What is the treatment and management approach for a patient with suspected myocarditis?

Treatment and Management of Suspected Myocarditis

All patients with suspected myocarditis require immediate hospitalization for cardiac monitoring, as myocarditis can rapidly progress to life-threatening arrhythmias and death. 1, 2

Immediate Diagnostic Workup

When myocarditis is suspected, three tests must be obtained immediately:

• 12-lead ECG to identify QRS width >120 ms, PR-segment depression with diffuse ST-elevation (suggesting pericarditis), or low voltage with thickened LV walls (suggesting myocardial edema) 1, 2
• Cardiac troponin (preferably high-sensitivity assay) - elevated levels indicate myocardial injury and are present in the vast majority of cases 1, 2
• Transthoracic echocardiography to assess for wall motion abnormalities, ventricular dysfunction, wall thickening, and pericardial effusion 1, 2

Additional baseline biomarkers should include BNP or NT-proBNP, total CK, and C-reactive protein 1, 2. A fasting lipid profile helps distinguish atherosclerosis-related troponin elevation from myocarditis 1.

Mandatory Hospitalization Criteria

Immediate hospital admission is required for any patient with:

• Ventricular arrhythmias or heart block - these patients are at extremely high risk of sudden cardiac death and require prolonged ECG monitoring 1, 2, 3
• Progressive wall motion abnormalities with deteriorating LV function 2, 3
• Persistent or fluctuating troponin concentrations 2, 3
• Widening QRS complex 2, 3
• Frequent non-sustained ventricular arrhythmias 2, 3
• Hemodynamic instability or need for inotropic support 1, 4

Patients with fulminant myocarditis (cardiogenic shock, sustained ventricular arrhythmias, or advanced AV block) must be managed at advanced heart failure centers with expertise in mechanical circulatory support and extracorporeal membrane oxygenation. 1

Cardiac MRI for Definitive Diagnosis

Cardiac MRI should be performed in all hemodynamically stable patients with suspected myocarditis - it has 78% sensitivity and 88% specificity and is the preferred non-invasive diagnostic method 1, 2. The 2018 Updated Lake Louise Criteria require BOTH:

• ≥1 T2-based criterion (myocardial edema), AND
• ≥1 T1-based criterion (myocardial injury/fibrosis with late gadolinium enhancement) 2

CMR is particularly valuable because it can detect characteristic epicardial or mid-wall delayed gadolinium enhancement patterns and assess the extent of inflammation 1, 2.

Endomyocardial Biopsy Indications

Endomyocardial biopsy is mandatory (Class I indication) in these specific scenarios: 2

• Acute fulminant myocarditis with hemodynamic compromise despite optimal medical management
• New-onset heart failure with dilated ventricle AND new ventricular arrhythmias or heart block
• Refractory sustained ventricular tachyarrhythmias
• Failure to respond to guideline-based therapy after 1-2 weeks
• Suspected giant cell myocarditis, cardiac sarcoidosis, or eosinophilic myocarditis 1

Pre-procedural CMR localization of inflammatory changes reduces sampling errors and improves diagnostic yield 2. However, endomyocardial biopsy is NOT routinely required for most stable patients with clinically suspected myocarditis 2.

Treatment Strategy

Supportive Care (All Patients)

Initiate guideline-directed medical therapy for heart failure immediately: 1

• ACE inhibitors or ARBs for neurohormonal blockade
• Beta-blockers (if hemodynamically stable) - use cautiously as they can precipitate cardiogenic shock in severely compromised patients 1
• Low-dose aldosterone antagonists for patients with mildly reduced LV systolic function and stable hemodynamics 1
• Diuretics as needed for volume management

Strict exercise restriction for 3-6 months - sustained aerobic exercise during acute viral myocarditis increases mortality in animal models and can cause sudden death 1. Competitive sports must be avoided, with reassessment before resumption 1.

Avoid NSAIDs - they increase inflammation and mortality risk 1.

