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Acute and Chronic Myocarditis

Chapter 268 | Part 6: Disorders of the Cardiovascular System · Part 6 – Cardiovascular Disorders · Chapter 268

Key Clinical Points

  1. Acute myocarditis typically affects men aged 30–45 years; chest pain is the most common symptom (>80%).
  2. Fulminant myocarditis occurs in 3–9% of cases and presents with early cardiogenic shock.
  3. Diagnosis requires a combination of clinical symptoms, elevated troponin, and MRI evidence of edema/non-ischemic injury.
  4. Chagas' disease is the most common infective cause of cardiomyopathy worldwide.
  5. Cardiac sarcoidosis often presents with right bundle branch block (RBBB) and ventricular tachyarrhythmias.
  6. Eosinophilic myocarditis is present in 3/4 of cases showing hypereosinophilia; may involve apical thrombi.
  7. Uncomplicated cases (LVEF ≥ 0.50) have a good prognosis with common spontaneous recovery.
  8. COVID-19 was associated with a 15-fold increase in myocarditis incidence during the pandemic.
  9. Differentiation from myocardial infarction (MI) is primarily achieved through coronary artery imaging.
  10. Specific treatments exist for Chagas' (Nifurtimox/Benznidazole), Sarcoidosis (Glucocorticoids), and Eosinophilic cases.

DEFINITION & CLASSIFICATION

• Definition (Harrison's 22e): inflammation of the heart muscle, which may present acutely, subacutely, or insidiously. • Acute Myocarditis: Presentation with less than a month of symptoms (often just a few days). • Chronic Myocarditis: Persistent inflammation contributing to dilated cardiomyopathy. • Fulminant Myocarditis: Clinical shock reported in 3–9% of cases. • Noninfective Inflammatory Myocarditis: Cardiac depression from noncellular mediators (antibodies, cytokines) and exposed myocardial antigens; can reverse quickly.

EPIDEMIOLOGY

• Demographics: Typically occurs in men aged 30–45 years. • COVID-19 Impact: Pandemic saw a 15-fold increase over pre-COVID incidence (estimated at 150/100,000 people). • HIV Association: Associated with dilated cardiomyopathy in 1–2% of cases; declining due to HAART. • Risk Factors: ◦ Modifiable: Viral infections (influenza, adenovirus, COVID-19), immunosuppression, genetic variants. ◦ Non-modifiable: Age, sex, race/ethnicity (especially in Chagas' disease endemic regions).

ETIOLOGY & PATHOPHYSIOLOGY

• Infection Mechanisms: ◦ Direct invasion → disruption of cellular processes. ◦ Activation of immune responses (host response) → macrophage activation, T- and B-cell expansion. ◦ 'Virally triggered' myocarditis: Damage from host response without direct viral-mediated injury. • Viral Pathogenesis Phases: ◦ Phase I: Direct invasion; entry enhanced by certain genetic variants; protease A degrades dystrophin → apoptosis/impaired autophagy. ◦ Phase II: Host response to common antigenic patterns (cytokine storm, etc.). ◦ Phase III: Progression to chronic cardiomyopathy (seen in animal models). • Specific Pathogens: ◦ Picornavirus: Enteroviruses (coxsackie, echovirus, poliovirus). ◦ DNA viruses: Adenovirus, vaccinia, herpesviruses (VZV, CMV, EBV, HHV6). ◦ RNA viruses: Influenza, RSV, arboviruses (dengue, yellow fever), arenaviruses (Lassa fever). ◦ Parasitic: Trypanosoma cruzi (Chagas' disease). ◦ Bacterial: Corynebacterium diphtheriae, Streptococcal, Brucellosis, Legionella, Mycoplasma, Salmonella, Tuberculosis, Whipple's. ◦ Tick-borne: Borrelia burgdorferi (Lyme), Q fever, Ehrlichiosis. • Noninfective Mechanisms: ◦ Cytokine storm and non-specific immune responses. ◦ Molecular mimicry between viral and cardiac antigens → autoreactive T cells. ◦ Viral 'hijacking' of cellular machinery to produce extracellular vesicles containing viral RNA.

CLINICAL FEATURES

• Prodrome: Symptoms of influenza, gastroenteritis, or URI occurring days to weeks prior. • Symptoms: ◦ Fever: Present in >50% of cases. ◦ Chest Pain: Most common symptom; present in >80% of patients. ◦ Other: Dyspnea, arrhythmias (palpitations, syncope, or sudden cardiac death). • Cardiac Function: Approximately 25% of acute myocarditis cases present with LVEF < 50%. • Temporal Course: ◦ Acute: <1 month symptoms. ◦ Subacute: Intermediate duration. ◦ Insidious: Gradual onset of dilated cardiomyopathy without prior acute episode. • Complications: ◦ Early: Cardiogenic shock, ventricular arrhythmias, conduction block. ◦ Late: Chronic cardiomyopathy, dilated ventricles, thrombogenic aneurysms. ◦ Fulminant: Refractory cardiogenic shock requiring mechanical support or transplantation.

