What are the different types of pulmonary hypertension?

Types of Pulmonary Hypertension

Pulmonary hypertension is classified into five distinct clinical groups based on shared pathophysiology, hemodynamics, and treatment approaches, as established by international consensus guidelines. 1

Hemodynamic Definition

Pulmonary hypertension is defined as a mean pulmonary arterial pressure ≥25 mmHg at rest measured by right heart catheterization. 1 This hemodynamic threshold is essential for diagnosis across all PH groups. 2

The Five Clinical Groups

Group 1: Pulmonary Arterial Hypertension (PAH)

This is pre-capillary PH characterized by pulmonary artery wedge pressure ≤15 mmHg and pulmonary vascular resistance >3 Wood units. 1

Subtypes include: 1

• Idiopathic PAH (formerly called primary pulmonary hypertension) - no identifiable cause 1
• Heritable PAH - associated with BMPR2 gene mutations and other genetic abnormalities 1
• Drug and toxin-induced PAH - particularly anorexigens and certain medications 1
• Associated PAH (APAH) with: 1
  • Connective tissue diseases (scleroderma, lupus)
  • Congenital heart disease with systemic-to-pulmonary shunts
  • Portal hypertension
  • HIV infection
  • Schistosomiasis
  • Chronic hemolytic anemia
• Pulmonary veno-occlusive disease (PVOD) and pulmonary capillary hemangiomatosis - now classified within Group 1 with distinct pathology 1

Group 2: PH Due to Left Heart Disease

This is post-capillary PH defined by mean pulmonary artery pressure ≥25 mmHg with pulmonary artery wedge pressure >15 mmHg. 1

Causes include: 1

• Left ventricular systolic dysfunction (heart failure with reduced ejection fraction)
• Left ventricular diastolic dysfunction (heart failure with preserved ejection fraction)
• Valvular heart disease (mitral valve disease, aortic stenosis)
• Congenital/acquired left heart inflow/outflow tract obstruction

Clinical significance: Up to 60% of patients with severe LV systolic dysfunction and up to 70% with heart failure with preserved ejection fraction develop PH. 1 Virtually all patients with severe symptomatic mitral valve disease have PH. 1

Group 3: PH Due to Lung Diseases and/or Hypoxia

This group encompasses PH secondary to chronic respiratory conditions. 1

Specific causes: 1

• Chronic obstructive pulmonary disease (COPD)
• Interstitial lung disease
• Mixed restrictive and obstructive pulmonary diseases
• Sleep-disordered breathing (obstructive sleep apnea)
• Alveolar hypoventilation disorders
• Chronic exposure to high altitude
• Developmental lung abnormalities

Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH)

This results from organized thrombi obstructing pulmonary arteries after pulmonary embolism. 1

Subtypes include: 1

• Chronic thromboembolic PH (proximal vessel obstruction)
• Other pulmonary artery obstructions:
  • Angiosarcoma and other intravascular tumors
  • Arteritis
  • Congenital pulmonary artery stenoses
  • Parasitic disease (hydatidosis)

Critical distinction: CTEPH is potentially curable with surgical pulmonary endarterectomy, making accurate diagnosis essential. 3

Group 5: PH with Unclear and/or Multifactorial Mechanisms

This heterogeneous group includes conditions where PH mechanisms are incompletely understood or involve multiple pathways. 1

Categories include: 1

• Hematological disorders: Myeloproliferative disorders, splenectomy, chronic hemolytic anemia
• Systemic disorders: Sarcoidosis, pulmonary histiocytosis (Langerhans cell), lymphangioleiomyomatosis, neurofibromatosis
• Metabolic disorders: Glycogen storage disease, Gaucher disease, thyroid disorders
• Other conditions: Pulmonary tumoral thrombotic microangiopathy, fibrosing mediastinitis, chronic renal failure on dialysis, segmental PH

Key Classification Principles

The classification evolved from earlier systems: The term "primary pulmonary hypertension" was abandoned in favor of "idiopathic PAH" to better reflect current understanding. 1 The Venice 2003 and Dana Point 2008 classifications refined earlier Evian 1998 criteria. 1

Diagnostic approach requires: Right heart catheterization remains the gold standard for confirming diagnosis and determining the specific PH group. 2, 4 Echocardiography alone is insufficient for treatment decisions. 2

Clinical pitfall: Exercise-induced PH (mean PAP >30 mmHg with exercise) is no longer part of the diagnostic criteria due to lack of robust normative data. 1