What is the appropriate workup for a patient with suspected myocarditis?

Myocarditis Workup

In a patient with suspected myocarditis, immediately obtain a 12-lead ECG, high-sensitivity cardiac troponin, and transthoracic echocardiogram; if these are abnormal, admit the patient to an advanced heart failure center and proceed with cardiac MRI for definitive diagnosis. 1

Initial Clinical Assessment

Presenting Symptoms to Evaluate

Myocarditis presents with a broad spectrum of symptoms that should trigger diagnostic workup, including: 2

• Chest pain (present in 82-95% of adult cases) 3
• Dyspnea (19-49% of cases) 3
• Fatigue, palpitations, or syncope (5-7% present with syncope) 2, 3
• Recent viral illness preceding cardiac symptoms 1

Exclude Alternative Diagnoses First

Acute coronary syndrome and stress-induced cardiomyopathy must be ruled out before confirming myocarditis, especially in patients presenting with chest pain, heart failure, or new arrhythmia. 2

Mandatory Initial Testing

12-Lead Electrocardiogram

Obtain immediately in all suspected cases. 2, 1 Look for specific abnormalities: 1

• Diffuse ST-segment elevation without reciprocal depression
• T-wave changes (diffuse T-wave inversion)
• Conduction abnormalities: AV block (first-, second-, or third-degree), bundle branch block, intraventricular conduction delays
• New Q waves or low voltage
• Arrhythmias: supraventricular tachycardia, atrial fibrillation, ventricular tachycardia

Important caveat: ECG findings are neither specific nor sensitive enough for definitive diagnosis as a stand-alone test. 2

Cardiac Biomarkers

Serial high-sensitivity cardiac troponin measurements are required for diagnosis and should be obtained in all patients with clinically suspected myocarditis. 2, 1

• Troponin elevation is useful for diagnosis but may be only mildly elevated despite severe left ventricular dysfunction 1
• Creatine kinase may also be elevated 2
• Serum markers of inflammation are not very sensitive and should not be relied upon 2

Transthoracic Echocardiography

Perform immediately in all suspected cases. 2, 1 Evaluate for: 1

• Non-coronary distribution wall motion abnormalities
• Reduced ejection fraction (regional or global systolic/diastolic dysfunction)
• Ventricular dilation
• Increased wall thickness secondary to edema
• Pericardial effusion or intracavitary thrombi

Echocardiography helps rule out other causes of heart failure (valvular disease, congenital heart disease, other cardiomyopathies) but findings are nonspecific. 2

Additional Baseline Laboratory Testing

Obtain: 1

• Complete blood count
• Electrolytes, BUN, creatinine
• Glucose, calcium, magnesium, phosphorus
• Chest radiograph to evaluate for pulmonary edema or cardiomegaly

Advanced Diagnostic Imaging

Cardiac Magnetic Resonance (CMR)

Cardiac MRI should be performed in all hemodynamically stable patients with suspected myocarditis to confirm the diagnosis—it is considered the gold-standard non-invasive test. 1, 4

Diagnostic criteria include: 1

• Non-ischemic late gadolinium enhancement
• Prolonged native T1/T2 relaxation times (indicating edema and inflammation)

CMR should be completed before discharge in stable patients and provides incremental data beyond other testing. 2, 1 It has shown good agreement with histologic findings and can guide disease management. 2

Endomyocardial Biopsy (EMB)

Endomyocardial biopsy has a low diagnostic yield (5-10% with strict histologic criteria) and is reserved for specific clinical scenarios. 1

Perform EMB in patients with: 2

• Unexplained acute myocarditis requiring inotropic support or mechanical circulatory support
• Mobitz type 2 second-degree or higher heart block
• Sustained or symptomatic ventricular tachycardia
• Failure to respond to guideline-based therapy
• Suspected specific etiologies: giant cell myocarditis, cardiac sarcoidosis, eosinophilic myocarditis 1

Testing NOT Recommended

Routine viral serology testing is not recommended because it is not very specific and has limited clinical utility. 2, 1

Viral nasal swab and stool testing may be considered in young patients with suspected myocarditis, but evidence is limited. 2

Risk Stratification and Hospitalization

All Patients with Definite Myocarditis

Hospitalize all patients meeting criteria for definite myocarditis (clinical symptoms + elevated troponin + abnormal ECG/echo/CMR) at an advanced heart failure center. 5, 1, 4

Fulminant Myocarditis

Immediately transfer patients with fulminant myocarditis to tertiary centers with mechanical circulatory support and transplant capabilities. 1

Fulminant myocarditis is characterized by: 1

• Cardiogenic shock
• Need for inotropic support
• Sustained ventricular arrhythmias
• High-grade AV block

Critical prognostic information: Fulminant myocarditis carries approximately 28% mortality at 60 days despite aggressive treatment, but survivors have a more favorable long-term prognosis than non-fulminant cases. 5, 1

Follow-Up Surveillance Testing

At 3-6 months post-diagnosis, perform comprehensive reassessment including: 1, 4

• Resting ECG
• Echocardiogram or CMR to evaluate ventricular function
• Cardiac biomarkers (troponin)
• Ambulatory rhythm monitoring
• Exercise stress testing if left ventricular systolic function remains reduced

Dilated cardiomyopathy develops in 21% of patients during long-term follow-up, making surveillance essential. 5

Common Pitfalls to Avoid

• Do not rely on ECG alone—it lacks sufficient sensitivity and specificity 2
• Do not skip CMR in stable patients—it is the gold standard for non-invasive diagnosis 1
• Do not perform routine viral serology—it adds little clinical value 2, 1
• Do not delay transfer of fulminant cases—early mechanical support improves outcomes 1
• Do not perform EMB routinely—reserve for specific high-risk scenarios or diagnostic uncertainty 1