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

Myocarditis in Adolescents: Causes and Treatment

Causes of Myocarditis in Adolescents

Viral infections are the predominant cause of myocarditis in adolescents, with enteroviruses, adenovirus, and parvovirus B19 accounting for the majority of cases. 1, 2

Infectious Etiologies

• Viral pathogens represent the most common cause, including enteroviruses, adenovirus, parvovirus B19, and influenza 1, 2, 3
• Chlamydia myocarditis has been specifically implicated in sudden cardiac death among young athletes 1, 2
• Bacterial infections such as Lyme disease and diphtheria can cause myocarditis, frequently presenting with heart block 2
• SARS-CoV-2 associated Multisystem Inflammatory Syndrome in Children (MIS-C) is an increasingly recognized cause, with older children more likely to develop myocarditis 2

Non-Infectious Etiologies

• Hypersensitivity reactions to drugs or vaccines can trigger eosinophilic myocarditis 1, 2, 4
• Autoimmune conditions including systemic lupus erythematosus can affect the myocardium 2, 3
• Giant cell myocarditis is a severe form with dramatic clinical course that frequently affects young patients 1, 2
• Cardiac sarcoidosis should be considered in the differential diagnosis 2

---

Treatment Approach

All adolescents with myocarditis must be hospitalized immediately at an advanced heart failure center for continuous cardiac monitoring, as ventricular arrhythmias carry a 5.4-fold increased risk of cardiac arrest, mechanical circulatory support need, or death. 1, 2, 5

Initial Stabilization and Monitoring

• Establish continuous ECG monitoring and invasive arterial line placement for hemodynamic monitoring in unstable patients 5
• Obtain ECG every 48 hours while hospitalized and at each follow-up visit to detect conduction abnormalities 2
• Monitor cardiac troponin and BNP/NT-proBNP levels sequentially to assess disease progression 2, 5
• Perform echocardiography at presentation, then repeat at 7-14 days and 4-6 weeks minimum 2, 5

Heart Failure Management

Initiate guideline-directed heart failure therapy with ACE inhibitors or ARBs for neurohormonal blockade once hemodynamically stable. 2, 5

• Start ACE inhibitors (e.g., captopril 1-6.25 mg) only if systolic blood pressure >100 mmHg 5
• Use beta-blockers cautiously and only if hemodynamically stable; avoid in overt heart failure with pulmonary congestion or low output 2, 5
• Add aldosterone antagonists for patients with mildly reduced LV function and stable hemodynamics 2
• Use diuretics for volume management as needed 2, 5

Inotropic Support for Cardiogenic Shock

• Initiate individualized inotropic support with epinephrine, levosimendan, dopamine, or dobutamine based on hemodynamic response 5
• Start dopamine at 5 mcg/kg/min, increasing in 5-10 mcg/kg/min increments up to 20-50 mcg/kg/min; use caution at doses >7 mcg/kg/min due to increased pulmonary vascular resistance 5
• Consider dobutamine 2-20 mcg/kg/min for myocardial dysfunction with adequate blood pressure 5

Mechanical Circulatory Support

Initiate mechanical circulatory support urgently if shock does not reverse rapidly with pharmacological therapy, as this bridges the acute but often curable stage and paradoxically leads to better long-term outcomes than non-fulminant presentations. 1, 2, 5

• Percutaneous cardiopulmonary support, ECMO, or intra-aortic balloon pump are recommended for fulminant myocarditis with refractory shock 1, 2, 5
• Initiate ECMO for refractory VT or VF not responding to 3-5 defibrillation attempts 1, 5
• Pre-cardiac arrest state in acute fulminant myocarditis is an indication for ECMO 5

Arrhythmia Management

Ventricular tachycardia accounts for 76% of sustained arrhythmias in pediatric myocarditis, and patients with sustained arrhythmias have a 5.4-fold increased risk of adverse outcomes. 1, 5

• Insert a temporary pacemaker for symptomatic heart block or high-grade AV block that triggers ventricular tachyarrhythmias 2
• Place patients with conduction abnormalities on telemetry while hospitalized 2
• Consider Holter monitoring at clinical follow-up for detected conduction issues 2
• Most acute arrhythmias resolve with resolution of inflammation and require only supportive management 2
• If persistent AV block develops, permanent pacing is indicated, but device selection must account for LV dysfunction extent and prognosis 1, 2

