Myocarditis

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CHAPTER 66 Myocarditis

Myocarditis—acute inflammatory syndrome of myocardium—is a rare cause of acute chest pain and an important cause of dilated cardiomyopathy. The most common cause of myocarditis in the Western world is viral infection. The patient presents acutely with chest pain and dyspnea or, rarely, hemodynamic compromise of the fulminant type. Chronic myocarditis usually is manifested with symptoms and signs of dilated cardiomyopathy. Clinical presentations, biochemistry, and echocardiographic findings may overlap with those of myocardial infarction or ischemic heart disease. Imaging is critical in the diagnosis. Currently, cardiac magnetic resonance imaging (MRI) has proved to be the most robust and accurate noninvasive imaging tool, not only in the diagnosis of myocarditis but also in guiding targeted endomyocardial biopsy and in the subsequent follow-up. Treatment of myocarditis is usually supportive. Cardiac transplantation may be considered for patients with deteriorating cardiac function in dilated cardiomyopathy.

Definition

Myocarditis refers to focal or diffuse inflammation of the cardiac muscle associated with myocyte damage or necrosis and lymphocyte infiltration as a result of various infectious, immune, or nonimmune insults in the absence of significant acute or chronic ischemia.¹^–³

Prevalence and Epidemiology

Myocarditis is found in 1% to 10% of postmortem examinations; however, the true prevalence is unknown because of its insidious and variable clinical presentation.¹^,² It accounts for 20% of cardiac causes of sudden deaths in military recruits¹ and 40% of acute presentations of dilated cardiomyopathy.² Up to 50% of patients with acquired immunodeficiency syndrome (AIDS) have evidence of myocarditis on biopsy.²

Infections are a major cause of myocarditis. Viruses, such as coxsackieviruses A and B and other enteroviruses, adenovirus, influenza virus, and Epstein-Barr virus, are the most important causes of myocarditis in the United States.²^,⁴ A wide range of bacteria (Streptococcus, Chlamydia, Neisseria, Borrelia) and parasites (Trypanosoma, Toxoplasma, Trichinella) can also cause myocarditis. Various medications, such as doxorubicin (Adriamycin) and sulfonamides, and toxins, such as cocaine, have also been associated with myocarditis. Large-vessel vasculitis, such as Takayasu arteritis, and autoimmune diseases, such as systemic lupus erythematosus, sarcoidosis, and Wegener granulomatosis, are also important but rare causes of myocarditis.²^,⁴

Manifestations of Disease

Clinical Presentation

The clinical manifestation of myocarditis is variable, ranging from progressive dyspnea and weakness to left ventricular failure to sudden death. Patients may present with influenza-like symptoms, such as fever, fatigue, malaise, and arthralgia.¹^–³ Arrhythmia is common.⁴ In addition, chest pain with abnormal electrocardiographic (ECG) recordings and serum troponin elevation in patients with myocarditis can mimic acute myocardial infarction.⁵ Patients may also present at a late stage with dilated cardiomyopathy.⁴

Imaging Indications and Algorithm

Imaging plays a pivotal role in the diagnosis of myocarditis. In the past, endomyocardial biopsy was once considered the gold standard for diagnosis of myocarditis; however, it has been shown to have low sensitivity due to sampling error related to the patchy nature of the disease.⁶ Echocardiography and cardiac MRI should be part of the initial diagnostic evaluation in conjunction with ECG and serum troponin evaluation. More selected biopsy, if needed, may be performed with the MRI result as a guide.⁵ Coronary computed tomographic angiography (CTA) can be performed in the acute setting to exclude significant coronary arterial stenosis in patients with myocarditis who are presenting with chest pain, raised abnormal cardiac enzymes, and abnormal ECG changes.

Imaging Technique and Findings

Radiography

Chest radiographs may be completely normal in patients with myocarditis, especially acutely (Fig. 66-1). Alternatively, cardiomegaly, interstitial or alveolar pulmonary edema, pleural effusions, and pericardial effusion may be detected as a result of left ventricular failure.² Less commonly, right ventricular failure may be manifested by right atrial enlargement, prominent azygos vein, and superior vena cava enlargement.

FIGURE 66-1 A 31-year-old patient who presented with acute chest pain, eventually diagnosed with acute myocarditis. A, An upright posteroanterior chest radiograph is essentially normal. The cardiac silhouette is at the upper limit of normal in size. There is no evidence of pulmonary edema or pleural effusions. B, Horizontal long-axis view of delayed postcontrast T1-weighted gradient-echo sequence shows dilation of the right ventricle (RV) relative to the left ventricle (LV) and linear subepicardial hyperenhancement of the anterior wall of the right ventricle (arrowhead). A nodular focus of non-subendocardial delayed hyperenhancement is also noted in the lateral myocardial wall of the left ventricle (arrow). C, Vertical long-axis view of delayed postcontrast T1-weighted gradient-echo sequence shows a well-defined oval focus of subepicardial delayed hyperenhancement (arrow) and subendocardial sparing (arrowhead). These features are consistent with acute myocarditis.

Ultrasonography

Echocardiographic findings of myocarditis are nonspecific, including segmental wall motion abnormalities and increased left ventricular volume.⁷ During the acute phase, transient left ventricular wall thickening can be observed, probably related to interstitial edema.⁸^,⁹ The average brightness of the myocardium is also higher in patients with myocarditis than in control patients.¹⁰

Computed Tomography

Recent literature shows that multidetector computed tomography (MDCT) may play a role in establishing the diagnosis of myocarditis in patients presenting in the acute setting as MDCT is more accessible and less time-consuming than MRI. In addition, ECG-gated MDCT also offers concurrent evaluation of the coronary arteries. However, the amount of iodinated contrast material administered must be considered in patients who may have already undergone conventional coronary arteriography.

On delayed enhanced images, nodular, patchy, bandlike enhancement of the mid and epicardial layer of the left ventricular wall can be seen in patients with myocarditis (Fig. 66-2).¹¹ In a study of 12 consecutive patients with acute chest pain consistent with myocardial ischemia and normal coronary angiogram, delayed enhanced MDCT performed 5 minutes after injection of contrast material demonstrated the same accuracy as MRI in differentiating between myocardial infarction and myocarditis in the acute phase.¹² Similarly, another study also showed good correlation in the extent and location of hyperenhancement at MDCT compared with cardiac MRI in the early phase of suspected acute myocarditis.¹³