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Pulmonary Hypertension for ABIM

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Pulmonary Hypertension for the American Board of Internal Medicine Exam
Pulmonary arterial pressure
Definition and Classification
  • Pulmonary Hypertension (PH):
    • Pulmonary hypertension (PH) is defined as a mean pulmonary artery pressure (mPAP) ≥ 20 mmHg at rest, measured by right heart catheterization (RHC). It results from elevated pressure in the pulmonary vasculature, leading to right ventricular (RV) dysfunction and heart failure.
  • WHO Classification:
    • PH is classified into five groups based on etiology and pathophysiology:
    • Group 1: Pulmonary arterial hypertension (PAH): Includes idiopathic PAH, heritable PAH, drug-induced, and associated conditions (e.g., connective tissue diseases, HIV, congenital heart disease).
    • Group 2: PH due to left heart disease: Includes left ventricular systolic or diastolic dysfunction, valvular heart disease, and congenital/acquired left heart inflow/outflow tract obstruction.
    • Group 3: PH due to lung diseases and/or hypoxia: Includes 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 embolism (PE) leading to chronic obstruction and vascular remodeling.
    • Group 5: PH with unclear or multifactorial mechanisms: Includes sarcoidosis, metabolic disorders, and hematologic disorders (e.g., myeloproliferative diseases).
Pathophysiology
  • Pulmonary Vascular Changes:
    • In PAH, there is dysfunction of the pulmonary endothelial cells, leading to vasoconstriction, vascular remodeling, and thrombosis within the small pulmonary arteries.
    • Increased pulmonary vascular resistance (PVR) eventually results in right ventricular hypertrophy and failure due to the increased afterload.
  • Right Ventricular Strain:
    • The right ventricle, designed to handle low pressures, hypertrophies and dilates in response to increased pulmonary pressures. Over time, this leads to right ventricular failure, with symptoms of cor pulmonale (peripheral edema, ascites, jugular venous distention).
  • V/Q Mismatch and Hypoxia:
    • In Group 3 PH (due to lung disease), chronic hypoxia results in vasoconstriction of the pulmonary arteries and increased pressure in the pulmonary circulation.
Risk Factors
  • Idiopathic and Heritable PAH:
    • Mutations in the BMPR2 gene are implicated in hereditary PAH, predisposing patients to abnormal vascular proliferation and increased pulmonary pressures.
    • Female sex, younger age, and the use of appetite suppressants (e.g., fenfluramine) are risk factors for idiopathic PAH.
  • Chronic Lung Disease:
    • Conditions such as COPD, interstitial lung disease, and obstructive sleep apnea contribute to PH through mechanisms of chronic hypoxia and alveolar destruction.
  • Left Heart Disease:
    • Heart failure with reduced or preserved ejection fraction (HFrEF or HFpEF), valvular heart diseases, and congenital heart defects are leading causes of Group 2 PH.
  • Thromboembolic Disease:
    • Patients with a history of pulmonary embolism are at risk of developing CTEPH, a condition where the emboli become chronic, causing increased pulmonary pressures.
Clinical Features
  • Symptoms:
    • Dyspnea on exertion: Most common presenting symptom, gradually progressive.
    • Fatigue: Due to impaired oxygen transport and poor cardiac output.
    • Chest pain: Often described as exertional angina due to RV ischemia.
    • Syncope: Associated with exertion due to decreased cardiac output and RV dysfunction.
    • Edema and Ascites: Signs of right heart failure and cor pulmonale.
  • Physical Exam Findings:
    • Loud P2: Accentuated second heart sound due to increased pressure in the pulmonary artery.
    • Jugular venous distention (JVD), peripheral edema, hepatomegaly, and ascites: Indicate right heart failure.
    • Right ventricular heave or palpable impulse due to RV hypertrophy.
Diagnosis
Non-Invasive Testing
  • Echocardiography:
    • First-line imaging test for suspected PH, showing elevated pulmonary artery pressures, right ventricular hypertrophy, and tricuspid regurgitation. It also helps to assess left heart function, which is critical for identifying Group 2 PH.
  • Electrocardiogram (ECG):
    • May show signs of right heart strain, including right axis deviation, RV hypertrophy, RBBB, or p-pulmonale (peaked P waves).
  • Chest X-ray:
    • Shows enlarged pulmonary arteries and right ventricular enlargement in advanced cases of PH. Additionally, it may show lung disease (e.g., emphysema) in Group 3 PH.
Right Heart Catheterization
  • Right Heart Catheterization (RHC):
    • Gold standard for confirming the diagnosis of PH. RHC measures the mean pulmonary artery pressure (mPAP), pulmonary vascular resistance (PVR), and right atrial pressure (RAP).
    • An mPAP ≥20 mmHg is diagnostic of PH, and increased PVR confirms PAH.
Other Tests
  • Pulmonary Function Tests (PFTs):
    • Useful in diagnosing underlying lung disease, particularly in Group 3 PH.
    • Decreased DLCO (diffusion capacity of the lung for carbon monoxide) is seen in PAH.
  • V/Q Scan:
    • Essential for diagnosing CTEPH, which presents as areas of ventilation-perfusion mismatch.
Management
General Measures
  • Oxygen Therapy:
    • Recommended in patients with Group 3 PH (due to chronic lung disease) to reduce hypoxic vasoconstriction and improve exercise tolerance.
  • Diuretics:
    • Used to manage right heart failure symptoms, such as edema and ascites, by reducing fluid overload.
  • Anticoagulation:
    • Lifelong anticoagulation is recommended in CTEPH and idiopathic PAH, given the increased risk of thrombotic events.
Specific Therapies for PAH (Group 1 PH)
  • Endothelin Receptor Antagonists (ERAs):
    • Bosentan and ambrisentan reduce vasoconstriction by blocking the endothelin pathway, improving exercise capacity and slowing disease progression.
  • Phosphodiesterase-5 Inhibitors:
    • Sildenafil and tadalafil promote vasodilation by increasing cyclic GMP levels, improving pulmonary hemodynamics and exercise capacity.
  • Prostacyclin Analogs:
    • Epoprostenol, treprostinil, and iloprost are potent vasodilators that improve survival in patients with severe PAH.
  • Soluble Guanylate Cyclase Stimulators:
    • Riociguat enhances nitric oxide signaling and is used in both PAH and CTEPH to reduce pulmonary artery pressures.
Surgical and Interventional Therapies
  • Pulmonary Endarterectomy:
    • A surgical option for patients with CTEPH to remove chronic thrombi from the pulmonary arteries, offering potential curative outcomes.
  • Atrial Septostomy:
    • Performed in severe PAH to create a right-to-left shunt, decreasing RV pressure and improving cardiac output in refractory cases.
  • Lung Transplantation:
    • Reserved for end-stage PH refractory to medical therapy, particularly in young patients with idiopathic PAH.
Key Points
  • Pulmonary hypertension is defined as a mean pulmonary artery pressure ≥20 mmHg and is classified into five groups based on underlying etiology.
  • Right heart failure is a major consequence of untreated PH, and symptoms include dyspnea, fatigue, chest pain, and signs of cor pulmonale (edema, ascites).
  • Diagnosis is confirmed with right heart catheterization, and echocardiography is the initial non-invasive test to assess pulmonary pressures and RV function.
  • Management includes oxygen therapy, diuretics, and disease-specific treatments such as endothelin receptor antagonists, phosphodiesterase-5 inhibitors, and prostacyclin analogs.
  • Patients with chronic thromboembolic pulmonary hypertension (CTEPH) may benefit from pulmonary endarterectomy.

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