Cardiomyopathies for USMLE Step 1
Start your One-Week Free Trial
Already subscribed? Log in »
Cardiomyopathies for the USMLE Step 1 Exam
- Definition: Cardiomyopathies are diseases of the myocardium (heart muscle) affecting the heart's ability to contract and pump blood effectively.
- Types: The three main types relevant for Step 1 are dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), and restrictive cardiomyopathy (RCM).
Dilated Cardiomyopathy (DCM)
- Definition: DCM involves enlargement and impaired contractility of one or both ventricles, leading to systolic dysfunction and decreased ejection fraction.
- Etiology:
- Idiopathic: Accounts for many cases without an identified cause.
- Genetic: Mutations in cytoskeletal proteins like dystrophin.
- Toxic: Alcohol, cocaine, and chemotherapy agents (e.g., doxorubicin).
- Infectious: Commonly viral, particularly Coxsackievirus B.
- Metabolic: Disorders such as hemochromatosis and thyroid dysfunction.
- Pathophysiology:
- Ventricular dilation increases wall stress and reduces contractility, leading to heart failure symptoms.
- Elevated left ventricular (LV) end-diastolic volume and pressure can cause pulmonary congestion.
- Clinical Manifestations:
- Symptoms of heart failure, including dyspnea, fatigue, orthopnea, and edema.
- Arrhythmias (e.g., atrial fibrillation) and risk of thromboembolism.
- Diagnosis:
- Echocardiogram: Enlarged ventricles with reduced ejection fraction.
- ECG: May show nonspecific changes, such as left bundle branch block (LBBB).
- Management:
- Focus on standard heart failure treatments: ACE inhibitors, beta-blockers, diuretics, and lifestyle modifications.
Hypertrophic Cardiomyopathy (HCM)
- Definition: HCM is a genetic disorder characterized by left ventricular hypertrophy (LVH), often asymmetric, that may obstruct blood flow.
- Etiology:
- Genetic: Autosomal dominant mutations in sarcomere proteins (e.g., MYH7, MYBPC3).
- Pathophysiology:
- Asymmetric septal hypertrophy can obstruct the left ventricular outflow tract (LVOT), increasing afterload and reducing cardiac output.
- Myocyte disarray and fibrosis increase arrhythmia risk and sudden cardiac death, particularly during exertion.
- Clinical Manifestations:
- Dyspnea on exertion, angina, and syncope.
- Harsh systolic murmur at the left sternal border, which increases with Valsalva maneuver or standing.
- Diagnosis:
- Echocardiogram: Asymmetric septal hypertrophy, often with LVOT obstruction.
- ECG: LVH and deep Q waves in the inferior and lateral leads.
- Management:
- Medications: Beta-blockers to reduce heart rate and improve filling time.
- Lifestyle: Patients are advised to avoid intense physical activity due to SCD risk.
Restrictive Cardiomyopathy (RCM)
- Definition: RCM is characterized by stiff ventricular walls, which impair diastolic filling but often preserve systolic function.
- Etiology:
- Infiltrative Diseases: Most commonly due to amyloidosis, sarcoidosis, or hemochromatosis.
- Idiopathic: No known underlying cause in some cases.
- Pathophysiology:
- Stiff, non-compliant ventricles increase atrial pressures, causing biatrial enlargement and elevated jugular venous pressure (JVP).
- Clinical Manifestations:
- Signs of right heart failure (e.g., peripheral edema, hepatomegaly).
- Kussmaul’s sign: Increased JVP with inspiration.
- Diagnosis:
- Echocardiogram: Normal ventricular size, restrictive filling pattern, and biatrial enlargement.
- Cardiac MRI: Helps distinguish from constrictive pericarditis.
- Management:
- Symptom Management: Diuretics for fluid overload; limited use of beta-blockers to control rate.
Key Points
- Dilated Cardiomyopathy (DCM):
- Causes include genetic mutations, viral infections, and toxins.
- Characterized by ventricular dilation and systolic dysfunction.
- Treated with standard heart failure medications.
- Hypertrophic Cardiomyopathy (HCM):
- Genetic mutations in sarcomere proteins lead to LVH and risk of sudden cardiac death.
- Causes a harsh murmur that increases with Valsalva.
- Managed with beta-blockers and lifestyle modifications to reduce SCD risk.
- Restrictive Cardiomyopathy (RCM):
- Primarily due to infiltrative diseases, such as amyloidosis.
- Characterized by diastolic dysfunction and right-sided heart failure symptoms.
- Management focuses on symptom relief and treating underlying causes.