Myocarditis in Children

Topic Name Introduction Etiology Pathophysiology Clinical Presentation Diagnosis Management Prognosis

Introduction to Myocarditis in Children

Myocarditis is an inflammatory disease of the myocardium, the middle layer of the heart wall. In children, it can be a significant cause of acute and chronic heart failure, and in severe cases, can lead to cardiac transplantation or death. The condition can affect previously healthy children and may present with a wide range of symptoms, from mild to life-threatening.

Myocarditis in children poses unique challenges in terms of diagnosis and management due to its varied presentation and the potential for rapid progression. Understanding this condition is crucial for pediatricians, cardiologists, and emergency physicians to ensure prompt recognition and appropriate treatment.

The incidence of myocarditis in children is difficult to determine accurately due to the challenges in diagnosis, but it is estimated to occur in 1-2 per 100,000 children annually. However, this figure likely underestimates the true incidence, as many cases may go undiagnosed or misdiagnosed.

Etiology of Myocarditis in Children

Myocarditis in children can result from various causes, including:

1. Infectious Causes:
   • Viral (most common): Enteroviruses (especially Coxsackievirus B), Adenovirus, Parvovirus B19, Human Herpesvirus 6, Influenza, COVID-19
   • Bacterial: Streptococcus, Staphylococcus, Mycoplasma pneumoniae
   • Fungal: Candida, Aspergillus (rare, usually in immunocompromised patients)
   • Parasitic: Trypanosoma cruzi (Chagas disease), Toxoplasma gondii
2. Immune-Mediated Causes:
   • Systemic autoimmune diseases (e.g., Lupus, Kawasaki disease)
   • Post-viral immune reaction
   • Drug hypersensitivity reactions
3. Toxic Causes:
   • Medications: Anthracyclines, chloroquine, sulfonamides
   • Recreational drugs: Cocaine, amphetamines
   • Environmental toxins: Carbon monoxide, heavy metals
4. Other Causes:
   • Hypersensitivity myocarditis
   • Eosinophilic myocarditis
   • Giant cell myocarditis (rare in children)

In many cases, especially in children, the exact cause remains unknown (idiopathic myocarditis). The most common identifiable cause in children is viral infection, with enteroviruses being the most frequently implicated pathogens.

Pathophysiology of Myocarditis in Children

The pathophysiology of myocarditis involves a complex interplay of direct cellular injury and immune-mediated damage:

1. Initial Injury:
   • In viral myocarditis, the virus enters cardiomyocytes via specific receptors
   • Direct viral replication leads to cell damage and death
   • Release of intracellular antigens triggers immune response
2. Immune Response:
   • Innate immune response: Activation of pattern recognition receptors, release of cytokines and chemokines
   • Adaptive immune response: T-cell mediated cytotoxicity, antibody production
   • Autoimmune reaction: Molecular mimicry can lead to sustained immune activation against cardiac antigens
3. Myocardial Dysfunction:
   • Inflammatory infiltrates disrupt cardiac contractility
   • Edema and necrosis of cardiomyocytes
   • Impaired electrical conduction leading to arrhythmias
4. Remodeling and Recovery or Progression:
   • Acute phase: Potential for complete recovery if inflammation resolves
   • Chronic phase: Ongoing inflammation can lead to fibrosis and dilated cardiomyopathy

The severity and course of myocarditis in children can vary greatly, depending on the causative agent, the extent of myocardial involvement, and the individual's immune response. The developing immune system and the unique physiological characteristics of the pediatric heart contribute to the distinct features of myocarditis in children compared to adults.

Clinical Presentation of Myocarditis in Children

The clinical presentation of myocarditis in children can be highly variable, ranging from asymptomatic cases to fulminant heart failure. Common presentations include:

1. Prodromal Phase:
   • Flu-like symptoms: Fever, fatigue, myalgia
   • Respiratory symptoms: Cough, rhinorrhea
   • Gastrointestinal symptoms: Nausea, vomiting, abdominal pain
2. Cardiac Symptoms:
   • Chest pain or discomfort
   • Palpitations
   • Syncope or presyncope
   • Dyspnea, especially with exertion
   • Orthopnea in older children
3. Signs of Heart Failure:
   • Tachycardia out of proportion to fever
   • Tachypnea, respiratory distress
   • Hepatomegaly
   • Peripheral edema (less common in children)
   • Poor peripheral perfusion, cool extremities
4. Other Presentations:
   • Sudden cardiac arrest (rare but can be the initial presentation)
   • Arrhythmias: Ventricular tachycardia, supraventricular tachycardia, heart block
   • Cardiogenic shock in fulminant cases

It's important to note that the presentation can mimic other conditions such as sepsis, pneumonia, or asthma exacerbation. A high index of suspicion is needed, especially in children presenting with respiratory or gastrointestinal symptoms accompanied by signs of cardiac dysfunction. Infants may present with nonspecific symptoms such as poor feeding, lethargy, or irritability, making diagnosis particularly challenging in this age group.

