Glenn then Fontan Circulation Simplified: Understanding Single-Ventricle Palliation

Mayta
Oct 23
3 min read

🫀 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	Name of Procedure	Typical Age	Goal	Pre-op Cath Required?
Stage 1	Initial palliation (BT shunt or Norwood)*	Neonate (0–1 month)	Provide controlled pulmonary blood flow (either augment or limit depending on anatomy)	Diagnostic only
Stage 2	Bidirectional Glenn / Hemi-Fontan	4–6 months	Connect SVC to pulmonary artery — upper body venous return goes directly to lungs	✅ Yes — Cath before Glenn
Stage 3	Fontan completion (Total Cavopulmonary Connection)	2–4 years	Connect IVC to pulmonary artery — all systemic venous blood now flows passively into lungs	✅ Yes — Cath before Fontan

🧭 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

⚙️ 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.

💡 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:

Continuity of care:GP needs to know what stage the child is in (e.g., post-Glenn vs post-Fontan) to interpret symptoms correctly.
Early detection of complications:
- Cyanosis or clubbing after Glenn = expected (only upper body oxygenated).
- New ascites, hepatomegaly, or edema after Fontan = concerning (Fontan failure).
Growth and nutrition monitoring:GPs monitor weight gain and oxygen saturation for readiness for next stage.
Vaccination and infection prevention:GPs ensure RSV prophylaxis, flu vaccine, and antibiotic prophylaxis as needed.
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.

🧠 Summary — “Fontan in One Page”

Step	Surgery	Age	Purpose	Why Cath?
Stage 1	BT Shunt / Norwood	Newborn	Stabilize circulation	Diagnostic
Stage 2	Bidirectional Glenn	4–6 mo	Divert SVC → PA	Measure PA pressure, PVR
Stage 3	Fontan	2–4 yr	Divert IVC → PA (complete Fontan)	Assess suitability, flow dynamics

🩺 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).