Myocarditis and Cardiomyopathies

Myocarditis - Heart's Inflamed Fury

⭐ Coxsackie B virus is the most common infectious cause of myocarditis in children.

• Definition: Myocardial inflammation causing cardiac dysfunction.
• Etiology:
  • Infectious: Viral (Coxsackie B, Adenovirus, Parvovirus B19), Bacterial.
  • Non-infectious: Autoimmune (SLE, Kawasaki), Drugs (Doxorubicin), Toxins.
• Clinical Features: Highly variable; may include fever, chest pain, dyspnea, arrhythmias, signs of heart failure (HF) (e.g., tachycardia, S3 gallop).
• Diagnosis:
  • ECG: Sinus tachycardia, ST-T changes, arrhythmias, AV block.
  • Biomarkers: ↑ Troponin, ↑ CK-MB.
  • Echocardiogram: Ventricular dysfunction (↓ EF), wall motion abnormalities.
  • Cardiac MRI (CMR): Gold standard non-invasive; detects edema, hyperemia, necrosis/fibrosis (Lake Louise Criteria).
  • Endomyocardial Biopsy (EMB): Definitive diagnosis (Dallas criteria); reserved for fulminant/unclear cases or when specific directed therapy is considered.
• Management:
  • Supportive: Bed rest, O2, diuretics, ACE-I/ARBs, Beta-blockers for HF.
  • Arrhythmia management.
  • Specific therapy (select cases): IVIG, immunosuppression (e.g., for giant cell, autoimmune).
  • Mechanical Circulatory Support (MCS) / Transplant for fulminant or refractory HF.

Dilated Cardiomyopathy (DCM) - The Baggy Heart

• Most common type; LV or biventricular dilation & impaired systolic function (EF < 40%).
• Etiology: Often idiopathic; genetic (TTN), post-myocarditis, alcohol, doxorubicin, peripartum.
• Sx: Progressive CHF (dyspnea, fatigue, edema), S3 gallop, functional MR/TR.
• Dx: Echo (key: dilated LV, global hypokinesia, ↓EF), CXR (cardiomegaly), ECG.
• Rx: Standard HF Rx (ACEi, βB, diuretics, MRA); ICD if EF ≤ 35%; transplant.

⭐ Duchenne Muscular Dystrophy is commonly associated with Dilated Cardiomyopathy in older boys.

Hypertrophic Cardiomyopathy (HCM) - Thick & Thumpy

• Genetic (Autosomal Dominant); asymmetric Left Ventricular Hypertrophy (LVH), especially septal (septal thickness > 15mm), leading to diastolic dysfunction.
• Symptoms: Dyspnea, angina, syncope/presyncope (often exertional), palpitations.
• Signs: Harsh crescendo-decrescendo systolic murmur at Left Lower Sternal Border (LLSB), S4 gallop.

• ECG: LVH criteria, deep, narrow ("dagger-like") Q waves in inferolateral leads. Echo: Confirms LVH, Systolic Anterior Motion (SAM) of mitral valve, LV Outflow Tract Obstruction (LVOTO).

⭐ Hypertrophic Cardiomyopathy (HCM) is the most common genetic cardiovascular disease and the leading cause of sudden cardiac death in young athletes.

• Management:
  • β-blockers (first-line), Verapamil.
  • Avoid: Nitrates, diuretics, digoxin (can worsen obstruction).
  • Septal myectomy or alcohol septal ablation for refractory severe LVOTO.
  • Implantable Cardioverter-Defibrillator (ICD) for high-risk individuals (prevents SCD).

Other Cardiomyopathies - Stiff & Scarred Variants

• Restrictive Cardiomyopathy (RCM):
  • Stiff ventricles → impaired diastolic filling; preserved systolic function.
  • Key causes: Amyloidosis (most common), sarcoidosis, hemochromatosis.
  • Echo: Biatrial enlargement. ECG: Low voltage QRS.
• Arrhythmogenic RV Dysplasia/Cardiomyopathy (ARVD/C):
  • Fibrofatty replacement of RV myocardium → RV dysfunction, arrhythmias.
  • ECG: Epsilon wave (pathognomonic), T-wave inversion V1-V3.

  ⭐ Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C) is characterized by fibrofatty replacement of the right ventricular myocardium and is associated with epsilon waves on ECG.

High‑Yield Points - ⚡ Biggest Takeaways

• Myocarditis: Most commonly viral (Coxsackie B, Adenovirus); endomyocardial biopsy is gold standard but rare.
• Dilated Cardiomyopathy (DCM): Most common pediatric cardiomyopathy; often idiopathic or post-myocarditis.
• Hypertrophic Cardiomyopathy (HCM): Autosomal dominant; key risks are syncope and sudden cardiac death.
• Restrictive Cardiomyopathy (RCM): Least common; characterized by severe diastolic dysfunction.
• ARVD: Fibrofatty replacement of RV; epsilon waves on ECG are characteristic.
• LVNC: Prominent trabeculations and deep intertrabecular recesses in LV_