What are the common complications of Fontan circulation in pediatric patients with complex congenital heart defects?

Common Complications of Fontan Circulation

The Fontan circulation, while life-saving for children with single-ventricle physiology, inevitably leads to a constellation of serious complications affecting multiple organ systems due to chronic systemic venous hypertension and impaired cardiac output—complications that include arrhythmias, thromboembolism, protein-losing enteropathy, ventricular dysfunction, hepatic disease, and exercise intolerance. 1

Cardiovascular Complications

Arrhythmias

• Supraventricular tachyarrhythmias develop in approximately 20% of patients by 10 years post-Fontan, including intra-atrial reentry tachycardia, atrial flutter, atrial fibrillation, and focal atrial tachycardia 1
• The incidence may be lower with total cavopulmonary connection (TCPC) compared to older atriopulmonary connection (APC) techniques, though this remains unproven 1
• Junctional rhythm is frequently observed on ECG monitoring 1

Ventricular Dysfunction and Heart Failure

• Progressive decline in systemic ventricular function occurs despite normal ventricular mass and volume in long-term survivors 1
• This deterioration results from the absence of normal biventricular interaction mediated by the interventricular septum, causing altered myocardial twist and strain 1
• Diastolic filling abnormalities are common regardless of ventricular morphology 1
• The systemic circulation is often supported by a morphologic right ventricle, which is ill-designed for this purpose and prone to late failure 1

Atrioventricular Valve Regurgitation

• Progressive AV valve regurgitation contributes significantly to late Fontan failure 1
• This complication compounds ventricular dysfunction and elevates systemic venous pressures 1

Thromboembolic Complications

• Atrial and pulmonary artery thrombus formation represents a major risk due to blood stasis and disturbed coagulation 1
• Subclinical recurrent pulmonary embolism may lead to progressive rise in pulmonary vascular resistance 1
• Long-term antiplatelet therapy is reasonable after Fontan procedure (Class IIa recommendation) 1
• Prophylaxis with warfarin or low-molecular-weight heparin may be reasonable for 3-12 months post-Fontan (Class IIb) 1
• Patients should be monitored with periodic transthoracic echocardiography focused on thrombus identification 1

Protein-Losing Enteropathy (PLE)

• PLE is a rare but devastating complication with 5-year survival of only 50% 1
• Clinical manifestations include peripheral edema, pleural effusions, and ascites 1
• Diagnosis requires documentation of low serum albumin and elevated α1-antitrypsin levels in stool 1
• Available treatments demonstrate limited effectiveness 1

Hepatic Complications

• Chronic systemic venous hypertension causes hepatic congestion and dysfunction 1
• Progressive hepatic fibrosis and cirrhosis develop over time 2
• Hepatic evaluation by ultrasound and CT is essential for monitoring fibrosis, cirrhosis, and malignancy risk 1
• Annual blood tests must include liver function assessment 1

Pulmonary Complications

Pulmonary Vascular Disease

• Progressive rise in pulmonary vascular resistance contributes to late Fontan failure 1
• Pulmonary venous obstruction may develop, particularly right pulmonary vein obstruction by enlarged right atrium 1

Pulmonary Arteriovenous Malformations

• These abnormal vascular connections develop in the pulmonary circulation 1, 3
• Progressive cyanosis may occur with bidirectional cavopulmonary anastomosis due to relatively greater inferior vena cava flow versus superior vena cava flow 1

Plastic Bronchitis

• This lymphatic dysfunction complication represents a severe manifestation of Fontan circulatory failure 3, 2

Exercise Intolerance and Functional Limitations

• Cardiorespiratory responses to exercise are markedly subnormal, including lower-than-expected VO2max, cardiac output, and heart rate responses 1
• Abnormal reduction of resting arterial oxygen saturation occurs at peak exercise 1
• Exercise capacity is reduced even when measured objectively in patients who appear clinically well during childhood and adolescence 1
• Pre-adolescents undergoing volume-unloading surgery at early age demonstrate better aerobic capacity than those with later surgery 1

Lymphatic Dysfunction

• Chronic venous insufficiency develops as a consequence of elevated systemic venous pressure 1
• Manifestations include ascites, peripheral edema, pleural effusions, and protein-losing enteropathy 3, 2

Pathway Obstruction and Vascular Abnormalities

• Fontan pathway obstruction may occur, manifesting as significant jugular venous distension and hepatomegaly 1
• Systemic arterial-to-pulmonary venous or systemic arterial-to-pulmonary arterial connections can develop 1
• Systemic-to-pulmonary venous collaterals form over time 1

Cyanosis

• Cyanosis may develop or persist, particularly in patients with fenestration 1
• Progressive cyanosis warrants cardiac catheterization to evaluate hemodynamics and vascular connections 1

Renal Dysfunction

• Renal dysfunction is common and may progress over time due to chronic low cardiac output and venous congestion 2

Neurodevelopmental and Psychosocial Complications

• Cognitive, neuropsychological, and behavioral deficits are highly prevalent 2
• These complications significantly impact quality of life and require ongoing surveillance 2

Critical Surveillance Requirements

All Fontan patients require lifelong follow-up with at least yearly evaluation including: 1, 4, 5

• Echocardiography with focused attention to thrombus identification
• ECG and Holter monitoring for arrhythmia detection
• Exercise testing to assess functional capacity
• Blood tests including hematology, serum albumin, liver and renal function
• Cardiac MRI at least once in adult age and further as indicated

Common Pitfalls

• Failure to recognize that even "successful" Fontan patients face inevitable premature decline in cardiovascular performance 1
• Underestimating the need for aggressive surveillance despite apparent clinical stability during childhood 1, 4
• Delaying advanced heart failure consultation when signs of circulatory dysfunction emerge 4, 5
• Inadequate attention to extracardiac complications, particularly hepatic and renal dysfunction 1, 2