Clinical Study to Assess the Efficacy, Safety and Tolerability of Macitentan in Subjects With Inoperable Chronic Thromboembolic Pulmonary Hypertension

Change From Baseline to Week 24 in Exercise Capacity, as Measured by the 6-minute Walk Distance (6MWD).

The purpose of the six minute walk is to test exercise tolerance and capacity. The test measures the distance an individual is able to walk over a total of six minutes on a hard, flat surface. The goal is for the individual to walk as far as possible in six minutes.

Time frame: From baseline to Week 24

Change From Baseline to Week 24 in Borg Dyspnea Index Collected at the End of the 6-minute Walk Test (6MWT).

This outcome measures the difference in the Borg dyspnea index collected at the end of the 6-minute walk test (6MWT) at Week 24 compared to baseline. The Borg dyspnea index rates the severity of dyspnea (difficult or labored breathing) on a scale from 0 ('Nothing at all') to 10 ('Very, very severe - maximal'). A decrease in the Borg dyspnea index indicates an improvement.

Time frame: From baseline to Week 24

Proportion of Subjects With Worsening in WHO Functional Class (FC) From Baseline to Week 24

WHO functional classes are defined as follows: 1) class I: no symptoms with exercise or at rest. No limitation of activity. 2) class II: No symptoms at rest but slight limitation with ordinary activities causing symptoms (e.g. short of breath with climbing a flight of stairs, grocery shopping, or making the bed). 3) class III: may not have symptoms at rest but activities greatly limited by shortness of breath, fatigue, or near fainting. 4) class IV: symptoms at rest (such as dyspnea and/or fatigue) and inability to carry out any physical activity without symptoms (e.g. may faint especially while bending over with their heads lowered). Patients in class IV manifest signs of right heart failure. Shifting to a higher class (e.g. from class III to class IV) represents a 'worsening' while shifting to a lower class (e.g. from class III to class II) means an 'improvement'.