How myocarditis is diagnosed:
tests, troponin and cardiac MRI

Article written and reviewed by Dr Luca Moretti

There is no single test that, on its own and in every situation, can confirm or exclude myocarditis. Diagnosis is based on the combination of symptoms and clinical history, electrocardiogram, blood tests, echocardiogram and, above all, when indicated, cardiac magnetic resonance imaging. In selected cases, an endomyocardial biopsy may be necessary.
An elevated troponin level may support suspicion of myocardial injury, but by itself it does not prove that the cause is myocarditis. Likewise, a normal troponin level, a normal ECG or a normal echocardiogram do not completely rule out the disease when clinical suspicion is high.

Investigations that may form part of the diagnostic pathway include:

• medical examination and reconstruction of symptoms and preceding events;
• electrocardiogram (ECG);
• troponin and other blood tests;
• echocardiogram;
• cardiac magnetic resonance imaging (CMR);
• tests to rule out other causes of cardiac injury, when necessary;
• endomyocardial biopsy in selected situations.

Myocarditis can mimic other heart conditions and can vary greatly in severity. For this reason, the diagnostic pathway is tailored to the individual patient and does not consist of a simple sequence of identical tests for everyone.

From suspected myocarditis to diagnosis

The first step is to understand how the problem began. Chest pain, shortness of breath, palpitations, syncope or symptoms of heart failure may lead the doctor to suspect possible myocardial inflammation, especially when there are factors such as a recent infection, an autoimmune disease, exposure to certain drugs or substances, or a previous episode of myocarditis.
These factors may increase or reduce suspicion, but none is specific. Chest pain and elevated troponin, for example, can also occur in a heart attack; dyspnea and fatigue can result from numerous cardiac or respiratory diseases.

For this reason, diagnosis also includes looking for alternative diagnoses. Depending on age, risk factors and the clinical picture, it may be necessary to exclude coronary artery disease by coronary CT angiography or coronary angiography. Other investigations may be required if pulmonary embolism, cardiomyopathies, systemic diseases or other causes of cardiac injury are suspected.

ECG, troponin and other blood tests

The ECG may show abnormalities of repolarization, the ST segment, conduction or rhythm, but findings are variable and there is no characteristic tracing that is present in every patient. A normal ECG, especially in mild forms or at certain stages of the disease, is not sufficient to rule out myocarditis.
Troponin is a marker of myocardial cell injury. When elevated, it can strengthen suspicion in the appropriate context, but it does not identify the cause of the injury and therefore cannot, on its own, distinguish myocarditis from a heart attack or other conditions.

Other tests may include C-reactive protein and other inflammatory markers, complete blood count, renal and liver function, electrolytes and natriuretic peptides when heart failure is suspected. The choice varies according to the presentation.
By contrast, indiscriminately testing the blood for every possible virus is generally not useful for establishing the cause of myocarditis: the presence of antibodies or a recent infection does not prove that that specific agent is causing the inflammation of the heart.

What the echocardiogram shows

The echocardiogram makes it possible to assess the size and function of the heart chambers, wall motion, ventricular function, valves and the possible presence of fluid in the pericardium. It is particularly important for understanding whether myocarditis has impaired the heart's pumping ability and for rapidly identifying higher-risk clinical pictures.
Ventricular function may be reduced globally or regionally, but it may also be preserved. A normal echocardiogram therefore does not exclude myocardial inflammation, especially if the disease is limited and has not caused obvious mechanical dysfunction.

In more severe forms, echocardiography helps assess the presence of heart failure, right ventricular impairment, elevated filling pressures and other abnormalities that are useful for deciding the level of care required. It can also be repeated during follow-up to document recovery of cardiac function.

Cardiac magnetic resonance imaging: why it is so important

Cardiac magnetic resonance imaging is now one of the central tools for the non-invasive diagnosis of myocarditis. In addition to measuring cardiac volumes and function, it allows characterization of myocardial tissue and assessment for signs of edema, meaning increased water content related to inflammation, as well as injury or scarring.
The criteria used include parameters sensitive to T1 and T2 changes and assessment of late gadolinium enhancement (LGE). The combination of these findings, interpreted in the correct clinical context, increases the likelihood that myocardial inflammation is present.

MRI should not be interpreted as a simple positive or negative result. The timing of the examination, image quality, type of presentation and extent of abnormalities all influence its diagnostic value. In addition, some findings may persist during healing and may have prognostic significance even when active inflammation has decreased.
In acute myocarditis, CMR therefore helps both to support the diagnosis and, subsequently, to assess how the injury evolves.

When a heart biopsy is needed

Endomyocardial biopsy involves taking small samples of tissue from the heart to analyze under a microscope and, when necessary, using immunohistochemical and molecular techniques. It is the test that can directly define the type of inflammation and can be decisive when knowing the etiology or histological form changes treatment.
However, it is not performed routinely in everyone with suspected myocarditis. Because it is an invasive procedure, it is reserved mainly for situations in which there is a clear diagnostic benefit, for example severe forms, rapid deterioration, particular arrhythmias or conduction disturbances, failure to respond to treatment, or suspected specific forms that require targeted therapies.

In a stable patient with a typical presentation and compatible MRI findings, the pathway may therefore be predominantly non-invasive. In an unstable patient or one with unusual features, however, much more extensive investigation may be required. Correct diagnosis does not depend on the number of tests performed, but on the ability to integrate them with the clinical picture.

Frequently asked questions about myocarditis diagnosis

Which tests are needed to diagnose myocarditis?
Assessment may include an ECG, troponin and other blood tests, an echocardiogram and cardiac magnetic resonance imaging. Investigations are selected according to symptoms, severity and clinical probability.

Does a high troponin level always mean myocarditis?
No. Troponin indicates damage to heart cells, but it can increase in many other conditions, including a heart attack. It must therefore be interpreted together with the clinical picture and the other tests.

Does a normal troponin level rule out myocarditis?
No. ECG, troponin and echocardiogram may be normal in some people with myocarditis; if clinical suspicion remains high, further investigations may be needed.

Is cardiac magnetic resonance imaging always necessary?
MRI has a central role in non-invasive diagnosis because it can show myocardial edema and damage, but the diagnostic pathway is tailored to the individual case and to the patient's stability.

Is a heart biopsy always needed to diagnose myocarditis?
No. Endomyocardial biopsy is not performed in every case. It is particularly important in selected situations, especially when the disease is severe or when identifying the precise type of inflammation may change treatment.