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Heart Failure for USMLE Step 2

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Heart Failure for the USMLE Step 2 Exam
  • Definition: Heart failure (HF) is a condition where the heart cannot pump sufficient blood to meet the body’s needs. It is commonly classified by ejection fraction:
    • Heart Failure with Reduced Ejection Fraction (HFrEF): EF ≤40%, typically involving systolic dysfunction.
    • Heart Failure with Preserved Ejection Fraction (HFpEF): EF ≥50%, involving diastolic dysfunction.
    • Heart Failure with Mid-Range Ejection Fraction (HFmrEF): EF 41-49%, with features of both HFrEF and HFpEF.
Pathophysiology
left heart failure pathophysiology
  • Systolic Dysfunction (HFrEF):
    • Results from impaired myocardial contractility, reducing stroke volume and ejection fraction.
    • Common causes include ischemic heart disease (e.g., myocardial infarction), chronic hypertension, and dilated cardiomyopathy.
    • Left ventricular (LV) dilation and increased wall stress lead to progressive remodeling and worsening cardiac function.
  • Diastolic Dysfunction (HFpEF):
    • Characterized by impaired ventricular relaxation and filling due to stiffened LV walls, leading to increased LV end-diastolic pressure.
    • Commonly associated with chronic hypertension, aging, left ventricular hypertrophy, and diabetes.
    • While EF is preserved, reduced diastolic filling limits cardiac output, especially under stress.
  • Compensatory Mechanisms:
    • Neurohormonal Activation:
    • The renin-angiotensin-aldosterone system (RAAS) increases blood volume and blood pressure but also causes fluid retention and increased afterload, exacerbating HF.
    • The Sympathetic Nervous System increases heart rate and contractility but can lead to long-term cardiac remodeling and increased oxygen demand.
    • Ventricular Remodeling: Persistent overload promotes hypertrophy, fibrosis, and structural changes, worsening HF over time.
Clinical Presentation
  • Left-Sided Heart Failure:
    • Symptoms: Dyspnea, orthopnea, and paroxysmal nocturnal dyspnea (PND) due to pulmonary congestion.
    • Signs: Pulmonary rales, S3 or S4 heart sounds, and pleural effusions.
  • Right-Sided Heart Failure:
    • Symptoms: Peripheral edema, ascites, and abdominal discomfort from hepatic congestion.
    • Signs: Jugular venous distention (JVD), hepatomegaly, and hepatojugular reflux.
  • General Findings: Fatigue, exercise intolerance, and signs of hypoperfusion in advanced HF, such as cool extremities.
Diagnostic Evaluation
  • Laboratory Tests:
    • Brain Natriuretic Peptide (BNP) and NT-proBNP: Elevated levels help diagnose HF and correlate with disease severity.
    • Electrolytes, Renal Function: Monitor due to potential neurohormonal activation and medication effects.
  • Imaging:
    • Echocardiography: Primary tool to assess ejection fraction, ventricular size, wall motion, and valvular function.
    • Chest X-ray: May reveal cardiomegaly, pulmonary congestion, or pleural effusion.
  • Functional Classification:
    • NYHA Class: Grades symptoms on exertion, from I (no limitation) to IV (symptoms at rest).
Management of Heart Failure
Heart Failure with Reduced Ejection Fraction (HFrEF)
  • Pharmacologic Therapy:
    • ACE Inhibitors or ARBs: Reduce afterload, improve survival, and reduce symptoms.
    • Beta-Blockers: Improve mortality and prevent remodeling; commonly used agents include carvedilol, metoprolol succinate, and bisoprolol.
    • Aldosterone Antagonists (e.g., spironolactone): Recommended for patients with symptomatic HF and EF ≤35% to reduce mortality.
    • SGLT2 Inhibitors (e.g., dapagliflozin): Shown to improve outcomes in HFrEF.
    • Diuretics: Provide symptomatic relief for volume overload; loop diuretics are preferred but do not impact mortality.
Heart Failure with Preserved Ejection Fraction (HFpEF)
  • Management:
    • Diuretics: Used to relieve volume overload.
    • Blood Pressure Control: Reduces risk of further LV stiffening and worsened diastolic dysfunction.
    • Mineralocorticoid Receptor Antagonists: Spironolactone may benefit select HFpEF patients by reducing hospitalizations.
    • SGLT2 Inhibitors: Emerging evidence shows benefit in reducing hospitalizations and improving quality of life.
  • Management of Comorbidities:
    • Control of hypertension, atrial fibrillation, diabetes, and obesity is crucial in HFpEF management.
Key Points
  • Types of Heart Failure:
    • HFrEF involves reduced ejection fraction and systolic dysfunction.
    • HFpEF involves preserved ejection fraction with diastolic dysfunction.
    • HFmrEF has features of both HFrEF and HFpEF, with an EF of 41-49%.
  • Pathophysiology:
    • Systolic dysfunction reduces stroke volume; diastolic dysfunction increases LV end-diastolic pressure.
    • Neurohormonal activation and remodeling worsen HF over time.
  • Clinical Features:
    • Left-sided HF causes pulmonary symptoms (dyspnea, orthopnea), while right-sided HF causes systemic symptoms (edema, ascites).
  • Diagnostics:
    • BNP/NT-proBNP levels aid diagnosis and assess severity.
    • Echocardiography is essential for evaluating ejection fraction and ventricular function.
  • Management of HFrEF:
    • ACE inhibitors, beta-blockers, aldosterone antagonists, and SGLT2 inhibitors improve outcomes.
    • Diuretics provide symptom relief but do not reduce mortality.
  • Management of HFpEF:
    • Focused on symptom control and management of comorbidities, with no proven mortality benefit.

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