4D cardiovascular magnetic resonance velocity mapping of alterations of right heart flow patterns and main pulmonary artery hemodynamics in tetralogy of Fallot

Abstract

Background: To assess changes in right heart flow and pulmonary artery hemodynamics in patients with repaired Tetralogy of Fallot (rTOF) we used whole heart, four dimensional (4D) velocity mapping (VM) cardiovascular magnetic resonance (CMR).

Methods: CMR studies were performed in 11 subjects with rTOF (5M/6F; 20.1 ± 12.4 years) and 10 normal volunteers (6M/4F; 34.2 ± 13.4 years) on clinical 1.5T and 3.0T MR scanners. 4D VM-CMR was performed using PC VIPR (Phase Contrast Vastly undersampled Isotropic Projection Reconstruction). Interactive streamline and particle trace visualizations of the superior and inferior vena cava (IVC and SVC, respectively), right atrium (RA), right ventricle (RV), and pulmonary artery (PA) were generated and reviewed by three experienced readers. Main PA net flow, retrograde flow, peak flow, time-to-peak flow, peak acceleration, resistance index and mean wall shear stress were quantified. Differences in flow patterns between the two groups were tested using Fisher's exact test. Differences in quantitative parameters were analyzed with the Kruskal-Wallis rank sum test.

Results: 4D VM-CMR was successfully performed in all volunteers and subjects with TOF. Right heart flow patterns in rTOF subjects were characterized by (a) greater SVC/IVC flow during diastole than systole, (b) increased vortical flow patterns in the RA and in the RV during diastole, and (c) increased helical or vortical flow features in the PA's. Differences in main PA retrograde flow, resistance index, peak flow, time-to-peak flow, peak acceleration and mean wall shear stress were statistically significant.

Conclusions: Whole heart 4D VM-CMR with PC VIPR enables detection of both normal and abnormal right heart flow patterns, which may allow for comprehensive studies to evaluate interdependencies of post-surgically altered geometries and hemodynamics.

Figure 1

15 year-old female with repaired Tetralogy of Fallot. Surface shaded RV anatomy based on angiograms calculated from PC VIPR dataset. White circles indicate the locations of analysis planes used for emitting particle traces and streamlines for intracardiac flow analysis. The RV cutplane was placed from the apex of the curvature between the inlet and infundibulum to the apex of the RV.

Figure 2

21 year-old healthy female volunteer. Streamline visualization in a right ventricular (RV) systolic phase. Right atrial (RA) filling primarily during systole, which is characterized by a single clockwise vortical flow pattern (A, curved dashed arrow). Simultaneously, smooth flow patterns are present in the main (MPA), right (RPA), and left (LPA) pulmonary arteries (B, curved solid arrows). Color-coding was achieved with respect the absolute acquired velocities.

Figure 3

28 year-old healthy male volunteer. Streamline visualization during an early diastolic phase. In this typical example, two vortical flow patterns in the right ventricle (RV, dashed arrows), one directed toward the right ventricular outflow tract and one directed toward the inferior wall and tricuspid valve, can be observed. Color-coding was achieved with respect the absolute acquired velocities.

Figure 4

9 year-old male with Tetralogy of Fallot status post Blalock-Taussig shunt and complete repair with transannular patch at 6 months of age. (A) Snapshot of particle traces in the right atrium during right ventricular diastole reveales two distinct vortices. In addition to the normal clockwise vortex (solid curved arrow), a second vortex in the cephalad aspect of the right atrium was depicted (RA, dashed curved arrow). In (B) normal uniform flow in the RV and pulmonary artery outflow tract can be appreciated in a RV systolic time frame using particle traces visualization (dashed curved arrow). Color-coding was achieved with respect the absolute acquired velocities. SVC = superior vena cava; IVC = inferior vena cava; RPA = right pulmonary artery; LPA = left pulmonary artery.

Figure 5

17 year-old female with Tetralogy of Fallot repaired with transannular patch at 2 years of age. Particle trace visualization during a right ventricular diastolic time frame demonstrates pulmonary regurgitation (closed arrow). The majority of the flow from the right atrium (RA) into the RV is directed abnormally toward the RV apex (curved dashed arrow) with a smaller vortex just beyond the tricuspid valve (open arrow). Color-coding was achieved with respect the absolute acquired velocities. SVC = superior vena cava; IVC = inferior vena cava; MPA = main pulmonary artery; RPA = right pulmonary artery.

Figure 6

38 year-old male with Tetralogy of Fallot status post complete repair and Waterston shunt takedown as infant. Streamline visualization during a late systolic phase reveals increased helical flow patterns are present in the pulmonary arteries (curved dashed lines). SVC = superior vena cava; RA = right atrium; RV = right ventricle; MPA = main pulmonary artery; LPA = left pulmonary artery.