Congenital Thrombophilia in Chronic Thromboembolic Pulmonary Hypertension (CTEPH): A Systematic Review of Prevalence, Clinical Phenotype, and Surgical Outcomes.

Background and Objectives: Congenital thrombophilias are biologically plausible contributors to chronic thromboembolic pulmonary hypertension (CTEPH), yet their frequency and clinical impact remain uncertain. We undertook a systematic review to (i) estimate the pooled prevalence of specific hereditary defects among adults with CTEPH, (ii) characterise associated demographic and haemodynamic phenotypes, and (iii) summarise peri-operative and survival outcomes after pulmonary endarterectomy (PEA) or balloon pulmonary angioplasty (BPA) in genetically defined subgroups. Methods: A protocol compliant with PRISMA-2020 was registered prospectively on the Open Science Framework (OSF). PubMed/MEDLINE, Scopus, and Web of Science were searched from inception to 1 June 2025 using validated, PRESS-reviewed strings combining CTEPH and thrombophilia terms. Observational cohorts, case-control studies and trials reporting laboratory-confirmed congenital thrombophilias in adults with right-heart-catheter-defined CTEPH were eligible. Results: Eight studies encompassing 677 unique CTEPH patients met the inclusion criteria. Among the 400 individuals screened for deficiencies of the natural anticoagulant pathways, 56 possessed a defect: protein S deficiency 5.3% (21/400; 95% CI 3.3-8.0), protein C deficiency 4.3% (17/400; 2.5-6.8), and antithrombin deficiency 1.5% (6/400; 0.6-3.3). In 520 genotyped patients, factor V Leiden and prothrombin G20210A were infrequent (1.3% and 1.0%, respectively) and confined to European/North American cohorts. Baseline haemodynamics were uniformly severe (mean mPAP 46.7 mm Hg; pulmonary vascular resistance ≈ 9 WU). Definitive reperfusion therapy was common (PEA 63%; BPA 18%), reducing mPAP to 20.5 mm Hg and yielding a weighted one-year survival of 96.2%. No study demonstrated a thrombophilia-specific effect on surgical candidacy or early survival. Conclusions: Approximately one in seven patients with CTEPH harbours a congenital thrombophilia, most often protein S or protein C deficiency, whereas classic venous-thrombo-embolism mutations are rare and ethnically restricted. Current evidence indicates that genetic status does not materially influence haemodynamic severity, uptake of PEA/BPA, or short-term survival, supporting guideline recommendations for universal referral to specialist reperfusion centres. Future multicentre registries integrating systematic genotyping and long-term outcome capture are needed to clarify genotype-specific prognostic and therapeutic implications.