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.MethodsPAH patients with low or high end-diastolic elastance (E_ed) (n=94) were compared with controls (n=31). Treatment response was evaluated in 62 patients. RV and RA longitudinal strain, RA emptying and RV filling were determined and diastole was divided into a passive and active phase. Vena cava backflow was calculated as RA active emptying−RV active filling and 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 patients with high E_ed, resulting in higher vena cava backflow. Upon treatment, E_ed was reduced in ~50% of the patients with high E_ed, 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 with 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 patients with high baseline E_ed, diastolic stiffness remained high, despite treatment. A reduction in E_ed coincided with a large reduction in afterload, increased RV active filling and decreased vena cava backflow.