Pilot Study to Evaluate Right Ventricular Function With Riociguat in CTEPH

It remains unclear as to why certain patients with PH develop right heart failure. Several lines of evidence suggests alterations in right ventricular (RV) function may be precipitated by RV ischemia. This ischemia results from both decreased right coronary artery perfusion pressure and from arteriolar- capillary rarefaction. It has been proposed that this contributes to insufficient oxygen delivery needed to support the increase RV demand in right heart failure (RHF), this stimulating glycolytic shift. However, this glycolysis is insufficient to compensate for suppression of glucose oxidation in severe right ventricular hypertrophy (RVH), resulting in a state of RV hibernation and progressive RHF. This study is designed to assess if 24 weeks of treatment with riociguat will be associated with changes in glucose metabolism and improved RV blood flow using N-13-ammonia (NH3) to measure myocardial perfusion. We will assess the response in both treatment naive patients as well as patients who have been titrated to maximally tolerated doses of riociguat with total treatment duration of at least 3 months. The assessment of quantitative myocardial blood flow will be combined with an advanced 3 dimensional echocardiographic assessment of RV volume and function and with cardiac magnetic resonance (MR).