Pulmonary Hypertension for USMLE Step 2
Pulmonary Hypertension for the USMLE Step 2 Exam
Definition and Classification
- Pulmonary Hypertension (PH):
- PH is defined as a 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, and PAH associated with connective tissue disease, congenital heart disease, or drugs.
- Group 2: PH due to left heart disease: Includes systolic or diastolic heart failure and valvular disease.
- Group 3: PH due to lung diseases and/or hypoxia: Chronic obstructive pulmonary disease (COPD), interstitial lung disease (ILD), and obstructive sleep apnea (OSA).
- Group 4: Chronic thromboembolic pulmonary hypertension (CTEPH): Caused by unresolved pulmonary emboli.
- Group 5: PH with unclear or multifactorial causes: Sarcoidosis, hematologic disorders, and metabolic diseases.
Pathophysiology
- Pulmonary Vascular Resistance (PVR):
- PH occurs due to vasoconstriction, vascular remodeling, and thrombosis in the pulmonary circulation, increasing pulmonary vascular resistance.
- Right Ventricular Hypertrophy:
- In response to increased afterload, the right ventricle (RV) undergoes hypertrophy and dilatation, eventually leading to right heart failure (cor pulmonale).
- Hypoxic Vasoconstriction:
- In Group 3 PH, chronic hypoxia from lung diseases like COPD and ILD induces pulmonary vasoconstriction, increasing pulmonary artery pressure.
Risk Factors
- Idiopathic and Heritable PAH:
- Mutations in BMPR2 are associated with hereditary PAH. Other risk factors include female sex, connective tissue diseases, and drugs (e.g., appetite suppressants).
- Left Heart Disease (Group 2 PH):
- Common causes include heart failure with reduced or preserved ejection fraction (HFrEF, HFpEF) and valvular heart disease (e.g., mitral stenosis).
- Chronic Lung Diseases (Group 3 PH):
- Lung conditions like COPD, ILD, and OSA cause chronic hypoxia, leading to pulmonary vasoconstriction and remodeling.
- CTEPH:
- Chronic unresolved pulmonary emboli lead to persistent obstruction and increased pulmonary pressures.
Clinical Features
- Symptoms:
- Dyspnea on exertion: Most common symptom, progressive over time.
- Fatigue, syncope, and chest pain: Present in advanced disease.
- Signs of right heart failure: Peripheral edema, ascites, hepatomegaly, and jugular venous distention (JVD).
- Physical Exam:
- Loud P2: Accentuated second heart sound due to elevated pulmonary pressures.
- Right ventricular heave: Reflects RV hypertrophy and increased workload.
Diagnosis
- Echocardiography:
- Initial screening test for PH. It estimates pulmonary artery pressures and assesses RV size and function. Helps identify underlying left heart disease.
- Right Heart Catheterization (RHC):
- Gold standard to confirm PH and measure hemodynamic parameters (mPAP, PVR).
- Pulmonary Function Tests (PFTs):
- Useful in diagnosing Group 3 PH related to chronic lung diseases. Decreased DLCO (diffusion capacity) is common in PAH.
- Ventilation-Perfusion (V/Q) Scan:
- Essential for diagnosing CTEPH, identifying ventilation-perfusion mismatch due to chronic emboli.
Management
General Management
- Oxygen Therapy:
- Indicated for Group 3 PH to alleviate hypoxia-induced vasoconstriction.
- Diuretics:
- Used to manage symptoms of right heart failure, such as edema and ascites.
PAH-Specific Therapy
- Endothelin Receptor Antagonists (ERAs):
- Bosentan and ambrisentan reduce pulmonary vasoconstriction and improve exercise capacity.
- Phosphodiesterase-5 Inhibitors (PDE-5 inhibitors):
- Sildenafil and tadalafil increase nitric oxide availability, promoting vasodilation.
- Prostacyclin Analogs:
- Epoprostenol and treprostinil are used in severe cases to improve survival.
Surgical Options
- Pulmonary Endarterectomy:
- A curative treatment for CTEPH by removing chronic thromboembolic material from the pulmonary arteries.
- Lung Transplantation:
- Considered for end-stage disease in patients with refractory PAH.
Key Points
- Pulmonary hypertension is defined as a mean pulmonary artery pressure (mPAP) ≥ 20 mmHg, classified into five groups based on etiology.
- Common symptoms include dyspnea on exertion, fatigue, and signs of right heart failure such as edema and ascites.
- Diagnosis is confirmed with right heart catheterization, but echocardiography is the initial test to assess pulmonary pressures and right heart function.
- Treatment involves oxygen therapy, diuretics, and group-specific therapies such as endothelin receptor antagonists or prostacyclin analogs for Group 1 PAH.
- Pulmonary endarterectomy is the definitive treatment for CTEPH, while lung transplantation is reserved for refractory or advanced cases.