Causes of Pulmonary Hypertension
Pulmonary hypertension is classified into five major groups based on underlying pathophysiological mechanisms, with left heart disease being the most common cause worldwide, accounting for up to 70% of all cases. 1, 2
Group 1: Pulmonary Arterial Hypertension (PAH)
- Idiopathic PAH (no identifiable cause)
- Heritable PAH:
- Drug and toxin-induced PAH:
- Definite associations: Appetite suppressants (aminorex, fenfluramine)
- Likely associations: Amphetamines, dasatinib 1
- Associated PAH (APAH):
- Connective tissue diseases (e.g., scleroderma)
- HIV infection
- Portal hypertension
- Congenital heart disease (e.g., Eisenmenger syndrome)
- Schistosomiasis
- Chronic hemolytic anemia 1
Group 2: PH Due to Left Heart Disease
- Left ventricular systolic dysfunction (up to 60% of patients with severe LV dysfunction) 1, 2
- Left ventricular diastolic dysfunction (up to 70% of patients with HFpEF) 2
- Valvular disease (virtually all patients with severe symptomatic mitral valve disease and up to 65% with symptomatic aortic stenosis) 1, 2
- Congenital/acquired left heart inflow/outflow tract obstruction
- Congenital/acquired pulmonary veins stenosis 1
Group 3: PH Due to Lung Diseases and/or Hypoxia
- Chronic obstructive pulmonary disease
- Interstitial lung disease
- Mixed restrictive and obstructive pattern lung diseases
- Sleep-disordered breathing
- Alveolar hypoventilation disorders
- Chronic exposure to high altitude
- Developmental lung diseases 1
Group 4: Chronic Thromboembolic PH and Other Pulmonary Artery Obstructions
- Chronic thromboembolic pulmonary hypertension
- Other pulmonary artery obstructions:
- Angiosarcoma and other intravascular tumors
- Arteritis
- Congenital pulmonary artery stenoses
- Parasites (hydatidosis) 1
Group 5: PH with Unclear and/or Multifactorial Mechanisms
- Hematological disorders: chronic hemolytic anemia, myeloproliferative disorders, splenectomy
- Systemic disorders: sarcoidosis, pulmonary histiocytosis, lymphangioleiomyomatosis, neurofibromatosis
- Metabolic disorders: glycogen storage disease, Gaucher disease, thyroid disorders
- Others: pulmonary tumoral thrombotic microangiopathy, fibrosing mediastinitis, chronic renal failure 1
Pathophysiological Considerations
The underlying mechanisms of pulmonary hypertension vary by group but generally involve:
- Group 1: Pulmonary vascular remodeling with proliferation of endothelial and smooth muscle cells, leading to increased pulmonary vascular resistance 3
- Group 2: Passive backward transmission of elevated left atrial pressure 2
- Group 3: Hypoxic vasoconstriction, mechanical destruction of the vascular bed, and inflammation 4
- Group 4: Mechanical obstruction of pulmonary arteries by organized thromboembolic material 4
- Group 5: Various mechanisms depending on the underlying condition 1
Clinical Implications
Understanding the cause of pulmonary hypertension is crucial as treatment strategies differ significantly between groups:
- Group 1 patients require specific PAH-targeted therapies
- Group 2 patients need treatment of the underlying left heart disease
- Group 3 patients require optimization of underlying lung disease and oxygen therapy
- Group 4 patients should be evaluated for pulmonary endarterectomy
- Group 5 patients need treatment directed at the underlying condition 4, 3
Early identification of the cause is essential as pulmonary hypertension, regardless of etiology, can lead to right ventricular failure, which is the main cause of death in these patients 3, 5.