Chronic thromboembolic pulmonary hypertension: a distinct disease entity.

Chronic thromboembolic pulmonary hypertension (CTEPH) is a distinct subtype of pulmonary hypertension (PH). One disease hypothesis is that CTEPH results from the non-resolution of venous thromboembolism. CTEPH is characterised by the presence of obstructive fibrotic thromboembolic material in the major pulmonary vessels, with concomitant microvascular arteriopathy, resulting in progressive PH. The clinical presentation of CTEPH is similar to pulmonary arterial hypertension with nonspecific symptoms, but it is distinguished from pulmonary arterial hypertension by the presence of mismatched segmental defects on the ventilation/perfusion scan. The exact prevalence and incidence of CTEPH are unknown, but are thought to have been underestimated in the past. CTEPH is unique among the subgroups of PH in that it is potentially curable with pulmonary endarterectomy, a surgical intervention intended to remove the occlusive material from the pulmonary vasculature. However, in some patients the obstructions are technically inaccessible or the risk/benefit ratios are unfavourable, making the condition inoperable. It is thought that the involvement of the smaller, more distal vessels is a target for medical treatment. Untreated, CTEPH may result in right heart failure and death. The pathophysiological mechanisms which cause CTEPH are complex and have not yet been fully elucidated.