WHO Classification of Pulmonary Hypertension

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The classification of pulmonary hypertension has recently been changed by the World Health Organization (WHO).

Pulmonary hypertension is the name given to the condition in which the pressure inside the pulmonary artery is abnormally elevated. Pulmonary hypertension always has the potential to become a very serious medical problem, so it's important to get appropriate treatment.

Until recently, pulmonary hypertension has been classified into two broad categories: primary or idiopathic (in which no underlying cause can be identified) and secondary (in which an underlying cause has been found).

This is still a useful classification system, because achieving a good outcome with pulmonary hypertension depends strongly on treating the underlying cause, and this "old" classification system emphasizes the critical importance of figuring out whether an underlying cause can be identified.

The WHO Classification of Pulmonary Hypertension

The new WHO classification system attempts to be more specific about the mechanism of pulmonary hypertension, and the expected response to treatment. It is a useful classification system for experts on pulmonary hypertension, but for patients and for many doctors it can be a little confusing.

The WHO classification system divides pulmonary hypertension into five categories:

Group 1: This group includes disorders in which the pulmonary hypertension is associated with abnormalities in the small branches of the pulmonary artery, the arterioles. Several types of pulmonary hypertension are in Group 1, including idiopathic pulmonary hypertension, and pulmonary hypertension due to several types of infection, connective tissue disorders, and some types of congenital heart disease.

Group 2: This group includes pulmonary hypertension caused by left-sided heart disease, such as cardiomyopathy, diastolic dysfunction, mitral stenosis, mitral regurgitation, aortic stenosis, and aortic regurgitation.

Group 3: This group includes pulmonary hypertension due to lung problems.

Group 4: This group includes pulmonary hypertension due to pulmonary embolus (blood clots that travel to the lungs) or pulmonary thrombosis (blood clots that form in the lungs).

Group 5: This group includes pulmonary hypertension due to other miscellaneous causes, which do not fit into the other four categories.


The WHO classification of pulmonary hypertension is useful to specialists who deal frequently with patients who have pulmonary hypertension. But it is a complex classification system with little conceptual coherence (so it must be memorized rather than "figured out"). For most patients and most doctors, the "old" classification system - which is much simpler and which makes intuitive sense - remains adequate.


Simonneau G, Robbins IM, Beghetti M, et al. Updated clinical classification of pulmonary hypertension. SO J Am Coll Cardiol. 2009 Jun 30;54(1 Suppl):S43-54.

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