Investigations Radiology The size of the heart may be normal on chest x-ray, particularly in the early period of the disease More frequently the heart will be enlarged, with normal lung fields Pulmonary venous congestion and even frank pulmonary edema may be evident Electrocardiography Electrocardiographic abnormalities are common in myocarditis but are nonspecific There is often a sinus tachycardia, with lowering of the QRS voltage in the standard leads and/or precordial leads, flattening or inversion of the T waves, and nonspecific changes in the ST segment (Fig 63.1) Arrhythmias are often present and may lead to unexpected death Occasionally disturbances of conduction are seen, with varying degrees of heart block Complete atrioventricular block is rare The QRS complexes may be widened, with a left or right bundle-branch-block configuration The electrocardiographic changes may disappear during the course of the disease, but abnormalities may also persist―most likely because of myocardial scarring―after the patient has recovered clinically FIG 63.1 Typical electrocardiogram from a patient with myocarditis Note the widespread ST-T wave changes throughout the limb and chest leads in this case the PR interval is normal, but beware of the patient with prolonged atrioventricular conduction, as complete heart block can evolve Echocardiography Echocardiography, although also nonspecific, is an important screening and diagnostic tool The findings of acute myocarditis can be identical to those of dilated cardiomyopathy Echocardiography is also important to rule out structural heart diseases that may mimic myocarditis, such as anomalous origin of the left coronary artery Echocardiography may also reveal complicating features such as a pericardial effusion or intracardiac thrombus Typical features of myocarditis include dilation and reduced function of the heart chambers, predominantly the left ventricle (Videos 63.1 to 63.4) When the onset is rapid, as with fulminant myocarditis, there may be little if any ventricular dilation Ventricular dysfunction is usually much more evident in the left ventricle than in the right and may be either global or segmental The left atrium may also be enlarged, especially in the presence of mitral insufficiency (Fig 63.2) Echocardiographic tissue characterization, tissue Doppler imaging and the measurements of myocardial velocity have been shown to be helpful in differentiating myocarditis from other causes of ventricular dysfunction, although further research will be needed to determine their value in a clinical setting FIG 63.2 Echocardiograms from a child with acute myocarditis, with subcostal (A), parasternal short-axis (B), parasternal long-axis (C), and apical long-axis (D) views The images show a globular, dilated left ventricular cavity The left ventricular ejection fraction measured 15% Cardiac Magnetic Resonance Although functional assessment can be performed by cardiac magnetic resonance (CMR), it rarely adds substantially to the results of echo in children However, the structural information provided by CMR is rapidly becoming key to diagnosis of myocarditis In particular, the pattern of gadolinium enhancement can be used to diagnose myocarditis with accuracy approaching 80%.14 Although consensus guidelines, the Lake Louise criteria, exist, their diagnostic accuracy has been called into question.15 Early gadolinium enhancement reflects areas of hyperemia, inflammation, and edema, whereas late gadolinium enhancement reflects areas of myocardial scar or fibrosis (Fig 63.3) Among