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Pulmonary Hypertension for USMLE Step 1

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Pulmonary Hypertension for the USMLE Step 1 Exam
Pulmonary arterial pressure
Definition and Classification
  • Pulmonary Hypertension (PH):
    • Defined as a mean pulmonary artery pressure (mPAP) ≥ 20 mmHg at rest, measured by right heart catheterization (RHC).
  • WHO Classification:
    • PH is classified into 5 groups:
    • Group 1: Pulmonary Arterial Hypertension (PAH): Includes idiopathic, heritable, and PAH associated with connective tissue diseases, congenital heart disease, and drugs.
    • Group 2: PH due to left heart disease: Results from left-sided heart failure, valvular disease, or congenital heart 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: Includes diseases such as sarcoidosis or metabolic disorders.
Pathophysiology
  • Increased Pulmonary Vascular Resistance:
    • PH results from vasoconstriction, vascular remodeling, and in situ thrombosis. Over time, this increases pulmonary vascular resistance (PVR), raising pressures in the pulmonary circulation.
  • Right Ventricular Hypertrophy and Failure:
    • The right ventricle compensates by hypertrophying to manage the increased afterload. Persistent pressure overload leads to right ventricular (RV) dilation and failure, also known as cor pulmonale.
  • Hypoxic Vasoconstriction:
    • In Group 3 PH, chronic lung diseases (e.g., COPD) cause alveolar hypoxia, leading to reflex pulmonary vasoconstriction and increased pulmonary artery pressures.
Risk Factors
  • Group 1 PAH:
    • Genetic mutations (e.g., BMPR2) are associated with heritable PAH. Other risk factors include female sex, HIV, and the use of appetite-suppressing drugs.
  • Group 2 PH:
    • Caused by heart diseases such as heart failure with reduced ejection fraction (HFrEF), heart failure with preserved ejection fraction (HFpEF), and mitral valve disease.
  • Group 3 PH:
    • Lung diseases like COPD, ILD, and sleep apnea are significant risk factors. These conditions cause chronic hypoxia, triggering pulmonary vasoconstriction and vascular remodeling.
  • Group 4 PH (CTEPH):
    • Chronic pulmonary embolism is the leading cause. Thrombi that remain unresolved cause pulmonary artery obstruction and increase pulmonary pressure.
Clinical Features
  • Symptoms:
    • Dyspnea on exertion: Most common presenting symptom due to impaired oxygen exchange and right heart strain.
    • Fatigue, syncope, and chest pain: Occur with advanced disease.
    • Peripheral edema, ascites, and jugular venous distension (JVD): Signs of right heart failure.
  • Physical Exam:
    • Loud P2 (accentuated second heart sound) due to increased pulmonary pressure.
    • Right ventricular heave: Due to RV hypertrophy.
    • Signs of RV failure: Peripheral edema, hepatomegaly, ascites.
Diagnosis
  • Echocardiography:
    • The initial test for assessing pulmonary pressures and RV function. It may show RV hypertrophy, dilatation, and elevated right-sided pressures.
  • Right Heart Catheterization (RHC):
    • The gold standard to confirm PH. It measures mPAP, pulmonary vascular resistance (PVR), and other hemodynamic parameters.
  • Other Diagnostic Tests:
    • Pulmonary Function Tests (PFTs): Useful in Group 3 PH to diagnose underlying lung disease.
    • Ventilation-Perfusion (V/Q) Scan: Key test for detecting CTEPH.
Management
General Management
  • Oxygen Therapy:
    • Indicated for patients with hypoxemia, especially in Group 3 PH due to chronic lung disease.
  • Diuretics:
    • Used to manage symptoms of right heart failure, such as peripheral edema and ascites.
Group 1 PAH-Specific Therapy
  • Endothelin Receptor Antagonists (ERAs):
    • Drugs like bosentan and ambrisentan reduce vasoconstriction, improving pulmonary artery pressure and symptoms.
  • Phosphodiesterase-5 Inhibitors (PDE-5 inhibitors):
    • Sildenafil and tadalafil increase nitric oxide availability, promoting vasodilation.
  • Prostacyclin Analogs:
    • Epoprostenol and treprostinil are potent vasodilators used in severe cases to improve survival.
  • Soluble Guanylate Cyclase (sGC) Stimulators:
    • Riociguat enhances the effects of nitric oxide, lowering pulmonary pressures.
Surgical Intervention
  • Pulmonary Endarterectomy:
    • Surgical removal of thromboembolic material in CTEPH, often curative.
  • Lung Transplant:
    • Considered for patients with refractory PAH or advanced disease despite medical therapy.
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, fatigue, syncope, and signs of right heart failure (e.g., edema, ascites).
  • Echocardiography is the first-line diagnostic tool, but right heart catheterization is needed to confirm the diagnosis.
  • Management involves oxygen therapy, diuretics, and disease-specific treatments like endothelin receptor antagonists or prostacyclin analogs for Group 1 PAH.
  • Surgical options such as pulmonary endarterectomy for CTEPH and lung transplantation are reserved for advanced cases.

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