FreeFlow Percutaneous Atrial Septal Shunt for IPAH

The goal of this clinical trial is to explore the safety and efficacy of the FreeFlow percutaneous atrial septal shunt for treatment of idiopathic pulmonary arterial hypertension. The main questions it aims to answer are: * Is the FreeFlow percutaneous atrial septal shunt safe to use in patients with idiopathic pulmonary arterial hypertension? * Does the FreeFlow percutaneous atrial septal shunt reduce all-cause mortality and readmission in patients with idiopathic pulmonary arterial hypertension, and how effective is it? Thirty subjects who met the inclusion and exclusion criteria were selected for selective implantation of FreeFlow percutaneous atrial septal shunts after balloon atrial septostomy. Participants will: * underwent balloon atrial septostomy and FreeFlow percutaneous atrial septal shunt implantation. * will be followed up at 24 hours after shunt implantation or before discharge, 1 month, 3 months, 6 months and 12 months.