Pulmonary Hypertension Subtypes Show Distinct PA Flow Hemodynamics

Advanced imaging technology can help clinicians better understand pulmonary artery (PA) remodeling and its relation to different types of pulmonary hypertension (PH), according to a new report. The study was published in the journal Pulmonary Circulation.¹

The analysis found that patients with pulmonary arterial hypertension (PAH) had distinct PA flow characteristics compared with those with heart failure with preserved ejection fraction and pulmonary hypertension (PH-HFpEF). These findings suggest the PA remodeling process differs by PH etiology, the authors explained.

Corresponding author James D. Thomas, MD, of Northwestern University, and colleagues, noted that PH subtypes—including PAH (Group 1) and PH due to left heart disease (Group 2 PH)—are definable by hemodynamic indices.

Group 2 PH is the most common type of PH, and Thomas and colleagues noted that many patients with Group 2 PH meet the criteria for PH-HFpEF, which itself can be subdivided into isolated postcapillary PH and combined pre- and postcapillary PH.

Yet differentiating between the different subtypes can be difficult and invasive. “While these subtypes are distinguishable in advanced disease, early differentiation often requires precise catheterization,” they wrote.

One possible solution the authors presented is the use of 4D flow cardiovascular magnetic resonance imaging (4D-flow CMR). It allows for comprehensive assessment of blood flow velocities in the PA, thereby helping clinicians track the progression of PH. The imaging method also makes it possible to track physiological parameters, helping clinicians better characterize vascular remodeling.

Recent research has highlighted the role of advanced MRI to track hemodynamic changes in pulmonary circulation,² Thomas and colleagues noted. Yet, while studies have examined its ability to track right ventricle (RV) and PA flow, little attention has been devoted toward identifying potential associations between PA flow features and PH etiologies, they said.

The investigators identified 13 patients with PAH and 15 patients with PH-HFpEF and performed echocardiography, 4D-flow CMR, and right heart catheterization on each. They then compared several parameters, including right ventricular outflow tract (RVOT) flow and main pulmonary artery (MPA) hemodynamics, including peak velocity and mean and maximum wall shear stress (WSS).

They found that mean PA pressure and pulmonary vascular resistance (PVR) were higher in patients with PAH. Eight of the 13 patients with PAH also had RVOT systolic notching, compared with 0 patients in the PH-HFpEF group. RVOT acceleration time was shorter in the PAH group, and people with PAH had lower MPA peak velocity, mean WSS, and maximal WSS. Thomas and colleagues also found PVR was negatively correlated with MPA mean WSS.

“These findings align with RHC and echocardiography results, showing higher PVR, more notching patterns, and altered RVOT flow in PAH patients,” Thomas and colleagues wrote. “These changes are well-known indicators of pulmonary vascular load and RV function.”

The investigators said their findings confirm that PA remodeling in PAH and PH-HFpEF are significantly different due to differences in flow characteristics. They added, though, that some patients with advanced PH-HFpEF and significant PA remodeling may benefit from drugs initially developed to treat PAH.

Thomas and colleagues noted their results should be interpreted with caution due to the study's small sample size. They also explained that their analysis was limited to PA flow, and thus did not capture changes at the cellular level that might further elucidate overall PA remodeling.

Still, they said these early data suggest MPA WSS may serve as an important novel indicator of PA remodeling in patients with PH.

References:

1. Kim BJ, Lee J, Berhane H, Freed BH, Shah SJ, Thomas JD. Differences in pulmonary artery flow hemodynamics between PAH and PH-HFpEF: Insights From 4D-Flow CMR. Pulm Circ. 2025;15(1):e70022. doi:10.1002/pul2.70022
2. Lin K, Sarnari R, Gordon DZ, Markl M, Carr JC. Cine MRI-derived radiomics features indicate hemodynamic changes in the pulmonary artery. Int J Cardiovasc Imaging. 2024;40(2):287-294. doi:10.1007/s10554-023-03007-5