What is the definition of pulmonary hypertension as measured by right heart catheterization?

Definition of Pulmonary Hypertension by Right Heart Catheterization

Pulmonary hypertension (PH) is defined as a mean pulmonary arterial pressure (mPAP) ≥20 mmHg at rest as measured by right heart catheterization (RHC). 1 This represents a recent update from the previous definition of mPAP ≥25 mmHg that was used for many years.

Hemodynamic Classifications of Pulmonary Hypertension

The complete hemodynamic definition requires additional measurements beyond just the mPAP:

Types of PH Based on Hemodynamic Parameters:

1. Pre-capillary PH:

   • mPAP >20 mmHg
   • Pulmonary arterial wedge pressure (PAWP) ≤15 mmHg
   • Pulmonary vascular resistance (PVR) >2 Wood Units 1
   • Found in: Groups 1,3,4, and some Group 5 PH

2. Isolated Post-capillary PH:

   • mPAP >20 mmHg
   • PAWP >15 mmHg
   • PVR ≤2 Wood Units 1
   • Found in: Group 2 and some Group 5 PH

3. Combined Pre- and Post-capillary PH:

   • mPAP >20 mmHg
   • PAWP >15 mmHg
   • PVR >2 Wood Units 1
   • Found in: Group 2 and some Group 5 PH

Historical Context and Evolution of Definition

• The original definition of PH (mPAP ≥25 mmHg) was established at the first World Symposium on Pulmonary Hypertension in 1973 2
• Normal mPAP at rest is 14 ± 3 mmHg, with an upper limit of normal of approximately 20 mmHg 3
• The 6th World Symposium on Pulmonary Hypertension (2018) revised the definition to mPAP >20 mmHg based on statistical analysis showing this value is 2 standard deviations above the normal mean 2

Clinical Classification Groups

Pulmonary hypertension is classified into five groups based on etiology:

1. Group 1: Pulmonary Arterial Hypertension (PAH)
2. Group 2: PH due to Left Heart Disease
3. Group 3: PH due to Lung Diseases and/or Hypoxemia
4. Group 4: Chronic Thromboembolic PH (CTEPH)
5. Group 5: PH with Unclear and/or Multifactorial Mechanisms 3

Importance of Right Heart Catheterization

• RHC remains the gold standard for diagnosing PH 4, 5
• Echocardiography can estimate pulmonary pressures but has limitations in accuracy, with correlation to RHC ranging from r=0.57 to r=0.95 3
• RHC allows for accurate measurement of:
  • Mean pulmonary arterial pressure
  • Pulmonary arterial wedge pressure
  • Pulmonary vascular resistance
  • Cardiac output

Clinical Implications

• Higher mPAP values correlate with increased mortality risk regardless of PH group 3
• Mortality increases significantly with elevated pulmonary pressures:
  • 5-year mortality: ~25% for mPAP 19-24 mmHg
  • 5-year mortality: ~40% for mPAP ≥25 mmHg 3

Common Pitfalls in PH Diagnosis

• Relying solely on echocardiography without confirmatory RHC can lead to misclassification 3
• Failing to distinguish between pre-capillary and post-capillary PH can result in inappropriate treatment decisions 3
• Overlooking the possibility of combined pre- and post-capillary PH in patients with left heart disease can lead to inadequate treatment 3

Key Considerations During RHC

• The pressure transducer zero level should be at the midthoracic line (at the level of the left atrium) for standardized measurements 5
• Volume or exercise challenge during RHC may help unmask left heart disease in borderline cases, though these approaches require further validation 5
• In patients with suspected PH, a complete hemodynamic assessment should include measurement of mPAP, PAWP, and calculation of PVR to properly classify the type of PH