What is Pulmonary Arterial Hypertension?

In healthy individuals, the mean pulmonary artery pressure (mPAP) as measured by right heart catheterisation is 14±3.3 mmHg (mean±SD) at rest, with an upper limit of approximately 20 mmHg.1

Pulmonary arterial hypertension (PAH) is a clinical condition characterised by the presence of elevated blood pressure in the pre-capillary pulmonary circulation, without any other cause of pulmonary hypertension (PH), for example: due to lung disease, chronic thromboembolic pulmonary hypertension, or other rare diseases.2

Specifically, the haemodynamic definition of PAH is as follows:1,2

  • mPAP >25 mmHg*
  • PAWP ≤15 mmHg
  • PVR ≥3 WU

*At the World Symposium of Pulmonary Hypertension (WSPH) meeting in December 2018, Simonneau and colleagues from the 6th WSPH Taskforce proposed changing the upper limit of normal mPAP to 20 mmHg.1 In Australia, in order to access PBS funding for PAH therapy, the mean pulmonary artery pressure (mPAP) should be ≥  to 25mmHg.

mPAP=mean pulmonary arterial pressure; PAWP=pulmonary arterial wedge pressure; PVR=pulmonary vascular resistance.

PAH is uncommon3

PAH is a rare disease, with an estimated prevalence of approximately 150 cases per million adult population in Australia.4 PAH is more common in women than men (approximately 70–80% of patients are female) with a mean age at diagnosis between 50 and 65 years in modern registries.3

Prognosis of untreated PAH is poor5

When left untreated, PAH is associated with high mortality.5 Median survival is <5 years even in mildly symptomatic patients, and as low as 6 months in patients with advanced disease.5 Due to the non-specific nature of the symptoms, PAH is unfortunately most frequently diagnosed when patients have reached this advanced stage.6 Prognosis also varies between subtypes of PAH, for example the prognosis is generally worse in patients with PAH associated with connective-tissue disease (CTD), while patients with congenital heart disease PAH usually have a better prognosis.3

PAH is just one type of PH2

As well as being split into subtypes based on specific aetiology, PAH forms 1 of 5 Groups of PH, which are separated and organised according to clinical presentation, pathological findings, haemodynamic characteristics and treatment strategy.2

The five Groups of PH are covered in more detail in the section ‘Types of PH’

References
  1. Simonneau G, et al. Eur Respir J 2019; 53(1):1801913
  2. Galiè N, et al. Eur Heart J 2016; 37:67–119.
  3. Hoeper MM. Gibbs JSR. Eur Respir Rev 2014; 23:450–7.
  4. Strange G, et al. Heart 2012; 98:1805–11.
  5. D’Alonzo GE, et al. Ann Intern Med 1991; 115:343–49.
  6. Humbert M, et al. Am J Respir Crit Care Med 2006; 173:1023–30.
Footnotes
PAH=pulmonary arterial hypertension; PH=pulmonary hypertension.

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This content is intended for Australian healthcare professionals. For more information on pulmonary hypertension, please contact your healthcare professional.
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World Health Organization functional class (WHO-FC) for patients with PH3,5

This system grades PH severity according to the patient’s functional status, by linking symptoms with activity limitations. WHO-FC remains a powerful predictor of outcomes in patients with PAH.

WHO - FC Description
I
Patients with PH in whom there is no limitation of usual physical activity; ordinary physical activity does not cause increased dyspnoea, fatigue, chest pain, or presyncope.
II
Patients with PH who have mild limitation of physical activity. There is no discomfort at rest, but normal physical activity causes increased dyspnoea, fatigue, chest pain, or presyncope.
III
Patients with PH who have a marked limitation of physical activity. There is no discomfort at rest, but less than ordinary activity causes increased dyspnoea, fatigue, chest pain, or presyncope.
IV
Patients with PH who are unable to perform any physical activity at rest and who may have signs of right ventricular failure. Dyspnoea and/or fatigue may be present at rest, and symptoms are increased by almost any physical activity.
Adapted from McGoon M, et al. 2004.5
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This website is intended for Australian healthcare professionals only