1. World Health Organisation/World Symposium classification of pulmonary hypertension.

WHO group	Classification
Group 1	Pulmonary arterial hypertension idiopathic PAH PAH with vasoreactivity heritable PAH drugs and toxins associated with: connective tissue disease; HIV; portal hypertension; congenital heart disease; schistosomiasis. Pulmonary veno‐occlusive disease/pulmonary capillary haemangiomatosis Persistent pulmonary hypertension of the newborn
Group 2	Pumonary hypertension due to left heart disease due to left heart failure with preserved ejection fraction due to left heart failure with reduced ejection fraction Valvular heart disease Congenital post‐capillary obstructive lesions
Group 3	Pulmonary hypertension due to chronic lung disease or chronic hypoxaemia, or both obstructive lung disease restrictive lung disease other lung diseases with a mixed obstructive/restrictive pattern sleep disordered breathing alveolar hypoventilation disorders chronic exposures to high altitudes developmental lung diseases
Group 4	Pulmonary hypertension due to pulmonary artery obstruction chronic thromboembolic pulmonary hypertension other pulmonary artery obstructions
Group 5	Pulmonary hypertension with unclear mechanisms haematologic disorders (chronic haemolytic anaemia, myeloproliferative disorders, splenectomy) systemic disorders (sarcoidosis, pulmonary histiocytosis, lymphangioleiomyomatosis, neurofibromatosis) metabolic disorders (glycogen storage disease, Gaucher disease, thyroid disorders) others (pulmonary tumoral thrombotic microangiopathy, fibrosing mediastinitis, chronic renal failure (with/without dialysis), segmental pulmonary hypertension)

PAH: pulmonary arterial hypertension