What is the recommended preoperative evaluation for a patient with complex congenital heart disease undergoing Fontan completion?

Preoperative Evaluation for Fontan Completion

Cardiac catheterization must be performed before initial Fontan surgery to definitively assess hemodynamic suitability, including pulmonary artery pressures, pulmonary vascular resistance, ventricular function, and anatomic adequacy of the pulmonary arteries. 1

Mandatory Hemodynamic Assessment via Cardiac Catheterization

The cornerstone of preoperative evaluation is invasive hemodynamic assessment, as Fontan physiology cannot tolerate elevated pulmonary vascular resistance or unfavorable pressures 1:

Critical Hemodynamic Parameters to Measure

• Mean pulmonary artery pressure: Should ideally be <15 mmHg, though recent data suggest patients with pressures 15-20 mmHg may still have acceptable outcomes with careful selection 2
• Pulmonary vascular resistance (PVR): This is the most critical parameter, as the Fontan circulation cannot compensate for elevated PVR; low resistance is essential for passive flow from systemic veins to pulmonary arteries 1, 2
• Ventricular end-diastolic pressure: Assess for diastolic dysfunction that would impair ventricular filling in the low-pressure Fontan system 1
• Pulmonary artery anatomy: Evaluate for stenosis, distortion, or hypoplasia of branch pulmonary arteries that would increase resistance 1
• Nakata index: Quantify adequacy of pulmonary artery size relative to body surface area 3

Additional Anatomic and Physiologic Assessment During Catheterization

• Systemic and pulmonary venous anatomy: Identify anomalous connections or obstructions 1
• Atrioventricular valve regurgitation: Quantify severity, as significant regurgitation predicts poor outcomes 1
• Ventricular systolic function: Preserved function is mandatory; dysfunction contraindicates Fontan completion 1
• Presence of aortopulmonary collaterals: Identify and consider occlusion of abnormal vessels (PDA, collaterals) that increase pulmonary blood flow and ventricular volume load 1
• Atrial septal defect/ventricular septal defect size: Assess adequacy for mixing if fenestration is planned 1

Comprehensive Noninvasive Imaging

Echocardiography

Detailed transthoracic echocardiography should be performed by staff with expertise in adult congenital heart disease 1, 4:

• Ventricular systolic function: Measure ejection fraction; dysfunction is a contraindication 1, 4
• Ventricular diastolic function: Assess filling pressures and compliance 4, 5
• Atrioventricular valve regurgitation: Grade severity; moderate-to-severe regurgitation may require valve repair at time of Fontan 1, 4
• Ventricular hypertrophy: Excessive hypertrophy (particularly if from long-standing pulmonary artery banding) increases risk of diastolic dysfunction and poor outcomes 3
• Outflow tract obstruction: Identify subaortic or subpulmonary stenosis requiring intervention 1
• Branch pulmonary artery flow patterns: Assess for stenosis or abnormal flow 4, 5

Cardiac MRI or CT

Advanced imaging provides detailed anatomic information when echocardiography is insufficient 1:

• Complete visualization of systemic and pulmonary venous anatomy 1
• Precise measurement of ventricular volumes and mass 3
• Pulmonary artery anatomy and size quantification 1
• Detection of venovenous collaterals 6

Laboratory and Functional Assessment

Hematologic and Biochemical Testing

• Hemoglobin and hematocrit: Elevated values suggest chronic hypoxemia and may indicate inadequate pulmonary blood flow 3
• Liver function tests: Baseline assessment for hepatic congestion from prior palliation 1
• Renal function: Baseline creatinine and GFR 1
• Coagulation profile: Assess baseline coagulopathy risk 6

Cardiopulmonary Exercise Testing

• Exercise capacity assessment: Provides objective measure of functional status and cardiac reserve 1
• Cardiac index response to exercise: Reduced rise in cardiac index with exercise may predict poor Fontan outcomes 7

Rhythm and Conduction Assessment

• 12-lead ECG: Document baseline rhythm and conduction abnormalities 1
• 24-hour Holter monitoring: Screen for atrial arrhythmias that increase thromboembolism risk and may require intervention at time of Fontan 1

Additional Organ System Evaluation

Pulmonary Function

• Pulmonary function tests and assessment for scoliosis: Restrictive lung disease or chest wall deformity may compromise already marginal pulmonary blood flow in Fontan physiology 1

Hepatic Imaging

• Liver ultrasound or MRI: Assess for pre-existing hepatic congestion or fibrosis from prior palliation 1

Critical Pitfalls to Avoid

Do not proceed with Fontan completion based on noninvasive imaging alone—catheterization is mandatory to directly measure pressures and resistance that determine candidacy 1. Even patients with mean pulmonary artery pressures slightly above traditional cutoffs (15-20 mmHg) may be candidates if PVR is low and other hemodynamics are favorable 2. Long-standing pulmonary artery banding should be avoided as it causes ventricular hypertrophy and mass increase that predicts poor outcomes, particularly severe pericardial effusions post-Fontan 3. Any degree of Fontan pathway obstruction is hemodynamically significant in this nonpulsatile system, so meticulous anatomic assessment is essential 4.