Andersons pediatric cardiology 1709

other features, increased native T1 and T2 values may be seen Identification of abnormal myocardium by CMR may be used to guide endomyocardial biopsy Serial assessment with CMR may be helpful in follow-up and prognosis FIG 63.3 These cardiac magnetic resonance images are from a 17-yearold male who presented with chest pain and acute troponin elevation The images show moderate subpericardial (A) early gadolinium enhancement (arrow) at 3 minutes post-contrast administration and (B) late gadolinium enhancement at 7 minutes post-contrast administration along the basal inferolateral segment of the left ventricle, indicative of myocardial inflammation (C) Increased signal intensity on T2-weighted imaging along the basal inferolateral segment (arrow), indicative of myocardial edema (Courtesy Dr Yue-Hin Loke, Children's National Medical Center Washington, DC.) Other Imaging Techniques Radionuclide scans have been used for the detection of myocarditis, using either gallium-67 scans or indium-111 antimyosin antibody.16 These techniques have generally fallen out of favor in the United States due to lack of availability, increased exposure to radiation, and limitations in sensitivity and specificity.17 Endomyocardial Biopsy The place of routine endomyocardial biopsy in suspected myocarditis is still controversial The histologic changes of myocarditis are patchy; thus a negative biopsy does not exclude myocarditis The degree and extent of myocardial necrosis and type of inflammation may vary (Fig 63.4) In order to improve diagnostic accuracy, various schemes for the histologic grading of myocarditis have been described The most widely used are the Dallas criteria, which define acute myocarditis as the presence of a lymphocytic infiltrate and myocardial injury.1 It has recently been established that the use of these criteria is unreliable when endomyocardial biopsies are being assessed to diagnose myocarditis.18 The myocardial changes are not uniform and the findings depend on the site of sampling Furthermore, there are significant differences in interpretation of the histology between histopathologists It is now established that virus may be present in the myocardium without the Dallas criteria for myocarditis being fulfilled.19 Most importantly, the Dallas classification does not predict prognosis or response to immunosuppressive therapy FIG 63.4 Typical histologic features of viral myocarditis There is heavy lymphocytic infiltration with myocardial cell degeneration and necrosis (Courtesy Professor Sebastian Lucas, Guy's and St Thomas's Hospital, London, United Kingdom.) When present, the histologic findings are nonspecific and usually are not diagnostic for specific pathogens Specific virus can be detected using PCR analysis of biopsy specimens.6 In more advanced stages of the disease, part of the damaged myocardium may be replaced by scar tissue Eventually, the histology of the affected heart may be dominated by interstitial fibrosis In such instances the condition is often described as chronic myocarditis There is little evidence that biopsy is of value in determining prognosis or in helping further management, although immunohistologic analysis of mononuclear infiltration may be useful for prognosis.20,21 The risk of the biopsy procedure is highest in the acutely unwell young child with severe ventricular dysfunction.22 The risks of endomyocardial biopsy include perforation, pericardial tamponade, arrhythmia, heart block, pulmonary embolism, pneumothorax, and damage to the tricuspid valve In summary, biopsy may be justified in selected cases with an unusual or rapidly progressive presentation or where histology is used to guide therapy.23