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Heart Failure for USMLE Step 3

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Heart Failure for the USMLE Step 3 Exam
  • Definition: Heart failure (HF) is a condition in which the heart is unable to pump adequate blood to meet the body’s needs. It is primarily classified by ejection fraction:
    • Heart Failure with Reduced Ejection Fraction (HFrEF): EF ≤40%, associated with systolic dysfunction.
    • Heart Failure with Preserved Ejection Fraction (HFpEF): EF ≥50%, associated with diastolic dysfunction.
    • Heart Failure with Mid-Range Ejection Fraction (HFmrEF): EF 41-49%, displaying characteristics of both HFrEF and HFpEF.
Pathophysiology
left heart failure pathophysiology
  • Systolic Dysfunction (HFrEF):
    • Occurs due to reduced myocardial contractility, leading to decreased ejection fraction and stroke volume.
    • Common causes include ischemic heart disease (e.g., myocardial infarction), chronic hypertension, and dilated cardiomyopathy.
    • Ventricular dilation and wall stress lead to progressive remodeling and worsening cardiac function.
  • Diastolic Dysfunction (HFpEF):
    • Characterized by impaired ventricular relaxation, resulting in reduced ventricular filling and elevated end-diastolic pressure.
    • Frequently associated with chronic hypertension, aging, diabetes, and left ventricular hypertrophy.
    • Leads to preserved EF but reduced filling volume and cardiac output, particularly under exertion.
  • Compensatory Mechanisms:
    • Neurohormonal Activation:
    • The renin-angiotensin-aldosterone system (RAAS) causes sodium and water retention, increasing blood volume and afterload, but also contributes to worsening HF over time.
    • The Sympathetic Nervous System increases heart rate and contractility, initially supporting cardiac output but later contributing to ventricular remodeling and fibrosis.
    • Ventricular Remodeling: Chronic overload causes hypertrophy and fibrosis, further impairing cardiac function and promoting disease progression.
Clinical Manifestations
  • Left-Sided Heart Failure:
    • Symptoms: Dyspnea, orthopnea, paroxysmal nocturnal dyspnea (PND) due to pulmonary congestion.
    • Signs: Pulmonary rales, S3 or S4 heart sounds, pleural effusion.
  • Right-Sided Heart Failure:
    • Symptoms: Peripheral edema, abdominal discomfort, and ascites from systemic congestion.
    • Signs: Jugular venous distention (JVD), hepatomegaly, and hepatojugular reflux.
  • General Symptoms: Fatigue, weakness, and exercise intolerance due to decreased cardiac output.
Diagnostic Evaluation
  • BNP and NT-proBNP Levels:
    • Useful in diagnosing HF and assessing severity, with higher levels indicating worse prognosis.
  • Echocardiography:
    • Essential to evaluate ejection fraction, wall motion, ventricular size, and valvular function.
  • Additional Imaging:
    • Chest X-ray: Identifies cardiomegaly, pulmonary congestion, and pleural effusions, often in acute HF exacerbations.
Management of Heart Failure
Heart Failure with Reduced Ejection Fraction (HFrEF)
  • Pharmacologic Therapy:
    • ACE Inhibitors/ARBs: First-line therapy to reduce afterload, improve survival, and decrease symptoms.
    • Beta-Blockers: Reduce mortality and prevent remodeling; commonly used agents include carvedilol, metoprolol succinate, and bisoprolol.
    • Aldosterone Antagonists (e.g., spironolactone): Indicated for patients with NYHA class II-IV HF and EF ≤35%, reducing mortality and hospitalizations.
    • SGLT2 Inhibitors (e.g., dapagliflozin): Recently approved to reduce HF exacerbations and improve survival.
    • Diuretics: Loop diuretics (e.g., furosemide) relieve volume overload but do not improve survival.
  • Device Therapy:
    • Implantable Cardioverter-Defibrillator (ICD): For primary prevention in patients with EF ≤35% at risk for sudden cardiac death.
    • Cardiac Resynchronization Therapy (CRT): For patients with EF ≤35%, NYHA class II-IV symptoms, and left bundle branch block with QRS ≥150 ms, improving symptoms and survival.
Heart Failure with Preserved Ejection Fraction (HFpEF)
  • Management Principles:
    • Focus is on symptom relief and management of comorbidities, as no therapies have shown mortality benefit in HFpEF.
    • Blood Pressure Control: Prevents further ventricular stiffening and optimizes cardiac function.
    • Diuretics: Used to manage volume overload in symptomatic patients.
    • Mineralocorticoid Receptor Antagonists (e.g., spironolactone): May benefit select patients, reducing hospitalizations.
    • SGLT2 Inhibitors: Emerging evidence supports their role in reducing hospitalizations and improving quality of life.
  • Management of Comorbidities:
    • Optimizing control of hypertension, atrial fibrillation, diabetes, and obesity is critical in HFpEF management.
Key Points
  • Types of Heart Failure:
    • HFrEF involves systolic dysfunction with EF ≤40%.
    • HFpEF involves diastolic dysfunction with EF ≥50%.
    • HFmrEF represents intermediate EF (41-49%) with mixed characteristics.
  • Compensatory Mechanisms:
    • RAAS and sympathetic activation support cardiac output but ultimately worsen HF through remodeling and fibrosis.
  • Clinical Features:
    • Left-sided HF presents with pulmonary symptoms; right-sided HF causes systemic congestion.
  • Diagnosis:
    • BNP/NT-proBNP and echocardiography are key diagnostic tools.
    • Chest X-ray can provide evidence of pulmonary congestion in acute cases.
  • Management of HFrEF:
    • ACE inhibitors, beta-blockers, aldosterone antagonists, and SGLT2 inhibitors improve survival.
    • ICD and CRT are recommended for select patients with reduced EF to prevent sudden cardiac death.
  • Management of HFpEF:
    • Primarily symptom-focused, with diuretics for volume overload and blood pressure management. No proven therapies for mortality benefit.

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