Myocarditis

Detailed Overview

Myocarditis has a highly variable clinical presentation, ranging from subclinical, self-limiting illness to fulminant cardiogenic shock. Viral infections are the most common cause in developed nations. The immune system's response to the pathogen (or a direct toxin/autoimmune trigger) causes cellular damage. Diagnosis is challenging and often relies on a combination of clinical presentation, elevated cardiac biomarkers, and Cardiac MRI, with endomyocardial biopsy reserved for specific acute, severe cases. Management is primarily supportive, focusing on heart failure and arrhythmia treatment.

Epidemiology & Demographics

Estimated global incidence is 10 to 20 cases per 100,000 persons annually. It disproportionately affects young adults and is a leading cause of sudden cardiac death in athletes (<35 years old). Slightly more common in males.

Etiological Mechanism

Most commonly viral in developed countries: Coxsackievirus B, Adenovirus, Parvovirus B19, Human Herpesvirus 6 (HHV-6), and SARS-CoV-2. Trypanosoma cruzi (Chagas disease) is a major cause in South America. Non-infectious causes include toxins (cocaine, anthracyclines), autoimmune diseases (Systemic Lupus Erythematosus), and immune checkpoint inhibitors.

Primary Causes

Viral infections (Parvovirus B19, Coxsackievirus)

Bacterial infections (Lyme disease/Borrelia burgdorferi, Diphtheria)

Parasites (Trypanosoma cruzi)

Toxins and drugs (Cocaine, Doxorubicin)

Autoimmune/Hypersensitivity reactions

• Recent viral illness: Upper respiratory or gastrointestinal infection within the past 1-2 weeks.
• Use of Immune Checkpoint Inhibitors: Oncology drugs like Pembrolizumab can trigger severe, autoimmune myocarditis.

The pathogenesis typically involves three phases: 1) Direct viral injury: Virus enters cardiomyocytes via receptors (e.g., CAR receptor for Coxsackievirus), replicates, and causes direct cellular destruction. 2) Immune activation: Macrophages, T-cells, and B-cells infiltrate the myocardium. While attempting to clear the virus, the inflammatory cytokines and autoantibodies cross-react with myocardial proteins (molecular mimicry), causing collateral damage. 3) Remodeling/Dilated Cardiomyopathy: Inflammation subsides, leaving fibrosis and scarring, leading to impaired contractility and dilated cardiomyopathy.

Characteristic Clinical Presentation

• Chest pain: Often sharp or pleuritic, especially if associated with pericarditis (myopericarditis).
• Dyspnea: Shortness of breath due to impaired left ventricular function.
• Palpitations/Syncope: Due to ventricular arrhythmias or high-grade AV block.
• Fatigue: Out of proportion to exertion, often following a flu-like prodrome.

Physical Examination Signs

• Tachycardia out of proportion to fever.
• S3 or S4 gallop rhythm.
• Pericardial friction rub (if concurrent pericarditis).
• Signs of fluid overload: JVD, pulmonary crackles, peripheral edema (in severe cases).

• Dilated Cardiomyopathy: Long-term scarring leading to chronic heart failure.
• Ventricular Arrhythmias: Scar tissue acts as a nidus for VT or VF, risking sudden cardiac death.
• Mural Thrombus: Blood pooling in a poorly contracting ventricle can form clots, risking stroke.

Diagnostic Criteria & Guidelines

A definitive diagnosis requires Endomyocardial Biopsy (Dallas criteria: inflammatory infiltrates with myocyte necrosis). However, clinically, diagnosis is made based on elevated troponin, suggestive ECG changes, exclusion of coronary artery disease via angiography, and Lake Louise Criteria on Cardiac MRI.

Differential Diagnosis

• Acute Coronary Syndrome (STEMI/NSTEMI)
• Pericarditis
• Stress-induced (Takotsubo) Cardiomyopathy
• Pulmonary Embolism

Laboratory Tests & Biomarkers

• High-Sensitivity Troponin: Elevated (e.g., > 14 ng/L), indicating acute myocardial necrosis.
• CRP and ESR: Typically elevated indicating systemic inflammation.
• ECG: Sinus tachycardia, diffuse ST-segment elevation, T-wave inversions, or AV block.

Imaging Modalities & Findings

• Echocardiogram:
• Cardiac Magnetic Resonance (CMR):

• Acute Subclinical
  Asymptomatic with transient ECG changes or mild troponin elevation.
• Acute Heart Failure
  New onset HF symptoms, LV dysfunction on echo.
• Fulminant
  Rapid onset of cardiogenic shock requiring inotropes or mechanical circulatory support.

Second-Line & Adjunctive Therapy

For specific etiologies: Immunosuppression (High-dose IV Corticosteroids) is used for Giant Cell Myocarditis, Eosinophilic Myocarditis, or Immune Checkpoint Inhibitor myocarditis. IVIG may be considered in fulminant cases, though evidence is mixed.

Surgical & Procedural Management

For fulminant myocarditis with cardiogenic shock: Mechanical circulatory support such as Venoarterial Extracorporeal Membrane Oxygenation (VA-ECMO) or Intra-aortic balloon pump (IABP) as a bridge to recovery or heart transplantation. Heart transplant for irreversible end-stage failure.

Recommended Lifestyle Changes

• Strict avoidance of competitive sports and strenuous exercise for at least 3 to 6 months to prevent sudden cardiac death.
• Low sodium diet if heart failure is present.

Patient Counseling & Advice

Inform the patient that their heart muscle is inflamed and needs rest. Emphasize the absolute necessity of exercise restriction until cleared by a cardiologist via repeat imaging and Holter monitoring. Discuss the signs of worsening heart failure.

Follow-Up & Monitoring Schedule

Cardiology follow-up within 1-2 weeks after discharge. Repeat Echocardiogram at 1, 3, and 6 months to assess LVEF recovery. Holter monitor before returning to sports.

Preventive Strategies

Vaccination against common viral pathogens (Influenza, COVID-19, Rubella) can reduce the risk of virally-mediated myocarditis.

Variable. About 50% of acute viral myocarditis cases resolve completely in 2-4 weeks. 25% develop persistent cardiac dysfunction, and 25% progress to severe heart failure requiring transplantation or resulting in death.