Myocarditis

Myocarditis, also known as inflammatory cardiomyopathy, is an acquired cardiomyopathy characterised by inflammation of the heart muscle. This condition can lead to symptoms such as shortness of breath, chest pain, decreased ability to exercise, and irregular heartbeat.

The duration of these symptoms can vary from hours to months, and complications may include heart failure due to dilated cardiomyopathy or cardiac arrest.

Signs and Symptoms

The signs and symptoms of myocarditis relate to both the inflammation of the myocardium and the resulting heart muscle dysfunction. Common symptoms include chest pain, often sharp or stabbing, shortness of breath that worsens when lying down, palpitations, and dizziness or fainting. Fever, especially when infectious, and dull heart sounds may also be observed.

Since myocarditis often follows a viral illness, symptoms like fever, rash, loss of appetite, abdominal pain, vomiting, diarrhoea, joint pains, and fatigue are also common. In children, respiratory symptoms can mimic asthma. Myocarditis can be classified as fulminant or acute based on symptom severity and progression, influencing treatment and outcomes.

Causes

While many cases of myocarditis are idiopathic, known causes include:

• Infections: Viral infections are prevalent in developed countries, with Coxsackie viruses being common culprits. Globally, Chagas disease, caused by Trypanosoma cruzi, is the leading cause.
• Immune conditions: Autoimmune disorders, allergic reactions, and toxic shock syndrome can trigger myocarditis.
• Drug reactions and toxins: Certain medications, alcohol, stimulants, and heavy metals can cause myocarditis.
• Vaccination: Rare side effects of some vaccines, such as the smallpox and COVID-19 mRNA vaccines, can include myocarditis.
• Physical injuries: Electric shock, hyperpyrexia, and radiation can lead to myocarditis.

Diagnosis

Diagnosis of myocarditis involves a combination of clinical evaluation and diagnostic tests. Elevated markers of inflammation and myocardial damage, such as C-reactive protein, erythrocyte sedimentation rate, troponin, and creatine kinase, can suggest myocarditis. ECG findings like sinus tachycardia, ST segment changes, and QT interval prolongation are common but non-specific.

The gold standard for diagnosis is endomyocardial biopsy, revealing myocardial tissue inflammation and damage. Cardiac MRI, particularly using the Lake Louise Criteria, is highly sensitive for detecting myocardial inflammation and assessing disease progression.

Diffuse ST elevation in a young male due to myocarditis and pericarditis

Lymphocytic myocarditis commonly showing myocyte necrosis

Endomyocardial biopsy specimen with extensive eosinophilic infiltrate

Giant-cell myocarditis with multinucleated giant cells

Treatment

The treatment of myocarditis focuses on supportive care and symptom management. Specific treatments depend on the underlying cause and may include corticosteroids or immunosuppressants for immune-mediated forms like eosinophilic and giant cell myocarditis.

Medication

Supportive care often involves medications similar to those used for heart failure management. These include ACE inhibitors or angiotensin receptor blockers, beta blockers, diuretics, and sometimes inotropes or antiarrhythmic drugs. In severe cases, medications to stabilise blood pressure and improve heart function, such as inotropes, are used.

Mechanical Support

In fulminant myocarditis, where medications are insufficient, mechanical circulatory support may be necessary. Options include ventricular assist devices, intra-aortic balloon pumps, and extracorporeal membrane oxygenation (ECMO). In some cases, heart transplantation may be required. Implantable cardioverter-defibrillators (ICDs) are considered for those at risk of fatal ventricular arrhythmias.

Prognosis

The prognosis of myocarditis varies widely. Most cases are mild and self-limited, with full recovery. However, severe cases with decreased ejection fraction, heart failure, or ventricular arrhythmias have a worse prognosis. Cardiac MRI findings, such as late gadolinium enhancement, and certain ECG changes can predict poorer outcomes. Myocarditis is a significant cause of sudden cardiac death, particularly in young adults, and is often underdiagnosed.

Epidemiology

The prevalence of myocarditis varies but is estimated at 1-10 cases per 100,000 persons annually, with higher rates in men aged 20-40. Viral infections are the most common cause, especially in children. Myocarditis is more common in males but tends to be more severe in females. It accounts for a significant proportion of sudden cardiac deaths in young adults and athletes.

Myocarditis and COVID-19

Myocarditis can occur in the context of COVID-19, with symptoms ranging from mild to fulminant. The incidence in COVID-19 patients varies, but severe myocarditis is more likely in those hospitalised with COVID-19 pneumonia. Myocarditis is also a rare side effect of mRNA COVID-19 vaccines, particularly in young males after the second dose.

A microscope image of myocarditis at autopsy in a person with acute onset of heart failure

Self-assessment MCQs (single best answer)

What is myocarditis also known as?

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Which of the following is a common symptom of myocarditis?

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What is the most common cause of myocarditis in developed countries?

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Which diagnostic test is considered the gold standard for diagnosing myocarditis?

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Which medication class is often used in the supportive care of myocarditis to manage heart failure symptoms?

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In severe cases of myocarditis where medications are insufficient, which of the following might be used?

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What is the estimated annual prevalence of myocarditis?

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Which of the following is a rare side effect of mRNA COVID-19 vaccines?

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Which of the following conditions is a potential complication of myocarditis?

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In the context of myocarditis, what does "fulminant" refer to?

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