Heart Failure for USMLE Step 1
Heart Failure for the USMLE Step 1 Exam
- Definition: Heart failure (HF) is a syndrome in which the heart cannot adequately pump blood to meet the body’s metabolic demands. It can be classified based on the type of dysfunction:
- Heart Failure with Reduced Ejection Fraction (HFrEF): EF ≤40%; primarily due to systolic dysfunction.
- Heart Failure with Preserved Ejection Fraction (HFpEF): EF ≥50%; primarily due to diastolic dysfunction.
Pathophysiology
- Systolic Dysfunction (HFrEF):
- Caused by impaired myocardial contractility, leading to reduced stroke volume and cardiac output.
- Common etiologies include ischemic heart disease (myocardial infarction), chronic hypertension, and dilated cardiomyopathy.
- Left ventricular (LV) dilation occurs as a compensatory response, but this increases wall stress, worsening contractility over time.
- Diastolic Dysfunction (HFpEF):
- Characterized by impaired ventricular filling due to stiff or hypertrophic ventricles, resulting in elevated end-diastolic pressure.
- Often due to chronic hypertension, aging, and left ventricular hypertrophy.
- Although EF is preserved, reduced diastolic filling limits stroke volume and leads to symptoms.
- Compensatory Mechanisms:
- Neurohormonal Activation:
- The renin-angiotensin-aldosterone system (RAAS) increases blood pressure and blood volume through vasoconstriction and sodium retention, leading to volume overload.
- The Sympathetic Nervous System increases heart rate and contractility but also raises myocardial oxygen demand and can lead to worsening fibrosis and remodeling.
- Ventricular Remodeling: Hypertrophy and fibrosis occur in response to chronic pressure or volume overload, leading to progressive decline in cardiac function.
Clinical Presentation
- Left-Sided Heart Failure:
- Symptoms: Dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea (PND) due to pulmonary congestion.
- Signs: Pulmonary rales, S3 heart sound, and possible pleural effusions.
- Right-Sided Heart Failure:
- Symptoms: Peripheral edema, ascites, and abdominal discomfort from liver congestion.
- Signs: Jugular venous distention (JVD), hepatomegaly, and hepatojugular reflux.
- General Symptoms: Fatigue, weakness, and exercise intolerance due to low cardiac output.
Diagnostic Evaluation
- BNP/NT-proBNP Levels:
- Biomarkers released in response to ventricular stretch; elevated levels support the diagnosis of HF and correlate with disease severity.
- Echocardiogram:
- Essential for assessing ejection fraction, ventricular size, wall motion abnormalities, and valvular function.
- Identifies type of dysfunction (systolic vs. diastolic) and other structural abnormalities.
- Chest X-Ray:
- May show cardiomegaly, pulmonary congestion, or pleural effusions in patients with HF.
Management of Heart Failure
Heart Failure with Reduced Ejection Fraction (HFrEF)
- Pharmacologic Therapy:
- ACE Inhibitors/ARBs: Reduce afterload and improve survival by inhibiting RAAS.
- Beta-Blockers: Improve mortality by reducing heart rate and myocardial oxygen demand. Common agents include carvedilol and metoprolol succinate.
- Aldosterone Antagonists: Used in patients with symptomatic HF to reduce fluid retention and improve outcomes.
- Diuretics: Primarily loop diuretics (e.g., furosemide) for volume control in symptomatic patients, though they do not improve mortality.
Heart Failure with Preserved Ejection Fraction (HFpEF)
- Management:
- No therapies have proven mortality benefit in HFpEF. Treatment focuses on symptom relief and controlling comorbidities like hypertension and diabetes.
- Diuretics: Used to manage volume overload.
- Blood Pressure Control: Essential to prevent further worsening of diastolic dysfunction.
Key Points
- Heart Failure Classifications:
- HFrEF (EF ≤40%) involves systolic dysfunction, commonly from myocardial infarction or dilated cardiomyopathy.
- HFpEF (EF ≥50%) involves diastolic dysfunction, often due to chronic hypertension and left ventricular hypertrophy.
- Pathophysiology:
- Systolic dysfunction leads to low cardiac output and ventricular dilation.
- Diastolic dysfunction causes elevated filling pressures, leading to pulmonary congestion.
- Neurohormonal Activation:
- RAAS and sympathetic activation help maintain perfusion but worsen HF over time through fluid retention, vasoconstriction, and fibrosis.
- Clinical Manifestations:
- Left-sided HF causes pulmonary symptoms (dyspnea, orthopnea); right-sided HF causes systemic symptoms (edema, ascites).
- Key Management for HFrEF:
- ACE inhibitors, beta-blockers, and aldosterone antagonists improve survival.
- Diuretics provide symptom relief for volume overload but do not affect survival.
- HFpEF Management:
- Primarily symptom-focused, with blood pressure control and diuretics for volume management.