Medical Therapy in Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare but life-threatening condition resulting from unresolved thromboembolic obstructions. Pulmonary endarterectomy surgery is currently the standard of treatment, as it is potentially curative; however, not all cases are amenable to surgical intervention due to distal distribution of the organized thromboembolic material or the presence of comorbidities. Up to one-third of patients have persistent or recurrent pulmonary hypertension after pulmonary endarterectomy. In addition to the occlusive organized thromboembolic material, there is a small-vessel vasculopathy in nonoccluded parts of the pulmonary circulation that is histologically similar to that described in pulmonary arterial hypertension. This observation has led to frequent off-license use of approved pulmonary arterial hypertension therapies in CTEPH. Small uncontrolled trials have investigated prostacyclin analogs, endothelin receptor antagonists, and phosphodiesterase type 5 inhibitors in CTEPH with mixed results. A phase III study of the endothelin receptor antagonist bosentan met only one of its two coprimary end points. The first large randomized controlled trial showing a positive treatment effect was the Chronic Thromboembolic Pulmonary Hypertension Soluble Guanylate Cyclase Stimulator Trial (CHEST). This study led to the licensing of riociguat for use in inoperable or persistent recurrent CTEPH. Rigorous randomized controlled trials of medical therapy for CTEPH are needed, and several are underway or planned. In the future, outcomes research may be facilitated by identification of novel end points specific to CTEPH.