Advanced Imaging Technologies for Assessing Tetralogy of Fallot: Insights Into Flow Dynamics

Figure 1. Plane wave imaging and parallel receive beamforming. A total of 3-9 plane wave directions to cover the Doppler sector width. For each plane wave transmitted, multiple image lines (16) were received simultaneously. Tracking can be done within the region covered by the 16 receive lines, where the frame rate equals the pulse repetition frequency. Adapted from Mawad et al.38

Figure 2. Residual lesions in repaired tetralogy of Fallot (rTOF) resulting in altered intracardiac ventricular flow dynamics and adverse right ventricular (RV) remodelling and dysfunction. High frame rate ultrasound (HFRUS) and 4D-flow magnetic resonance imaging (MRI) can quantify these flow alterations with novel quantitative flow parameters. RBBB, right bundle brach block.

Figure 3. Typical examples of right ventricle intracardiac velocities, energy loss, and vorticity mapping in diastole and systole in repaired tetralogy of Fallot. In diastole, regurgitant pulmonary flow collides with the tricuspid inflow, resulting in disorganized apical vortices (A, indicated by a white arrow) with an additional area apical energy loss and vorticity (C, D, indicated by a white arrow). The schematic in the upper left of each panel illustrates the imaging plane and areas of high energy loss in orange. Adapted from Mawad et al.38

Figure 4. Analysis of the energy loss metric in a computer simulation model mimicking 3D ventricular flow. Bottom left: snapshot of the flow pattern in the model in late diastole. Upper left: bull’s eye view marking the mitral valve and outflow tract of the phantom along with the imaging plane/position of the selected standard examination views. Top right: the energy losses for standard views are traced along with variation resulting from the ±5° change in angle in the shaded lines. Little variation is noted in diastole, with some more important variations in systole from the ALAX view. Bottom right: the influence of the estimated values after postprocessing operations is plotted for the ALAX view with varying degrees of smoothing parameters. This indicates that increasing spatial smoothing reduces the EL magnitude but retains the curve shape (red dotted line). Wall filtering (yellow line) has a little effect on EL magnitude and curve shape. ALAX, apical long axis; AO, aorta; A2C, apical 2-chamber; A4C, apical 4-chamber; DIA, diastolic; EL, energy loss; IVRT, isovolumic relaxation time; LVOT, left ventricle outflow tract; MV, mitral valve; SYS, systole. Adapted from Mawad et al.38

Figure 5. Comprehensive flow haemodynamic evaluation of patients after the surgical repair of different conotruncal lesions. (A) An example of typical 4D-flow haemodynamic patterns in a teenage patient with tetralogy of Fallot (TOF) who underwent initial repair using transannular patch, showing distorted flow through pulmonary arteries in the form of recirculating vortices (arrows). One can also appreciate the prominent helix along the inner aortic curve. (B) Supraphysiologic helical flow along the inner curve of the aorta is also visible in a patient with truncus arteriosus. In addition, there is a strong helical flow in the left pulmonary artery. (C) Patient with TOF-type double outlet right ventricle (DORV) revealing small aneurysmal dilation inside the aortic root. Furthermore, there is a large vortex recirculation in the posterior aspect of the main pulmonary artery. AAo, ascending aorta'; DAo, descending aorta; MPA, main pulmonary artery; RVOT, right ventricular outflow tract.

Figure 6. Pulmonary arterial flow visualization using the 4D-flow magnetic resonance imaging in an adult patient with repaired tetralogy of Fallot by transannular patch. One can appreciate the abnormal flow pattern at the dilated region bounded by transannular patch. Vortical recirculation at this region gives rise to abnormal inflow to branch pulmonary arteries, which can further remodel vascular shape and vessel wall character. LPA, 'left pulmonary artery; MPA, main pulmonary artery; RPA, right pulmonary artery.

Figure 7. Analysis of the intracardiac flow and right ventricular (RV) diastolic function using 4D-flow magnetic resonance imaging–derived vorticity fields. (A) The very right-top panel shows the plot of velocity and vorticity vector fields during early diastole for both ventricles from the 4-chamber and short-axis view perspectives. (B) Middle panel portrays RV vorticity plotted throughout the cardiac cycle along with a typical Doppler waveform. (C) Isolated RV vorticity vector field from the short-axis view perspective sampled from early diastole. TCV, tricuspid valve.