New Study Provides Insights on Cardiac MRI Predictors of Sudden Cardiac Events in Fontan Patients
March 18, 2025
Sudden cardiac death (SCD) remains one of the leading causes of mortality among patients with Fontan circulation, a complex congenital heart condition affecting individuals born with a single functional ventricle.
A new study1 published in the Journal of the American College of Cardiology provides insights into the risk factors for sudden cardiac events (SCE) in this population, leveraging data from the Fontan Outcomes Registry Using CMR Examinations (FORCE), an international registry.
Leading the study from the Heart Institute at UPMC Children’s Hospital of Pittsburgh were first author Natasha K. Wolfe, MD, assistant professor of Medicine and Pediatrics, and senior author Tarek Alsaied, MD, MSc, FACC, associate professor of Pediatrics. Other contributors to the study from UPMC Children’s were Adam B. Christopher, MD, and Laura J. Olivieri, MD.
The study examined 3,132 Fontan patients in the FORCE Registry to identify clinical and imaging predictors of SCE. Using cardiac magnetic resonance imaging (CMR) and clinical assessments, the study team aimed to determine which patients were at higher risk of experiencing serious arrhythmic events, including ventricular tachycardia, cardiac arrest, and the need for emergency defibrillation.
Over a median follow-up of four years, 3.5% of the patients experienced an SCE, and of those, 36% died. Identifying early risk markers is important in this population, as these events often occur unexpectedly.
Risk Factors Identified by CMRI Findings
The study found that NYHA functional class III or IV, a history of protein-losing enteropathy (PLE) or plastic bronchitis, single-ventricle end-diastolic volume index (EDVi) greater than 104 mL/m², and ejection fraction (EF) below 50% were associated with an increased risk of SCE. Patients with moderate limitations in daily activities had nearly five times the risk of SCE.
“For Fontan patients, even moderate limitations in daily activities—classified as NYHA Class III or IV—are associated with a nearly fivefold increase in SCE risk,” says Dr. Wolfe.
Additionally, noncardiac conditions such as PLE and plastic bronchitis were found to significantly impact overall health and the risk of SCE.
“These complications, though not directly cardiac in nature, significantly impact overall health and correlate with a higher likelihood of SCE,” says Dr. Alsaied.
The study also confirmed that an enlarged ventricle and mild declines in heart function were strong predictors of risk.
“When we see ventricular dilation beyond this threshold, we know that the heart is struggling, and the risk of life-threatening arrhythmias increases,” says Dr. Wolfe.
Similarly, an EF of less than 50% was associated with greater risk, even though traditional heart failure patients are usually considered high risk only at EF below 35%.
“This finding is notable because it suggests that even subtle declines in heart function should not be ignored,” says Dr. Alsaied.
Clinical Implications
Fontan patients often undergo routine cardiac MRI for monitoring, but this study reinforces its importance as a risk stratification tool.
“Even mild abnormalities in ventricular size or function were linked to increased SCE risk. This supports the practice of serial MRIs in tracking changes over time,” says Dr. Alsaied.
The findings also raise the question of whether some patients should receive primary prevention measures, such as implantable cardioverter-defibrillators (ICDs), before experiencing an SCE. Currently, ICDs in single ventricle patients are primarily implanted for secondary prevention — after a patient survives an SCE.
“We are not at the point of routinely recommending ICDs preemptively for this population, but this study contributes data that may inform future decisions,” says Dr. Wolfe.
Another key takeaway is the multidisciplinary nature of Fontan care. The association of noncardiac factors (PLE and plastic bronchitis) with SCE risk highlights the need for a comprehensive approach to longitudinal surveillance and follow-up.
“This study underscores the importance of coordinated care across specialties—cardiology, pulmonology, gastroenterology — all working together to optimize patient outcomes,” says Dr. Alsaied.
Future Research
The FORCE registry continues to grow, and its researchers aim to build on these findings.
“Ideally, we want to develop a validated risk score that integrates multiple factors to guide clinical decision-making,” says Dr. Wolfe.
However, creating such a score requires a large validation cohort, and further studies are needed to refine the predictive model. In the meantime, the study provides evidence that early detection and continuous monitoring of even mild functional changes can help mitigate risks.
“We now have stronger data supporting the proactive management of Fontan patients with respect to SCE. Hopefully, this will lead to earlier interventions and better long-term outcomes,” says Dr. Alsaied.
“This study highlights how common sudden cardiac events are in the Fontan population,” says Dr. Wolfe. “We need to be thinking about these risks at every clinical visit, just as we do for other congenital heart conditions.”
Study Reference
1. Wolfe NK, Schiff MD, Olivieri LJ, et al. Cardiac MRI Predictors of Arrhythmic Sudden Cardiac Events in Patients with Fontan Circulation. J Am Coll Cardiol. 2024; 84(25): 2417-2426. DOI: 10.1016/j.jacc.2024.08.063.
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