What are the primary goals of the Fontan procedure?

Primary Goals of the Fontan Procedure

The primary goal of the Fontan procedure is to separate the systemic and pulmonary circulations in patients with single-ventricle physiology by directing systemic venous return directly to the pulmonary arteries without a subpulmonary ventricle, thereby eliminating mixing of oxygenated and deoxygenated blood and improving systemic oxygen saturation. 1

Hemodynamic Goals

The Fontan procedure aims to achieve several specific hemodynamic objectives:

1. Creation of a series circulation: Connecting systemic and pulmonary circulations in series rather than in parallel 1

2. Passive pulmonary blood flow: Establishing a passive flow of systemic venous blood directly to the pulmonary arteries without requiring a pumping ventricle 1

3. Normalization of systemic oxygen saturation: Eliminating mixing of oxygenated and deoxygenated blood, which improves tissue oxygenation 1

4. Volume unloading of the single ventricle: Reducing the volume load on the single functioning ventricle, which previously had to pump blood to both systemic and pulmonary circulations 1

Anatomical Considerations

The Fontan procedure is indicated when:

• A patient has a functional or anatomical single ventricle
• The rudimentary pulmonary ventricle is less than 30% of its normal volume
• Biventricular repair is not feasible 1

Evolution of Surgical Techniques

The Fontan procedure has evolved through several modifications, all with the same fundamental goal:

• Atriopulmonary connection (classic Fontan): Direct connection between right atrium/atrial appendage and pulmonary artery (rarely used now) 1

• Intracardiac lateral tunnel: Creates a baffle inside the right atrium to channel blood from IVC to pulmonary artery 1

• Extracardiac conduit: Uses a conduit outside the heart to connect IVC to pulmonary artery 1

• Fenestration: Creation of a small communication between the systemic venous pathway and left atrium to serve as a "pop-off" valve, allowing right-to-left shunting to maintain cardiac output at the expense of some oxygen desaturation 1

Clinical Benefits and Outcomes

When successful, the Fontan procedure provides:

• Improved survival: Approximately 90% survival at 10 years in the absence of risk factors; 80% at 10 years for all patients 1

• Reduction in cyanosis: Separation of circulations leads to improved systemic oxygen saturation 1

• Prevention of volume overload: Reduces the risk of ventricular dilatation and failure compared to other palliative options 1

Important Caveats and Complications

Despite its benefits, the Fontan circulation has inherent physiological limitations:

• Elevated central venous pressure: The lack of a subpulmonary ventricle results in chronically elevated systemic venous pressure (typically >10 mmHg) 1, 2

• Reduced cardiac output: Fontan circulation is characterized by lower cardiac output compared to normal biventricular circulation 2

• Late complications: Include atrial arrhythmias, thrombus formation, protein-losing enteropathy, progressive systemic ventricular failure, and progressive AV valve regurgitation 1

• Fontan failure: Can occur due to systolic or diastolic ventricular dysfunction, atrioventricular valve disease, elevated pulmonary vascular resistance, recurrent arrhythmia, or lymphatic insufficiency 1, 3

Conclusion

The Fontan procedure represents a critical palliative strategy for patients with single-ventricle physiology. While not curative, it significantly improves survival and quality of life by establishing a more physiologic circulation pattern that reduces cyanosis and ventricular volume overload. However, the inherent hemodynamic limitations of this circulation require careful patient selection and lifelong specialized follow-up.