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Background Pulmonary arterial hypertension (PAH) manifests with progressive right ventricular (RV) dysfunction, which eventually impairs the left ventricular function. We hypothesized that 4-dimensional-flow magnetic resonance imaging can detect flow hemodynamic changes associated with efficient intracardiac flow during noninvasive inhaled nitric oxide (iNO) challenge in children with PAH. Methods and Results Children with PAH (n=10) underwent 2 same-day separate iNO challenge tests using: (1) 4-dimensional-flow magnetic resonance imaging and (2) standard catheterization hemodynamics. Intracardiac flow was evaluated using the particle tracking 4-flow component analysis technique evaluating the direct flow , retained inflow , delayed ejection flow , and residual volume . Respective flow hemodynamic changes were compared with the corresponding catheterization iNO challenge results. The RV analysis revealed decreased direct flow in patients with PAH when compared with controls ( P <0.001) and increase in residual volume ( P <0.001). Similarly, the left ventricular analysis revealed decreased direct flow in patients with PAH when compared with controls ( P =0.004) and increased proportion of the residual volume ( P =0.014). There was an increase in the RV direct flow during iNO delivery ( P =0.009), with parallel decrease in the residual volume ( P =0.008). Conclusions Children with PAH have abnormal biventricular flow associated with impaired diastolic filling. The flow efficiency is significantly improved in the RV on iNO administration with no change in the left ventricle. The changes in the RV flow have occurred despite the minimal change in catheterization hemodynamics, suggesting that flow hemodynamic evaluation might provide more quantitative insights into vasoreactivity testing in PAH.

Background: In pulmonary arterial hypertension (PAH), right ventricular (RV) failure is the main cause of mortality. Non-invasive estimation of ventricular-vascular coupling ratio (VVCR), describing contractile response to afterload, could be a valuable tool for monitoring clinical course in children with PAH. This study aimed to test two hypotheses: VVCR by cardiac magnetic resonance (VVCR CMR ) correlates with conventional VVCR by right heart catheterization (VVCR RHC ) and both correlate with disease severity., Methods and Results: Twenty-seven patients diagnosed with idiopathic and associated PAH without post-tricuspid shunt, who underwent RHC and CMR within 17 days at two specialized centers for pediatric PAH were retrospectively studied. Clinical functional status and hemodynamic data were collected. Median age at time of MRI was 14.3 years (IQR: 11.1-16.8), median PVRi 7.6 WU × m 2 (IQR: 4.1-12.2), median mPAP 40 mm Hg (IQR: 28-55) and median WHO-FC 2 (IQR: 2-3). VVCR CMR, defined as stroke volume/end-systolic volume ratio was compared to VVCR RHC by single-beat pressure method using correlation and Bland-Altman plots. VVCR CMR and VVCR RHC showed a strong correlation (r = 0.83, p < 0.001). VVCR CMR and VVCR RHC both correlated with clinical measures of disease severity (pulmonary vascular resistance index [PVRi], mean pulmonary artery pressure [mPAP], mean right atrial pressure [mRAP], and World Health Organization functional class [WHO-FC]; all p ≤ 0.02)., Conclusions: Non-invasively measured VVCR CMR is feasible in pediatric PAH and comparable to invasively assessed VVCR RHC . Both correlate with functional and hemodynamic measures of disease severity. The role of VVCR assessed by CMR and RHC in clinical decision-making and follow-up in pediatric PAH warrants further clinical investigation., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Despite different developmental and pathological processes affecting lung vascular remodeling in both patient populations, differences in 4D MRI findings between children and adults with PAH have not been studied. The purpose of this study was to compare flow hemodynamic state, including flow-mediated shear forces, between pediatric and adult patients with PAH matched by severity of pulmonary vascular resistance index (PVRi). Adults ( n = 10) and children ( n = 10) with PAH matched by pulmonary vascular resistance index (PVRi) and healthy adult ( n = 10) and pediatric ( n = 10) subjects underwent comprehensive 4D-flow MRI to assess peak systolic wall shear stress (WSS max ) measured in the main (MPA), right (RPA), and left pulmonary arteries (LPA), viscous energy loss (E L ) along the MPA-RPA and MPA-LPA tract, and qualitative analysis of secondary flow hemodynamics. WSS max was decreased in all pulmonary vessels in children with PAH when compared with the same age group (all P < 0.05). Similarly, WSS max was decreased in all pulmonary vessels in adult PAH patients when compared with healthy adult subjects (all P < 0.01). Average E L was increased in adult patients with PAH when compared with the same age group along both MPA-RPA ( P = 0.020) and MPA-LPA ( P = 0.025) tracts. There were no differences in E L indices between adults and pediatric patients. Children and adult patients with PAH have decreased shear hemodynamic forces. However, pathological flow hemodynamic formations appear to be more consistent in adult patients, whereas flow hemodynamic abnormalities appear to be more variable in children with PAH for comparable severity of PVRi. NEW & NOTEWORTHY Both children and adult patients with PAH have decreased shear hemodynamic forces inside the pulmonary arteries associated with the degree of vessel dilation and stiffness. These differences also exist between healthy normotensive children and adults. However, pathological flow hemodynamic formations appear to more uniform in adult patients, whereas in children with PAH flow, hemodynamic abnormalities appear to be more variable. Pathological flow formations appear not to have a major effect on viscous energy loss associated with the flow conduction through proximal pulmonary arteries.

Aims: Paediatric pulmonary arterial hypertension (PAH) is manifested as increased arterial pressure and vascular resistive changes followed by progressive arterial stiffening. The aim of this study was to characterize regional flow haemodynamic patterns and markers of vascular stiffness in the proximal pulmonary arteries of paediatric PAH patients, and to explore the association with right ventricular (RV) function., Methods and Results: Forty paediatric PAH patients and 26 age- and size-matched controls underwent cardiac magnetic resonance studies in order to compute time-resolved wall shear stress metrics, oscillatory shear index (OSI), and vascular strain as measured by relative area change (RAC), and RV volumetric and functional parameters. Phase-contrast imaging planes were positioned perpendicular to the mid-main and right pulmonary arteries (MPA and RPA, respectively). Compared with controls, the PAH group had decreased systolic wall shear stress (dyne cm-2) and RAC (%) in both MPA (WSSsys: 6.5 vs. 4.3, P < 0.0001; RAC: 36 vs. 25, P < 0.0001) and RPA (WSSsys: 11.2 vs. 7.3, P < 0.0001; strain: 37 vs. 30, P < 0.05). The OSI was significantly higher in the MPA of PAH subjects (0.46 vs. 0.17, P < 0.05). WSS measured in the MPA correlated positively with RAC (r = 0.63, P < 0.0001) and RV ejection fraction (%) (r = 0.63, P < 0.0001)., Conclusion: Wall shear stress, the principal haemodynamic force driving endothelial functional changes, is severely decreased in paediatric PAH patients and correlates with increased stiffness in the proximal pulmonary vasculature and reduced RV function., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.)