Safety of Transition From Selexipag to Remodulin® Then Oral Treprostinil in Symptomatic Adult PAH

Inclusion Criteria: 1. Subject has a diagnosis of symptomatic idiopathic or heritable PAH, PAH associated with connective tissue disease, PAH associated with HIV infection, PAH associated with repaired congenital systemic-to-pulmonary shunt (at least 1 year since repair with respect to the date of providing informed consent), or PAH associated with appetite suppressant or toxin use. 2. The subject must be classified as WHO FC II or III at Baseline. 3. The subject is receiving selexipag for the treatment of WHO Group 1 PAH for a minimum of 90 days from Baseline. 4. Subject is in need of escalation of therapy, as determined by the Investigator. 5. Subject must be receiving a Food and Drug Administration (FDA)-approved PDE5-I or sGC stimulator and/or an ERA and has been at the current stable dose for at least 28 days prior to Baseline. Exclusion Criteria: 1. The subject is receiving selexipag for any other disease or condition other than the treatment of WHO Group 1 PAH. 2. The subject has a Baseline 6MWD of less than 150 meters. 3. The subject's Baseline 6MWD has decreased more than 40% from the pre-selexipag baseline. 4. The subject has a history of ischemic heart disease (defined as either symptomatic or requiring anti-anginal therapy or experienced a documented myocardial infarction within the previous 6 months of Baseline), or a history of left sided myocardial dysfunction as evidenced by a PAWP greater than 15 mmHg or a left ventricular ejection fraction less than 40%. 5. The subject has previously been treated with any parenteral prostacyclin or oral treprostinil for a period of 90 days or more. 6. The subject has a history of 1 or more of the following signs of relevant lung disease within 180 days before Baseline: 1. Total lung capacity less than 60% of predicted normal. 2. Forced expiratory volume in 1 second is less than 55% of predicted normal.