Pulmonary hypertension (PH) is a complex clinical syndrome characterized by elevated pressure in the pulmonary circulation, resulting from a diversity of underlying causes. Because its symptoms are often non-specific—such as dyspnea, fatigue, and sometimes syncope—its diagnosis relies on a structured, multi-step approach that integrates clinical suspicion, noninvasive screening, and confirmatory hemodynamic studies. Accurate diagnosis, including classification by World Health Organization (WHO, formerly WPHS) groups 1 through 5, is essential for selecting appropriate therapies and predicting outcomes.
Types of Pulmonary Hypertension
WPHS (WHO) Classification: Groups 1–5
Pulmonary hypertension is classified into five groups based on similar clinical presentations, pathophysiology, hemodynamic profiles, and management approaches:
Group 1: Pulmonary Arterial Hypertension (PAH)
- Characterized by pre-capillary PH (mPAP ≥20 mmHg, PAWP ≤15 mmHg, PVR ≥3 WU).
- Includes idiopathic, heritable, drug/toxin-induced, associated with connective tissue diseases, HIV infection, portal hypertension, congenital heart diseases, and some rare conditions.
- Diagnosis: Requires exclusion of other causes; comprehensive workup to rule out Groups 2–5. Vasoreactivity testing is performed in idiopathic, heritable, and drug-induced cases.
Group 2: PH Due to Left Heart Disease
- Most common cause of PH in developed countries.
- Includes heart failure with reduced or preserved ejection fraction, valvular heart diseases, and congenital/acquired left heart inflow/outflow tract obstruction.
- Diagnosis: Echocardiography and RHC show elevated left-sided filling pressures (PAWP >15 mmHg); left ventricular dysfunction or significant valve disease is evident.
Group 3: PH Due to Lung Diseases and/or Hypoxia
- Caused by chronic obstructive pulmonary disease (COPD), interstitial lung disease, other restrictive/obstructive diseases, sleep-disordered breathing, alveolar hypoventilation disorders, high-altitude exposure, and developmental lung diseases.
- Diagnosis: Pulmonary function testing, arterial blood gases, and imaging confirm underlying respiratory disease; PH is usually mild to moderate in these patients.
Group 4: PH Due to Pulmonary Artery Obstructions (Chronic Thromboembolic Pulmonary Hypertension, CTEPH)
- Results from unresolved pulmonary emboli leading to organized thrombi obstructing the pulmonary arteries.
- Can also be caused by other intravascular obstructions (tumors, parasites, arteritis).
- Diagnosis: V/Q scan is the preferred screening tool; CT pulmonary angiography and pulmonary angiography confirm the diagnosis. RHC quantifies hemodynamic burden.
Group 5: PH with Unclear and/or Multifactorial Mechanisms
- Includes various diseases with complex or poorly understood mechanisms, such as hematological disorders (sickle cell disease), systemic disorders (sarcoidosis), metabolic disorders, and others.
- Diagnosis: Requires exclusion of Groups 1–4; diagnosis is often by clinical context and exclusion.