What is the initial treatment for acute myocarditis?

Initial Treatment of Acute Myocarditis

Acute myocarditis requires immediate supportive care with guideline-directed heart failure therapy, strict activity restriction for 3-6 months, avoidance of NSAIDs, and cardiac monitoring during the acute phase, while immunosuppression is reserved only for specific etiologies such as giant cell myocarditis, cardiac sarcoidosis, or eosinophilic myocarditis. 1, 2

Immediate Supportive Measures

Hemodynamic Support and Monitoring

• All patients with acute myocarditis require cardiac monitoring during the acute phase to detect life-threatening arrhythmias, particularly ventricular tachycardia (the most common sustained arrhythmia) and high-grade AV blocks 1, 2, 3
• Patients presenting with hemodynamic instability (inability to maintain adequate end-organ perfusion) require aggressive hemodynamic support with inotropic agents or mechanical circulatory support such as percutaneous cardiopulmonary support or intra-aortic balloon pump 3, 4
• Temporary pacemaker insertion is indicated for symptomatic heart block in acute myocarditis; permanent pacing is required if AV blocks persist 3
• Mechanical circulatory support should be initiated early in fulminant cases, particularly if ventricular arrhythmias are refractory to 3-5 defibrillation attempts 3

Heart Failure Management

• Treat myocarditis presenting as dilated cardiomyopathy according to current heart failure guidelines with neurohormonal blockade using ACE inhibitors (or ARNIs) and beta-blockers 1, 2, 3
• This applies to approximately 75% of admitted patients who have an uncomplicated course 4
• Patients with severe heart failure may require endotracheal intubation and mechanical ventilation 1

Critical Restrictions and Contraindications

Activity Restriction

• Competitive sports and sustained aerobic exercise must be avoided for 3-6 months after diagnosis due to increased mortality risk demonstrated in animal models and risk of sudden death 1, 2
• Reassessment with clinical evaluation and functional testing is mandatory before resuming competitive activities 1, 2
• Bed rest is recommended for the first 12-24 hours in patients with significant ventricular damage 1

Medication Contraindications

• NSAIDs are absolutely contraindicated due to increased inflammation and mortality risk 1, 2
• Long-acting oral nitrate preparations should be avoided in acute management 1

Immunosuppression: When and When Not

Generally NOT Indicated

• Immunosuppression is generally not indicated for acute lymphocytic myocarditis in adults based on individual trials and meta-analyses 1, 2
• Premature immunosuppression in viral myocarditis may be harmful 2

Specific Indications for Immunosuppression

Immunosuppression should be considered only for:

• Giant cell myocarditis 1, 2
• Cardiac sarcoidosis 1, 2
• Eosinophilic myocarditis 1, 2
• Immune checkpoint inhibitor-related myocarditis (high-dose corticosteroids recommended) 2
• Myocarditis due to systemic autoimmune disorders 4

Arrhythmia Management

Acute Phase

• Arrhythmia management is primarily supportive, as arrhythmias often resolve with resolution of acute inflammation 1
• Ventricular tachycardia triggered by high-grade AV block requires temporary pacemaker insertion 3
• For drug-refractory ventricular arrhythmias after myocarditis, endocardial and epicardial radiofrequency catheter ablation can be effective 1

ICD Considerations

• Implantable cardioverter-defibrillator placement should be delayed during the acute phase to allow for left ventricular ejection fraction recovery 5
• A wearable cardioverter-defibrillator may be beneficial as a bridge during this recovery period 5
• Standard ICD indications for nonischemic cardiomyopathy apply after the acute phase if LVEF remains ≤35% 5

Endomyocardial Biopsy Indications

EMB should be performed in patients with:

• Unexplained acute myocarditis requiring inotropic support or mechanical circulatory support 1, 2
• Mobitz type 2 second-degree or higher heart block 1, 2
• Sustained or symptomatic ventricular tachycardia 1, 2
• Failure to respond to guideline-based therapy 1, 2

Prognostic Considerations

Risk Stratification

• Uncomplicated myocarditis has approximately 0% mortality 4
• Myocarditis complicated by acute heart failure or ventricular arrhythmias carries a 12% rate of in-hospital mortality or need for heart transplant 4
• Hemodynamically unstable patients (2-9% of cases) have approximately 28% mortality or transplant rate at 60 days 4
• Paradoxically, fulminant myocarditis has better long-term prognosis than non-fulminant forms (93% vs 45% alive without transplant at 11 years) 3

Common Pitfalls to Avoid

• Failure to restrict physical activity during acute phase can lead to increased mortality and sudden death 2
• Delaying cardiac MRI may miss the diagnostic window for definitive diagnosis 2
• Relying solely on ECG or standard laboratory markers is insufficient due to low sensitivity and specificity 2
• Undiagnosed myocarditis accounts for 8.6-44% of sudden cardiac deaths in young adults 3