Cardiac Imaging

What Is the Best Imaging for Pre-Fontan Evaluation in a Child with Single Ventricle Physiology?

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What Is the Best Imaging for Pre-Fontan Evaluation in a Child with Single Ventricle Physiology?

A three-year-old with hypoplastic left heart syndrome, having previously undergone stage 1 and 2 palliation, is in your clinic for preoperative planning. The next and final planned surgery is the total cavopulmonary connection, or Fontan procedure. The preoperative transthoracic echocardiogram shows preserved single ventricle function, but the distal pulmonary arteries are poorly visualized, and you cannot rule out significant aortopulmonary collaterals. To ensure the child is a suitable candidate for the Fontan circuit, you need a definitive map of the cardiovascular anatomy and precise hemodynamic measurements. This clinical workflow details the imaging decision for this specific scenario: a child with known single ventricle physiology needing preoperative evaluation for stage 3 palliation after an incomplete echocardiogram. For this presentation, the American College of Radiology (ACR) rates invasive cardiac catheterization, specifically `Arteriography coronary with ventriculography`, as Usually appropriate.

Who Fits This Clinical Scenario?

This guidance applies to a specific pediatric population: children with functional single ventricle physiology who are being considered for stage 3 surgical palliation (the Fontan procedure or total cavopulmonary connection). These patients have typically already undergone the first two stages of palliation, such as a Norwood procedure followed by a bidirectional Glenn shunt. The key trigger for this workflow is that the standard, non-invasive imaging—transthoracic echocardiography (TTE)—has failed to provide a complete assessment of the critical anatomical and functional parameters needed for surgical decision-making.

This article is NOT for:

  • Patients undergoing evaluation for stage 2 palliation (Glenn shunt): The hemodynamic questions and anatomical focus are different. This is addressed in a separate ACR variant.
  • Patients with postoperative complications after a Fontan procedure: Evaluating a failing Fontan circuit involves a distinct diagnostic algorithm, often focused on identifying thrombosis, fenestration patency, or protein-losing enteropathy.
  • Patients with biventricular congenital heart disease: Conditions like a repaired tetralogy of Fallot or transposition of the great arteries have entirely different anatomical substrates and follow-up imaging needs.

The focus here is strictly on the comprehensive preoperative assessment when TTE is insufficient to clear the patient for the final stage of single ventricle palliation.

What Anatomic and Physiologic Questions Are You Answering?

The goal of imaging before a Fontan procedure is not to find a single diagnosis but to answer a series of critical questions that determine surgical candidacy and strategy. A successful Fontan circulation relies on low pulmonary vascular resistance, unobstructed blood flow, and a healthy single ventricle. The imaging study must definitively assess the following key parameters.

Pulmonary Artery (PA) Anatomy and Pressure: The most critical factor for Fontan success is low pulmonary vascular resistance. The imaging must delineate the size and anatomy of the central and branch pulmonary arteries, identifying any stenosis that would impede passive blood flow from the systemic veins. Crucially, it must allow for direct measurement of mean PA pressure; a high pressure is a primary contraindication to the procedure.

Aortopulmonary Collaterals (APCs): Over time, children with single ventricle physiology can develop abnormal vessels connecting the systemic arterial circulation (aorta) to the pulmonary circulation. Significant APCs “steal” blood flow, increasing pulmonary blood flow and volume-loading the single ventricle, which can lead to heart failure and jeopardize the low-pressure Fontan circuit. Identifying and often occluding these vessels is a primary goal.

Single Ventricle Function and Valvular Competence: The single ventricle must be strong enough to pump blood to the entire body without the help of a sub-pulmonic ventricle. The imaging must provide an accurate assessment of ventricular systolic and diastolic function. Significant atrioventricular valve regurgitation can also lead to elevated atrial pressures and is poorly tolerated after a Fontan, so its severity must be quantified.

Systemic and Pulmonary Venous Pathways: The surgeon needs a clear map of the systemic veins (superior and inferior vena cava) and pulmonary veins to plan the surgical connections. Anomalies such as a persistent left superior vena cava or interrupted inferior vena cava must be identified preoperatively.

Why Arteriography Is a Key Study for This Preoperative Evaluation

For the preoperative evaluation of a child for stage 3 single ventricle palliation, several imaging modalities are rated as Usually appropriate by the ACR, including cardiac MRI, cardiac CT, and invasive cardiac catheterization. While non-invasive options are powerful, `Arteriography coronary with ventriculography` (cardiac catheterization) holds a unique and often essential role because it combines high-resolution diagnostic imaging with direct hemodynamic measurement and the potential for immediate intervention.

The primary advantage of catheterization is its ability to measure pressures directly within the heart and blood vessels—the gold standard for assessing pulmonary artery pressures and resistance. This data is non-negotiable for determining Fontan candidacy. Angiography performed during the procedure provides unparalleled spatial resolution for visualizing small collateral vessels (APCs) that may be missed by other modalities. If significant APCs are found, they can often be occluded with coils during the same procedure, combining diagnosis and therapy into a single session.

