Incorporating the Venous Excess Ultrasound Score (VExUS Score) Into Contemporary Haemodynamic Risk Assessment in Pulmonary Arterial Hypertension: The INVEXUS-PAH Study

Inclusion Criteria * Adults aged ≥18 years * Established diagnosis of WHO Group 1 pulmonary arterial hypertension (PAH) * Stable outpatient clinical status at the time of VExUS ultrasonography * Venous Excess Ultrasound Score (VExUS) evaluation performed with adequate ultrasonographic acoustic windows * Clinically indicated right heart catheterisation (RHC) performed within ±60 days of VExUS assessment * Availability of ESC/ERS 2022 simplified risk assessment variables (WHO functional class, BNP/NT-proBNP, and 6-minute walk distance) * Ability to provide written informed consent Exclusion Criteria * Pulmonary hypertension other than WHO Group 1, including: * PH due to left heart disease (WHO Group 2) * PH due to chronic lung disease or hypoxaemia (WHO Group 3) * Chronic thromboembolic pulmonary hypertension (CTEPH; WHO Group 4) * Multifactorial PH (WHO Group 5) * Eisenmenger syndrome * Complex or unrepaired congenital heart disease * Suspected pulmonary veno-occlusive disease (PVOD) * Pulmonary capillary haemangiomatosis (PCH) * Acute decompensated right heart failure * Severe renal dysfunction (eGFR \<30 mL/min/1.73 m²) * Severe hepatic impairment (Child-Pugh Class C) * Congestive hepatopathy * Active infection * Pregnancy * Inability or unwillingness to provide informed consent * Poor ultrasonographic acoustic window preventing adequate VExUS scoring