What are the diagnostic criteria for pulmonary hypertension, including the hemodynamic thresholds for pre‑capillary and post‑capillary disease?

Diagnostic Criteria for Pulmonary Hypertension

Pulmonary hypertension is now defined as a mean pulmonary arterial pressure (mPAP) >20 mmHg at rest measured by right heart catheterization, representing an updated threshold from the previous ≥25 mmHg cutoff. 1, 2

Core Hemodynamic Definition

The fundamental diagnostic criterion requires:

• mPAP >20 mmHg at rest (updated from ≥25 mmHg in 2015 guidelines) 1, 2
• All measurements must be obtained during right heart catheterization in stable clinical conditions 3
• Pressure transducer zero level should be standardized at the midthoracic line at the level of the left atrium 4

Important caveat: While the 2015 ESC/ERS guidelines used mPAP ≥25 mmHg 3, the most recent 2022 ESC/ERS guidelines lowered this threshold to >20 mmHg, resulting in a 9.8% net increase in overall PH diagnosis 5. However, this change primarily affected post-capillary PH detection, with minimal impact on pre-capillary and combined phenotypes (only 0.8% and 0.3% increases respectively) 5.

Pre-Capillary Pulmonary Hypertension

Pre-capillary PH is defined by the following hemodynamic criteria:

• mPAP >20 mmHg 1, 2
• Pulmonary arterial wedge pressure (PAWP) ≤15 mmHg 3, 1
• Pulmonary vascular resistance (PVR) >2 Wood Units 1, 2

Note the critical update: The PVR threshold was lowered from >3 Wood Units in 2015 guidelines 3 to >2 Wood Units in current guidelines 1, 2. This PVR criterion maintains specificity for discriminating pre-capillary from post-capillary PH even with the lowered mPAP threshold 5.

Pre-capillary PH encompasses:

• Group 1: Pulmonary arterial hypertension (PAH) 3
• Group 3: PH due to lung diseases and/or hypoxia 3
• Group 4: Chronic thromboembolic pulmonary hypertension (CTEPH) 3
• Group 5: PH with unclear/multifactorial mechanisms 3

Post-Capillary Pulmonary Hypertension

Post-capillary PH (primarily Group 2: PH due to left heart disease) is defined by:

• mPAP >20 mmHg 1, 2
• PAWP >15 mmHg 3, 1

Post-capillary PH is further subdivided into two phenotypes:

Isolated Post-Capillary PH (Ipc-PH)

• Diastolic pressure gradient (DPG) <7 mmHg and/or PVR ≤2 Wood Units 1 (updated from ≤3 WU 3)

Combined Post-Capillary and Pre-Capillary PH (Cpc-PH)

• DPG ≥7 mmHg and/or PVR >2 Wood Units 1 (updated from >3 WU 3)

Critical diagnostic pitfall: A normal PAWP does not rule out heart failure with preserved ejection fraction (HFpEF) 4. Volume or exercise challenge during right heart catheterization may unmask left heart disease, though these tools require further validation before routine use 4.

Exercise Pulmonary Hypertension

Exercise PH is a distinct hemodynamic entity defined as:

• Normal mPAP at rest with abnormal increase during exercise 1
• mPAP/cardiac output slope >3 mmHg/L/min between rest and exercise 1, 6

This definition lacks prospective outcome validation and is not yet incorporated into standard diagnostic criteria 3.

Essential Diagnostic Requirements

Right heart catheterization remains mandatory for definitive PH diagnosis 4. The procedure requires:

• Standardized pressure transducer positioning at the midthoracic line 4
• Measurements at rest in stable clinical conditions 3
• Assessment of mPAP, PAWP, cardiac output, and calculation of PVR and DPG 3
• Wood Units are preferred over dynes·s·cm⁻⁵ for PVR reporting 3