From the Guidelines
Myocarditis is diagnosed based on a combination of clinical, laboratory, and imaging findings, including cardiac symptoms, elevated troponin levels, and abnormal electrocardiographic, echocardiographic, and cardiac magnetic resonance (CMR) findings, as stated in the 2022 ACC expert consensus decision pathway 1.
Diagnostic Criteria
The diagnosis of myocarditis can be made when there is:
- Histological evidence of myocardial inflammation on endomyocardial biopsy
- Elevated troponin levels, typically above 0.1 ng/mL
- Abnormal ECG findings, such as ST-segment elevation or Q-waves
- Abnormal cardiac imaging results, such as reduced left ventricular function on echocardiography or late gadolinium enhancement on cardiac MRI
- Symptoms consistent with myocarditis, such as chest pain, shortness of breath, or palpitations, as outlined in the 2022 ACC expert consensus decision pathway 1 and supported by the European Society of Cardiology guidelines 1.
Classification of Myocarditis
Myocarditis can be classified into three levels of certainty:
- Possible myocarditis: characterized by cardiac symptoms, elevated troponin levels, and abnormal electrocardiographic and/or echocardiographic findings, but without definitive evidence of myocarditis on biopsy or CMR 1
- Probable myocarditis: characterized by all features of possible myocarditis, with follow-up CMR and/or biopsy showing abnormalities consistent with previous myocarditis 1
- Definite myocarditis: characterized by all features of possible myocarditis, with CMR and/or biopsy performed at the time of presentation demonstrating findings consistent with active myocarditis 1, as also recommended by the European Society of Cardiology guidelines 1. The use of CMR has become a key evaluation tool in patients with suspected myocardial inflammation, providing non-invasive, biopsy-like imaging features of myocardial inflammation, as stated in the 2018 expert recommendations on cardiovascular magnetic resonance in nonischemic myocardial inflammation 1.
From the Research
Diagnostic Criteria for Myocarditis
The diagnostic criteria for myocarditis, an inflammatory heart muscle disease, have been established and include clinical and imaging findings, particularly the use of cardiac magnetic resonance and positron emission tomography 2. According to the European Society of Cardiology task force on myocardial and pericardial diseases, a correct diagnosis is fundamental to proper patient management and should always be sought, although a definite diagnosis is only provided by endomyocardial biopsy 3.
Clinical Presentation and Diagnosis
Myocarditis can present with a range of clinical symptoms, including an asymptomatic, subacute, acute, fulminant, or chronic course, and may have focal or diffuse involvement of the myocardium depending on the cause and time point of the disease 2. The diagnosis of myocarditis can be challenging due to non-specific symptoms and lack of specific blood biomarkers, but cardiac imaging plays an important role in the evaluation of myocarditis 4.
Imaging Findings
Cardiac magnetic resonance imaging (CMR) has become the method of choice for the diagnosis of myocarditis, offering non-invasive and accurate diagnosis and clinical follow-up of patients with myocarditis 5, 6. CMR findings at diagnosis and during follow-up, as well as differential diagnosis with other acute processes like myocardial infarction, are essential for proper patient management 6.
Key Points
- Myocarditis is an inflammatory heart muscle disease with heterogeneous clinical presentation and outcome 3
- Diagnostic criteria include clinical and imaging findings, particularly the use of cardiac magnetic resonance and positron emission tomography 2
- Cardiac magnetic resonance imaging (CMR) is the method of choice for the diagnosis of myocarditis 5, 6
- Endomyocardial biopsy is the diagnostic choice in life-threatening cases with suspicion of fulminant myocarditis 5