Classification and functional assessment of pulmonary hypertension

Pulmonary hypertension is classified according to both aetiology and severity (ie the degree of functional impairment; see World Health Organization (WHO) functional classification of pulmonary hypertension), which are determined by expert evaluation in a specialised pulmonary hypertension clinic. The aetiology and severity provide prognostic information and determine the appropriate therapy.

The World Health Organization (WHO) classifies pulmonary hypertension into 5 categories according to aetiology:

• pulmonary arterial hypertension (PAH) (group 1)
  • idiopathic PAH
  • heritable PAH
  • drug- and toxin-associated PAH
  • PAH associated with connective tissue disease, HIV infection, portal hypertension, congenital heart disease or schistosomiasis
  • PAH with features of venous or capillary involvement
  • persistent pulmonary hypertension of the newborn
• pulmonary hypertension due to left heart disease (group 2)
• pulmonary hypertension due to lung diseases and/or hypoxia (group 3)
• pulmonary hypertension due to pulmonary artery obstruction (group 4)
  • chronic thromboembolic pulmonary hypertension (CTEPH)
  • other pulmonary artery obstructions
• pulmonary hypertension with unclear and/or multifactorial mechanisms (group 5).

PAH (group 1) is a distinct condition for which specific therapies can be used; for groups 2 to 5 (as above), the priority is to treat the underlying cause.

Pulmonary hypertension is also classified by WHO into 4 functional classes, based on the extent of physical limitation experienced by the patient—see World Health Organization (WHO) functional classification of pulmonary hypertension.