New pulmonary hypertension definition is mean pulmonary arterial pressure (mPAP)>20 mmHg and pulmonary vascular resistance (PVR)<2WU*. We investigated if wall shear stress (WSS) and viscous energy loss (EL) on four-dimensional flow MR imaging can predict PH using updated thresholds 

Thirty-five subjects (25 PH,10 healthy volunteers) had MRI with cine imaging & 4D-flow. Circle Cardiovascular Imaging software used to extract 4D flow-derived main, left and right PA (MPA, LPA, RPA) profiles.Total peak and total average WSS and EL obtained by computing arithmetic mean. Total peak and total average WSS (0.55 + 0.10 and 0.18 + 0.02) and EL (1.38 and 0.50) significantly (P <0.001) greater in healthy controls compared to patients? WSS (0.25 + 0.10 and 0.10 + 0.04) and EL (0.77 and 0.31). PH patients underwent invasive catheterisation with significant associations between PA diastolic pressure/mPAP and WSS. PVR strongly related to total peak EL (p=0.002). WSS and EL significantly correlated (all p<0.005) with RV functional parameters. Strongest relationship observed between ejection fraction, global longitudinal strain (GLS) and total peak WSS. WSS and EL were able to accurately distinguish PH patients from healthy controls. Total peak WSS (cut-point <0.37) performed best at identifying both mPAP > 20 mmHg (AUC 0.96) and PVR >2 WU (AUC 0.98). Using deformation (RV GLS > -15.3%) and volumetric approximations (RVSV/RVESV ratio<1), WSS and EL predicted RV-PA uncoupling with similar high accuracy and comparable cut-points.

4Dflow distinguishes PH patients from healthy controls, identifies PH using lower hemodyamic threshold & predicts RV-PA uncoupling

 *2022ESC/ERS guidelines for diagnosis & treatment of PH