Congestive Heart Failure (CHF) for USMLE Step 3 / COMLEX-USA Level 3
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Overview of Congestive Heart Failure (CHF)
- Definition: CHF is a clinical syndrome where the heart cannot pump sufficient blood to meet the body’s needs, leading to symptoms like fluid retention and reduced oxygen delivery.
Pathophysiology
- Decreased Cardiac Output: Results from impaired contractility, increased afterload, or impaired diastolic filling.
- Compensatory Mechanisms:
- Activation of the renin-angiotensin-aldosterone system (RAAS), leading to sodium and water retention.
- Sympathetic nervous system activation, causing vasoconstriction.
- Left ventricular hypertrophy and remodeling, which worsen heart failure over time.
Causes
- Ischemic Heart Disease: The most common cause of CHF in developed countries.
- Hypertension: Leads to left ventricular hypertrophy and increased myocardial oxygen demand.
- Cardiomyopathies: Includes dilated, hypertrophic, and restrictive cardiomyopathy.
- Valvular Heart Disease: Disorders such as aortic stenosis or mitral regurgitation.
- Other Causes: Alcohol use, drugs (e.g., chemotherapy agents like doxorubicin), infections, and endocrine disorders like hyperthyroidism.
Symptoms and Signs
- Left-Sided Heart Failure:
- Pulmonary symptoms: Dyspnea, orthopnea, and paroxysmal nocturnal dyspnea (PND).
- Signs of pulmonary congestion: Crackles, pulmonary edema, and reduced oxygen saturation.
- Right-Sided Heart Failure:
- Peripheral symptoms: Peripheral edema, ascites, hepatomegaly, and jugular venous distention (JVD).
- Systemic Symptoms: Fatigue, decreased exercise tolerance, anorexia, and weight gain due to fluid retention.
Diagnostic Workup
- Echocardiography: Key test to assess ejection fraction and heart structure.
- BNP/NT-proBNP Levels: Elevated in heart failure, helping differentiate CHF from other causes of dyspnea.
- Chest X-ray: Can show cardiomegaly, pulmonary edema, or pleural effusions.
- ECG: May show ischemia, arrhythmias, or evidence of left ventricular hypertrophy.
Management
- Diuretics: For symptomatic relief of fluid overload (e.g., furosemide).
- RAAS Inhibitors: ACE inhibitors or ARBs to reduce mortality and disease progression.
- Beta-Blockers: Improve survival and reduce hospitalizations.
- Mineralocorticoid Receptor Antagonists: Spironolactone to reduce morbidity and mortality.
- Device Therapy: Implantable cardioverter-defibrillators (ICDs) and biventricular pacemakers for selected patients.
- Lifestyle Modifications: Dietary sodium restriction, fluid management, and exercise.
Essential Points
- Key Diagnostic Tools: Echocardiography, BNP/NT-proBNP, and chest X-ray are essential for diagnosis and monitoring.
- Compensatory Mechanisms: RAAS and sympathetic nervous system activation initially help but ultimately worsen CHF.
- Prognosis and Management: Focus on reducing mortality and improving quality of life through medical therapy, device therapy, and lifestyle changes.
- Heart Failure with Preserved Ejection Fraction (HFpEF): Requires different management strategies, focusing more on symptom relief.