Myocarditis

Overview

Definition

Myocarditis is an inflammatory disease of the myocardium.

Epidemiology

• Incidence: approximately 10–22 cases per 100,000 people
• About 1%–5% of viral infections involve the myocardium.
• Affects more men than women
• More common in young adults

Etiology

• Idiopathic (50% of cases)
• Infectious organisms:
  • Viral (most common in North America and Europe)
  • Bacterial
  • Protozoal (most common in Africa, Asia, and South America)
  • Fungal
• Immune-mediated disorders:
  • Rheumatic fever
  • Allergic reactions
  • Transplant rejection
  • Kawasaki disease
  • Sarcoidosis
  • Systemic lupus erythematosus
  • Polymyositis
  • Dermatomyositis
  • Scleroderma
  • Juvenile idiopathic arthritis
  • Vasculitis
• Exogenous agents
• Genetic predisposition:
  • Genetic defects in the structural proteins of myocytes
  • ↑ Susceptibility to myocyte damage
• Environmental causes:
  • Exposure to carbon monoxide
  • Heavy-metal toxicity
  • Black widow venom
• Drugs:
  • Doxorubicin
  • Cyclophosphamide
  • Cocaine
  • Amphetamines
  • Ethanol

Causes of infectious myocarditis

The following table summarizes the infectious causes of myocarditis. Keep in mind that this list is not exhaustive.

Pathophysiology

Inflammation due to various etiologies leads to enlargement of the heart and dilation of all chambers.

• Causes of myocyte injury:
  • Viral: direct viral toxicity, lymphocytic infiltration, and cytokines
  • Bacterial: direct invasion or bacterial toxins
  • Autoimmune: autoantibodies to myocyte components
  • Toxins: hypersensitivity or direct effects
• Myocardial inflammation and injury → myocardial necrosis
• Severe and prolonged damage → fibrosis → chamber remodeling → dilated cardiomyopathy
• Consequences:
  • Heart failure
  • Cardiac arrhythmia
  • Extension to the pericardium → pericarditis

Clinical Presentation

The clinical presentation can vary based on the severity and temporal progression of symptoms. Most signs and symptoms are related to heart failure.

Classification

Myocarditis is classified based on temporal progression.

• Subclinical: absent or minimal symptoms
• Acute: heart failure develops in < 3 months.
• Chronic: heart failure develops in > 3 months.

Symptoms

• Fever
• Chest pain
• Dyspnea
• Orthopnea
• Loss of appetite
• Abdominal pain
• Fatigue
• Decreased exercise tolerance

Physical exam

• Tachycardia
• Arrhythmia
• Peripheral edema
• Hepatomegaly
• Pulmonary rales
• Jugular venous distention
• Murmur → may indicate chamber enlargement:
  • Mitral regurgitation
  • Tricuspid regurgitation
• S3 and S4 gallops
• Pericardial friction rub (pericarditis)

Complications

• Cardiogenic shock
• Myocardial infarction
• Dilated cardiomyopathy
• Cardiac arrhythmias
• Mural thrombus with systemic emboli
• Sudden cardiac arrest

Diagnosis

Initial evaluation

Laboratory studies:

• ↑ Erythrocyte sedimentation rate
• ↑ CRP
• ↑ Troponin
• ↑ Natriuretic peptide
• Viral testing may aid in identifying the causative agent.
• Rheumatological screening for autoimmune causes

ECG:

• ST changes:
  • Often nonspecific
  • Diffuse ST elevation signals seen in pericarditis
• Arrhythmia
• Conduction delays

Chest X-ray:

• Normal to enlarged heart
• Indications of heart failure:
  • Pulmonary venous congestion
  • Pleural effusion

Cardiac imaging

Echocardiogram:

• Should be performed in all patients with suspected myocarditis
• May be normal in early or mild disease
• Possible findings:
  • Left ventricular dilation
  • Ventricular systolic dysfunction
  • Mitral or tricuspid regurgitation
  • Pericardial effusion
  • Intracardiac thrombi
• Excludes other causes of heart failure

Cardiac MRI:

• Characteristic enhancement of the myocardial wall
• Myocardial edema
• Myocardial hyperemia

Endomyocardial biopsy

Endomyocardial biopsy is the gold standard for diagnosis; however, it is rarely needed.

Indications:

• Acute deterioration of cardiac function without a known etiology
• Failure to respond to therapy

Findings:

• Cellular infiltrates may be:
  • Lymphocytic
  • Eosinophilic
  • Neutrophilic
  • Mononuclear
• Myocyte necrosis
• Interstitial fibrosis
• Myofiber hypertrophy
• Granulomatous changes:
  • Mycobacterium
  • Fungi
  • Parasitic
  • Sarcoid myocarditis (noncaseating)
• Giant cells: giant-cell myocarditis

Management

General principles

Management for myocarditis is generally supportive, but often includes:

• Heart failure management
• Arrhythmia management
• Treating the underlying etiology (when possible)

Heart failure management

Medical therapy for heart failure:

• Diuretics
• ACE inhibitors
• Beta-adrenergic blockers
• Angiotensin II receptor blockers
• Aldosterone antagonists

For fulminant heart failure:

• Inotropic support
• Intraaortic balloon pump
• Left ventricular assist device
• Cardiac transplantation

Arrhythmia management

• Antiarrhythmic therapy
• Cardioversion
• Temporary or permanent pacing

Other considerations

• Anticoagulants are indicated for:
  • Intracardiac thrombi
  • Evidence of systemic embolism
  • Atrial fibrillation
• Avoidance of:
  • NSAIDs
  • Alcohol consumption
  • Exercise

Long term follow-up

Most patients will have a partial or full recovery. However, long-term follow-up and monitoring are recommended.

• Gradual resumption of physical activities
• Serial echocardiography monitoring
• Re-evaluation and titration of medications, as appropriate

Differential Diagnosis

• Pericarditis: an inflammation of the outer lining of the heart resulting from infection, autoimmune disease, radiation, surgery, or myocardial infarction. Pericarditis clinically presents with fever and pleuritic chest pain that increases with lying supine, and pericardial rub on auscultation. An ECG with diffuse ST-segment elevation and an echocardiogram showing pericardial effusion can confirm the diagnosis. Management is supportive.
• Myocardial infarction: ischemia of the myocardium due to partial or complete obstruction of the coronary arteries. Patients present with acute onset chest pain. As in the case of myocarditis, heart failure can develop, which is usually accompanied by elevated troponins and typical ischemic ECG changes (ST elevations or depressions). Wall-motion abnormalities can be diagnosed based on a transthoracic echo. Management is with antiplatelet medications, nitrates, beta blockers, and revascularization.
• Pericardial effusion and tamponade: the presence of fluid in the pericardial sac, which can cause compression of the heart and lead to tamponade physiology. Tamponade physiology prevents the heart from filling and results in hemodynamic collapse. Beck’s triad of distended neck veins, hypotension, and muffled heart sounds is often noted on physical exam. Diagnosis is confirmed using transthoracic echocardiography, and management involves drainage of the pericardium.
• Pulmonary embolism: obstruction of the pulmonary arteries, which is most often due to thrombus migration from the deep venous system. Signs and symptoms include pleuritic chest pain, dyspnea, tachypnea, and tachycardia. Severe cases of pulmonary embolism can result in hemodynamic instability or cardiopulmonary arrest. A chest CT with angiography is the primary method of diagnosis. Management includes oxygenation, and anticoagulant and thrombolytic therapies for unstable patients.