Are Pulmonary Arterial Hypertension (PAH) and pulmonary hypertension different?

Pulmonary Arterial Hypertension vs. Pulmonary Hypertension: Understanding the Difference

Yes, Pulmonary Arterial Hypertension (PAH) and Pulmonary Hypertension (PH) are different - PAH is specifically Group 1 of the five clinical classifications of PH, representing a distinct pathophysiological entity with specific treatments, while PH is the broader hemodynamic condition defined as elevated mean pulmonary arterial pressure ≥25 mmHg at rest. 1

Definitions and Hemodynamic Parameters

Pulmonary Hypertension (PH)

• Defined as mean pulmonary arterial pressure (mPAP) ≥25 mmHg at rest 1
• Normal pulmonary artery pressure is 14 ± 3 mmHg, with upper limit of normal approximately 20 mmHg 1
• Requires right heart catheterization for definitive diagnosis 1

Pulmonary Arterial Hypertension (PAH)

• Specifically refers to Group 1 PH in the clinical classification system 1
• Characterized by pre-capillary PH with:
  • mPAP ≥25 mmHg
  • Pulmonary artery wedge pressure (PAWP) ≤15 mmHg
  • Pulmonary vascular resistance (PVR) >3 Wood Units 1

Clinical Classification System

The current clinical classification divides PH into five main groups based on etiology 2, 1:

1. Group 1: Pulmonary Arterial Hypertension (PAH)

   • Idiopathic PAH
   • Familial/Heritable PAH
   • PAH associated with:
     • Connective tissue diseases
     • Congenital heart disease
     • Portal hypertension
     • HIV infection
     • Drugs and toxins
     • Other conditions

2. Group 2: PH due to Left Heart Disease

   • Left ventricular systolic/diastolic dysfunction
   • Valvular disease

3. Group 3: PH due to Lung Diseases and/or Hypoxemia

   • COPD
   • Interstitial lung disease
   • Sleep-disordered breathing

4. Group 4: Chronic Thromboembolic PH (CTEPH)

5. Group 5: PH with Unclear/Multifactorial Mechanisms

   • Hematologic disorders
   • Systemic disorders
   • Metabolic disorders

Key Differences

Pathophysiology

• PAH (Group 1): Characterized by progressive remodeling of distal pulmonary arteries with multiple pathogenic pathways including vasoconstrictor/vasodilator imbalance, proliferation/apoptosis imbalance, vascular remodeling, thrombosis in situ, and inflammation 2, 3
• Other PH Groups: Have distinct pathophysiological mechanisms related to their underlying causes 4

Treatment Approaches

• PAH (Group 1): Specific PAH-targeted therapies are indicated, including:

  • Prostacyclin analogues
  • Endothelin receptor antagonists
  • Phosphodiesterase-5 inhibitors 5, 3

• Non-PAH PH: Treatment focuses on the underlying cause:

  • Group 2: Treat left heart disease
  • Group 3: Optimize respiratory management
  • Group 4: Pulmonary endarterectomy for eligible patients
  • Group 5: Address underlying condition 1

Clinical Implications

Treatment Cautions

• PAH-specific therapies should NOT be used in non-PAH forms of PH, particularly in PH due to left heart disease, as they can be harmful 1, 4
• For example, sildenafil is specifically indicated for "pulmonary arterial hypertension (WHO Group I)" to improve exercise ability and delay clinical worsening 5

Diagnostic Approach

• Right heart catheterization is essential for definitive diagnosis and classification of PH 1
• Ventilation-perfusion scanning is crucial to exclude CTEPH in all patients with suspected PH 1

Prognosis

• PAH has poor prognosis with approximately 15% mortality within 1 year even with modern therapy 1
• Higher mPAP values correlate with increased mortality risk regardless of PH group 1
• The presence of right ventricular dysfunction significantly worsens prognosis 1

Common Pitfalls to Avoid

1. Misclassification: Relying solely on echocardiography without confirmatory right heart catheterization can lead to misclassification 1

2. Inappropriate Treatment: Using PAH-specific therapies in non-PAH forms of PH can be harmful, especially in PH due to left heart disease 1, 4

3. Missed Diagnosis: Failing to perform ventilation-perfusion scanning may miss potentially treatable CTEPH 1

4. Overlooking Combined Forms: Missing combined pre- and post-capillary PH in patients with left heart disease can lead to inadequate treatment 1

Understanding the distinction between PAH and PH is crucial for appropriate diagnosis, treatment selection, and patient management to improve outcomes in this complex group of disorders.