• PAH represents the Group 1 in the pulmonary hypertension clinical classification defined during the 3^rd World symposium on PAH held in 2003 in Venice, Italy (Table 2).

Table 2: Clinical classification of PH – Venice 2003¹¹

Group I. Pulmonary arterial hypertension (PAH)

• Idiopathic (IPAH)
• Familial (FPAH)
• Associated with (APAH):
  • Connective tissue disease
  • Congenital systemic-to-pulmonary shunts (eg. Eisenmenger’s)
  • Portal hypertension
  • Drugs and toxins
  • Other (thyroid disorders, glycogen storage disease, Gaucher’s disease, hereditary haemorrhagic telangiectasia, haemog
• Associated with significant venous or capillary involvement
  • Pulmonary veno-occlusive disease (PVOD)
  • Pulmonary capillary haemangiomatosis (PCH)
• Persistent pulmonary hypertension of the newborn (PPHN)

Group II. Pulmonary venous hypertension with left heart diseases

Group III. Pulmorary hypertension associated with respiratory diseases and / or hypoxemia (including chronic obstructive pulmonary disease)

Group IV.  Pulmonary hypertension due to chronic thrombotic and/or embolic disease

Group V.  Miscellaneous group 

• eg. sarcoidosis, histiocytosis X and lymphangiomatosis