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?

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${}_L^{\prime }$) - 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. Thirty-five patients with TOF and 14 controls underwent comprehensive 4D-Flow MRI evaluation for qualitative flow analysis and to calculate E${}_L^{\prime }$ in the main and right pulmonary arteries. Sampled E${}_L^{\prime }$ indices were correlated with the MRI-derived RV size and functional indices. All patients with TOF exhibited abnormal, supra-physiologic helical/vortical formations in the PAs. Patients with TOF had significantly increased peak systolic E${}_L^{\prime }$ (8.0 vs 0.5 mW, p < 0.001), time-averaged E${}_L^{\prime }$ (2.5 vs. 0.2 mW, p < 0.001), and peak systolic E${}_L^{\prime }$ indexed to stroke volume (0.082 vs. 0.012 mW/mL, p < 0.001). E${}_L^{\prime }$ 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${}_L^{\prime }$ with regard to input RV mechanical power was 4.7%. This study demonstrates that patients with repaired TOF have highly abnormal flow conduction through the PAs which result into extensive viscous energy loss. This significant flow-mediated energy loss is associated with the RV volume and function, and might represent considerable loss of mechanical power generated by each cardiac cycle. Future studies are required to assess whether the abnormal flow conduction adds to the RV afterload and remodeling. Abnormal flow patterns through proximal pulmonary arteries in patients with TOF are associated with excessive viscous energy loss. Inefficient flow conduction is associated with the RV dilation and reduced function and might contribute to the RV adaptive remodeling.