While also rated Usually appropriate, other modalities have specific trade-offs in this context:

  • MRI heart function and morphology without and with IV contrast: This is an excellent non-radiation alternative for assessing ventricular volumes, function, and blood flow (e.g., Qp:Qs). It provides superb anatomical detail of the great vessels and venous connections. However, it cannot measure pressures directly and offers no therapeutic capability. Anesthesia is often required for young children.
  • CTA chest with IV contrast: CT provides rapid, high-resolution anatomical imaging of the heart, great vessels, and collaterals. It is less susceptible to motion artifact than MRI. The main drawbacks are the significant radiation dose (Pediatric RRL ☢☢☢☢, 3-10 mSv) and the lack of hemodynamic data or interventional capability.

Ultimately, the choice between catheterization, MRI, and CT depends on institutional expertise and the specific clinical questions that remain after echocardiography. However, because direct pressure measurement and collateral assessment are so central to the pre-Fontan workup, cardiac catheterization is frequently the definitive next step.

What’s Next After Imaging? Downstream Workflow

The results of the comprehensive preoperative assessment will direct the patient down one of three main pathways. This decision is typically made by a multidisciplinary team including pediatric cardiologists, congenital heart surgeons, and cardiac anesthesiologists.

  • If the study confirms favorable anatomy and hemodynamics: The patient is deemed a good candidate for the Fontan procedure. Key findings include low mean pulmonary artery pressure (e.g., <15 mmHg), unobstructed pulmonary arteries, no significant atrioventricular valve regurgitation, and preserved ventricular function. The patient proceeds to surgical consultation for scheduling the total cavopulmonary connection.
  • If the study reveals correctable issues: The patient may still be a candidate after an intervention. For example, if significant aortopulmonary collaterals are found, they can be coiled during catheterization. If a branch pulmonary artery stenosis is identified, it may be treated with balloon angioplasty or a stent. After these interventions, the patient may be re-evaluated to confirm suitability for the Fontan.
  • If the study reveals non-correctable contraindications: The patient is deemed a poor candidate for the Fontan procedure at this time. This may be due to prohibitively high pulmonary vascular resistance, severely depressed ventricular function, or severe atrioventricular valve regurgitation. The focus of care shifts to medical management of heart failure, and in some cases, evaluation for a heart transplant may be considered.

Pitfalls to Avoid (and When to Get Help)

Navigating the pre-Fontan evaluation requires careful attention to detail. Common pitfalls include underestimating the importance of hemodynamic data; relying solely on anatomical imaging from CT or MRI may lead to proceeding with surgery in a patient with unacceptably high pulmonary pressures. Another pitfall is failing to actively search for and manage aortopulmonary collaterals, as these can compromise the long-term success of the Fontan circulation. Finally, given the radiation exposure from both CT and catheterization (Pediatric RRL ☢☢☢☢), it is critical to adhere to ALARA (As Low As Reasonably Achievable) principles and ensure the study is performed at a center with pediatric expertise. If there is any ambiguity in the non-invasive data or if your center lacks experience with complex congenital heart disease, escalation to a specialized pediatric heart center is the most appropriate next step.

Related ACR Topics and Tools

For a comprehensive overview of imaging in various congenital and acquired heart disease scenarios, or to explore the technical details of specific imaging studies, the following resources are available.

Frequently Asked Questions

Why is cardiac catheterization often performed even if a cardiac MRI is also ordered?

They answer different, complementary questions. Cardiac MRI is superior for quantifying ventricular volume and function without radiation. Cardiac catheterization is the gold standard for directly measuring pressures (like pulmonary artery pressure), which is a critical factor for Fontan success, and it allows for simultaneous intervention, such as coiling collateral vessels.

What specific pressure measurement is most critical for the pre-Fontan evaluation?

The mean pulmonary artery (PA) pressure is one of the most critical hemodynamic parameters. A low mean PA pressure, typically under 15 mmHg, is a prerequisite for a successful Fontan circulation, which relies on passive blood flow through the lungs.

Is a cardiac CT a reasonable alternative to catheterization or MRI in this scenario?

Yes, a cardiac CT (specifically CTA chest or CT heart function) is rated ‘Usually appropriate’ by the ACR. It provides excellent, rapid, high-resolution anatomical detail of the heart and great vessels. Its main limitations are the radiation dose and its inability to provide hemodynamic pressure data or allow for intervention, which are often essential in this specific workup.

What happens if the preoperative evaluation shows the patient is not a candidate for a Fontan procedure?

If contraindications are found, such as severely elevated pulmonary vascular resistance or poor ventricular function, the patient will not proceed with the Fontan. The medical team will focus on managing the patient’s heart failure with medications. In some cases, the patient may be evaluated for alternative therapies, including potential listing for a heart transplant.

Does this guidance apply to adults with single ventricle physiology?

While the principles are similar, this specific ACR variant is for a ‘Child.’ Adults with congenital heart disease, including those with single ventricle physiology who may be considered for a Fontan late in life or are being evaluated for complications, represent a distinct clinical population with different comorbidities and considerations.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 30, 2026