Fontan Circulation
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Direct answer
A single functional ventricle cannot directly sustain two circulations, so the Fontan strategy channels systemic venous blood to the pulmonary arteries without a subpulmonary pump — an entirely passive circulation — staged across three operations: neonatal palliation (Norwood, shunt or banding as anatomy dictates), bidirectional Glenn at four to six months, and completion Fontan, by extracardiac conduit or lateral tunnel, at two to four years. Selection still honours Choussat's "ten commandments" in spirit: good ventricular function, low pulmonary vascular resistance, unobstructed pulmonary arteries and competent atrioventricular valves. Protein-losing enteropathy, plastic bronchitis and the failing Fontan dominate long-term follow-up, because the Fontan is a palliation, not a correction.
What you must remember
- The three stages: neonatal palliation establishing stable flow (Norwood with a Blalock-Taussig shunt or Sano modification for hypoplastic left heart; banding for others); bidirectional Glenn joining the superior vena cava to the pulmonary arteries; completion Fontan finishing the total cavopulmonary connection.
- Completion options: an extracardiac polytetrafluoroethylene conduit (18–20 mm) from inferior vena cava to pulmonary artery, or the intra-atrial lateral tunnel — the conduit avoids intracardiac suture lines and arrhythmogenic scarring, the tunnel grows with the child.
- A fenestration — a hole of about 4 mm in the circuit — decompresses the Fontan into the atrium, trading slight arterial desaturation for protection against effusions and low output in high-risk candidates.
- Choussat's ten criteria, worth naming in part: age above roughly four years, sinus rhythm, normal venous drainage, mean pulmonary artery pressure 15 mmHg or less, pulmonary vascular resistance below 2–3 Wood units per square metre, competent atrioventricular valve, good ventricular function, adequate pulmonary arteries (McGoon ratio above about 1.8).
- Early postoperative morbidity: pleural effusions and chylothorax — persistence beyond two weeks signals a struggling circuit; treat with drainage, medium-chain triglyceride diet, and a low threshold to fenestrate.
- Late complications: protein-losing enteropathy in roughly 3–5% (hypoalbuminaemia, diarrhoea, ascites, poor prognosis), plastic bronchitis, atrial arrhythmia, thromboembolism, hepatic congestion progressing to fibrosis, and Fontan failure culminating in transplant assessment.
- The physiology in one sentence: venous pressure is the pump, so anything raising pulmonary resistance (acidosis, pneumonia, positive-pressure ventilation) or impeding venous return (arrhythmia, valve regurgitation) threatens the whole circulation.
Why three stages, not one
The staging exists because each step's physiology becomes intolerable, and explaining that earns more than any list. A newborn's pulmonary vascular resistance is high, so hooking systemic veins straight to pulmonary arteries at birth would fail; stage one buys time with controlled pulmonary flow while the resistance falls. By four to six months the Glenn becomes possible: routing the superior vena cava to the lungs halves the volume load on the single ventricle. The Glenn is tolerated precisely because it is partial — patients remain mildly cyanotic, but the ventricle is protected. At two to four years, resistance is low enough to add the inferior vena cava: the completion Fontan, after which cyanosis largely resolves. Every long-term complication — effusions, enteropathy, hepatic congestion — flows from the final step's premise: maintaining pulmonary flow at central venous pressure, with no pump, forever.
Viva favourites
Expect Choussat by name ("name five of the ten"), and expect the fenestration debate: it lowers early morbidity in high-risk Fontans at the cost of persistent right-to-left shunting and possible later transcatheter closure. Expect protein-losing enteropathy as the complication to define — stool alpha-1 antitrypsin loss in the classic workup, albumin and immunoglobulin falling, management escalating from diuretics and sildenafil to transplantation. And expect the one-liner: the Fontan is a palliation, not a repair — the patient survives with a circulation, not a normal heart, which is why follow-up never ends.
Frequently asked questions
What are the three stages of single-ventricle palliation?
Neonatal palliation (Norwood, shunt or band), bidirectional Glenn at four to six months, and completion Fontan — total cavopulmonary connection — at two to four years.
What is a fenestration and why is it created?
A deliberate small communication between the Fontan circuit and the atrium, decompressing the passive circulation in high-risk patients. It reduces effusions and low output at the price of mild persistent cyanosis, and can often be closed later by catheter.
What is protein-losing enteropathy?
Loss of protein across the intestinal mucosa in Fontan patients — hypoalbuminaemia, oedema, diarrhoea and ascites — in roughly 3–5%, carrying a poor prognosis. Treatment escalates from diuretics and sildenafil to transplant assessment.
Name some of Choussat's criteria for a successful Fontan.
Sinus rhythm, normal venous anatomy, mean pulmonary artery pressure 15 mmHg or less, pulmonary vascular resistance under 2–3 Wood units per square metre, competent atrioventricular valve, preserved ventricular function and adequate pulmonary arteries (McGoon ratio above about 1.8).
Why does the Fontan circulation fail?
When anything raises pulmonary resistance or impedes passive flow — arrhythmia, valve regurgitation, thromboembolism, ventricular dysfunction — or years of venous hypertension generate hepatic fibrosis. Failure ends in transplant assessment.
Which anticoagulation is standard after Fontan completion?
Warfarin in many programmes, or at minimum aspirin, because the venous circuit flows slowly and thrombosis risk is lifelong.