs post-Fontan) to interpret symptoms correctly.
2. Early detection of complications:
   • Cyanosis or clubbing after Glenn = expected (only upper body oxygenated).
   • New ascites, hepatomegaly, or edema after Fontan = concerning (Fontan failure).
3. Growth and nutrition monitoring:GPs monitor weight gain and oxygen saturation for readiness for next stage.
4. Vaccination and infection prevention:GPs ensure RSV prophylaxis, flu vaccine, and antibiotic prophylaxis as needed.
5. Emergency communication:If the child presents acutely ill, GP can immediately tell emergency doctors:“This child is post-Glenn / pre-Fontan” → changes how you handle fluids and oxygen.

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🧠 Summary — “Fontan in One Page”

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🩺 Key Teaching Pearl (for exams & clinical logic)

Fontan success = “low PVR + good ventricle + competent AV valve.”

Otherwise → Fontan failure (manifest as edema, pleural effusion, protein-losing enteropathy, cyanosis).