Diagnosis of Myocarditis

The diagnosis of the patient is usually presumptive, since myocarditis does not have any obvious signs. Patients with myocarditis usually present with symptoms of acute heart failure, which can lead the doctor to believe that the underlying cause is myocarditis.

• Physical examination. During physical examination the symptoms that the patient displays may vary from slight tachycardia to severe left- or right-sided congestive heart failure, leading to a variety of symptoms described above. The doctor should also find out whether the patient had any diseases in the past (or if the patient currently has some diseases) which could possibly result in myocarditis. The doctor should also inquire if the patient came in contact with toxins and whether the patient took any substances which could have caused an allergic reaction.
• Biopsy of the heart’s tissues is still the gold standard for diagnosing myocarditis despite all the modern advancements. Biopsy is usually taken during angiography from the myocardium and endocardium, which is then examined by a pathologist. This method, however, can result in a large number of false-negative and inconclusive results. Also, it is rarely helpful clinically, since it has no impact on the treatment unless giant cell myocarditis is suspected. Repeated biopsy can be used to evaluate the success of treatment.
• ECG (electrocardiography). The signs which can be seen on ECG are very non-specific and can often be mistaken for a heart attack or pericarditis. Arrhythmias are quite common, since the inflammation of the heart’s cells damages the electrical conduction system of the heart.
• X-rays. Myocarditis leads to the damage and weakening of muscle cells. This causes the heart to dilate, which can be clearly seen on the X-rays. If the myocarditis led to left-sided congestive heart failure, this can be seen as accumulation of mucus within the bronchial tree.
• MRI (magnetic resonance imaging). Also known as cardiac magnetic resonance imaging has proved to be a valuable ally in diagnosing myocarditis, as it allows visualizing the markers of inflammation in the myocardium. In order to assess the extent of the damage done by inflammation, a gadolinium-enhanced magnetic resonance imaging can be used. This technique allows for a more accurate investigation.
• Echocardiography. This method allows not only to view the heart, but also to measure the ejection fraction, diastolic function, and cardiac output, possibly diagnosing a heart failure caused by myocarditis. The biggest advantage of this method is that it has no side effects and is noninvasive.
• Cardiac angiography. Angiography is primarily used in order to rule out heart failure caused by coronary ischemia. During this procedure biopsy samples can also be taken.
• Antimyosin scintigraphy using antimyosin-indium 111. This type of scintigraphy allows for a high degree of accuracy when diagnosing myocarditis. This technique has showed a much higher success rate in comparison to endomyocardial biopsy, which misses clinically proven myocarditis 65% of the time.

Laboratory studies

Laboratory studies are very inconclusive and non-specific. Cardiac enzyme levels (including cardiac troponins and creative kinase) may rise, though not as much as during a heart attack. However, it is not always the case, and levels of cardiac enzymes might remain normal.

Increase in titers of serum viral antibodies is probably the most informative laboratory method, since viruses are usually the main culprits behind myocarditis.