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Pressure gradient before and after transcatheter pulmonary valve implantation for repaired tetralogy of Fallot: a new 4D flow MRI measurement

Michinobu Nagao¹, Tomohito Kogure¹, Hiroshi Hamano², Yashuhiro Goto¹, Isao Shiina¹, Kazuo Kodaira¹, Mana Kato¹, Masami Yoneyama², Akihiro Inoue¹, Atsushi Yamamoto¹, Kei Inai¹, and Shuji Sakai¹
¹Tokyo Women's Medical University, Tokyo, Japan, ²Philips Japan, Tokyo, Japan

Synopsis

Keywords: Flow, Cardiovascular

Motivation: Estimating pressure gradients due to valvular disease using 4D flow MRI in repaired TOF

Goal(s): Identify the location and extent of the pressure gradient

Approach: new 4D flow MRI software for pressure gradient measurement

Results: In right heart catheter-defined pulmonary hypertension, this software showed a right ventricular outflow tract to pulmonary artery pressure gradient.

Impact: Whereas pressure gradients used to require invasive catheterization, our method is a noninvasive test that does not use contrast media. It also has the advantage of being able to locate the site of the pressure gradient.

Introduction

Tetralogy of Fallot (TOF) repair was once considered a curative procedure, but studies of long-term outcomes show that many patients develop sequelae 20 to 30 years after surgery, with about half requiring reoperation. Until recently, open chest surgery was the only treatment option, but recently a minimally invasive transcatheter pulmonary valve implantation (TPVI) procedure has been developed that is less invasive and results in shorter hospital stays1). TPVI is gaining popularity as a minimally invasive treatment, its indication must be carefully determined in cases of right ventricle (RV) pressure overload. Detection of pulmonary hypertension (PH) is necessary pre-treatment information, and is also important to monitor after TPVI. In this study, a new software dedicated to 4D flow MRI will measure the pressure gradient in the pulmonary artery from the right ventricular outflow tract and examine the concordance with the results of right heart catheter and changes before and after TPVI.

Materials and Methods

10 patients with repaired TOF scheduled for TPVI (mean age, 44 years) who underwent cardiac MRI and right heart catheterization were enrolled. All participants underwent MRI using a 3.0-Tesla whole-body imager (Ingenia 3 T Release 5.6; Philips Healthcare, Best, the Netherlands) equipped with a dual-source parallel resonance frequency (RF) transmission and 32-element D torso coil for RF reception. A flow-sensitive 3D gradient sequence with echo planar imaging (EPI), VENC 150–200 cm/s, and 14 frames/cycle was used as a 4D flow MRI. Free breathing was allowed and no respiratory motion compensation was performed. The 4D flow imaging and pressure gradient calculations were performed using a dedicated post-processing software for 4D flow MRI (ISP, Philips Healthcare, Best, the Netherlands).Stream images and wall shear stress images were reconstructed (Fig. 1) and pressure gradient were calculated (Fig. 2).

Results and Discussion

When pulmonary artery pressure is normal (n=7), the pressure gradient increases slowly with increasing distance from the starting point. In cases of pulmonary hypertension (n=3), a sudden drop in pressure occurs between the right ventricular outflow tract and the pulmonary artery bifurcation (Fig. 3). It has been demonstrated that a pressure gradient occurs in pulmonary hypertension. 4D flow imaging was also compared in three patients who underwent cardiac MRI before and after TPVI. In common with the three patients, pulmonary regurgitation and vortical flow disappeared after TPVI and wall shear stress was increased at the stenting site. A new in-stent pressure gradient developed in a case with increased wall shear stress over the entire length of the stent (Fig. 4 and 5). New pressure loading is a risk for right heart failure and requires further follow-up. Various cardiac function indices have been proposed from 4D flow MRI2, 3), but this is the first method to present absolute values of the pressure range.

Conclusion

Dedicated 4D flow MRI pressure gradient measurements can be a noninvasive method to identify the site and degree of pressure gradient in the right ventricular outflow tract to the pulmonary artery in the remote postoperative period after repaired TOF. The presence or absence of a pressure gradient is important information for the indication of TPVI and postoperative monitoring.

Acknowledgements

No acknowledgement found.

References

1. L Bergersen et. al., JACC: Cardiovascular Interventions, 20172.

2. Shiina Y, et al. 4D flow MRI-derived energy loss and RV workload in adults with tetralogy of Fallot. Journal of Cardiology 2023. DOI: 10.1016/j.jjcc2023.10.0033.

3. Tsuchiya N, et al. Circulation derived from 4D flow MRI correlates with right ventricular dysfunction in patients with tetralogy of Fallot. Scientific Reports 2021; 11: 11623.

Figures

40s, woman with repaired tetralogy of FallotOn the stream image, the site of stenosis of the main pulmonary artery generates an accelerated flow during systole. On the wall shear stress image, wall shear stress is increased circumferentially from the main pulmonary artery to the bifurcation.

40s, woman with repaired tetralogy of Fallot, same case as Figure 1The algorithm for pressure gradient measurement is based on Bernoulli's theorem. Continuously measure the pressure gradient between distal cross sections starting at the right ventricular outflow tract (left). The cross section where the pressure gradient occurs is displayed in blue, and the pressure drop from the starting point can be measured (right).

When pulmonary artery pressure is normal, the pressure gradient increases slowly with increasing distance from the starting point. In cases of pulmonary hypertension, a sudden drop in pressure (arrow) occurs between the right ventricular outflow tract and the pulmonary artery bifurcation.

40s, woman with repaired tetralogy of Fallot who has right pulmonary artery occlusion and severe pulmonary regurgitation.After TPVI, pulmonary arterial vortex flow on stream image has disappeared and left pulmonary flow increased. In addition, wall shear stress is increased at the site of stent placement (arrow). After TPVI, pulmonary regurgitation disappeared and RV end-diastolic volume decreased from 194 ml to 93 ml. However, RV ejection fraction did not improve from 24% to 21%.

40s, woman with repaired tetralogy of Fallot, same case as Figure 4After TPVI, a pressure gradient is observed at the site of increased wall shear stress at the level of stenting (arrow). The appearance of a pressure gradient may be a new right heart load.

Proc. Intl. Soc. Mag. Reson. Med. 32 (2024)

3537

DOI: https://doi.org/10.58530/2024/3537