DIFFERENTIAL DIAGNOSIS

• Myocardial Infarction (MI): Overlaps in chest pain, ECG changes, and troponin; first step is coronary artery imaging. • Genetic Cardiomyopathy: Similar fibrosis patterns; requires evaluation of family history and genetic variants. • Sarcoidosis: High suspicion if ventricular tachycardia or conduction block dominates heart failure without CAD. • MINOCA: Up to 1/3 of patients with MI and nonobstructed coronary arteries may have myocarditis. • Giant Cell Myocarditis: 10–20% of biopsy-proven cases; acute presentation with rapid heart failure and tachyarrhythmias. • Chagas' Disease: Suspected in endemic regions; features include sinus/AV node conduction disease and eosinophilia. • Distinguishing Features Table (Table 1): ◦ Acute Myocarditis: Chest pain, fever, troponin elevation, ECG changes, LGE on MRI. ◦ MI: Obstructive CAD, ischemic LGE pattern. ◦ Sarcoidosis: RBB, regional wall motion abnormalities, noncaseating granulomas. ◦ Chagas' Disease: Endemic regions, conduction disease, eosinophilia.

DIAGNOSTIC APPROACH

  1. Initial Screening (Probable Myocarditis): Identify ≥ 1 symptom (chest pain, dyspnea, arrhythmias) AND ≥ 1 finding (elevated troponin, ECG changes, decreased LVEF, or wall motion abnormality).
  2. Confirmatory Testing (Definite Myocarditis): Typical symptomatic presentation + elevated troponin + MRI findings (myocardial edema and nonischemic injury) - no other known cause.
  3. Imaging Findings: • Cardiac MRI: Often sufficient for diagnosis; look for mid-wall LGE, myocardial edema, and nonischemic injury. • Clinical Correlation: Identify 'nondilated' or 'minimally dilated' cardiomyopathy when LV function is only mildly reduced.
  4. Specialized Investigations: • Endomyocardial Biopsy: Perform if arrhythmias, conduction block, high eosinophil count, or systemic autoimmune disease suggests specific etiologies. • Laboratory: Routine check of CPK, CRP, and eosinophil counts; viral panels (influenza, adenovirus) and specific serologies (HIV, Chagas', CMV, Dengue, Lyme).

MANAGEMENT & TREATMENT

  1. General Management: • Uncomplicated (LVEF ≥ 0.50): Supportive care; diuretics and nonsteroidal analgesics for chest pain. • Fulminant: High-dose inotropic therapy or mechanical circulatory support. • Heart Failure: Patients with reduced LVEF managed per HFrEF guidelines.
  2. Specific Etiology - Chagas' Disease: • Acute: Nifurtimox or Benznidazole (monitor liver function, CBC). • Chronic: General HFrEF therapy; increased focus on anticoagulation and ICDs.
  3. Specific Etiology - Sarcoidosis: • Initial: Glucocorticoids (30–40 mg daily) + steroid-sparing agents (Methotrexate or Mycophenolate). • Advanced: TNF-alpha inhibitors or other immunomodulators.
  4. Specific Etiology - Eosinophilic Myocarditis: • Action: Identify and withdraw offending agent; initiate acute steroid therapy.
  5. Other Specific Conditions: • Diphtheria: Antitoxin and antibiotics as soon as possible. • HIV: Highly active antiretroviral therapy (HAART). • Trichinellosis: Anthelmintic drugs and glucocorticoids if inflammation is severe.
  6. Device Therapy: • Indicated for tachyarrhythmias or conduction disease; should include both pacing and defibrillation capability.
  7. Drug Summary Table (Table 2): • Chagas' Disease: Nifurtimox/Benznidazole (Daily); monitor LFTs, CBC. • Sarcoidosis: Glucocorticoids (30–40 mg daily); monitor BP, glucose. • Eosinophilic Myocarditis: Corticosteroids; monitor eosinophil count.

COMPLICATIONS & PROGNOSIS

• Uncomplicated Cases: ◦ Represent ~75% of patients (LVEF ≥ 0.50, no shock/arrhythmia). ◦ High survival; common spontaneous recovery; LVEF usually remains ≥ 0.50 at 5 years. • Complicated Cases: ◦ Represent ~25% of patients. ◦ ~18% mortality or heart transplantation within 5 years. • Fulminant Cases (3–10%): ◦ Initial risk of refractory shock; however, >50% recover to near-normal LVEF. • Long-term Outcomes: ◦ Improvement of LVEF is uncommon after the onset of overt clinical heart failure. ◦ Risk of complications: Acute coronary syndrome, thromboemboli, pericarditis.

SPECIAL POPULATIONS

• Chagas' Disease: ◦ High risk in endemic regions; requires specific antiparasitic treatment (Nifurtimox/Benznidazole). ◦ Risk of conduction disease and apical thrombi. • Sarcoidosis: ◦ Often presents with RBB and tachycardia; management involves multidisciplinary team oversight. • Eosinophilic Myocarditis: ◦ Present in 3/4 of cases with hypereosinophilia; may be caused by drugs, parasites (Mediterranean/Africa), or EGPA/HES. • Trichinellosis: ◦ Characterized by myalgias, weakness, fever, and periorbital edema; diagnosis via serology and eosinophilia.

KEY PEARLS & HIGH-YIELD POINTS

• Clinical Rule of Thumb: Chest pain is the hallmark (>80%), but heart failure/arrhythmias are common complications. • Diagnostic Thresholds: 'Probable' requires 1 symptom + 1 finding; 'Definite' requires troponin + MRI evidence of edema/non-ischemic injury. • Sarcoidosis Clue: If tachycardia and RBB dominate the presentation without CAD, suspect sarcoidosis. • Eosinophil Check: Always check eosinophil counts to rule out eosinophilic myocarditis (present in 75% of such cases). • Chagas' Alert: In endemic areas, any cardiomyopathy with conduction disease should be screened for Chagas'.