Acute and Chronic Myocarditis¶
Chapter 268 | Part 6: Disorders of the Cardiovascular System
KEY CLINICAL POINTS¶
- Acute myocarditis is typically caused by viral infections (e.g., enteroviruses, influenza, HIV) but can also result from non-infectious causes (e.g., sarcoidosis, autoimmune diseases).
- Diagnosis requires integration of clinical presentation (chest pain, arrhythmias, elevated troponin), imaging (MRI with late gadolinium enhancement), and exclusion of myocardial infarction.
- Chronic myocarditis may evolve into dilated cardiomyopathy, with genetic factors increasingly implicated in both acute and chronic forms.
- Fulminant myocarditis (LVEF <0.50) has a high mortality rate (18% within 5 years) and often requires mechanical circulatory support.
- Noninfectious causes like sarcoidosis and eosinophilic myocarditis require immunosuppressive therapy and endomyocardial biopsy for confirmation.
1. DEFINITION & OVERVIEW¶
Myocarditis is inflammation of the heart muscle, presenting acutely, subacutely, or insidiously. Outcomes range from resolution to progression to chronic cardiomyopathy. Acute myocarditis is defined as symptoms lasting <1 month, while chronic myocarditis is associated with persistent inflammation and fibrosis.
Diagnostic Criteria for Acute Myocarditis¶
| Criteria | Description |
|---|---|
| Probable Myocarditis | New symptoms + at least one supportive finding (elevated troponin, ECG changes, LGE on MRI) |
| Definite Myocarditis | Biopsy showing inflammatory infiltrates or LGE with histologic evidence of inflammation |
| Fulminant Myocarditis | LVEF <0.50 with rapid progression to shock or cardiac arrest |
1.1 Classification¶
Acute myocarditis: <1 month duration; Chronic myocarditis: persistent inflammation with fibrosis. Differentiated from myocardial infarction by absence of coronary artery obstruction and presence of inflammatory markers.
1.2 Diagnostic Criteria¶
Probable myocarditis: new symptoms + elevated troponin/ECG changes/MRI findings. Definite myocarditis: biopsy showing inflammatory infiltrates. MRI patterns of late gadolinium enhancement (LGE) are critical for noninvasive diagnosis.
2. EPIDEMIOLOGY¶
Acute myocarditis peaks in adults 30–45 years old (men > women). Pandemic incidence of myocarditis was 150/100,000 (15× pre-pandemic). Chagas’ disease affects ~300,000 in the US, with 20–40% of dilated cardiomyopathy cases linked to genetic variants.
Incidence and Prevalence¶
| Condition | Incidence | Prevalence |
|---|---|---|
| Acute Myocarditis | 150/100,000 during pandemic | N/A |
| Chagas’ Disease | 300,000 in US | 6 million globally |
| Dilated Cardiomyopathy | 1–2% in HIV patients | 10–15% of cases have genetic variants |
2.1 Risk Factors¶
Viral infections (enteroviruses, HIV, influenza), autoimmune diseases, immunosuppression, and parasitic infections (e.g., Chagas’ disease).
2.2 Demographics¶
Young men (30–40 years) most affected by viral myocarditis; Chagas’ disease more common in Latin America and the southern US.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Viral pathogens (enteroviruses, HIV, influenza) cause direct injury or immune-mediated damage. Non-infectious causes include sarcoidosis, autoimmune diseases, and eosinophilic infiltration. Three phases of viral myocarditis: direct viral invasion, immune response, and chronic fibrosis.
Common Viral Causes¶
| Virus | Prevalence | Clinical Features |
|---|---|---|
| Enteroviruses | Most common | Acute onset, viral prodrome, LGE on MRI |
| HIV | 1–2% incidence | Dilated cardiomyopathy, immune reconstitution inflammatory syndrome |
| Influenza | Seasonal outbreaks | Myocardial inflammation, arrhythmias |
3.1 Viral Mechanisms¶
Enteroviruses cause direct myocyte damage via protease A degradation of dystrophin. HIV and dengue virus may induce cytokine storms. Molecular mimicry triggers autoimmune T-cell responses.
3.2 Non-Infectious Causes¶
Sarcoidosis (granulomatous inflammation), eosinophilic myocarditis (hypereosinophilia), and autoimmune diseases (e.g., lupus, vasculitis).
4. CLINICAL FEATURES¶
Symptoms include chest pain (>80%), dyspnea, arrhythmias, and fever. Signs include ST elevation, conduction blocks, and ventricular dysfunction. Complications include sudden cardiac death, heart failure, and arrhythmias.
