Pulmonary arterial hypertension (PAH) is a progressive disease caused by narrowing or tightening (constriction) of the pulmonary arteries, which connect the right side of the heart to the lungs. Untreated, PAH is a disease with a very poor prognosis.

By definition, PAH is characterized by an increase in mean pulmonary arterial pressure (PAP) to ≥25mmHg at rest, and a mean primary capillary wedge pressure of ≤15 mmHg.


Pulmonary arterial hypertension (PAH) represents Group 1 within the Pulmonary Hypertension World Health Organisation (WHO) clinical classification system (ESC Guidelines, European Heart Journal 2015) and is one of five such groups. The groups are divided based on etiology as shown in the following table.


Group 1











Pulmonary Arterial Hypertension (PAH)

  • Idiopathic PAH (iPAH)
  • Heritable PAH
  • Drug and toxin induced
  • Associated with (APAH):
    • Connective tissue disease
    • HIV infection
    • Portal hypertension
    • Congenital heart disease
    • Schistosomiasis
Group 1' 

Pulmonary veno-occlusive disease (PVOD) and/or pulmonary capillary haemangiomatosis (PCH) 

  • Idiopathic
  • Heritable
    • EIF2AK4 mutation
    • Other mutations
  • Drugs, toxins and radiation induced
  • Associated with:
    • Connective tissue disease
    • HIV infection
Group 1''

Persistent pulmonary hypertension of the newborn

Group 2 




Pulmonary hypertension due to left heart diseases

  • Left ventricular systolic dysfunction
  • Left ventricular diastolic dysfunction
  • Valvular disease
  • Congenital / acquired left heart inflow / outflow tract obstruction and congenital cardiomyopathies
  • Congenital / acquired pulmonary veins stenosis

Group 3  










Pulmonary hypertension due to lung diseases and/or hypoxemia

  • Chronic obstructive pulmonary disease (COPD)
  • Interstitial lung disease (ILD)
  • Other pulmonary diseases with mixed restrictive and obstructive pattern
  • Sleep-disordered breathing
  • Alveolar hypoventilation disorders
  • Chronic exposure to high altitude
  • Developmental abnormalities 
Group 4 

Chronic thromboembolic pulmonary hypertension (CTEPH) 

  • Chronic thromboembolic pulmonary hypertension
  • Other pulmonary artery obstructions
    • Angiosarcoma
    • Other intravascular tumors
    • Arteritis
    • Congenital pulmonary arteries stenosis
    • Parasites (hydatidosis)

Group 5  









PH with unclear multifactorial mechanisms and/or multifactorial mechanisms

  • Haematological disorders: chronic haemolytic anaemia, myeloproliferative disorders, splenectomy
  • Systemic disorders, sarcoidosis, pulmonary histiocytosis, lymphangioleiomyomatosis
  • Metabolic disorders: glycogen storage disease, Gaucher disease, thyroid disorders
  • Others: pulmonary tumoral thrombothic microangiopathy, osing mediastinitis, chronic renal failure (with/without dialysis), segmental pulmonary hypertension

Although Pulmonary arterial hypertension (PAH) is a rare disease, with an estimated prevalence of 15-50 cases per million, the prevalence of PAH in certain at-risk groups is substantially higher. For example, in HIV-infected patients the prevalence is 0.5%, in patients with systemic sclerosis it has been reported to be 7-12%, and in patients with sickle cell disease the prevalence is around 2-3.75%.

Idiopathic PAH (IPAH), one of the more common forms of PAH, has an annual incidence of 1-2 cases per million people in the US and Europe and is 2-4 times as common in women as in men. The mean age at diagnosis is around 45 years, although the onset of symptoms can occur at any age. Despite the true relative prevalence of IPAH, heritable PAH (HPAH), and associated PAH (APAH) being unknown, it is likely that IPAH accounts for at least 40% of cases of PAH, with APAH accounting for the majority of the remaining cases.



Please note that the information contained in this section of the website is not intended for US residents. Please visit our US webpage.

Please note that the information contained in this section of the website is not intended for US residents. Please visit our US webpage.