Myocarditis, Acute

Sudden 2
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Diagnosis and reasoning

This young woman has presented with exertional dyspnea of acute onset, while her examination shows ankle edema, an elevated JVP, bibasal lung crackles, cardiomegaly and a gallop rhythm. These clinical findings indicate the presence of acute heart failure. Heart failure in young patients is most frequently due to congenital heart disease. Most of the remaining cases are related to poor myocardial function, usually due to either myocarditis or dilated cardiomyopathy. Coronary artery disease is rare in patients of this age. In this patient, the history of a recent upper respiratory tract infection raises the suspicion of viral myocarditis. Another possibility is decompensation of pre-existing cardiac disease due to the infection. Her ECG shows non-specific T-wave abnormalities, while the echocardiogram shows depressed left ventricular function and cardiac dilation, with no valvular or structural cardiac defects. These findings make myocarditis the most likely diagnosis, although pre-existing dilated cardiomyopathy (with acute worsening) is still possible. An endomyocardial biopsy is required for differentiation between myocarditis and dilated cardiomyopathy. The presence of an inflammatory cellular infiltrate with or without associated myocyte necrosis upon histology is diagnostic of myocarditis. Note that endomyocardial biopsy is an invasive procedure associated with significant complication rates. As her acute presentation is more compatible with viral myocarditis, and as many patients with viral myocarditis experience spontaneous recovery, most clinicians would only perform a biopsy if her symptoms persist. Diuretics will reduce the fluid overload resulting from her heart failure. IV antibiotics are of no benefit, while calcium channel blockers should be avoided as they will further depress cardiac function. Corticosteroids have not been shown to be of benefit in these patients.


Discussion

Myocarditis is defined as inflammation of the myocardium, and often manifests in otherwise healthy people. The majority of cases are believed to be due to common viral infections (especially adenovirus and coxsackievirus), although a vast array of other conditions have been implicated. Viral myocarditis can be divided into three distinct, chronologically successive stages : initial myocardial injury, autoimmune injury, and dilated cardiomyopathy. In the first phase, it is believed that viruses enter cardiac myocytes and cause injury via a direct cytotoxic effect. Overt heart failure usually does not occur and the initial insult may go unnoticed. After resolution of the initial injury, the second phase develops as a result of autoimmunity triggered by that injury. Due to extensive myocardial damage, overt heart failure frequently develops. In a subset of patients, there is progress into the final phase - dilated cardiomyopathy. This is largely a result of viral and autoimmune injury but may progress even after cessation of injury. Viral myocarditis has a wide spectrum of presentation ranging from mild illness to sudden cardiac death. If cardiac contractility is affected, acute heart failure or even cardiogenic shock may be present. If the conduction system is affected, arrhythmias manifesting as palpitations or syncopal episodes may be noted. Chest pain may occur in patients in whom concurrent pericarditis is present. These patients may give a history suggestive of a viral infection (for example, an upper respiratory tract infection), several days to weeks prior to presentation. Examination may reveal signs of acute heart failure (such as an elevated JVP, cardiomegaly and a gallop rhythm), while an altered sensorium, cold peripheries and a weak or impalpable pulse may be noted if cardiogenic shock occurs. If concomitant pericarditis is present a pericardial friction rub may be noted. The ECGs of these patients often show non-specific ST segment and T wave changes and/or sinus tachycardia. Less often, heart blocks or ventricular arrhythmias may be present (and signify severe disease), while significant myocyte necrosis may give rise to ST segment elevations mimicking those of an acute coronary syndrome. If significant myocyte necrosis is present cardiac enzymes (especially troponins) may be elevated. In such patients, serial cardiac enzyme levels may be of benefit in monitoring resolution of the myocarditis. The main role of echocardiography is to exclude other causes of heart failure and determine the degree of cardiac dysfunction. The most common findings are global hypokinesis and diastolic dysfunction, with or without a pericardial effusion. Echocardiography is also of use in evaluating the progression of disease. Coronary angiography may be indicated in patients whose clinical presentation mimics that of an acute coronary syndrome. The most frequent findings are high filling pressures and a reduced cardiac output. The diagnosis of myocarditis requires an endomyocardial biopsy, with histological analysis showing lymphocytic infiltration with or without myocyte necrosis. Note however, that the sensitivity and specificity of endomyocardial biopsy is limited (as there is a possibility of the biopsy been obtained from an unaffected area). In addition, it is an invasive procedure with a risk of complications such as cardiac perforation. Last, but not least, a histologic diagnosis usually does not change the management of the patient. Thus, this procedure is not performed routinely. Note also that viral antibody titers testing is usually not performed as it is of low specificity and does not alter the management. The management of viral myocarditis depends on the clinical presentation of the patient. Patients with acute heart failure should be managed in accordance with standard heart failure guidelines. Inotropic support may be required in patients with severe hemodynamic compromise. Anticoagulation may be considered in patients with arrhythmias (as well as bed bound patients), while high degree heart blocks may require temporary pacing. Antiviral therapy has a limited role, as these patients typically present after the the initial viral infection. In addition, although part of the mypcardial injury is autoimmune in origin, trials with immunosuppressants have shown little or no benefit. After resolution of the acute episode, patients should refrain from aerobic exercise for several months. In addition, they should be monitored in the long term as almost a third of them progress to develop dilated cardiomyopathy.


Take home messages

  1. The most common causes of heart failure in the young are congenital heart disease, myocarditis and dilated cardiomyopathy.
  2. Myocarditis may occur in previously healthy patients and is most often due to infection by common viruses.
  3. These patients may present with clinical and ECG features similar to that of an acute coronary syndrome, leading to a diagnostic dilemma.
  4. While endomycardial biopsy is required for definitive diagnosis, this is not routinely performed.
  5. Long term monitoring for potential progression into dilated cardiomyopathy is important.

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  1. Cardiovascular research : Myocarditis and dilated cardiomyopathy - an inflammatory link (2003)
  2. Circulation : Advances in the Understanding of Myocarditis (2001)
  3. Heart : Heart failure in the young (2002)
  4. Mayo clinic proceedings : Diagnosis and treatment of myocarditis (2009)
  5. NEJM : Myocarditis (2006)