Common Symptoms and Signs¶
| Symptom | Prevalence | Associated Finding |
|---|---|---|
| Chest pain | >80% | ST elevation, pericarditis |
| Arrhythmias | Common | Tachyarrhythmias, conduction blocks |
| Fever | 50% | Inflammatory response, viral infection |
4.1 Presentation¶
Prodromal viral symptoms (flu-like), chest pain, palpitations, syncope. Fulminant myocarditis presents with shock and LVEF <0.50.
4.2 Complications¶
Progression to dilated cardiomyopathy, ventricular aneurysms, and sudden cardiac death (3–9% of cases).
5. DIFFERENTIAL DIAGNOSIS¶
Differentiate from myocardial infarction (MI) using coronary imaging and troponin kinetics. Consider other causes of heart failure (e.g., valvular disease, hypertrophic cardiomyopathy) and systemic infections.
5.1 Key Differentiators¶
Acute myocarditis vs MI: no coronary obstruction, inflammatory markers, and LGE on MRI. Non-infectious causes include sarcoidosis and autoimmune diseases.
5.2 Red Flags¶
Eosinophilia (eosinophilic myocarditis), right bundle branch block (sarcoidosis), and hypereosinophilia (EGPA).
6. INVESTIGATIONS & DIAGNOSIS¶
Diagnostic workup includes troponin, ECG, MRI (LGE), and endomyocardial biopsy. PCR detects viral genomes, while immunohistochemistry identifies inflammatory infiltrates.
Diagnostic Algorithms¶
| Step | Test | Interpretation |
|---|---|---|
| 1 | ECG and troponin | ST elevation, elevated troponin suggests MI or myocarditis |
| 2 | Coronary angiography | Rule out obstructive coronary disease |
| 3 | MRI (LGE) | Confirm myocardial inflammation without infarction |
6.1 Laboratory Tests¶
Elevated troponin, creatine kinase, C-reactive protein. PCR for viral genomes (e.g., enteroviruses, HIV).
6.2 Imaging¶
MRI with LGE for fibrosis; echocardiography for LVEF. Coronary angiography to exclude MI.
7. MANAGEMENT & TREATMENT¶
Supportive care (diuretics, beta-blockers) for uncomplicated cases. Immunosuppression (corticosteroids, methotrexate) for autoimmune or eosinophilic causes. Mechanical support for fulminant myocarditis.
Treatment by Etiology¶
| Cause | Treatment | Monitoring |
|---|---|---|
| Viral | Supportive care, antivirals | Troponin, LVEF, ECG |
| Sarcoidosis | Corticosteroids, immunosuppressants | MRI, biopsy |
| Eosinophilic | Glucocorticoids, antihistamines | Eosinophil count, LGE |
7.1 Pharmacologic Therapy¶
Antiarrhythmics for arrhythmias, anticoagulation for heart failure, and immunosuppression for non-infectious causes.
7.2 Surgical Interventions¶
Heart transplantation for end-stage disease; mechanical circulatory support for refractory shock.
8. PROGNOSIS & COMPLICATIONS¶
Uncomplicated acute myocarditis has >75% spontaneous recovery. Fulminant myocarditis has 18% mortality within 5 years. Chronic myocarditis may progress to dilated cardiomyopathy with reduced LVEF.
Prognostic Outcomes¶
| Group | Survival | Complications |
|---|---|---|
| Uncomplicated | 75% recovery | None or minimal |
| Fulminant | 18% mortality | Heart failure, shock |
| Chronic | Lower survival | Dilated cardiomyopathy, arrhythmias |
8.1 Prognostic Factors¶
LVEF at presentation, presence of arrhythmias, and response to immunosuppression. Genetic variants increase risk of chronic disease.
8.2 Long-Term Risks¶
Heart failure, arrhythmias, and sudden cardiac death. 30% of HES cases progress to end-stage heart failure.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: monitor for arrhythmias and fetal complications. Pediatrics: viral etiology dominates; avoid immunosuppression unless autoimmune. Elderly: higher risk of complications from immunosuppression.
9.1 Pregnancy¶
Avoid immunosuppressants; monitor for arrhythmias and fetal heart rate abnormalities.
9.2 Pediatrics¶
Viral myocarditis is most common; avoid corticosteroids unless autoimmune etiology is confirmed.
10. KEY POINTS & CLINICAL PEARLS¶
- Acute myocarditis is often viral but can have non-infectious causes. 2. MRI with LGE is critical for noninvasive diagnosis. 3. Fulminant myocarditis requires mechanical support. 4. Genetic variants contribute to chronic disease. 5. Immunosuppression is key for sarcoidosis and eosinophilic cases.