Myocarditis

A 30-year-old man presents with a 3-day history of fever, myalgia, and chest pain which is relieved by leaning forward. He also reports shortness of breath. An ECG shows non-specific T wave changes, and his troponin is elevated.

Pathophysiology

Myocarditis is inflammation of the myocardium, the muscular layer of the heart. This can be caused by a variety of factors, leading to myocardial damage and dysfunction.

• Inflammation can lead to myocardial oedema, necrosis, and fibrosis, impairing the heart's ability to pump blood effectively.
• Myocarditis can also disrupt the electrical conduction system of the heart, causing conduction delays and arrhythmias.

Aetiology

A wide range of infectious and non-infectious agents can cause myocarditis.

Infectious causes are the most common, particularly viruses. Examples include:

• Viruses: Coxsackie viruses, adenoviruses, parvovirus B19, HIV, influenza, and herpesviruses
• Bacteria: Staphylococcus aureus, Streptococcus species, Clostridium difficile, Corynebacterium diphtheriae, Mycobacterium tuberculosis, Borrelia burgdorferi (Lyme disease)
• Parasites: Trypanosoma cruzi (Chagas disease), Toxoplasma gondii
• Fungi: Candida species, Aspergillus species

Non-infectious causes include:

• Autoimmune diseases: Systemic lupus erythematosus (SLE), giant cell myocarditis, dermatomyositis, sarcoidosis
• Drugs: Doxorubicin, cyclophosphamide, penicillin, and Herceptin (trastuzumab)
• Toxins: Heavy metals, radiation
• Hypersensitivity Reactions

In many cases, the exact cause of myocarditis remains unknown.

Epidemiology & Risk Factors

The exact incidence of myocarditis is difficult to determine as it is often underdiagnosed due to its variable and often non-specific presentation. However, it is estimated to be a significant cause of heart failure, especially in younger individuals.

Coxackie B viruses represent ~50% of all cases.

Risk factors for developing myocarditis include:

• Peripartum Period
• Recent viral infection: A history of a recent upper respiratory tract infection or flu-like illness is a common risk factor, particularly for viral myocarditis.
• Immunosuppression: Individuals with weakened immune systems, such as those with HIV/AIDS or taking immunosuppressive medications, are more vulnerable to developing myocarditis, including from opportunistic infections.
• Exposure to certain drugs or toxins: Certain medications and environmental toxins can damage the heart muscle and trigger myocarditis.

Clinical Features

Myocarditis presents with a wide range of symptoms, from mild and non-specific to severe and life-threatening.

• Chest pain: A common presenting symptom, often described as sharp or stabbing, and may mimic angina. Typically worse on lying flat and relieved by sitting forward.
• Fatigue: A common symptom, particularly in individuals with more chronic disease.
• Shortness of breath: Can be a sign of impending heart failure, particularly in severe cases.
• Palpitations.
• Flu-like symptoms: Fever, muscle aches, and sore throat may precede the onset of cardiac symptoms, particularly in viral myocarditis.
• Signs of heart failure: In severe cases, individuals may develop pulmonary and peripheral oedema.

It's important to note that some individuals with myocarditis may be asymptomatic, with the condition only being detected incidentally during routine medical examinations.

Investigations

The diagnosis of myocarditis is often challenging due to its variable presentation. A combination of clinical evaluation, laboratory tests, and imaging studies is typically required.

• Electrocardiogram: May show non-specific ST-T wave changes, arrhythmias, or signs of heart block. Features seen in pericarditis (such as PR depression or saddle-shaped ST elevation) can also be seen.
• Blood tests:
  • Cardiac biomarkers: Elevated troponin levels (troponin T or I) indicate myocardial damage.
  • Inflammatory markers: Elevated CRP and ESR.
  • Blood Cultures: In suspected bacterial infection.
  • Viral serology: Can help identify specific viral causes, although often negative.
• Echocardiogram: Assess heart function, wall motion abnormalities and the presence of pericardial effusion.
• Cardiac magnetic resonance imaging: Can provide detailed images of the heart muscle, revealing inflammation, oedema or fibrosis.
• Endomyocardial biopsy: Considered the gold standard for diagnosis, but invasive and not routinely performed.

Management

The management of myocarditis depends on the underlying cause, the severity of symptoms, and the presence of complications.

• Supportive care: Rest, fluid management, and oxygen therapy may be necessary, especially in individuals with heart failure.
• Treatment of the underlying cause:
  • Antibiotics: Used for bacterial myocarditis.
  • Antiviral medications: May be considered for viral myocarditis, although their efficacy is often limited.
  • Immunosuppressive therapy: May be used for autoimmune myocarditis.
• Management of heart failure: Diuretics, ACE inhibitors, beta-blockers and digoxin may be used to improve heart function and reduce symptoms. Intensive Care admission may be required for inotropic support.
• Treatment of arrhythmias: Medications or implantable devices (pacemaker or defibrillator) may be necessary to control abnormal heart rhythms.
• Lifestyle modifications: Limiting alcohol consumption, avoiding strenuous activity, and managing stress are important for recovery and long-term heart health.

Complications & Prognosis

The prognosis of myocarditis is variable and depends on factors such as the underlying cause, the extent of myocardial damage, and the presence of complications.

Potential complications include:

• Heart failure: Inflammation and damage to the heart muscle can lead to contractile impairment.
• Arrhythmias: Myocarditis can disrupt the electrical conduction system of the heart, causing abnormal heart rhythms, including potentially fatal ventricular tachycardia or ventricular fibrillation.
• Dilated cardiomyopathy: In some cases, myocarditis can progress to DCM, a condition where the heart becomes enlarged and weakened.
• Cardiac tamponade: Inflammation of the pericardium (pericarditis) can sometimes occur with myocarditis and lead to fluid build-up in the pericardial sac (pericardial effusion). If the fluid compresses the heart, it can cause cardiac tamponade, a life-threatening condition requiring emergency drainage.

Prognosis:

• Many individuals with myocarditis experience a full recovery with conservative management.
• However, some individuals may develop chronic myocarditis or heart failure, requiring long-term management.
• Early diagnosis and treatment are crucial for improving outcomes and minimizing the risk of complications.