What is the appropriate management and treatment for a patient with suspected myocarditis, particularly those with severe symptoms or a history of underlying heart disease?

Management and Treatment of Suspected Myocarditis

All patients with definite myocarditis—whether mild, moderate, or severe—require hospitalization at an advanced heart failure center, with fulminant cases transferred to centers with mechanical circulatory support capabilities. 1, 2

Initial Diagnostic Workup

When myocarditis is suspected based on cardiac symptoms (chest pain, dyspnea, palpitations, syncope), immediately obtain:

• ECG to identify arrhythmias, conduction abnormalities, or ST-segment changes 1
• High-sensitivity cardiac troponin (elevated in myocarditis, though only 34% sensitive in some cohorts) 1
• Transthoracic echocardiogram to assess ventricular function and wall motion abnormalities 1

Cardiology consultation is mandatory for patients with rising troponin and/or ECG or echocardiographic abnormalities. 1

Advanced Imaging

Cardiac MRI is recommended in all hemodynamically stable patients with suspected myocarditis to confirm the diagnosis using Lake Louise criteria. 1 The characteristic pattern shows epicardial or midwall late gadolinium enhancement (LGE), distinguishing it from ischemic cardiomyopathy which shows endocardial enhancement in coronary distributions. 1 Importantly, patients with normal CMR (normal LV volumes, normal ejection fraction, no LGE) have excellent prognosis regardless of symptoms. 3

Endomyocardial Biopsy

While the 2022 ACC guidelines focus on non-invasive diagnosis, the 2016 AHA statement supports broader use of EMB for histologic confirmation, particularly when giant cell myocarditis, cardiac sarcoidosis, or eosinophilic myocarditis are suspected (sensitivity 80-85% for giant cell). 1 Consider EMB in patients not responding to standard therapy or when specific immunosuppressive treatment is contemplated. 4

Acute Management by Severity

Mild to Moderate Myocarditis

Hospitalize at an advanced heart failure center for continuous cardiac monitoring. 1, 2 The mortality rate for uncomplicated myocarditis is approximately 0%, but hospitalization allows detection of life-threatening arrhythmias. 5

Initiate guideline-directed medical therapy for heart failure before discharge:

• ACE inhibitors or ARBs for neurohormonal blockade 2, 6
• Beta-blockers only if hemodynamically stable, particularly for supraventricular arrhythmias 2, 6
• Aldosterone antagonists for mildly reduced LV function with stable hemodynamics 2
• Diuretics and digitalis as needed for symptomatic heart failure 6

Fulminant Myocarditis

Transfer immediately to centers with mechanical circulatory support expertise. 1, 2 Fulminant myocarditis carries 28% mortality at 60 days despite aggressive treatment, though survivors have better long-term prognosis than non-fulminant forms. 2

Initiate mechanical circulatory support urgently if shock does not reverse rapidly with inotropes or vasopressors. 2 Options include percutaneous cardiopulmonary support, ECMO, or intra-aortic balloon pump. 2

Immunosuppressive Therapy

Immunosuppression is NOT indicated for routine acute lymphocytic or viral myocarditis in adults. 2, 7 However, consider corticosteroids in specific circumstances:

• Giant cell myocarditis, cardiac sarcoidosis, or eosinophilic myocarditis (definitive indications) 2, 5
• COVID-19 myocarditis with hemodynamic compromise or multisystem inflammatory syndrome 1
• Immune checkpoint inhibitor-induced myocarditis: permanently discontinue immunotherapy and start high-dose methylprednisolone 2
• Biopsy-proven severe myocardial infiltrates, balanced against infection risk 1

Critical Restrictions and Contraindications

Exercise Abstinence

Mandate complete exercise abstinence for 3-6 months after diagnosis. 1, 2 This is non-negotiable—sudden cardiac death has been reported in athletes after strenuous exertion, and animal models show NSAIDs and exercise during acute myocarditis increase mortality. 1, 8

Before clearing return to exercise, document:

• Absence of cardiopulmonary symptoms 1
• Resolution of laboratory evidence of myocardial injury 1
• Normalization of LV systolic function 1
• Absence of arrhythmias on ECG monitoring and exercise stress testing 1

Medication Contraindications

Absolutely avoid NSAIDs unless there is documented isolated pericardial involvement without myocardial injury. 1, 9, 7 Animal models demonstrate NSAIDs enhance myocardial inflammation and increase mortality in myocarditis. 1

For pericardial involvement, NSAIDs, colchicine, and/or prednisone are reasonable. 1

Arrhythmia Management

Acute arrhythmias typically resolve with resolution of inflammation and require only supportive management. 2, 7 Insert a temporary pacemaker for symptomatic or high-grade AV block that triggers ventricular tachyarrhythmias. 2, 7

QRS width >120 ms on ECG predicts higher risk of death or transplantation. 1

Follow-Up Surveillance

Perform follow-up testing at 3-6 months to assess recovery: 2, 7

• Repeat echocardiography or cardiac MRI to assess ventricular function 2
• Reassess cardiac biomarkers 2
• Consider ambulatory rhythm monitoring and maximal-effort exercise testing 1

Dilated cardiomyopathy develops in 21% of patients during long-term follow-up, necessitating continued surveillance. 2, 7 The presence of LGE on CMR may predict subsequent ventricular arrhythmias and cardiovascular death. 1

Special Populations

COVID-19-Related Myocarditis

Patients with myocarditis and COVID-19 pneumonia requiring supplemental oxygen should receive corticosteroids. 1 Vaccine-associated myocarditis (most common in males aged 12-17 after second mRNA dose) should be diagnosed and treated analogously to infection-related myocarditis. 1

Patients with Underlying Heart Disease

These patients warrant particularly aggressive monitoring and earlier consideration for advanced therapies given their reduced cardiac reserve. Ensure continuation of baseline cardiac medications unless contraindicated by acute hemodynamic status. 2