What is Fontan syndrome?

What is Fontan Syndrome?

Fontan syndrome refers to the constellation of progressive multi-organ complications that inevitably develop in patients living with Fontan circulation—a palliative surgical state created for congenital heart defects with a single functional ventricle, where systemic venous blood flows directly to the lungs without a subpulmonary ventricle. 1

The Underlying Pathophysiology

The Fontan circulation fundamentally alters normal cardiovascular hemodynamics in three critical ways 1:

• Chronic systemic venous hypertension: Central venous pressure remains persistently elevated (typically >10 mmHg) because systemic venous blood connects directly to pulmonary arteries without the protective tricuspid valve that normally guards against right ventricular pressure 1

• Chronically preload-deprived ventricle: Despite elevated venous pressure, the single ventricle operates in a preload-deficient state because blood must traverse the pulmonary circuit before filling the ventricle, resulting in cardiac output reduced to approximately 80% of normal at rest 1

• Non-pulsatile pulmonary blood flow: Blood flows passively through the lungs without active ventricular propulsion, relying instead on the thoracic pump, muscle pump, and low pulmonary vascular resistance 1

The Inevitable Decline: Fontan Circulatory Failure

A premature decline in cardiovascular performance with reduced survival is inevitable even in the best Fontan patients. 1 The probability of remaining free from Fontan circulatory failure is 93% at age 20, but drops dramatically to 77% at age 30,62% at age 40, and only 30% at age 50 1. This represents the highest mortality ratio of any congenital heart disease, with a more than 20-fold increased risk of death compared to age-matched populations 1.

Fontan circulatory failure is defined as deteriorated clinical status affecting the patient's ability to carry out daily activities, resulting from 1:

• Progressive systemic ventricular dysfunction (systolic or diastolic)
• Atrioventricular valve regurgitation
• Rising pulmonary vascular resistance
• Recurrent arrhythmias
• Lymphatic insufficiency
• End-organ complications

Multi-Organ Complications: The Hallmark of Fontan Syndrome

Cardiovascular Complications

Arrhythmias develop in 20% of patients by 10 years post-Fontan, including intra-atrial re-entry tachycardia, atrial flutter, atrial fibrillation, and focal atrial tachycardia 1. The prevalence reaches 16-34% in long-term follow-up 1.

Exercise intolerance is universal, with objectively reduced exercise capacity even in patients who subjectively feel well during childhood and adolescence 1.

Hepatic Complications (Fontan-Associated Liver Disease - FALD)

Some degree of FALD is universally present after Fontan-type surgery, with prevalence ranging from 13-86% depending on diagnostic methods 1. The spectrum includes 1:

• Hepatic congestion and fibrosis progressing to cirrhosis
• Portal hypertension with esophageal varices, ascites, and splenomegaly
• Hepatocellular carcinoma (HCC) risk
• Time elapsed from Fontan surgery is the main risk factor for advanced FALD 1

Gastrointestinal Complications

Protein-losing enteropathy (PLE) occurs in 1-5% of patients and carries a devastating prognosis with 5-year survival of only 50% 1. It presents with 1:

• Peripheral edema, pleural effusions, and ascites
• Low serum albumin
• Elevated α1-antitrypsin levels in stool
• Available treatments are of limited effectiveness 1

Renal Complications

Fontan-associated chronic kidney disease develops in 10-50% of patients due to chronic venous congestion and low cardiac output 1.

Lymphatic System Complications

Lymphatic dysfunction manifests as 1:

• Chylothorax and chylous ascites
• Plastic bronchitis (1-4% prevalence) with proteinaceous material leaking into airways
• Chronic pleural effusions

Vascular Complications

• Thromboembolism risk due to right atrial blood stasis and disturbed coagulation 1
• Peripheral edema and lower extremity venous insufficiency (50-60% prevalence) 1
• Development of pulmonary arteriovenous malformations and systemic-to-pulmonary collaterals 1

Neurological Complications

Neurocognitive disorders and behavioral deficits occur due to chronic hypoxemia and altered cerebral perfusion 1.

Clinical Recognition

Common clinical findings include mild, non-pulsatile jugular venous distension 1. However, significant jugular venous distension with hepatomegaly should raise immediate suspicion for Fontan pathway obstruction or ventricular failure 1.

Pleural effusion on chest X-ray is a red flag for protein-losing enteropathy 1.

The ECG frequently shows junctional rhythm or atrial arrhythmias 1.

Critical Pitfall to Avoid

Do not assume that young Fontan patients who feel well are truly stable—exercise capacity is objectively reduced even when patients report feeling fine, and complications progressively accumulate with age 1. The term "Fontan syndrome" emphasizes that this is not simply a cardiovascular condition but rather a progressive multi-organ disease requiring lifelong multidisciplinary surveillance 1, 2.