WHAT IS PH? : DEFINITION AND CLASSIFICATION

Pulmonary arterial hypertension (PAH) is caused by a progressive increase in pulmonary vascular resistance (PVR) leading to right ventricular failure and premature death. The condition is diagnosed at right heart catheterisation by physiological variables, namely:

• sustained elevation of mean pulmonary arterial pressure to >25 mmHg at rest or >30 mm Hg with exercise AND
• a mean pulmonary artery occlusion pressure of <15 mmHg

Pulmonary hypertension (PH), conversely, simply represents an elevated mean pulmonary artery pressure and can be a consequence of PAH or other conditions such as left-sided heart disease or hypoxic lung disease. The current classification of conditions leading to pulmonary hypertension is clinically based and is called the Venice classification (shown below).

1. Pulmonary arterial hypertension
   • Idiopathic PAH
   • Familial PAH
   • Associated with:
     • Connective tissue disease
     • Congenital heart disease
     • Portal hypertension
     • HIV infection
     • Drugs and toxins
     • Others (thyroid disorders, glycogen storage disease, Gaucher?s disease, hereditary haemorrhagic telangiectasia, haemoglobinopathies, myeloproliferative disorders, splenectomy)
   • Other:
     • Venous/capillary involvement (pulmonary veno-occlusive disease, pulmonary capillary haemangiomatosis)
     • Persistent pulmonary hypertension of the newborn
   
   
2. PH with left heart disease
   • Atrial or ventricular
   • Valvular
   
   
3. PH with lung diseases/ hypoxaemia
   • Chronic obstructive pulmonary disease
   • Interstitial lung disease
   • Sleep disordered breathing
   • Alveolar hypoventilation disorders
   • Altitude
   • Developmental abnormalities
   
   
4. PH due to chronic thrombotic and/or embolic disease
   • Thromboembolic obstruction of proximal pulmonary arteries
   • Thromboembolic obstruction of distal pulmonary arteriese
   • Non-thrombotic pulmonary embolism (tumour, parasites, foreign material)
   
   
5. Miscellaneous
   • Sarcoidosis, histiocytosis X, lymphangiomatosis, compression of pulmonary vessels (adenopathy, tumour, fibrosing mediastinitis)