Fontan Circulation

The Fontan circulation represents the final stage of surgical palliation for single-ventricle physiology. It is designed to achieve complete separation of systemic and pulmonary circulations in the absence of a functional subpulmonary ventricle.

Concept and Hemodynamics

In the Fontan pathway, systemic venous return flows passively into the pulmonary arteries without the aid of a right ventricular pump. The inferior vena cava (IVC) is redirected to the pulmonary circulation, which results in improved systemic oxygen saturation. This is the culmination of staged palliation beginning with the Norwood (Stage 1) and Glenn (Stage 2) procedures.

For the Fontan circulation to function effectively, certain hemodynamic conditions are essential. Pulmonary artery pressure (PAP) must be lower than central venous pressure (CVP) to allow forward venous flow. Optimal Fontan physiology requires low pulmonary vascular resistance (PVR) and moderate CVP, creating a gradient sufficient to drive pulmonary blood flow.

Fontan as a Pressure-Loaded Circulation

Although the Fontan achieves complete separation of systemic and pulmonary flows, it creates a unique hemodynamic burden. The single ventricle now supports the entire circulation and faces the combined afterload of both the systemic and pulmonary vascular beds. This leads to a pressure-loaded ventricle, which over time may impair systolic and diastolic function.

Systemic Venous Hypertension and Complications

A hallmark of Fontan physiology is chronic systemic venous hypertension, the inevitable result of driving pulmonary blood flow passively. Persistent venous hypertension produces a characteristic set of complications:

• Pleural effusions in the early postoperative period
• Protein-losing enteropathy (PLE) due to intestinal lymphatic congestion
• Congestive hepatopathy, progressing to fibrosis and cirrhosis in long-term survivors

Additionally, impaired lymphatic drainage is common, further contributing to effusions, ascites, and PLE.

Summary

Fontan circulation is the definitive stage of palliation for single-ventricle patients, rerouting IVC blood to the pulmonary arteries and thereby improving systemic oxygenation. Its success depends on low PVR and adequate venous-to-pulmonary pressure gradients. However, the circulation is inherently pressure-loaded, with systemic venous hypertension predisposing to pleural effusions, PLE, hepatopathy, and lymphatic complications. These physiological constraints explain both the achievements and long-term limitations of the Fontan strategy.