5D Flow MRI Reveals Respiration‐Driven Changes in Blood Flow Energetics in Congenital Heart Disease

ABSTRACT Purpose Hemodynamic monitoring is essential for patients with right‐sided congenital heart disease (CHD). Respiration may have an increased impact on pulmonary flow in these patients that cannot be assessed by standard tools including 4D flow MRI. This study uses 5D flow MRI to assess respiratory‐cycle variations in flow energetics in patients with CHD. Methods 5D flow was acquired with four respiratory states in 14 Fontan patients (21 ± 8 years, 8 female), 10 intracardiac shunt patients (19 ± 13 years, 8 female), and 9 controls (26 ± 6 years, 1 female). Blood kinetic energy (KE mean ), viscous energy loss (EL total ), and EL fraction (EL total /KE mean ) as a measure of flow inefficiency were calculated in inferior and superior caval veins (IVC, SVC), pulmonary arteries (PA), and aorta. Correlations were assessed with clinical markers of altered cardiac flow function. Results 5D flow was acquired with acceleration factor R = 37–93 varying between respiratory states. Fontan and shunt patients demonstrated significant respiratory‐driven changes in pulmonary flow energetics compared to controls. Fontan IVC and PA KE mean were increased during inspiration (+43%, +37%, p < 0.001) and decreased during expiration (−40%, −35%, p < 0.001), resulting in increased expiratory EL fraction (+34%, +30%, p < 0.05). Shunt patients showed a similar effect in IVC KE mean (+28%, −25%, p < 0.05). Decreased expiratory IVC KE mean was associated with increased Fontan left–right PA flow differential (ρ = −0.68, p < 0.05) and increased shunt Qp/Qs (ρ = −0.70, p < 0.05). Conclusions The findings of this study show that CHD flow energetics and efficiency are modulated by respiration. Respiratory‐resolved imaging is needed to identify these dynamics and their relationships to overall cardiac function.