Fontan Procedure: A Surgical Overview

The Fontan procedure is the final stage in a series of palliative surgeries designed for patients with “single ventricle” physiology—congenital heart defects where only one chamber is functionally capable of supporting systemic circulation (e.g., tricuspid atresia, hypoplastic left heart syndrome, or double inlet left ventricle). The primary goal is to separate the systemic and pulmonary circulations in series, directing deoxygenated systemic venous return directly to the pulmonary arteries without the assistance of a sub-pulmonary pump.

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Evolution of Surgical Techniques

The surgical approach has evolved significantly to improve hemodynamics and reduce long-term complications like atrial arrhythmias.

1. Classical Fontan (Atriopulmonary Connection)

Initially described in 1971, this involved connecting the right atrium directly to the pulmonary artery. This is largely obsolete today because the resulting massive right atrial dilation frequently led to refractory atrial arrhythmias and thrombus formation.

2. Lateral Tunnel (Endocardiac Conduit)

A baffle is created within the right atrium using prosthetic material or atrial wall to channel blood from the inferior vena cava (IVC) to the pulmonary artery. This keeps the high-pressure venous return separate from the rest of the atrium.

3. Extracardiac Conduit (ECC)

The current gold standard. A prosthetic tube (usually Gore-Tex) is used to connect the IVC directly to the pulmonary artery, bypassing the right atrium entirely.

• Advantages: Lower risk of atrial arrhythmias, improved laminar flow, and the ability to perform the procedure without cross-clamping the heart or using cardiopulmonary bypass in some cases.

Superior venacaval blood reaches the pulmonary artery through a bidirectional Glenn procedure.

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Hemodynamic Principles

The Fontan circulation relies on a passive flow of blood into the lungs, driven primarily by central venous pressure (CVP) rather than a ventricular pulse.

• Driving Force: The pressure gradient between the systemic venous system (P_svc/ivc) and the common pulmonary venous atrium (P_pva).
• The Fenestration: Often, a small hole (fenestration) is left between the Fontan circuit and the atrium. This acts as a “pop-off” valve, allowing right-to-left shunting to maintain cardiac output at the cost of mild cyanosis if pulmonary vascular resistance (PVR) rises acutely.

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Long-Term Complications

Despite improved survival, the “Fontan physiology” is inherently limited by chronic venous hypertension and low cardiac output.

System	Complication	Pathophysiology
Hepatic	FALD	Fontan-associated liver disease; chronic congestion leading to cirrhosis and HCC risk.
Gastrointestinal	PLE	Protein-losing enteropathy; leakage of serum proteins into the gut due to high venous pressure.
Respiratory	Plastic Bronchitis	Formation of cast-like plugs in the airways; highly morbid.
Hematologic	Thromboembolism	Sluggish flow and endothelial dysfunction increase stroke and PE risk.
Cardiac	Arrhythmias	Particularly Intra-atrial Reentrant Tachycardia (IART).

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Diagnostic Evaluation

Follow-up typically involves a multi-modality approach:

• Echocardiography: To assess single ventricle function, AV valve regurgitation, and Fontan circuit patency.
• Cardiac MRI: The gold standard for quantifying ventricular volumes and flow (Qp:Qs).
• Cardiac Catheterization: Essential for measuring transpulmonary gradients and PVR before and after the procedure.