Myocarditis overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor-In-Chief: Varun Kumar, M.B.B.S. Maliha Shakil, M.D. [2] Homa Najafi, M.D.[3]

Overview

Myocarditis is defined as inflammation of the myocardium. It may present with chest pain, ST segment elevation, elevated biomarkers of myonecrosis, heart failure, and/ or sudden death. Myocarditis can be classified clinicopathologically into fulminant myocarditis, acute myocarditis, chronic active myocarditis, and chronic persistent myocarditis. During either an infection or a hypersensitivity reaction, the inflammatory response may cause myonecrosis either directly or indirectly as part of an autoimmune reaction. Life-threatening causes of myocarditis include carbon monoxide poisoning and Dengue fever. Common causes of myocarditis include infections, Lyme disease, and medications. Idiopathic myocarditis is the most common type of myocarditis and is often suspected to be secondary to a viral infection. Myocarditis must be distinguished from pericarditis and the life threatening condition of ST elevation myocardial infarction. In young adults, up to 20% of all cases of sudden death are due to myocarditis. Myocarditis is slightly more frequent among males than females. Myocarditis is usually self limiting and is associated with a good prognosis especially if it is secondary to a viral infection. Patients rarely develop cardiac failure, pulmonary edema, arrhythmias, or cardiogenic shock. In some instances, myocarditis may be associated with sudden death. Patients with fulminant myocarditis have a good long term prognosis if they survive the acute phase of the disease. The prognosis of fulminant myocarditis is better than that of either acute myocarditis or giant cell myocarditis. The presence of left bundle branch block, q waves, AV block, syncope and a left ventricular ejection fraction < 40% are associated with sudden death and cardiac transplantation. The physical examination in patients with myocarditis may reveal tachycardia, a cardiac gallop, mitral regurgitation due to left ventricular dilation, and pedal edema suggestive of cardiac failure. A pericardial friction rub may be noted in presence of concomitant pericarditis, a condition sometimes referred to as myopericarditis.

Historical Perspective

Cases of myocarditis have been documented as early as the 1600s. The term myocarditis was introduced by German physician Joseph Friedrich Sobernheim in 1837. The Dallas criteria was published in 1986 as a guideline for classification of myocarditis.

Classification

Myocarditis can be classified based on the causative, histological, and clinicopathological criteria. Combination of the histologic data and clinical course of the disease resulted in clinicopathologic classification of myocarditis. Parameters such as onset of the disease, initial clinical and histological presentation, disease course and cardiac dysfunction define acute, fulminant, chronic active and chronic persistent subtypes of myocarditis. Acute myocarditis represents the most common type of myocarditis, in which symptoms last typically for days or weeks and the acute phase is followed by spontaneous improvement or development of stable DCM. In patients with fulminant myocarditis disease progresses rapidly resulting in severe heart failure and cardiogenic shock with mortality rate of 30–40% during the acute phase. Patients diagnosed with fulminant myocarditis surviving the acute phase have been instead suggested to have excellent long-term prognosis. In its chronic form, myocarditis is detected over a period of three or more months. Clinical and histologic relapses and development of ventricular dysfunction is characteristic for chronic active myocarditis, whereas chronic persistent myocarditis is characterized by persistent presence of inflammatory cells in the myocardium, but it is usually not associated with ventricular dysfunction.

Pathophysiology

During either an infection or a hypersensitivity reaction, the inflammatory response may cause myonecrosis either directly or indirectly as part of an autoimmune reaction.

Causes

Life-threatening causes of myocarditis include carbon monoxide poisoning and Dengue fever. Common causes of myocarditis include infections such as Lyme disease and medications. Idiopathic myocarditis is the most common type of myocarditis and is often suspected to be secondary to a viral infection.

Differentiating Myocarditis from other Diseases

Myocarditis must be distinguished from pericarditis and the life threatening condition of ST elevation myocardial infarction.

Epidemiology and Demographics

In young adults, up to 20% of all cases of sudden death are due to myocarditis. Myocarditis is slightly more frequent among males than females.

Natural History, Complications and Prognosis

Myocarditis is usually self limiting and is associated with a good prognosis especially if it is secondary to a viral infection. Patients rarely develop cardiac failure, pulmonary edema, arrhythmias or cardiogenic shock. In some instances, myocarditis may be associated with sudden death. Patients with fulminant myocarditis have a good long term prognosis if they survive the acute phase of the disease. The prognosis of fulminant myocarditis is better than that of either acute myocarditis or giant cell myocarditis. The presence of left bundle branch block, q waves, AV block, syncope and a left ventricular ejection fraction < 40% are associated with cardiac transplantation and sudden death.

