Definition and Diagnosis of Pulmonary Hypertension

Current Definition and Classification

Pulmonary hypertension (PH) is defined as a mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest as assessed by right heart catheterization, according to the European Heart Journal 1, 2, 3
The European Society of Cardiology defines PH as a hemodynamic and pathophysiological condition characterized by elevated pressure in the pulmonary arteries, with a diagnostic threshold of mPAP ≥25 mmHg at rest measured via right heart catheterization 1, 3
The definition of PH on exercise is not supported by sufficient published data and is no longer recommended by the European Heart Journal 1, 3

Pre-capillary PH is characterized by mPAP ≥25 mmHg with pulmonary wedge pressure (PWP) ≤15 mmHg and pulmonary vascular resistance (PVR) ≥3 Wood units, as defined by the European Heart Journal 3
Post-capillary PH is characterized by mPAP ≥25 mmHg with PWP >15 mmHg, according to the European Heart Journal 3
Passive post-capillary PH is characterized by a transpulmonary pressure gradient (TPG) ≤12 mmHg, while reactive post-capillary PH is characterized by a TPG >12 mmHg, as defined by the European Heart Journal 3

PH is categorized into five major groups based on etiology, pathophysiology, and therapeutic approaches, including Group 1: Pulmonary Arterial Hypertension (PAH), Group 2: PH Due to Left Heart Disease, Group 3: PH Due to Lung Diseases and/or Hypoxia, Group 4: Chronic Thromboembolic PH (CTEPH), and Group 5: PH with Unclear and/or Multifactorial Mechanisms, as classified by the European Heart Journal and Praxis Medical Insights 1, 3
Group 1: PAH includes idiopathic PAH, heritable PAH, drug and toxin-induced PAH, and PAH associated with other conditions, such as connective tissue diseases, HIV, portal hypertension, and congenital heart disease, according to the European Heart Journal and Praxis Medical Insights 1, 3
Group 2: PH Due to Left Heart Disease includes left ventricular systolic dysfunction, left ventricular diastolic dysfunction, and valvular disease, as defined by the European Heart Journal and Praxis Medical Insights 1, 3

The median life expectancy from diagnosis in patients with idiopathic PAH, before the availability of disease-specific therapy, was 2.8 years, according to the European Heart Journal 2
Right heart catheterization remains the gold standard for confirming PH diagnosis, as recommended by Praxis Medical Insights and the Journal of the American College of Radiology 1, 4
The 2022 ACR Appropriateness Criteria update acknowledges the redefinition of PH as mPAP >20 mmHg at rest, according to the Journal of the American College of Radiology 4
Precapillary PH is characterized by mPAP >20 mmHg, PAWP ≤15 mmHg, and PVR ≥3 Wood units, while combined pre- and postcapillary PH is characterized by mPAP >20 mmHg, PAWP >15 mmHg, and PVR ≥3 Wood units, as defined by the Journal of the American College of Radiology 4

A mean pulmonary artery pressure (mPAP) ≥ 25 mmHg at rest, measured by right‑heart catheterization, is the traditional definition used to diagnose pulmonary hypertension. 5
This 25 mmHg cutoff has been the basis for patient selection in all randomized controlled trials and registries of pulmonary arterial hypertension. 6
Normal resting mPAP ranges from 14 mmHg to 20 mmHg; the upper limit of normal is 20 mmHg. 5
Resting mPAP values of 21–24 mmHg are of uncertain clinical significance and merit close follow‑up rather than an immediate diagnosis of pulmonary hypertension. 5

Pulmonary artery wedge pressure (PAWP) ≤ 15 mmHg confirms a pre‑capillary pattern and is required for a PAH diagnosis. 5
Pulmonary vascular resistance (PVR) > 3 Wood units (traditional) or > 2 Wood units (newer recommendations) must be present to classify PAH. 5
A PAWP > 15 mmHg indicates pulmonary hypertension secondary to left‑heart disease, distinguishing it from PAH. 6

RHC is the gold‑standard test and must be performed before initiating PAH‑specific therapy. 7
Measurements should be obtained at rest with the patient in the supine position, using a standardized technique (pressure transducer zeroed at the mid‑thoracic line). 7

Exercise‑induced definitions (mPAP > 30 mmHg on exertion) are no longer endorsed because of limited data and high variability among healthy individuals. 5
Transthoracic echocardiography can estimate pulmonary pressures but cannot replace catheter‑based measurement for definitive diagnosis. 7
Intra‑patient spontaneous variability of pulmonary arterial pressure may reach up to 20 mmHg, with an average coefficient of variation of about 8 %. 7

Prior to the availability of disease‑specific therapies, the median survival after diagnosis of idiopathic PAH was approximately 2.8 years. 6