Pulmonary Artery Remodelling Assessed by 4D Flow MRI in Pulmonary Arterial Hypertension and Atrial Septal Defect

Background
Pulmonary artery (PA) stiffness plays a significant role on right ventricular (RV) function, as evidenced in pulmonary arterial hypertension (PAH). In patients with atrial septal defect-related PAH (ASD-PAH), prognosis is dependent on RV function. We aimed to characterize PA remodelling and its relationship with RV function using 4-dimensional flow magnetic resonance imaging (4D flow MRI) in patients with ASD-PAH.

Methods
We prospectively included 24 adults with ASD-PAH. They underwent 4D flow MRI and right heart catheterization within 24-48 hours. Remodelling of PA was analysed (stiffness, compliance, distensibility, elastance, and pulsatility) and PA vortex was evaluated. RV adaptation was measured by RV ejection fraction and RV-PA coupling.

Results
The median age was 50 [41-55] years, and the median mean PA pressure and pulmonary vascular resistance were 50 [39-58] mm Hg and 8.0 [6.8-11.3] WU, respectively. Fourteen patients (58.3%) had RV dysfunction (RV ejection fraction <45%). All presented PA dilation (median main PA diameter: 42 [37-48] mm) and an increase in PA stiffness (10 [7.4-15.3]), whereas compliance and distensibility were decreased (2.1 [1.8-4.1] mm2/mm Hg and 0.19 [0.13-0.29] %/mm Hg). No correlation was found between PA dilation and indexes of PA remodelling. PA remodelling parameters were more severely impaired in patients with preserved RV function, with an increased stiffness (P = 0.01) and a decreased compliance and distensibility (P = 0.02).

Conclusions
PA stiffness parameters characterized by 4D flow MRI were impaired in the population with ASD-PAH, and PA remodelling appears to be influenced by volumetric overload from the left-to-right shunt through the ASD.