What is the approach to diagnosing and managing myocarditis (inflammation of the heart muscle)?

Myocarditis Work-Up

The diagnostic work-up for suspected myocarditis requires a systematic approach starting with ECG, cardiac troponins, and echocardiography, followed by cardiac MRI for hemodynamically stable patients, with endomyocardial biopsy reserved for fulminant cases or when specific etiologies requiring targeted therapy are suspected. 1

Clinical Suspicion Criteria

Myocarditis should be suspected when ≥1 clinical presentation AND ≥1 diagnostic criterion from different categories are present, after excluding coronary stenosis ≥50% and other known cardiovascular causes. 1

Key Clinical Presentations:

• Acute chest pain (pericarditic or pseudoischemic pattern) 1
• New-onset dyspnea, fatigue, or heart failure symptoms (days to 3 months) 1
• Palpitations, syncope, or aborted sudden cardiac death 1
• Unexplained cardiogenic shock 1

Initial Diagnostic Testing

First-Line Tests (Perform in All Suspected Cases):

12-Lead ECG/Holter Monitoring: 1, 2

• Look for ST-segment elevation without reciprocal depression (common finding) 3
• Diffuse T-wave inversion across multiple leads 3
• QRS prolongation ≥120 ms (associated with worse prognosis) 3, 2
• AV blocks (first to third degree), bundle branch blocks 1, 3
• PR-segment depression suggesting associated pericarditis 2
• Low voltage with thickened LV walls suggesting myocardial edema 2

Cardiac Biomarkers: 1

• Troponin I or T (elevated in only 34% of biopsy-proven cases, but high-sensitivity assays may improve detection) 1, 4
• Troponin I is superior to CK-MB for detecting myocyte injury in myocarditis 4
• Troponin elevations correlate with ≤1 month symptom duration, suggesting early myocyte necrosis 4
• CK-MB (less sensitive, elevated in only 5.7% of biopsy-proven cases) 4
• ESR and CRP (nonspecific markers of inflammation) 1, 2

Transthoracic Echocardiography: 1, 2

• Assess for regional or global wall motion abnormalities 1, 2
• Evaluate ventricular systolic and diastolic function 1, 2
• Look for increased wall thickness (secondary to edema in acute phase) 1
• Identify pericardial effusion or intracavitary thrombi 1
• Rule out valvular disease, congenital heart disease, or other cardiomyopathies 1

Advanced Imaging

Cardiac MRI (CMR) - Recommended for Hemodynamically Stable Patients: 1, 3, 2

• CMR should be performed even before endomyocardial biopsy as it is highly sensitive for confirming acute myocarditis 2
• Look for the classic triad: myocardial edema (T2-weighted sequences), hyperemia/capillary leak (early gadolinium enhancement), and irreversible injury/necrosis (late gadolinium enhancement with epicardial or mid-wall pattern) 1, 3, 2
• CMR provides tissue characterization that echocardiography cannot 1

Endomyocardial Biopsy Indications

EMB should be performed in specific high-risk scenarios only: 1, 2, 5

Class I Indications (Life-Threatening Disease):

• Acute fulminant myocarditis with refractory ventricular tachyarrhythmias in severe acute heart failure 2
• Hemodynamically compromising sustained ventricular arrhythmias or aborted cardiac arrest 2
• Clinical deterioration with heart block or ventricular arrhythmias after excluding obstructive coronary disease 3
• Suspected giant cell myocarditis or cardiac sarcoidosis (requires specific immunosuppression) 2, 5

EMB has <1% complication rate when performed by experienced operators and provides definitive histologic, immunohistochemical, and molecular biological diagnosis. 1, 5

Risk Stratification and Triage

High-Risk Features Requiring Advanced Heart Failure Center Evaluation: 3, 2

• Hypotension or cardiogenic shock 3
• Ventricular arrhythmias (sustained or non-sustained) 3, 2
• Advanced heart block 3, 2
• Progressive wall motion abnormalities with deteriorating LV function 2
• Persistent or fluctuating troponin concentrations 2
• Widening QRS complex 2

Mandatory Hospital Admission Criteria: 2

• Any ventricular arrhythmias or heart block (high risk of sudden cardiac death) 2
• Requires prolonged ECG monitoring 2

Clinical Phenotypes

Distinguish between two critical settings: 2

Acute Fulminant Myocarditis:

• Refractory malignant ventricular tachyarrhythmias with severe acute heart failure 2
• Adverse short-term prognosis with early death from multisystem failure 2
• Approximately 28% mortality or heart transplant rate at 60 days in hemodynamically unstable patients 6
• May require inotropic agents or mechanical circulatory support (e.g., ECMO) 6

Chronic Inflammatory Cardiomyopathy:

• Different prognosis and treatment approach 2
• May develop years after initial recovery 7

Additional Diagnostic Considerations

Viral Serology: Not routinely recommended as it lacks specificity 1

PET Imaging: Shows good agreement with CMR criteria but limited by availability and cost 1

Exclude Coronary Disease: Coronary angiography or CT angiography to rule out coronary stenosis ≥50% 1

Common Pitfalls

• Do not rely on ECG alone - it is neither sensitive nor specific enough for definitive diagnosis 1
• Troponin may be normal in up to 66% of biopsy-proven cases, especially beyond the first month of symptoms 1, 4
• Do not aggressively pursue EMB in stable patients with typical presentations - approximately 75% have uncomplicated course with <1% mortality 6
• Routine immunosuppression is not indicated for lymphocytic myocarditis (no benefit shown in Myocarditis Treatment Trial), but is appropriate for eosinophilic, giant cell, or autoimmune-related myocarditis 1, 6