Patients with Tetralogy of Fallot (TOF) have multiple surgical sequelae altering the pulmonary flow hemodynamics. Repaired TOF (rTOF) adults frequently develop pulmonary regurgitation impacting the blood flow pressure, right ventricle load, and pulmonary hemodynamics. We aimed to evaluate the pulmonary flow hemodynamics using 4D-flow magnetic resonance imaging (MRI) for characterizing altered blood flow, viscous energy loss (EL), wall shear stress (WSS), pressure drop (PD), and ventricular flow analysis (VFA) in rTOF patients. We hypothesized that 4D-flow based parameters can identify pulmonary blood flow alterations. A total of 17 rTOF patients (age: 29 ± 10 years, 35% women) and 20 controls (age: 36 ± 12 years, 25% women) were scanned using a dedicated cardiac MRI protocol. Peak velocity and regurgitant fraction were significantly higher for rTOF patients (p < 0.001). WSS was consistently elevated along the PA in the rTOF (p ≤ 0.05). The rTOF average circumferential WSS was higher than axial WSS at the main pulmonary artery (p ≤ 0.001). PD and EL were consistently higher in the rTOF as compared with controls (p < 0.05). For VFA, delayed ejection increased and retained inflow decreased in rTOF patients (p < 0.001). To conclude, this study demonstrated that 4D-flow MRI pulmonary flow in the rTOF can exhibit altered peak velocity, valvular regurgitation, WSS, EL, PD, and VFA.
Blood flow through the heart and great vessels moves in three dimensions (3D) throughout time. However, the assessment of its 3D nature has been limited in the human body. Recent advances in magnetic resonance imaging (MRI) allow for the comprehensive visualization and quantification of in-vivo flow dynamics using four-dimensional (4D) flow MRI. In addition, this technique provides the opportunity to obtain advanced hemodynamic biomarkers such as vorticity, helicity, wall shear stress (WSS), pressure gradients, viscous energy loss (EL), and turbulent kinetic energy (TKE). This chapter will introduce 4D flow MRI which is currently used for blood flow visualization and advanced quantification of cardiac hemodynamic biomarkers. We will discuss its advantages relative to other in-vivo flow imaging techniques and describe its potential clinical applications in cardiology.
Tetralogy of Fallot (TOF) is the most prevalent cyanotic congenital heart defect (CHD) that alters normal blood flow through the heart and accounts for 10% of all CHD. Pulmonary stenosis and regurgitation are common in adults who have undergone TOF repair (rTOF) and can impact the load on the right ventricle, blood flow pressure, and pulmonary hemodynamics. Pressure mapping, obtained through 4D-flow magnetic resonance imaging (4D-flow MRI), has been applied to identify abnormal heart hemodynamics in CHD. Hence, the aim of this research was to compare pressure drop and relative pressures between patients with repaired TOF (rTOF) and healthy volunteers. An in vitro validation was performed, followed by an in vivo validation. We hypothesized that pressure drop is a more stable pressure mapping method than relative pressures to detect altered hemodynamics. A total of 36 subjects, 18 rTOF patients and 18 controls underwent cardiac MRI scans and 4D-flow MRI. Pressure drops and relative pressures in the MPA were higher in rTOF patients compared to the controls (p < 0.05). Following the in vitro validation, pressure drops proved to be a more stable pressure mapping method than relative pressures, as the flow loses its laminarity and becomes more turbulent. In conclusion, this study demonstrated that flow hemodynamics in rTOF can exhibit altered pressure maps. Pressure mapping can help provide further insight into rTOF patients’ hemodynamics to improve patient care and clinical decisions.
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