Cardiomyopathies for USMLE Step 2
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Cardiomyopathies for the USMLE Step 2 Exam
- Definition: Cardiomyopathies are disorders affecting the heart muscle, impacting the heart's structure and function. For Step 2, focus is on dilated, hypertrophic, and restrictive cardiomyopathies, as well as arrhythmogenic right ventricular cardiomyopathy (ARVC).
- Clinical Importance: Cardiomyopathies are a leading cause of heart failure, arrhythmias, and sudden cardiac death.
Dilated Cardiomyopathy (DCM)
- Definition: DCM involves dilation and impaired contractility of the left or both ventricles, leading to systolic dysfunction and heart failure.
- Etiology:
- Idiopathic: Most common cause of DCM.
- Genetic: Often involves mutations in genes coding for cytoskeletal proteins.
- Toxic: Alcohol, cocaine, and chemotherapeutic agents (e.g., doxorubicin).
- Infectious: Viral myocarditis, particularly from Coxsackievirus B.
- Metabolic: Hemochromatosis, thyroid disease.
- Pathophysiology:
- Ventricular dilation leads to increased wall stress and decreased contractility, with a reduced ejection fraction.
- Progressive remodeling worsens heart failure over time.
- Clinical Manifestations:
- Signs of left and right heart failure (e.g., dyspnea, orthopnea, peripheral edema).
- Arrhythmias, especially atrial fibrillation, are common.
- Diagnosis:
- Echocardiogram: Enlarged ventricles, reduced ejection fraction.
- ECG: Left bundle branch block, nonspecific ST-T changes.
- Management:
- Medications: ACE inhibitors, beta-blockers, diuretics, and aldosterone antagonists.
- Device Therapy: ICDs may be indicated for high-risk patients to prevent sudden cardiac death.
Hypertrophic Cardiomyopathy (HCM)
- Definition: HCM is a genetic disorder leading to left ventricular hypertrophy (LVH) that can obstruct blood flow out of the left ventricle.
- Etiology:
- Genetic: Autosomal dominant mutations in sarcomere proteins (e.g., MYH7, MYBPC3).
- Pathophysiology:
- Asymmetric hypertrophy, often affecting the septum, may obstruct the left ventricular outflow tract (LVOT).
- Myocyte disarray and fibrosis contribute to increased risk of arrhythmias and sudden cardiac death, particularly in young athletes.
- Clinical Manifestations:
- Dyspnea on exertion, chest pain, syncope, and sudden cardiac death.
- Murmur: Harsh systolic murmur at the left sternal border, which increases with Valsalva or standing.
- Diagnosis:
- Echocardiogram: Shows asymmetric septal hypertrophy and potential LVOT obstruction.
- ECG: LVH, deep Q waves in inferior and lateral leads.
- Management:
- Medications: Beta-blockers or non-dihydropyridine calcium channel blockers (e.g., verapamil) to improve filling and reduce symptoms.
- Interventional Therapy: Septal myectomy or alcohol septal ablation if LVOT obstruction is severe.
- ICD: Recommended for patients at high risk of sudden cardiac death.
Restrictive Cardiomyopathy (RCM)
- Definition: RCM is characterized by stiff ventricular walls that impair diastolic filling, usually without significant hypertrophy.
- Etiology:
- Infiltrative Diseases: Amyloidosis is the most common cause, followed by sarcoidosis.
- Fibrotic Diseases: Radiation-induced fibrosis and endomyocardial fibrosis.
- Pathophysiology:
- Increased stiffness limits ventricular filling, leading to elevated atrial pressures and biatrial enlargement.
- Systolic function is often preserved until later stages.
- Clinical Manifestations:
- Signs of right heart failure, including peripheral edema, hepatomegaly, and jugular venous distension.
- Kussmaul’s sign: Increased jugular venous pressure with inspiration.
- Diagnosis:
- Echocardiogram: Normal ventricular size, restrictive filling pattern, biatrial enlargement.
- Cardiac MRI: Useful for identifying amyloid or fibrotic infiltration.
- Management:
- Treat Underlying Cause: For example, chemotherapy for amyloidosis.
- Symptomatic Treatment: Diuretics for volume overload, cautious use of beta-blockers.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
- Definition: ARVC is a genetic disorder causing fibro-fatty replacement of the right ventricular myocardium, leading to arrhythmias.
- Etiology:
- Genetic: Autosomal dominant mutations in desmosomal proteins (e.g., plakoglobin, desmoplakin).
- Pathophysiology:
- Fibro-fatty infiltration causes conduction abnormalities and increases risk of ventricular arrhythmias, especially during exercise.
- Clinical Manifestations:
- Palpitations, syncope, and sudden cardiac death.
- Diagnosis:
- ECG: Epsilon wave in leads V1-V3 (small positive deflection at the end of QRS).
- Cardiac MRI: Shows characteristic right ventricular fatty infiltration.
- Management:
- Lifestyle Modification: Avoid strenuous exercise.
- ICD: Recommended for patients at high risk of sudden cardiac death.
Key Points
- Dilated Cardiomyopathy (DCM):
- Causes include genetics, toxins, infections, and metabolic diseases.
- Presents with systolic dysfunction and heart failure symptoms.
- Managed with heart failure medications and ICDs for select patients.
- Hypertrophic Cardiomyopathy (HCM):
- Caused by genetic mutations in sarcomere proteins.
- Can lead to LVOT obstruction, SCD, and presents with a murmur that increases with Valsalva.
- Managed with beta-blockers, lifestyle modifications, and ICDs for high-risk individuals.
- Restrictive Cardiomyopathy (RCM):
- Often due to infiltrative diseases, such as amyloidosis.
- Characterized by diastolic dysfunction and right-sided heart failure symptoms.
- Treatment focuses on symptom management and addressing the underlying disease.
- Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC):
- Genetic disease with risk of ventricular arrhythmias.
- Presents with Epsilon waves on ECG and fibro-fatty changes on cardiac MRI.
- Managed with lifestyle changes and ICD for SCD prevention.