Risk factors for chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a form of pulmonary hypertension caused by obstruction and vascular remodelling of pulmonary arteries following pulmonary embolism. Risk factors that predispose patients to CTEPH include the size of the initial thrombus and numerous associated host or medical conditions. Haemostatic risk factors include elevated levels of factor VIII and phospholipid antibodies or intrinsic abnormalities in fibrinogen. Medical conditions that are associated with an increased risk of CTEPH include a history of splenectomy, cancer, ventriculoatrial shunt, chronic inflammatory disease, antiphospholipid antibodies and hypothyroidism. Although CTEPH is potentially curable by pulmonary endarterectomy (PEA), up to 40% of patients evaluated for PEA may be denied surgery depending on the level of surgical experience and disease accessibility after pre-operative assessment. Furthermore, an estimated 10-15% of patients are at risk for residual pulmonary hypertension following PEA surgery, due to significant concomitant small-vessel disease. However, pre-operative identification of small-vessel involvement remains a challenge. The current medications effective in the treatment of pulmonary arterial hypertension have not demonstrated efficacy in CTEPH. Accordingly, identification of CTEPH, followed by early referral for evaluation and treatment by an experienced PEA centre, is recommended.