Diagnosis of Myocarditis in Children

Diagnosing myocarditis in children can be challenging due to its varied presentation. A combination of clinical, laboratory, and imaging findings is typically used:

1. Clinical Evaluation:
   • Detailed history, including recent illnesses or exposures
   • Physical examination: Focus on cardiovascular and respiratory systems
2. Laboratory Tests:
   • Cardiac biomarkers: Troponin I or T, CK-MB
   • Inflammatory markers: ESR, CRP
   • BNP or NT-proBNP for heart failure assessment
   • Viral studies: PCR for common viral pathogens
   • Complete blood count, liver function tests
3. Electrocardiogram (ECG):
   • Sinus tachycardia, ST-segment and T-wave abnormalities
   • Low voltage QRS complexes
   • Conduction abnormalities or arrhythmias
4. Imaging Studies:
   • Echocardiography: Assessment of ventricular function, wall motion abnormalities, pericardial effusion
   • Chest X-ray: Cardiomegaly, pulmonary edema
   • Cardiac MRI: Gold standard for non-invasive diagnosis, shows myocardial edema and late gadolinium enhancement
5. Endomyocardial Biopsy:
   • Historically considered the gold standard, but less commonly performed in children due to risks
   • May be considered in cases of unexplained cardiomyopathy or when specific therapies depend on histological findings

Diagnosis often relies on a combination of clinical suspicion, elevated cardiac biomarkers, and imaging findings suggestive of myocardial inflammation. The Lake Louise Criteria, which incorporate cardiac MRI findings, are increasingly used for non-invasive diagnosis. In children, the risks of endomyocardial biopsy often outweigh the benefits, and diagnosis is typically made based on non-invasive criteria.

Management of Myocarditis in Children

Management of myocarditis in children focuses on supportive care, treatment of heart failure, and specific therapies based on etiology when identified:

1. Supportive Care:
   • Hospitalization and monitoring in a pediatric intensive care unit for moderate to severe cases
   • Bed rest and activity restriction during acute phase
   • Fluid and electrolyte management
   • Respiratory support as needed (oxygen therapy, mechanical ventilation)
2. Heart Failure Management:
   • Diuretics for volume overload
   • ACE inhibitors or ARBs to reduce afterload
   • Beta-blockers in stable patients
   • Inotropic support (e.g., milrinone, dobutamine) for severe cases
3. Arrhythmia Management:
   • Antiarrhythmic medications as needed
   • Temporary pacing for heart block if necessary
4. Immunomodulatory Therapy:
   • Intravenous immunoglobulin (IVIG): Considered in many centers, though evidence is mixed
   • Corticosteroids: Used in some cases, especially with autoimmune etiology
   • Other immunosuppressants (e.g., cyclosporine) in select cases
5. Mechanical Circulatory Support:
   • ECMO (Extracorporeal Membrane Oxygenation) for fulminant myocarditis with cardiogenic shock
   • Ventricular assist devices as a bridge to recovery or transplantation
6. Specific Treatments:
   • Antiviral therapy if a treatable viral cause is identified
   • Antibiotics for bacterial myocarditis
7. Long-term Management:
   • Gradual return to activity under close monitoring
   • Serial echocardiograms and cardiac MRI to assess recovery
   • Continued heart failure therapy as needed
   • Consideration for cardiac transplantation in severe, unresponsive cases

Management should be tailored to the individual patient based on the severity of presentation, hemodynamic status, and response to initial therapies. A multidisciplinary approach involving pediatric cardiologists, intensivists, and infectious disease specialists is often necessary for optimal management.

