Pulmonary Hypertension for USMLE Step 3
Pulmonary Hypertension for the USMLE Step 3 Exam
Definition and Classification
- Pulmonary Hypertension (PH):
- Defined as mean pulmonary artery pressure (mPAP) ≥ 20 mmHg at rest, measured by right heart catheterization (RHC).
- WHO Classification:
- PH is categorized into 5 groups based on etiology:
- Group 1: Pulmonary Arterial Hypertension (PAH): Idiopathic, heritable, or associated with conditions like connective tissue diseases or drug use.
- Group 2: PH due to left heart disease: Includes heart failure with reduced or preserved ejection fraction (HFrEF/HFpEF) and valvular diseases.
- Group 3: PH due to lung diseases/hypoxia: Chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), and obstructive sleep apnea (OSA).
- Group 4: Chronic thromboembolic pulmonary hypertension (CTEPH): Results from chronic unresolved pulmonary embolism.
- Group 5: PH with multifactorial mechanisms: Includes conditions like sarcoidosis and hematologic disorders.
Pathophysiology
- Increased Pulmonary Vascular Resistance (PVR):
- PH results from vasoconstriction, vascular remodeling, and in situ thrombosis, leading to increased PVR and elevated pulmonary artery pressures.
- Right Ventricular Hypertrophy:
- The right ventricle (RV) hypertrophies to overcome increased afterload, leading to right heart failure (cor pulmonale) over time due to sustained pressure overload.
- Hypoxic Vasoconstriction:
- In Group 3 PH, chronic hypoxia from lung diseases like COPD or ILD causes pulmonary vasoconstriction, increasing pulmonary artery pressures.
Risk Factors
- Idiopathic PAH and Heritable PAH:
- Risk factors include mutations in the BMPR2 gene, female sex, connective tissue diseases, and the use of appetite-suppressing drugs.
- Group 2 PH:
- Commonly due to heart failure (both HFrEF and HFpEF) or valvular disease, such as mitral stenosis.
- Group 3 PH:
- Lung diseases such as COPD, ILD, and OSA cause chronic alveolar hypoxia, leading to pulmonary vasoconstriction and vascular remodeling.
- Group 4 PH (CTEPH):
- Caused by chronic unresolved pulmonary emboli, which obstruct the pulmonary arteries, increasing pressure.
Clinical Features
- Symptoms:
- Dyspnea on exertion: The most common symptom, usually progressive.
- Fatigue, syncope, chest pain: Seen in advanced disease.
- Peripheral edema, ascites, and jugular venous distention (JVD): Indicate right heart failure.
- Physical Exam:
- Loud P2 (accentuated second heart sound) due to increased pulmonary pressures.
- Right ventricular heave: Indicative of right ventricular hypertrophy.
- Signs of right heart failure: Peripheral edema, hepatomegaly, and ascites.
Diagnosis
- Echocardiography:
- The initial test for assessing pulmonary artery pressures and right ventricular function. It can detect RV hypertrophy, RV dilation, and tricuspid regurgitation.
- Right Heart Catheterization (RHC):
- The gold standard for diagnosing PH, confirming increased mPAP and pulmonary vascular resistance (PVR).
- Pulmonary Function Tests (PFTs):
- Used in Group 3 PH to assess underlying lung disease. A reduced DLCO (diffusion capacity) is typical in PAH.
- Ventilation-Perfusion (V/Q) Scan:
- The preferred imaging study to diagnose CTEPH, showing areas of ventilation-perfusion mismatch.
Management
General Management
- Oxygen Therapy:
- Indicated for Group 3 PH (lung disease-related) to correct hypoxia and reduce pulmonary vasoconstriction.
- Diuretics:
- Useful for managing right heart failure symptoms like peripheral edema and ascites.
PAH-Specific Therapy (Group 1 PH)
- Endothelin Receptor Antagonists (ERAs):
- Bosentan and ambrisentan reduce pulmonary vasoconstriction and improve exercise capacity in PAH.
- Phosphodiesterase-5 Inhibitors (PDE-5 inhibitors):
- Sildenafil and tadalafil promote vasodilation by increasing nitric oxide levels.
- Prostacyclin Analogs:
- Epoprostenol and treprostinil are potent vasodilators used in severe PAH cases.
Surgical Options
- Pulmonary Endarterectomy:
- Used in CTEPH to remove thromboembolic material from the pulmonary arteries, potentially curative.
- Lung Transplantation:
- Reserved for advanced cases of PAH or PH that are refractory to medical treatment.
Key Points
- Pulmonary hypertension is defined as mean pulmonary artery pressure ≥ 20 mmHg, classified into five groups based on etiology.
- Symptoms include dyspnea on exertion, fatigue, and signs of right heart failure (e.g., peripheral edema, ascites).
- Echocardiography is the first-line diagnostic tool, but right heart catheterization is required for confirmation.
- Treatment involves oxygen therapy, diuretics, and PAH-specific therapies such as endothelin receptor antagonists and prostacyclin analogs.
- Surgical options like pulmonary endarterectomy for CTEPH and lung transplantation are reserved for advanced cases.