Altered Caval Flow and Wall Shear Stress in Single Ventricle Circulation: Insights from Ferumoxytol-enhanced 4D Flow MRI

Aims Patients with single ventricle (SV) congenital heart disease typically undergo surgical palliation that reroutes superior/inferior vena cava (SVC/IVC) directly to the pulmonary arteries, which alter vascular flow dynamics. Four-dimensional flow (4DF) cardiovascular magnetic resonance (CMR), particularly with ferumoxytol contrast, enables comprehensive assessment of flow distribution and wall shear stress (WSS) in small pediatric vessels. This study aimed to evaluate the differences in caval flow and WSS between SV and BiV patients. Methods We retrospectively analyzed patients who underwent clinically indicated ferumoxytol-enhanced (FE) 4DF CMR between 2019 and 2024. Patients with anomalous systemic or pulmonary venous return were excluded. 4DF data were evaluated on the cloud-based Tempus platform. Flow in the SVC, IVC, aorta and descending aorta was quantified and indexed to body surface area. The average WSS over time was measured. Results Among 387 patients (n = 126 for SV; n = 261 for BiV), SV patients had lower indexed SVC flow (1.11 ± 0.51 vs. 1.50 ± 0.69 L/min/m2, p < 0.0001) and lower WSS (16.0 ± 6.4 vs. 22.7 ± 9.1 cPa, p < 0.0001) compared to BiV patients. The SVC/caval flow ratio declined with age and body surface area, remaining independently lower in the SV group after multivariable adjustment (p = 0.0005). Conclusions SV physiology is associated with lower SVC flow and WSS independent of age or body size, suggesting altered systemic venous return intrinsic to cavopulmonary circulation. 4DF CMR is a valuable tool for assessing and monitoring systemic venous physiology in congenital heart disease.