Context-Specific Immunosuppression

The decision to use immunosuppression depends critically on the clinical context:

COVID-19-related myocarditis with pneumonia requiring supplemental oxygen: Treat with corticosteroids 1

Hemodynamic compromise or MIS-A (multi-inflammatory syndrome in adults): Consider intravenous corticosteroids - this hyper-inflammatory state with acute heart failure/cardiogenic shock in the absence of sepsis may benefit from immunosuppression 1

Fulminant myocarditis or biopsy-proven severe inflammatory infiltrates: Empiric corticosteroids may be considered, balanced against infection risk 1

Giant cell myocarditis, cardiac sarcoidosis, or eosinophilic myocarditis: Immunosuppression should be strongly considered 1, 4

Lymphocytic myocarditis in adults: Immunosuppression is generally NOT indicated based on meta-analyses showing no benefit 1. This is a critical distinction - routine use of steroids in typical viral myocarditis is not supported by evidence.

Immune checkpoint inhibitor-induced myocarditis: Patients with confirmed myocarditis require emergent high-dose corticosteroids and immediate discontinuation of immunotherapy 1

Pericardial Involvement

For associated pericarditis: NSAIDs (despite general avoidance in pure myocarditis), colchicine, and/or prednisone are reasonable to alleviate chest pain and inflammation 1.

Mechanical Circulatory Support

For patients with cardiogenic shock despite optimal medical management: 1, 3

• Aggressive hemodynamic support with percutaneous cardiopulmonary support or intra-aortic balloon pump is recommended
• If VT/VF is refractory to 3-5 defibrillation attempts, initiate percutaneous cardiopulmonary support immediately 3
• Some patients can be bridged to recovery with mechanical support 1

The short-term survival rate for fulminant myocarditis is only 58%, but paradoxically, those who survive the acute phase have better long-term outcomes than non-fulminant cases (93% vs 45% alive without transplant at 11 years) 3.

Arrhythmia Management

Temporary pacemaker insertion is recommended for: 3

• Symptomatic heart block in acute myocarditis
• Ventricular tachyarrhythmias triggered by high-grade AV block

Permanent pacemaker is indicated for persistent AV block after myocarditis 3.

Acute arrhythmias often resolve with resolution of inflammation, so management is initially supportive 1. For drug-refractory ventricular arrhythmias after myocarditis, endocardial and epicardial radiofrequency catheter ablation can be effective 1.

Critical Pitfalls to Avoid

Do not rely on a single normal test to rule out myocarditis: Troponin can be normal in subacute/chronic presentations, ECG may be normal in up to 10% of cases, and echocardiography has lower sensitivity than CMR 2.

In immune checkpoint inhibitor patients, normal cardiac enzymes cannot always rule out myocarditis - these patients can have life-threatening myocarditis with associated myasthenia gravis or myositis 2.

Ventricular tachycardia is the most common sustained arrhythmia (76% of arrhythmia cases in pediatric series), and patients with sustained arrhythmias have very high risk of cardiac arrest, need for mechanical support, and death 3.

Undiagnosed myocarditis accounts for 8.6-44% of sudden cardiac deaths in young adults 3, emphasizing the importance of maintaining high clinical suspicion.

Follow-up and Surveillance

All patients require follow-up surveillance testing at 3-6 months: 1

• ECG
• Echocardiogram
• Ambulatory rhythm monitor
• Consider repeat CMR, particularly in those with ongoing symptoms or findings suggesting significant myocardial involvement

This surveillance helps gauge recovery of cardiac function and inflammation, guide heart failure management, and assess prognosis 1. In athletes with clinical or subclinical myocarditis, 41% showed complete resolution of CMR abnormalities after median 8 weeks, though only 1 of 6 with clinical myocarditis had resolution after 10 weeks 1.

Cardiology consultation is mandatory for: 1, 2

• Rising troponin and/or ECG or echocardiographic abnormalities concerning for myocarditis
• All patients with abnormal cardiac test results
• Active, ongoing consultation to discuss risk/benefit of treatments and cardiac interventions 1