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Domain

Pulmonary Hypertension

Modules

Classification & Workup

Group 1 through 5 — a common phenotype, five very different diseases.

Pulmonary Vascular Remodeling in PAH

Group 1 PAH arises from progressive remodeling of the distal pulmonary arterioles driven by endothelial dysfunction, with reduced production of vasodilators (nitric oxide, prostacyclin) and relative excess of vasoconstrictors (endothelin-1). This imbalance promotes smooth muscle and endothelial cell proliferation, in situ microthrombosis, and formation of plexiform lesions that progressively obliterate the vascular lumen. The result is a fixed rise in pulmonary vascular resistance that increases right ventricular afterload, distinguishing PAH from pulmonary venous hypertension due to left heart disease, where the elevated pressure is transmitted backward rather than generated by primary arteriolar disease. Unchecked, this remodeling drives right ventricular hypertrophy, dilation, and eventual right heart failure.

Hemodynamic Definition (2022 ESC)

Mean PAP >20 mmHg (lowered from 25). Pre-capillary: PCWP ≤15, PVR >2 WU. Combined: PCWP >15, PVR >2. Isolated post-capillary: PCWP >15, PVR ≤2.

WHO Groups

Group 1PAHIdiopathic,heritable, CTD,portal HTNGroup 2Left heartdisease(most commonoverall)Group 3Lung diseaseor hypoxiaGroup 4CTEPHChronicthromboembolicGroup 5Unclear ormultifactorialGroup 1: PAH (idiopathic, heritable, drug/toxin, CTD, portal HTN, congenital, schistosomiasis). Group 2: left heart disease (most common). Group 3: lung disease/hypoxia. Group 4: CTEPH. Group 5: unclear/multifactorial.

Workup

Ventilation-perfusion scintigraphy showing a V/Q mismatch (Wikimedia Commons, CC BY-SA 4.0)TTE (screen). CT chest/PE. PFTs. V/Q scan (mandatory to exclude CTEPH). Sleep study. HIV, autoimmune workup. RHC confirms diagnosis and enables vasoreactivity testing.

Right Heart Catheterization Criteria

Confirmatory right heart catheterization requires a mean pulmonary artery pressure above the diagnostic threshold with a pulmonary vascular resistance elevated above normal, distinguishing pre-capillary PAH from pulmonary hypertension due to left heart disease. Vasoreactivity testing at catheterization identifies the small subset of Group 1 patients who may benefit from high-dose calcium channel blockers.
Clinical pearls
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V/Q scan is superior to CT-PA for CTEPH screening — CT may miss chronic organized clot.
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A significant proportion of "unexplained" PAH is actually Group 2 with occult HFpEF — exercise-invasive hemodynamics unmask it.
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The 2022 ESC/ERS criteria require a pulmonary vascular resistance >2 Wood units in addition to mPAP >20 mmHg to define precapillary PH, not mPAP alone.
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Combined pre- and post-capillary PH (CpcPH) is defined by an elevated PVR despite an elevated PAWP, distinguishing it from isolated post-capillary PH due to left heart disease.
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Echocardiography is the first-line screening test for PH, but right heart catheterization is required to confirm the diagnosis and hemodynamic subtype.
Related guidelines
TropOnTop — Cardiology Study Platform