Table 3. Classification of PAH.

Category	Etiology
Group 1	Idiopathic
	Heritable
	Drug and toxin-induced
	Association with connective tissue disease
	HIV infection
	Portal hypertension
	Congenital heart disease and schistosomiasis
	Pulmonary veno-occlusive disease and/or pulmonary capillary hemangiomatosis
	Persistent pulmonary hypertension of the newborn
Group 2	Secondary to left heart disease
Group 3	Secondary to lung diseases and/or hypoxia
Group 4	Chronic thromboembolic pulmonary hypertension (CTEPH)
Group 5	Unclear multifactorial mechanism

PAH, pulmonary artery hypertension.