Chronic thromboembolic pulmonary hypertension: the magic of pathophysiology

Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare and underdiagnosed complication of acute pulmonary embolism (APE). CTEPH is a common cause of pulmonary hypertension (PH) with distinct management strategy including pulmonary endarterectomy, balloon pulmonary angioplasty, long-term anticoagulation and PH drugs targeting endothelial cell dysfunction. Initially, PH in chronic thromboembolic pulmonary disease (CTEPD) was thought to be due exclusively to the intravascular obstruction of pulmonary arteries by unresolved fibrotic clots. However, it is now well accepted that pulmonary vascular remodelling can include significant pulmonary microvasculopathy, which plays a role in the development of CTEPH. The histological description and clinical consequences of CTEPH microvasculopathy are now better understood. These lesions may involve not only small muscular pulmonary arteries <500 µm, but also pulmonary capillaries and veins. In addition, enlargement and proliferation of systemic bronchial arteries as well as anastomoses between the systemic and pulmonary circulations contribute to the development of microvasculopathy. In this review, we discuss the recent advances in the understanding of the pathophysiology of CTEPH.