Characterization and z-score calculation of cardiovascular magnetic resonance imaging parameters in patients after the Fontan operation: A Fontan Outcome Registry using Cardiovascular Magnetic Resonance Examinations study

Abstract

Background: Cardiac magnetic resonance (CMR) offers valuable hemodynamic insights post-Fontan, but is limited by the absence of normative single ventricle data. The Fontan Outcomes Registry using CMR Examinations (FORCE) is a large international Fontan-specific CMR registry. This study used FORCE registry data to evaluate expected CMR ventricular size/function and create Fontan-specific z-scores adjusting for ventricular morphology (VM) in healthier Fontan patients.

Methods: "Healthier" Fontan patients were defined as patients free of adverse outcomes, who are New York Heart Association class I, have mild or less valve disease, and <30% aortopulmonary collateral burden. General linear modeling was performed on 70% of the dataset to create z-scores for volumes and function. Models were tested using the remainder (30%) of the data. The z-scores were compared between children and adults. The z-scores were also compared between "healthier" Fontan and patients with adverse outcomes (death, listing for transplantation, or multiorgan disease).

Results: The "healthier" Fontan population included 885 patients (15.0 ± 7.6 years) from 18 institutions with 1156 CMR examinations. Patients with left ventricle morphology had lower volume, mass and higher ejection fraction (EF) compared to right or mixed (two ventricles) morphology (p < 0.001 for all pairwise comparisons). Gender, body surface area, and VM were used in z-scores. Of the "healthier" Fontan patients, 647 were children <18 years and 238 were adults. Adults had lower ascending aorta flow (2.9 ± 0.7 vs 3.3 ± 0.8 L/min/m², p < 0.001) and ascending aorta flow z-scores (-0.16 ± 1.23 vs 0.05 ± 0.95, 0.02) compared to children. Additionally, there were 1595 patients with adverse outcomes who were older (16.1 ± 9.3 vs 15.0 ± 7.6, p < 0.001) and less likely to have left VM (35 vs 47%, p < 0.001). Patients with adverse outcomes had higher z-scores for ventricular volume and mass and lower z-scores for EF and ascending aorta flow compared to the "healthier" Fontan cohort.

Conclusion: This is the first study to generate CMR z-scores post-Fontan. Importantly, the z-scores were generated and tested in "healthier" Fontan patients and both pediatric and adult Fontan patients. These equations may improve CMR-based risk stratification after the Fontan operation.

Keywords: Congenital heart disease; Fontan; Normal values; Z-scores.

Graphical abstract showing the differences in ventricular volume and function between different study groups.

Fig. 1

Baseline ventricular size and function by cardiac diagnosis. Other categories not included in the diagnosis (include complex two ventricles). AVC atrioventricular canal, DILV double inlet left ventricle, DORV double outlet right ventricle, HLH hypoplastic left heart syndrome, PA/IVS pulmonary atresia with intact ventricular septum, TA tricuspid atresia, BSA body surface area

Fig. 2

Scatter plots of EDV, ESV, EF, mass, stroke volume, and ascending aorta flow with predicted lines (solid), and z = ±1 and 2 RMSE lines (dashed) for Fontan patients. BSA body surface area, EDV end-diastolic volume, ESV end-systolic volume, EF ejection fraction, RMSE root mean square error

Fig. 2

Scatter plots of EDV, ESV, EF, mass, stroke volume, and ascending aorta flow with predicted lines (solid), and z = ±1 and 2 RMSE lines (dashed) for Fontan patients. BSA body surface area, EDV end-diastolic volume, ESV end-systolic volume, EF ejection fraction, RMSE root mean square error