Immunosuppression: Etiology-Specific Approach

Immunosuppression is generally NOT indicated for typical viral myocarditis in adolescents, but should be considered for specific subtypes. 2, 6, 3

When to Use Immunosuppression:

• Giant cell myocarditis requires immunosuppressive therapy due to severe prognosis 1, 2, 3
• Eosinophilic myocarditis may benefit from corticosteroid therapy, though efficacy is not well-supported 1, 2, 4
• Cardiac sarcoidosis warrants immunosuppression 2
• MIS-C patients require immunomodulatory treatment with IVIG (2 g/kg based on ideal body weight) and corticosteroids (1-2 mg/kg/day), particularly those with life-threatening manifestations 2, 5

Critical Caveat:

• Do NOT use corticosteroids as monotherapy without IVIG in pediatric myocarditis, as this approach shows no benefit 5
• Classic immunosuppressive drugs like cyclosporine A and cyclophosphamide are not effective against all types of immunity and may interfere with host control of persistent viral infection 6

---

Critical Activity Restrictions

Mandate complete exercise abstinence for 3-6 months after diagnosis, as sustained aerobic exercise during acute viral myocarditis increases mortality and can cause sudden death. 2

• Prohibit all competitive sports participation for the entire 3-6 month period 2
• This restriction is critical as myocarditis is an important cause of sudden cardiac death in young athletes, with post-mortem data implicating myocarditis in 8.6-44% of sudden deaths in young adults 1, 2

---

Medications to Avoid

Absolutely avoid NSAIDs due to increased inflammation and mortality risk in myocarditis. 2

---

Diagnostic Evaluation

Cardiac MRI

Cardiac MRI with gadolinium contrast using the 2009 Lake Louise Criteria is indicated to confirm myocardial inflammation, with 82% sensitivity in pediatric myocarditis. 1, 5

• The Lake Louise Criteria require two positive findings: one T2-based marker (edema) and one T1-based marker (T1-weighted LGE showing necrosis/scarring) 1
• CMR shows characteristic subepicardial or patchy LGE enhancement (non-coronary distribution) distinguishing myocarditis from myocardial infarction 1, 5
• Consider cardiac MRI at 2-6 months post-acute illness for patients with moderate-to-severe LV dysfunction to evaluate for myocardial fibrosis and scarring 2, 5

Endomyocardial Biopsy

• Consider EMB in patients who fail to recover clinically to guide targeted therapy, particularly for giant cell or eosinophilic myocarditis requiring immunomodulator therapy 1, 5
• Giant cell myocarditis diagnosis is confirmed by endomyocardial biopsy showing typical multinucleated giant cells in inflammatory lesions 1

---

Follow-Up Surveillance

Perform follow-up testing at 3-6 months to assess recovery, as 21% of myocarditis patients develop dilated cardiomyopathy during long-term follow-up. 1, 2

• Repeat echocardiography at minimum 7-14 days, 4-6 weeks, and consider at 1 year for those with acute cardiac involvement 2, 5
• Patients with LV dysfunction and coronary artery aneurysms require more frequent echocardiograms 2
• Cardiac MRI at 2-6 months allows evaluation for myocardial fibrosis and scarring, which represent potential long-term complications 2, 5
• Continue serial monitoring of inflammatory markers, BNP/NT-proBNP, and troponin to guide treatment decisions 5

---

Prognostic Considerations

Fulminant myocarditis has an adverse short-term prognosis (58% short-term survival) but paradoxically better long-term outcomes than non-fulminant forms, with 93% alive without transplant at 11 years versus 45% for non-fulminant cases. 1

• Younger patients (<1 year) have worse outcomes than older children and adolescents 7
• Approximately 75% of patients admitted with myocarditis have an uncomplicated course with 0% mortality 3
• Myocarditis complicated by acute heart failure or ventricular arrhythmias has a 12% rate of in-hospital mortality or need for heart transplant 3
• Patients requiring mechanical circulatory support have approximately 28% mortality or heart transplant rate at 60 days 3