What is a normal Fontan circuit pressure?

Normal Fontan Circuit Pressure

Normal Fontan pathway pressure is typically greater than 10 mmHg but less than 15 mmHg, with pressures ≥20 mmHg indicating major hemodynamic disturbance requiring advanced heart failure consultation. 1, 2

Understanding Fontan Hemodynamics

The Fontan circulation fundamentally differs from normal cardiac physiology because systemic venous blood is directly channeled into the pulmonary arteries without an intervening sub-pulmonary ventricle. 1, 2 This creates an obligate elevation in central venous pressure compared to healthy individuals. 1

Key Pressure Parameters

• Normal range: Fontan pathway pressure >10 mmHg is expected due to the passive flow system 1, 2
• Concerning threshold: Fontan pressure of 15 mmHg represents the upper limit of normal in most studies 3, 4
• Pathological elevation: Fontan pressure ≥20 mmHg indicates major hemodynamic disturbance and warrants advanced heart failure consultation 1, 2

Clinical Context and Interpretation

The 2023 Circulation guidelines from the ACTION consortium specifically define hemodynamic thresholds for advanced heart failure referral, including Fontan pressure ≥20 mmHg, ventricular end-diastolic pressure >15 mmHg, or cardiac index <2 L/min/m². 1

Prognostic Significance

Research demonstrates that hemodynamic profiles matter significantly for outcomes:

• Normal cardiac index with high Fontan pressure (≥15 mmHg) was an independent predictor of mortality with a hazard ratio of 4.1 3
• Elevated filling pressures or Fontan pathway pressure are independent predictors of adverse events in multiple studies 1
• Even small gradients in the Fontan circuit can be associated with protein-losing enteropathy, making precise pressure measurement critical 2

Physiological Drivers of Pressure

In Fontan circulation, pulmonary artery pressure equals central venous pressure because there is no intervening ventricle. 1, 2 The pressure is determined by:

• Pulmonary vascular resistance: Elevated PVR from lung disease or chronic nonpulsatile flow increases Fontan pressure 1
• Ventricular end-diastolic pressure: Diastolic dysfunction or elevated filling pressures directly transmit backward to the Fontan pathway 1
• Mechanical obstruction: Stenosis of the Fontan pathway or branch pulmonary arteries 1

Measurement Considerations

Invasive catheterization should only be performed at regional centers with expertise in adult congenital heart disease given the technical complexity. 2 During catheterization, comprehensive assessment includes:

• Direct measurement of Fontan pathway pressure in the cavopulmonary connection and branch pulmonary arteries 2
• Pulmonary vascular resistance calculation 2
• Ventricular end-diastolic pressure 2
• Cardiac output and cardiac index (typically reduced to 80% of normal at rest) 1, 2
• Oxygen saturation throughout the circuit to identify shunts 2

Important Caveats

Many individuals with Fontan circulation have normal end-diastolic pressure at rest during catheterization, but demonstrate pathological increases with rapid volume expansion. 1 This dynamic response is common and contributes to Fontan-related complications even when resting pressures appear acceptable. 1

The 2023 EASL-ERN position paper emphasizes that compared to healthy individuals (CVP <10 mmHg), the cavopulmonary connection results in obligate higher CVP (>10 mmHg), which is physiologically "normal" for Fontan patients but represents chronic systemic venous congestion. 1