Diagnosis

History and Symptoms

The symptoms and the intensity of symptoms associated with myocarditis are variable. Myocarditis may be associated with no symptoms. If symptoms are present, they may be similar to the flu. Patients may present with chest pain as a result of the inflammatory process involving the myocardium or with symptoms of congestive heart failure. Patients may complain of palpitations, a racing heart, or syncope. In fulminant myocarditis, patients present with the abrupt onset of flu-like symptoms and the abrupt onset of heart failure symptoms. In chronic and acute myocarditis, the onset of symptoms may be more insidious.

Physical Examination

Common findings on physical examination include tachycardia, a cardiac gallop, mitral regurgitation due to left ventricular dilation and pedal edema suggestive of cardiac failure. A pericardial friction rub may be noted in presence of concomitant pericarditis, a condition sometimes referred to as myopericarditis.

Laboratory Findings

Laboratory findings consistent with the diagnosis of myocarditis include elevated markers of myonecrosis, inflammatory markers, and other biomarkers. Markers of myonecrosis include creatine kinase (CK-MB), cardiac troponin I (cTnI) or T (cTnT), lactate dehydrogenase (LDH), alanine transaminase (ALT), and aspartate transaminase (AST). Elevated levels of C-reactive protein and erythrocyte sedimentation rate (ESR), and leukocytosis are suggestive of myocarditis. Serological markers such as Fas, Fas ligand, interleukin-10 or antimyosin autoantibodies are of prognostic value in myocarditis. Other auto-antibodies such as ANA and rheumatoid factor may also be detected.

Electrocardiogram

The presence of ST segment elevation in patients with myocarditis can mimic pericarditis and myocardial infarction. Arrhythmias and heart block may also be observed in myocarditis patients. Myocarditis can be distinguished from pericarditis by the presence of PR depression in the patient with pericarditis.

Endomyocardial Biopsy

Endomyocardial biopsy remains the gold standard test to evaluate for the presence of and to subclassify the type of myocarditis. A small tissue sample of the endocardium and myocardium is obtained via right sided cardiac catheterization. The sample is then evaluated by a pathologist using immunochemistry and special staining techniques as necessary. Histopathological features include abundant edema in the myocardial interstitium and an inflammatory infiltrate which is rich in lymphocytes and macrophages. Focal destruction of myocytes as a result of the inflammatory process results in left ventricular dysfunction. Endomyocardial biopsy is recommended when the results would identify an underlying disease that is amenable to therapy. Routine performance of endomyocardial biopsy is not recommended in all patients with myocarditis.

Chest X Ray

Findings on chest x-ray suggestive of myocarditis include cardiomegaly, pericardial thickening in presence of pericarditis, pulmonary edema, and pleural effusion.

MRI

Cardiac MRI findings associated with myocarditis include myocardial inflammation, myocardial edema, capillary leak, and reduced left ventricular function. While the cardiac MRI pattern of gadolinium hyperenhancement in ST segment elevation myocardial infarction is transmural and extends from the endocardium to the epicardium, the patchy, non-segmental hyperenhancement pattern in myocarditis in contrast involves the epicardium and spares the subendocardium.

Echocardiography

Echocardiography in patients with myocarditis allows for serial assessment of left ventricular dysfunction and can be used to distinguish fulminant (non-dilated hypocontractile left ventricle with thick interventricular septum) from acute myocarditis (dilated hypocontractile left ventricle with normal interventricular septum).

Other Imaging Findings

Coronary angiography may be helpful in excluding either myocardial ischemia or infarction as the cause of ST segment elevation, elevated cardiac biomarkers, or left ventricular dysfunction.

Treatment

Medical Therapy

Symptomatic treatment is the mainstay of therapy for patients with viral myocarditis. Supportive therapy includes diuretics and inotropes for left ventricular failure. ACE inhibitor therapy may aid in left ventricular remodeling. Among patients with fulminant myocarditis, placement of either an intra-aortic balloon pump or a left ventricular assist device may be necessary as bridge to recovery. Administration of antimicrobial therapy is recommended for bacterial myocarditis. Immunosuppressive therapy may be effective in the management of giant cell myocarditis, autoimmune myocarditis, and eosinophilic myocarditis.

Cardiac Transplantation

Cardiac transplantation is sometimes required to treat refractory giant cell myocarditis. However, the condition can recur in post-transplant patients. Recurrence of biopsy proven giant cell myocarditis between 3 weeks to 9 years was observed in 9 of 34 cardiac transplant patients .