Diagnosis

Myocarditis

Etiology

Cause [5bf]

• Virus: Enterovirus, coxsackie B, adenovirus, influenza, cytomegalovirus, poliomyelitis, Epstein-Barr virus, HIV, viral hepatitis, mumps, rubeola, varicella, variola/vaccinia, arbovirus, respiratory syncytial virus, herpes simplex virus, yellow fever virus, rabies, parvovirus, SARS-CoV2

• Rickettsia: Scrub typhus, Rocky Mountain spotted fever, Q fever

• Bacteria: Diphtheria, tuberculosis, streptococci, meningococci, brucellosis, clostridia, staphylococci, melioidosis, Mycoplasma pneumoniae, psittacosis

• Spirochete: Syphilis, leptospirosis/Weil disease, relapsing fever/Borrelia, Lyme disease

• Fungus: Candidiasis, aspergillosis, cryptococcosis, histoplasmosis, actinomycosis, blastomycosis, coccidioidomycosis, mucormycosis

• Protozoa: Chagas disease, toxoplasmosis, trypanosomiasis, malaria, leishmaniasis, balantidiasis, sarcosporidiosis

• Helminth: Trichinosis, echinococcosis, schistosomiasis, heterophyiasis, cysticercosis, visceral larva migrans, filariasis

• Bites/stings: Scorpion venom, snake venom, black widow spider venom, wasp venom, tick paralysis

• Drugs: hypersensitivity myocarditis, mRNA vaccines

  • Chemotherapeutic drugs: Doxorubicin and anthracyclines, streptomycin, cyclophosphamide, interleukin-2, anti-HER-2 receptor antibody/Herceptin

  • Antibiotics: Penicillin, chloramphenicol, sulfonamides

  • Antihypertensive drugs: Methyldopa, spironolactone

  • Antiseizure drugs: Phenytoin, carbamazepine

  • Stimulants: Amphetamines, cocaine, catecholamines

• Chemicals: Hydrocarbons, carbon monoxide, arsenic, lead, phosphorus, mercury, cobalt

• Physical agents: radiation, heatstroke, hypothermia

• Autoimmune disease: Acute rheumatic fever, Giant cell myocarditis, Sarcoidosis, Kawasaki disease, Crohn disease, systemic lupus erythematosus, ulcerative colitis, Wegener granulomatosis, thyrotoxicosis, scleroderma, dermatomyositis, rheumatoid arthritis

• Peripartum cardiomyopathy

• Posttransplant cellular rejection

• Idiopathic

Pathogenesis [5bf]

1. Phase I:

   • Direct cytotoxic effect (virus, bacteria, fungi, parasite, toxin, drug, or autoimmunity)

2. Phase II:

   • Secondary dysregulated immune response due to molecular mimicry

   • Cytokine expression (TNF-α, IL-1, IL-6) --> recruitment of immune cells

   • Myocardial inflammation --> myocardial damage

3. Phase III:

   • Resolution

   • Chronic inflammation (T-cell activation, antibody production) --> fibroblast activation --> deposition of collagen --> scar tissue --> cardiac remodeling --> cardiomyopathy

Classification [tnr]

1. Fulminant myocarditis: severe cardiovascular compromise and ventricular dysfunction (pulmonary hypertension --> pulmonary edema). Either resolves spontaneously or results in death.

2. Acute myocarditis - Less distinct onset of illness, with established ventricular dysfunction; may progress to dilated cardiomyopathy.

3. Chronic active myocarditis - Less distinct onset of illness, with clinical and histologic relapses. Ventricular dysfunction due to chronic inflammatory changes (giant cells).

4. Chronic persistent myocarditis - Less distinct onset of illness, persistent histologic infiltrate with foci of myocyte necrosis but without ventricular dysfunction.

Complication [tnr]

• Acute complications:

  • Left ventricular dysfunction --> heart failure

  • Cardiogenic shock

  • Ventricular tachycardia/fibrillation --> risk of sudden cardiac death

  • Bradyarrhythmia

  • Atrial arrhythmia

  • Thromboembolic events

• Long term complications:

  • Myocardial fibrosis --> risk of arrhythmias and sudden cardiac death

  • Dilated cardiomyopathy --> heart failure --> heart transplantation

Epidemiology

Incidence per 100.000 [y2c][vcw][bp8][27n][qye][ra6][9zd][5ka]

Approach

• Blood test: complete blood count, sedimentation rate, Rheumatologic screening, Cardiac enzyme levels, Serum viral antibody titers

• Endomyocardial biopsy (the gold standard): Viral genome testing

• ECG

• Echocardiography

• Antimyosin scintigraphy

• Coronary angiography: To rule out coronary ischemia

• Cardiac MRI

Treatment

1. Myocarditis with left ventricular dysfunction --> heart-failure regimen: [nzq][5bf]

   • ACE-inhibitor or AT-blocker

   • Beta-blocker

   • Diuretic

   • Mechanical circulatory support:

     • Left ventricular assist devices (LVAD) or extracorporeal membrane oxygenation (ECMO) as a bridge to transplantation or recovery

2. Myocarditis with arrhythmia --> supportive therapy

   • Bradycardia or complete heart block --> temporary pacemaker

   • Ventricular arrhythmia --> amiodarone and implantable cardioverter–defibrillator

   • Anticoagulation

3. Antiviral therapy: Since most patients with acute myocarditis are diagnosed weeks after viral infection --> uncertain benefit of antiviral therapy

4. Intravenous immune globulin and immunosuppression: lack of evidence

5. Avoid exercise until full recovery (3-6 months)

6. Low-sodium diet

Differential diagnoses

Amyloidosis, Cardiac tamponade, Cardiomyopathy, Chagas disease, Drug side effects, Endocarditis, Heart failure, Myocardial infarction, Pericarditis, Pulmonary edema, Pulmonary fibrosis, Sepsis, Shock, Sudden cardiac death, Takotsubo cardiomyopathy, Thyrotoxicosis, Unstable angina, Ventricular tachycardia