What are the common causes and treatment options for myocarditis in an adolescent?

Myocarditis in Adolescents: Causes and Treatment

Common Causes

Viral infections are the most common cause of myocarditis in adolescents in North America and Western Europe, with enteroviruses (particularly Coxsackie B), adenoviruses, and parvovirus B19 being the predominant pathogens. 1

Infectious Etiologies

Viral Causes (Most Common):

• Enteroviruses (Coxsackie B virus) remain the most important pathogens in acute and fulminant myocarditis in adolescents 1
• Parvovirus B19 and human herpes virus 6 are the most frequent viruses identified in Western Europe 1
• Adenoviruses are another common viral cause in the pediatric population 1
• COVID-19 mRNA vaccination causes myocarditis rarely, with highest rates in male adolescents aged 12-17 years after the second vaccine dose 1

Other Infectious Causes:

• Post-streptococcal rheumatic heart disease (important in specific geographic regions) 1
• HIV (in endemic areas or at-risk populations) 1
• Diphtheria, typhoid fever, and rubella (in specific world regions based on travel history) 1

Non-Infectious Etiologies

Autoimmune/Inflammatory:

• Kawasaki disease is an important non-infectious cause in specific demographic groups where immunomodulatory therapy can impact outcomes 1
• Giant cell myocarditis is an aggressive autoimmune disorder that is rapidly fatal without advanced heart failure treatment and multidrug immunosuppression 1
• Cardiac sarcoidosis often affects the heart without clinical evidence of extracardiac disease 1
• Eosinophilic myocarditis from hypereosinophilic syndrome (eosinophils >1500/μL) 1

Drug-Related:

• Hypersensitivity reactions to medications 2

Clinical Presentation

Key Features to Identify:

• Cardiac symptoms: acute chest pain (pericarditic or pseudoischemic), dyspnea at rest or with exercise, fatigue, palpitations, syncope, or aborted sudden cardiac death 1
• Preceding viral illness: recent upper respiratory or gastrointestinal symptoms (days to weeks prior) 3
• Systolic dysfunction, arrhythmias, and low cardiac output syndrome are the classic triad 1
• Fulminant myocarditis presents with higher cardiac troponin levels and lower left ventricular ejection fraction compared to acute myocarditis 1

Diagnostic Approach

Initial Testing Algorithm:

1. ECG looking for: ST/T-wave changes, atrioventricular blocks, bundle branch blocks, ventricular arrhythmias, atrial fibrillation, reduced R-wave height, or abnormal Q waves 1

2. Elevated cardiac troponin (preferably high-sensitivity assay) is essential for diagnosis 1

3. Echocardiogram to assess for: regional wall motion abnormalities, global systolic or diastolic dysfunction, ventricular dilatation, increased wall thickness, pericardial effusion, or endocavitary thrombi 1

4. Cardiology consultation is recommended for rising troponin and/or ECG or echocardiographic abnormalities 1

5. Cardiac MRI with gadolinium is recommended in hemodynamically stable patients with suspected myocarditis to confirm myocardial inflammation 1

   • Lake Louise Criteria (2009) should be used for diagnosing myocardial inflammation 1
   • Look for subepicardial or mid-myocardial late gadolinium enhancement (LGE) in a non-coronary distribution, typically involving the lateral wall 1, 3
   • T2-weighted imaging or T2-mapping demonstrates myocardial edema 1

6. Endomyocardial biopsy remains the gold standard, particularly when specific etiologies requiring immunomodulation (giant cell or eosinophilic myocarditis) are suspected 1

Additional Workup:

• Travel and exposure history is essential to identify region-specific causes 1
• Screen for coinfection with ≥2 viruses, which occurs in a substantial minority of cases 1
• First-degree relative screening should be undertaken, as familial cardiomyopathy occurs in 30% of pediatric cases 1

Treatment Strategies

Acute Management

Hospitalization:

• All adolescents with definite myocarditis should be hospitalized, ideally at an advanced heart failure center 1
• Fulminant myocarditis requires management at centers with expertise in advanced heart failure, mechanical circulatory support, and advanced therapies 1

Supportive Care:

• Guideline-directed medical therapy for heart failure should be initiated and continued after discharge 1
• Standard heart failure therapy is the cornerstone, as most patients respond well 4

Immunosuppressive Therapy

Critical Decision Points:

DO NOT use corticosteroids for lymphocytic (viral) myocarditis - the American Heart Association definitively showed no beneficial effect of prednisone with either azathioprine or cyclosporine, and corticosteroids can reactivate viral infections leading to ongoing inflammation 5

DO use corticosteroids for:

• Myocarditis with COVID-19 pneumonia requiring supplemental oxygen 1
• Eosinophilic myocarditis (corticosteroid therapy is generally considered primary therapy, though efficacy is not well supported) 1
• Suspected or confirmed COVID-19 myocarditis with hemodynamic compromise or multisystem inflammatory syndrome in adults (MIS-A) 1
• Biopsy evidence of severe myocardial infiltrates or fulminant myocarditis (empiric use may be considered, balanced against infection risk) 1

Specific Immunomodulation:

• Giant cell myocarditis requires multidrug immunosuppression to prevent rapid fatality 1
• Cardiac sarcoidosis benefits from immune-modulating therapy in collaboration with pulmonology or rheumatology 1
• Recurrent or severe myocarditis may warrant intravenous immunoglobulin (IVIG) and steroids based on case reports 6

Pericardial Involvement

For suspected pericardial involvement, treatment with NSAIDs, colchicine, and/or prednisone is reasonable 1

Arrhythmia Management

ICD implantation:

• ICD implantation is reasonable for patients with cardiac sarcoidosis 1
• For other myocarditis etiologies, ICD use for primary prevention is controversial in adolescents, as deaths from advanced heart failure are more common than sudden death 1
• Risk factors for sudden cardiac death include: age at diagnosis <14.3 years, LV dilation, and LV posterior wall thinning 1
• Extensive LGE on CMR is the strongest independent predictor of sudden cardiac death and warrants shared decision-making about ICD implantation 3

Prognosis

Favorable Prognostic Factors:

• Younger age (especially <2 years) 1
• Higher ejection fraction at presentation 1
• Presence of biopsy-confirmed or probable myocarditis (better outcomes than idiopathic dilated cardiomyopathy) 1

Poor Prognostic Indicators:

• BNP level >300 pg/mL is a strong predictor of death, transplantation, or heart failure hospitalization 1
• Death or transplant occurs in nearly half of pediatric dilated cardiomyopathy patients within the first 2 years of diagnosis 1
• Giant cell myocarditis has the worst prognosis without aggressive treatment 1

Critical Pitfalls to Avoid

• Do not assume all myocarditis is viral - obtain careful travel history and consider non-infectious causes, especially in cases not responding to supportive care 1
• Do not use empiric corticosteroids for presumed viral myocarditis - this can worsen outcomes by promoting viral persistence 5
• Do not discharge without cardiology follow-up - repeat CMR may be needed to assess for resolution of inflammation 1
• Do not miss vaccine-associated myocarditis - maintain high suspicion in male adolescents presenting within 4 days after second mRNA COVID-19 vaccine dose 1, 7