How is pulmonary artery pressure measured invasively in patients with Fontan (total cavopulmonary) circulation?

Invasive Pulmonary Artery Pressure Measurement in Fontan Circulation

In Fontan circulation, pulmonary artery pressure is measured invasively via cardiac catheterization by directly accessing the Fontan pathway (the cavopulmonary connection) through venous access, with the catheter advanced from the systemic veins (IVC or SVC) directly into the pulmonary arteries, since there is no intervening subpulmonary ventricle. 1

Technical Approach to Catheterization

Access and Catheter Navigation

• Venous access is obtained through standard routes (femoral, jugular, or subclavian veins), and the catheter is advanced through the Fontan pathway—either the lateral tunnel, extracardiac conduit, or atriopulmonary connection—directly into the pulmonary arteries 1

• The anatomy must be well understood before catheterization, as the Fontan circuit varies significantly based on surgical technique (atriopulmonary connection, lateral tunnel, or extracardiac conduit), and physicians unfamiliar with the complex venous anatomy can encounter significant complications 1

• Catheterization should only be performed at regional centers with expertise in adult congenital heart disease (ACHD), as this is a Class I recommendation given the technical complexity and potential for complications 1

Critical Pitfall to Avoid

Traditional Swan-Ganz catheter placement techniques do not apply in Fontan circulation. Attempts at central line or Swan placement by physicians unfamiliar with the patient's complex venous anatomy represent a major pitfall that can lead to serious complications 1

Hemodynamic Measurements Obtained

Pressure Measurements

• Fontan pathway pressure (equivalent to pulmonary artery pressure) is measured directly in the cavopulmonary connection and branch pulmonary arteries 1

• In Fontan circulation, pulmonary artery pressure equals central venous pressure (CVP) because systemic venous blood is directly channeled into the pulmonary arteries without an intervening ventricle 1

• Normal Fontan pathway pressure is typically >10 mmHg (compared to normal CVP <10 mmHg), with pressures ≥20 mmHg indicating major hemodynamic disturbance requiring advanced heart failure consultation 1, 2

• Pulmonary artery pressure in Fontan patients will almost never reach conventional thresholds used to define pulmonary arterial hypertension because there is no subpulmonary ventricle to generate high pressures 3

Comprehensive Hemodynamic Assessment

During catheterization, the following should be measured 1:

• Fontan pathway pressure and pulmonary artery pressures (main and branch pulmonary arteries)
• Pulmonary vascular resistance (PVR), which is critical as the Fontan circulation cannot compensate for elevated PVR 1, 3
• Cardiac output and cardiac index, typically reduced to 80% of normal at rest in Fontan patients 1
• Ventricular end-diastolic pressure, with values >15 mmHg indicating major hemodynamic disturbance 1
• Oxygen saturation throughout the circuit to identify shunts 1

Vasoreactivity Testing

• Acute vasodilator testing with inhaled nitric oxide should be performed to assess pulmonary vascular responsiveness, particularly when evaluating for pulmonary vasodilator therapies or transplantation 1, 2

• Pulmonary vasoreactivity testing can demonstrate significant decreases in PVR (median 1.8 to 1.4 Wood units × m² with nitric oxide) and increases in cardiac index 2

Unique Physiological Considerations

Why Measurement Differs from Normal Circulation

In Fontan circulation, pulmonary pressure is a result of pulmonary artery resistance and pulmonary blood flow, which is passive and dependent on central venous pressure, not generated by ventricular contraction 1

The three driving forces for pulmonary blood flow are 1:

1. The "suction effect" of left atrial emptying from good ventricular function
2. The "lung and muscle pump" from negative intrathoracic pressure during inspiration
3. Low resistance in the pulmonary circuit without mechanical stenosis

Clinical Implications

• Any degree of obstruction in the nonpulsatile Fontan circuit is hemodynamically significant and should be identified during catheterization 1

• Pulmonary artery pressure becomes nonpulsatile in Fontan circulation, representing a fundamental difference from normal physiology 4

• Small gradients in the Fontan circuit can be associated with protein-losing enteropathy (PLE), making precise pressure measurement critical 1

Indications for Invasive Measurement

Cardiac catheterization with pressure measurement is indicated to investigate 1:

• Unexplained volume retention, fatigue, or exercise limitation
• Atrial arrhythmias
• Cyanosis and hemoptysis
• Protein-losing enteropathy
• Assessment before pulmonary vasodilator therapy or transplantation evaluation
• Routine surveillance approximately 10 years after Fontan completion in stable patients 2

Additional Diagnostic Components

Beyond pressure measurement, comprehensive catheterization includes 1:

• Angiography to assess Fontan pathway anatomy, branch pulmonary arteries, and identify stenoses or collateral vessels
• Search for right-to-left shunts including fenestrations, venovenous collaterals, and pulmonary arteriovenous malformations
• Assessment of systemic-to-pulmonary arterial connections that may require occlusion