Fontan Circulation

Concept and Background

• Miller's Anesthesia, 10e, p. 10879

Surgical Stages

Stage 1 - Initial Palliation (Neonatal)

• If pulmonary blood flow is too low: Modified Blalock-Taussig (BT) shunt - a Gore-Tex conduit between the subclavian artery and pulmonary artery
• If pulmonary blood flow is excessive: Pulmonary artery banding to protect against high pulmonary vascular resistance (PVR)

Stage 2 - Bidirectional Glenn Shunt (4-6 months)

• Partially separates circulations (SVC blood goes directly to lungs)
• Volume-unloads the single ventricle (critical preparatory step before Fontan)
• Maintains systemic cardiac output while reducing volume overload

Stage 3 - Fontan Completion (2-4 years of age)

• Fuster & Hurst's The Heart, 15th Ed., p. 2033
• Sabiston Textbook of Surgery, p. 2587

Surgical Variants

Prerequisites for an Effective Fontan Circulation

1. Low pulmonary vascular resistance (PVR) and low mean pulmonary artery pressure
2. Good ventricular function (low end-diastolic pressure, no significant diastolic dysfunction)
3. Adequate pulmonary artery architecture - no branch PA stenosis or hypoplasia
4. No significant AV valve regurgitation (increases atrial pressure)
5. Unobstructed systemic arterial outlet and normal semilunar valve
6. Normal pulmonary venous drainage and low left atrial pressure
7. Normal sinus rhythm (atrial arrhythmias are very poorly tolerated)

• Sabiston Textbook of Surgery, p. 2587

Fontan Physiology - Key Hemodynamics

• Central venous pressure rises acutely to 12-15 mmHg post-operatively
• Expected O2 saturation post-Fontan: ≥95% (lower values suggest Fontan failure or significant shunting)
• Pulmonary blood flow depends on respiratory mechanics: spontaneous ventilation augments Fontan flow; positive pressure ventilation (PPV) and PEEP impede it
• Any increase in PVR, decreased venous volume, or myocardial depressants is poorly tolerated

Fenestration

• Acts as a "pop-off valve" when pulmonary pressures are elevated
• Preserves ventricular preload at the cost of mild desaturation (right-to-left shunt)
• Reduces post-operative pleural effusions and ascites
• Can be closed percutaneously later if hemodynamics permit

Long-Term Complications

1. Fontan-Associated Liver Disease (FALD)

• Ubiquitous in long-term survivors
• Caused by chronically elevated central venous pressure leading to passive hepatic congestion, eventually progressing to cardiac cirrhosis
• Serum transaminases and GGT may be mildly elevated; synthetic function preserved until late stages
• Hepatocellular carcinoma (HCC) is a rare but serious complication - screen with AFP and imaging
• Surveillance: ultrasound or MRI every 1-2 years
• Combined heart-liver transplantation is increasingly performed for advanced FALD
• Braunwald's Heart Disease, p. (ACHD chapter)

2. Protein-Losing Enteropathy (PLE)

• Serious complication from elevated systemic venous pressure leading to gut lymphatic dysfunction
• Protein loss via gut leads to hypoalbuminemia, edema, ascites, immunodeficiency
• High mortality if untreated

3. Atrial Arrhythmias

• Atrial flutter and fibrillation are very common (especially in old atriopulmonary connections with massive RA dilation)
• Very poorly tolerated hemodynamically due to loss of atrial contribution to ventricular filling and passive PA flow
• Modern TCPC designs reduced (but did not eliminate) arrhythmia risk

4. Thromboembolism

• Sluggish venous flow in the Fontan circuit promotes thrombus formation
• Risk of stroke and pulmonary embolism
• Chronic anticoagulation considered for high-risk patients

5. Progressive Ventricular Dysfunction

• The single ventricle (often a morphological RV acting as systemic ventricle) is inherently prone to long-term failure
• HF therapies proven in two-ventricle patients may not be efficacious here

6. Plastic Bronchitis

• Rare - formation of bronchial casts from lymphatic leak into airways

Survival and Outcomes

• 90% survive to age 30
• 80% survive to age 40
• Only 53% are in NYHA class I at age 30
• Survival significantly worse for atriopulmonary connections vs. cavopulmonary connections
• Common causes of death: thromboembolism, heart failure, protein-losing enteropathy, arrhythmias
• Miller's Anesthesia, 10e, p. 10880

Anesthesia / Perioperative Considerations

• Avoid PPV with high PEEP - directly impairs passive pulmonary blood flow; favor early extubation
• Avoid hypovolemia - reduces venous pressure driving pulmonary flow
• Avoid vasodilators - reduce systemic venous return
• Avoid myocardial depressants
• Maintain normal PVR - avoid hypoxia, hypercarbia, acidosis, high airway pressures (all raise PVR)
• Failing Fontan patients are at extreme risk during abdominal surgery or procedures with large fluid shifts
• Check coagulation status - hepatic dysfunction from FALD can cause coagulopathy
• Chronic anticoagulation is common - manage perioperatively

Pregnancy in Fontan Patients

• Impaired ability to increase cardiac output during pregnancy
• Risk of SVT (~9%), heart failure (~4%); maternal mortality low with careful selection
• Fetal/neonatal outcomes poor: miscarriage 45%, high rates of prematurity and cesarean delivery
• Antiplatelet therapy (low-dose aspirin) recommended; LMWH for those with arrhythmias or prior embolism
• Vaginal delivery preferred; delivery at a specialized center with a maternal heart team is mandatory
• Braunwald's Heart Disease, p. 1084

Recent Evidence (2024-2026)

• Cardiac rehabilitation in Fontan patients shows benefit [PMID: 39597002] (Medicina, Nov 2024) - exercise training is feasible and improves outcomes
• Extracardiac conduit long-term outcomes meta-analysis [PMID: 39952466] (Can J Cardiol, Jun 2025) - confirms good intermediate-term survival
• Combined heart-liver transplantation for failing Fontan [PMID: 40320589] (Transplantation, Nov 2025) - single-arm meta-analysis showing good survival, supporting this as a valid option for end-stage disease