Definition of CTEPH
CTEPH is defined as precapillary pulmonary hypertension (mean PAP ≥25 mmHg with PAWP ≤15 mmHg) with chronic organized thromboembolic material obstructing the pulmonary arteries, confirmed after at least 3 months of effective anticoagulation, and demonstrated by specific imaging findings such as ring-like stenoses, webs/slits, or chronic total occlusions. 1
Core Diagnostic Criteria
The diagnosis requires meeting three essential criteria simultaneously 2:
1. Hemodynamic Confirmation
- Mean pulmonary artery pressure ≥25 mmHg at rest by right heart catheterization
- Pulmonary vascular resistance ≥3 Wood units
- Pulmonary capillary wedge pressure ≤15 mmHg (to exclude left heart disease)
- Systolic pulmonary artery pressure typically exceeds 40 mmHg
Important caveat: Some patients with complete unilateral obstruction may have normal resting hemodynamics despite symptomatic disease—these are still considered CTEPH and managed accordingly 1.
2. Imaging Evidence of Chronic Thromboembolism
Must demonstrate obstruction in main, lobar, segmental, or subsegmental pulmonary arteries despite at least 3 months of therapeutic anticoagulation 1, 2. This time requirement distinguishes CTEPH from "subacute" PE.
Specific diagnostic signs include 1:
- Ring-like stenoses
- Webs and slits
- Chronic total occlusions (pouch lesions or tapered lesions)
- Organized thromboembolic material incorporated into vessel walls
Imaging modalities:
- V/Q scan: 96-97% sensitivity, 90-95% specificity—shows mismatched segmental perfusion defects 1
- CT pulmonary angiography: Can appear relatively normal despite significant V/Q abnormalities 2
- Conventional pulmonary angiography: Gold standard for anatomic definition
3. Exclusion of Other Causes
Must rule out 2:
- WHO Group II: Left-sided heart disease (requires wedge pressure ≤15 mmHg)
- WHO Group III: Parenchymal lung disease
- Other mimics: PA sarcoma, tumor emboli, parasites, congenital PA stenosis 1
Key Distinguishing Features
CTEPH differs from other forms of pulmonary hypertension by:
- Presence of organized fibrotic thromboembolic material in elastic pulmonary arteries 3
- Mismatched segmental perfusion defects on V/Q scan (versus non-segmental or normal in idiopathic PAH) 1
- Potential surgical curability with pulmonary endarterectomy 4, 5
Clinical Context
Common pitfall: Up to 63% of CTEPH patients have no documented history of acute PE 2, so absence of prior PE does not exclude the diagnosis. The median time from symptom onset to diagnosis is 14 months even in expert centers 1, reflecting the nonspecific nature of symptoms (progressive dyspnea, exercise intolerance).
Pathophysiology: Results from non-resolution of venous thromboembolism with incorporation of embolic material into vessel walls, plus secondary small-vessel arteriopathy resembling idiopathic PAH 2, 5.