BackgroundPulmonary arterial hypertension (PAH) patients have altered right atrial (RA) function and right ventricular (RV) diastolic stiffness. This study assessed the impact of RV diastolic stiffness on RA-RV interaction.MethodsLow or high end-diastolic elastance (E_ed) PAH patients (n=94) were compared to controls (n=31). Treatment response was evaluated in n=62 patients. RV and RA longitudinal strain, RA emptying and RV filling were determined and diastole was divided in a passive and active phase. Vena cava backflow was calculated as RV active filling-RA active emptying; RA stroke work as RA active emptying*RV end-diastolic pressure.ResultsWith increased E_ed, RA and RV passive strain were reduced while active strain was preserved. In comparison to controls, patients had lower RV passive filling, but higher RA active emptying and RA stroke work. RV active filling was lower in high E_ed patients, resulting in higher vena cava backflow. Upon treatment, E_ed reduced in half of high E_edpatients, which coincided with larger reductions in afterload, RV mass and vena cava backflow and greater improvements in RV active filling and stroke volume in comparison to patients in whom E_ed remained high.ConclusionsIn PAH, RA function is associated with changes in RV function. Despite increased RA stroke work, severe RV diastolic stiffness is associated with reduced RV active filling and increased vena cava backflow. In 50% of high baseline E_ed patients, diastolic stiffness remains high, despite treatment. E_ed reduction coincided with a large reduction in afterload, increased RV active filling and decreased vena cava backflow.