Differences in Pulmonary Artery Flow Hemodynamics Between PAH and PH-HFpEF: Insights From 4D-Flow CMR

Pulmonary artery (PA) flow analysis is crucial for understanding the progression of pulmonary hypertension (PH). We hypothesized that PA flow characteristics vary according to PH etiology. In this study, we used 4D flow cardiovascular magnetic resonance imaging (CMR) to compare PA flow velocity and wall shear stress (WSS) between patients with pulmonary arterial hypertension (PAH) and those with heart failure with preserved ejection fraction and pulmonary hypertension (PH-HFpEF). We enrolled 13 PAH and 15 PH-HFpEF patients. All participants underwent echocardiography, 4D flow CMR, and right heart catheterization. We compared right ventricular outflow tract (RVOT) flow and main pulmonary artery (MPA) hemodynamics, including peak velocity and mean and maximum WSS, between groups. PH-HFpEF patients were older and more likely to have hypertension. PAH patients had higher mean PA pressure (47.8 ± 8.8 vs. 32.9 ± 6.9 mmHg, p < 0.001) and pulmonary vascular resistance (PVR) (8.6 ± 4.6 vs. 2.6 ± 2.2 wood unit, p < 0.001). RVOT systolic notching was more common in PAH patients (8 of 13 vs. 0 of 15), and they had shorter RVOT acceleration time (85.5 ± 20.9 vs. 135.0 ± 21.7 ms, p < 0.001). PAH patients had lower MPA Vmax (0.8 ± 0.2 vs. 1.1 ± 0.4 m/s, p = 0.032), mean WSS (0.29 ± 0.09 vs. 0.36 ± 0.06 Pa, p = 0.035), and maximal WSS (0.99 ± 0.18 vs. 1.21 ± 0.19 Pa, p = 0.011). Anterior MPA analysis confirmed lower WSS in PAH patients. PVR was negatively correlated with MPA mean WSS (r = -0.630, p = 0.002). PAH patients had lower MPA Vmax and lower mean MPA WSS in 4D flow CMR compared to PH-HFpEF patients. These distinct PA flow characteristics suggest that the flow hemodynamics of the PA remodeling process differ depending on the underlying etiology of PH.