Prognosis of Myocarditis in Children

The prognosis of myocarditis in children can vary widely, depending on the etiology, severity of presentation, and timeliness of treatment:

• Acute Phase:
  • Many children recover completely with supportive care
  • Mortality rate in acute phase ranges from 0-5% in most series, but can be higher in fulminant cases
  • Fulminant myocarditis, paradoxically, may have a better long-term prognosis if the patient survives the acute phase
• Long-term Outcomes:
  • 50-80% of children have complete or near-complete recovery of cardiac function
  • 10-20% may develop chronic dilated cardiomyopathy
  • Risk factors for poor outcomes include severe presentation, need for mechanical circulatory support, and specific histological findings (if biopsy performed)
• Recurrence:
  • Recurrence is rare but possible, especially in autoimmune or recurrent viral cases
  • Long-term follow-up is important to monitor for late deterioration
• Complications:
  • Chronic heart failure
  • Arrhythmias, including risk of sudden cardiac death
  • Thromboembolic events
• Factors Influencing Prognosis:
  • Age at presentation (infants may have worse outcomes)
  • Severity of initial cardiac dysfunction
  • Presence of ventricular arrhythmias
  • Time to diagnosis and initiation of treatment
  • Response to initial therapy
• Follow-up:
  • Regular cardiac evaluations, including echocardiography
  • Gradual return to normal activities under medical supervision
  • Counseling regarding potential future pregnancy risks in female patients

While the acute mortality of myocarditis in children can be significant, especially in severe cases, the overall prognosis is generally favorable with appropriate management. However, a subset of patients may develop chronic cardiac dysfunction, necessitating long-term follow-up and management. Ongoing research aims to identify predictors of poor outcomes and develop targeted therapies to improve long-term prognosis.

Objective QnA: Myocarditis in Children

1. What is myocarditis?
   Inflammation of the heart muscle (myocardium)
2. What is the most common cause of myocarditis in children?
   Viral infections
3. Which virus is most frequently associated with myocarditis in children?
   Coxsackievirus B
4. What is the typical age range for viral myocarditis in children?
   Infants and young children under 2 years old
5. Which cardiac biomarker is commonly elevated in acute myocarditis?
   Troponin
6. What is the gold standard for diagnosing myocarditis?
   Endomyocardial biopsy
7. Which imaging modality is preferred for evaluating myocardial function and inflammation in myocarditis?
   Cardiac MRI
8. What is the most common presenting symptom of myocarditis in children?
   Shortness of breath
9. Which ECG finding is commonly seen in acute myocarditis?
   ST-segment and T-wave abnormalities
10. What is the term for inflammation of both the myocardium and pericardium?
    Myopericarditis
11. Which non-infectious cause of myocarditis is more common in adolescents and young adults?
    Drug-induced myocarditis
12. What percentage of children with acute myocarditis develop dilated cardiomyopathy?
    Approximately 20-30%
13. Which medication class is typically avoided in acute myocarditis due to its potential to worsen inflammation?
    Non-steroidal anti-inflammatory drugs (NSAIDs)
14. What is the primary treatment approach for acute viral myocarditis in children?
    Supportive care and management of heart failure symptoms
15. In which cases of myocarditis are corticosteroids sometimes used?
    Autoimmune or eosinophilic myocarditis
16. What is the most severe complication of acute myocarditis?
    Cardiogenic shock
17. Which arrhythmia is commonly associated with acute myocarditis?
    Ventricular tachycardia
18. What is the typical duration of the acute phase of viral myocarditis?
    1-4 weeks
19. Which immunosuppressive medication is sometimes used in chronic myocarditis?
    Azathioprine
20. What is the mortality rate for acute fulminant myocarditis in children?
    Approximately 10-20%
21. Which mechanical circulatory support device is commonly used in severe cases of myocarditis?
    Extracorporeal membrane oxygenation (ECMO)
22. What is the term for myocarditis associated with eosinophilic infiltration of the myocardium?
    Eosinophilic myocarditis
23. Which autoimmune disease is associated with an increased risk of myocarditis?
    Systemic lupus erythematosus
24. What is the most common long-term sequela of viral myocarditis in children?
    Dilated cardiomyopathy
25. Which cardiac chamber is typically most affected in acute myocarditis?
    Left ventricle
26. What is the role of endomyocardial biopsy in pediatric myocarditis?
    To confirm diagnosis and determine etiology in unclear cases
27. Which echocardiographic finding is commonly seen in acute myocarditis?
    Decreased left ventricular ejection fraction
28. What is the typical initial management for heart failure symptoms in myocarditis?
    Diuretics and afterload reduction
29. Which viral infection has been associated with myocarditis in COVID-19?
    SARS-CoV-2
30. What is the name of the condition characterized by myocarditis following COVID-19 vaccination?
    Post-vaccination myocarditis

Further Reading

• Myocarditis in Pediatric Patients - Circulation
• Diagnosis and Management of Myocarditis in Children - The Journal of Pediatrics
• Current State of Knowledge on Aetiology, Diagnosis, Management, and Therapy of Myocarditis: A Position Statement of the European Society of Cardiology Working Group on Myocardial and Pericardial Diseases - Journal of the American College of Cardiology
• Myocarditis - New England Journal of Medicine