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Cardiomyopathies for ABIM

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Cardiomyopathies for the American Board of Internal Medicine Exam
  • Definition: Cardiomyopathies are diseases of the heart muscle that impair its ability to pump blood. They can be classified as primary (inherited or idiopathic) or secondary (due to systemic diseases or conditions).
  • Types: The main types are dilated, hypertrophic, restrictive, and arrhythmogenic right ventricular cardiomyopathy (ARVC).
Dilated Cardiomyopathy (DCM)
  • Definition: DCM is characterized by enlargement and impaired contraction of the left or both ventricles.
  • Etiology:
    • Idiopathic: Accounts for about 50% of cases.
    • Genetic: Often associated with mutations in genes related to cytoskeletal and sarcomeric proteins.
    • Infectious: Viral myocarditis (e.g., Coxsackievirus B) is a common infectious cause.
    • Toxic: Alcohol, cocaine, and chemotherapy agents (e.g., doxorubicin).
    • Metabolic: Diabetes, thyroid dysfunction.
  • Pathophysiology:
    • Left ventricular dilation leads to systolic dysfunction, reduced ejection fraction (EF), and subsequent heart failure.
    • Elevated ventricular volumes increase wall stress, which can lead to remodeling and worsening function.
dilated cardiomyopathy
  • Clinical Manifestations:
    • Symptoms of heart failure: dyspnea, fatigue, orthopnea, paroxysmal nocturnal dyspnea.
    • Arrhythmias, especially atrial fibrillation.
    • Embolic events due to blood stasis in the dilated ventricle.
  • Diagnosis:
    • Echocardiogram: Shows dilated left ventricle, reduced EF.
    • ECG: Nonspecific findings; may show left ventricular hypertrophy, bundle branch block.
    • Cardiac MRI: Useful for assessing myocardial fibrosis.
  • Management:
    • Medications: Beta-blockers, ACE inhibitors or ARBs, diuretics, and aldosterone antagonists.
    • Device Therapy: Implantable cardioverter-defibrillator (ICD) for patients at risk of sudden cardiac death (SCD).
    • Advanced Therapies: Heart transplant for refractory cases.
Hypertrophic Cardiomyopathy (HCM)
  • Definition: HCM is a genetic disorder characterized by abnormal myocardial hypertrophy, primarily affecting the left ventricle.
  • Etiology:
    • Genetic: Autosomal dominant mutations in sarcomere genes (e.g., MYH7, MYBPC3).
  • Pathophysiology:
    • Asymmetric septal hypertrophy can obstruct left ventricular outflow, leading to increased afterload and diastolic dysfunction.
    • Myocyte disarray and fibrosis increase the risk of arrhythmias and sudden cardiac death.
  • Clinical Manifestations:
    • Often asymptomatic but may present with dyspnea, angina, syncope, or sudden cardiac death (particularly in young athletes).
    • Murmur: Harsh systolic murmur at the left sternal border, which increases with Valsalva maneuver.
  • Diagnosis:
    • Echocardiogram: Shows asymmetric septal hypertrophy and potential left ventricular outflow tract (LVOT) obstruction.
    • ECG: Left ventricular hypertrophy, Q waves in inferior/lateral leads.
    • Genetic Testing: Confirms diagnosis in families with HCM history.
  • Management:
    • Medications: Beta-blockers or calcium channel blockers (e.g., verapamil) to reduce symptoms.
    • Procedures: Septal myectomy or alcohol septal ablation for significant LVOT obstruction.
    • ICD: Indicated for those at high risk for SCD, such as those with a family history of SCD, unexplained syncope, or marked hypertrophy.
Restrictive Cardiomyopathy (RCM)
  • Definition: RCM is characterized by decreased ventricular compliance, leading to impaired diastolic filling without significant hypertrophy.
  • Etiology:
    • Infiltrative Diseases: Amyloidosis (most common), sarcoidosis.
    • Storage Disorders: Hemochromatosis, Fabry disease.
    • Fibrotic Conditions: Endomyocardial fibrosis, radiation therapy.
  • Pathophysiology:
    • Stiff ventricles lead to increased diastolic pressures and preserved systolic function in early stages.
    • Elevated atrial pressures result in atrial enlargement and may cause atrial fibrillation.
  • Clinical Manifestations:
    • Symptoms of right-sided heart failure (e.g., peripheral edema, ascites) are common.
    • Pulmonary symptoms due to left-sided involvement may also occur.
    • Kussmaul’s sign: Jugular venous pressure increases with inspiration.
  • Diagnosis:
    • Echocardiogram: Normal ventricular size, biatrial enlargement, restrictive filling pattern.
    • Cardiac MRI: Helps differentiate RCM from constrictive pericarditis.
    • Biopsy: May be necessary to identify amyloid deposits or sarcoid granulomas.
  • Management:
    • Treat Underlying Cause: For instance, chemotherapy for amyloidosis or iron chelation for hemochromatosis.
    • Symptomatic Management: Diuretics for volume overload, cautious use of beta-blockers for rate control.
    • Advanced Therapies: Consider heart transplant in severe cases.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
  • Definition: ARVC is an inherited disease characterized by progressive fibrofatty replacement of the right ventricular myocardium.
  • Etiology:
    • Genetic: Mutations in desmosomal proteins (e.g., plakoglobin, desmoplakin).
    • Commonly inherited in an autosomal dominant manner.
  • Pathophysiology:
    • Myocardial fibro-fatty infiltration disrupts electrical conduction, leading to arrhythmias.
    • Predominantly affects the right ventricle but can involve the left ventricle in advanced stages.
  • Clinical Manifestations:
    • Palpitations, syncope, and increased risk of sudden cardiac death, especially during exercise.
    • Right-sided heart failure symptoms in advanced cases.
  • Diagnosis:
    • ECG: Epsilon wave (small positive deflection at the end of the QRS complex) in leads V1-V3.
    • Echocardiogram: Right ventricular dilation and dysfunction.
    • Cardiac MRI: Characteristic fibro-fatty infiltration of the right ventricle.
  • Management:
    • Activity Restriction: Patients are advised to avoid strenuous exercise.
    • ICD: For primary prevention of sudden cardiac death in high-risk patients.
    • Medications: Antiarrhythmic drugs like sotalol or amiodarone for arrhythmia management.
Key Points
  • Dilated Cardiomyopathy:
    • Common causes include genetic factors, myocarditis, and toxins.
    • Presents with systolic dysfunction and heart failure symptoms.
    • Management includes standard heart failure therapies and ICD for high-risk patients.
  • Hypertrophic Cardiomyopathy:
    • Caused by mutations in sarcomere genes; risk of sudden cardiac death.
    • Characterized by asymmetric septal hypertrophy, often causing LVOT obstruction.
    • Managed with beta-blockers, septal reduction therapy, and ICD for high-risk individuals.
  • Restrictive Cardiomyopathy:
    • Most commonly due to infiltrative diseases (e.g., amyloidosis).
    • Features diastolic dysfunction with normal ventricular size and atrial enlargement.
    • Treatment focuses on managing symptoms and underlying causes.
  • Arrhythmogenic Right Ventricular Cardiomyopathy:
    • Genetic disease leading to fibro-fatty replacement of right ventricular myocardium.
    • Presents with ventricular arrhythmias and risk of sudden cardiac death.
    • Management includes exercise restriction, antiarrhythmics, and ICD for prevention.

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