Abnormal flow conduction through pulmonary arteries is associated with right ventricular volume and function in patients with repaired tetralogy of Fallot: does flow quality affect afterload?

Objectives Flow through the proximal pulmonary arteries (PAs) of patients with repaired Tetralogy of Fallot (TOF) is known to be highly disordered and associated with significant regurgitation. The purpose of this study was to evaluate 4D-Flow MRI–derived viscous energy loss (E_L^' )—as a result of non-efficient flow propagation, and relate this parameter to standard right ventricular (RV) size and function markers in patients with repaired TOF. Methods Thirty-five patients with TOF and 14 controls underwent comprehensive 4D-Flow MRI evaluation for qualitative flow analysis and to calculate E_L^' in the main and right pulmonary arteries. Sampled E_L^' indices were correlated with the MRI-derived RV size and functional indices. Results All patients with TOF exhibited abnormal, supra-physiologic helical/vortical formations in the PAs. Patients with TOF had significantly increased peak systolic E_L^' (8.0 vs 0.5 mW, p < 0.001), time-averaged E_L^' (2.5 vs. 0.2 mW, p < 0.001), and peak systolic E_L^' indexed to stroke volume (0.082 vs. 0.012 mW/mL, p < 0.001). E_L^' indexed to stroke volume correlated with the RV end-diastolic volume ( R = 0.68, p < 0.001), end-systolic volume ( R = 0.62, p < 0.001), ejection fraction ( R = −0.45, p = 0.002), and cardiac index ( R = 0.45, p = 0.002). The mean estimated energy loss due to E_L^' with regard to input RV mechanical power was 4.7