Hemodynamics assessment using 4D flow CMR before and after balloon pulmonary angioplasty in chronic thromboembolic pulmonary hypertension: A retrospective observational study

Background: Patients with chronic thromboembolic pulmonary hypertension (CTEPH) with mean pulmonary artery pressure (mPAP) greater than 30 mmHg have poor prognoses [1]. The impact of balloon pulmonary angioplasty (BPA) on hemodynamics in CTEPH, assessed using time-resolved three-dimensional cine phase-contrast (4D flow) cardiac magnetic resonance (CMR), remains unclear. Therefore, the present study aimed to investigate the hemodynamic features of the pulmonary artery (PA) before and after BPA and the predictive value of 4D flow CMR-derived parameters before BPA for the achievement of mPAP < 30 mmHg after BPA.

Methods: Twenty-one patients with CTEPH who were scheduled for BPA between December 2017 and December 2022 were retrospectively enrolled. All patients underwent pathophysiological evaluations by a right heart catheterization (RHC) and 3T CMR (Discovery MR750, GE Healthcare, Waukesha, WI, USA), including 4D flow CMR, both before and three months after BPA. Cardiac volume and function were assessed using two-dimensional short-axis cine imaging. 4D flow CMR assessment included peak flow volume and velocity at the main PA, and peak systolic three-dimensional wall shear stress (WSS).

Results: Patients underwent a median of 5.0 (interquartile range, 4.0 – 7.0) BPA sessions. Seventeen patients achieved a mPAP < 30 mmHg after BPA. RHC and CMR findings before and after the BPA were summarized in Table 1. Right ventricular end-diastolic volume index decreased (95.2 ± 17.8 mL/m2 vs. 71.3 ± 17.9 mL/m2, p < 0.001) and right ventricular ejection fraction increased (44.1 ± 10.8 mmHg vs. 56.2 ± 8.5 mmHg, p < 0.001) after BPA. Peak flow velocity at the main PA (262.8 ± 52.3 mm/s vs. 298.5 ± 68.3 mm/s, p = 0.015) and peak WSS (0.97 ± 0.26 Pa vs. 1.13 ± 0.37 Pa, p = 0.044) both increased after BPA compared to those before BPA. Receiver operating characteristic analysis to predict mPAP ≥ 30 mmHg after BPA based on peak flow velocity before BPA revealed an area under the curve of 0.926 (p < 0.001) for peak flow velocity before BPA (Figure 1a, sensitivity, 0.765; specificity 0.750; cut-off, < 251 mm/s) and 0.971 (p < 0.001) for peak WSS before BPA (Figure 1b, sensitivity, 0.882; specificity, 1.00; cut-off, < 0.89 Pa).

Conclusion: Based on the study results, 4D flow CMR imaging revealed significant improvement in hemodynamics following BPA. Furthermore, peak flow velocity and peak WSS were valuable predictors for the achievement of RHC-based BPA therapy target of mPAP < 30 mmHg, potentially aiding in prognostic assessment and treatment planning.

RHC and CMR before and 3 months after the BPA

	Before BPA	3 months after BPA	P
RHC
Mean PAP, mmHg	36.0 (32.0 ‒ 47.5)	24.0 (21.0 ‒ 28.0)	< 0.001
Mean PAWP, mmHg	11.0 (7.5 ‒ 15.0)	11.0 (6.0 ‒ 13.0)	0.243
PVR, Wood Unit	6.1 (4.5 ‒ 11.9)	3.4 (2.5 ‒ 4.4)	< 0.001
Cardiac output, L/min	3.9 ± 1.3	4.2 ± 1.1	0.230
Cardiac index, L/min/m2	2.5 ± 0.7	2.7 ± 0.6	0.227
CMR
Heart rate, beat/min	68.9 ± 10.9	68.1 ± 10.8	0.748
RVEdVI, mL/m2	95.2 ± 17.8	71.3 ± 17.9	< 0.001
RVEsVI, mL/m2	54.3 ± 17.6	31.8 ± 12.0	< 0.001
RVEF, %	44.1 ± 10.8	56.2 ± 8.5	< 0.001
RVSV/RVEsV	0.68 (0.56 ‒ 1.23)	1.29 (1.07 ‒ 1.69)	< 0.001
Main PA diameter, mm	33.0 ± 4.0	30.6 ± 4.1	< 0.001
4D flow CMR
Peak flow volume, 103 mm3/s	200.6 ± 43.3	203.6 ± 54.2	0.757
Peak flow velocity, mm/s	262.8 ± 52.3	298.5 ± 68.3	0.015
Peak WSS, Pa	0.97 ± 0.26	1.13 ± 0.37	0.044
Mean OSI	0.12 (0.11 ‒ 0.12)	0.12 (0.09 ‒ 0.13)	0.931

Data are expressed as means ± standard deviation or medians (interquartile range).

BPA, balloon pulmonary angioplasty; CMR, cardiac magnetic resonance imaging; OSI, oscillatory shear index; PA, pulmonary artery; PAP, pulmonary artery pressure; PAWP, pulmonary artery wedge pressure; PVR, pulmonary vascular resistance; RHC, right heart catheterization; RVEdVI, right ventricular end-diastolic volume index; RVEF, right ventricular ejection fraction; RVEsVI, right ventricular end-systolic volume index; RVSV/RVEsV, right ventricular stroke volume divided by right ventricular end-systolic volume; WSS, wall shear stress; The ROC for prediction of mPAP after BPA ≥ 30 mmHg by peak flow velocity before BPA (c) and peak WSS before BPA (d). AUC, area under the curve; CI, confidence interval; mPAP, mean pulmonary artery pressure; ROC: receiver operating characteristic; WSS, wall shear stress.