14 Multimodality Imaging Echocardiography remains the primary modality for investigating patients with suspected acute pericarditis.38,39 It can be used to detect a new or worsening pericardial effusion — one of the principal clinical diagnostic features of acute pericarditis.38,40 Pericardial effusions are typically small and reported to occur in up to 60% of those patients with acute pericarditis.38 Detailed evaluation for echocardiographic features of cardiac tamponade is warranted regardless of pericardial effusion size. Echocardiographic features of cardiac tamponade include cardiac chamber compression, respirophasic ventricular interdependence, expiratory hepatic venous diastolic flow reversals, exaggerated respirophasic variation in mitral and tricuspid Doppler inflow patterns, and a dilated inferior vena cava consistent with an elevated central venous pressure. Effusive-constrictive pericardial physiology may be demonstrated by echocardiography in patients with severe pericardial inflammation with associated pericardial edema. It can also be used to help evaluate the hemodynamic effects of any effusion and can play a role in the differential diagnosis of chest pain, identifying potential alternative causes (e.g., a new regional wall motion abnormality pointing toward an acute coronary syndrome, or LV dysfunction suggesting a concomitant myocardial pathology).38 Cardiovascular magnetic resonance can play an important role in confirming the presence of acute pericarditis, particularly where the history may be atypical or if a patient with a history of pericarditis presents with chest pain but normal inflammatory markers.38,40 Where the rate of resorption of pericardial fluid matches the rate of production, an effusion may not develop, obscuring the presence of pericarditis on echocardiography.41 The healthy pericardium is a relatively avascular structure and therefore does not take up gadolinium contrast.41 However, in the setting of acute pericarditis, there is often neovascularization of the inflamed pericardium and increased pericardial water content due to capillary leak and pericardial edema. The latter can be detected on high resolution T2-weighted turbo spin echo sequences as pericardial T2 hyperintensity.41 For the same reasons, the inflamed pericardium will appear hyper-enhanced in the late phase after administration of gadolinium contrast agents. The absence of these features lowers the probability of acute pericarditis. Delayed gadolinium contrast enhancement can persist for more than 12 months following an acute episode of pericarditis despite symptomatic resolution, as pericardial vascular changes take time to resolve.42,43 Hence, the presence of mild delayed gadolinium enhancement without T2 hyperintensity may suggest prior pericardial inflammation without ongoing acute pericardial inflammation. CMR should be considered where a patient presents with a troponin rise or evidence of new contractile dysfunction on echo to identify concomitant myocardial inflammation.44 This is termed myopericarditis where the dominant pathology is pericarditis or peri-myocarditis where there is extensive myocardial inflammation or LV dysfunction, and pericardial involvement is the more peripheral process.41 In patients at risk of developing constriction, pericardial late gadolinium hyperenhancement may identify a subset of patients where this may be aborted by appropriate antiinflammatory therapy.45 Cardiovascular computed tomography may be valuable again in the differential diagnosis of chest pain in the setting of suspected pericarditis, e.g., acute aortic syndromes.38,41 Pericardial inflammation may manifest as pericardial thickening or hyperenhancement postcontrast. Cardiovascular CT should also be considered where there is a history of thoracic trauma, of if concomitant pleuropulmonary pathology or neoplastic cause for pericarditis is suspected.41 In patients with chronic pericardial constriction, cardiovascular CT may be of value in delineating areas of pericardial calcification as well as ruling out concomitant bystander coronary disease, which may require revascularization at the time of cardiothoracic surgery. Cardiovascular and wider whole-body fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging may be of value in patients with suspected systemic autoimmune rheumatic disease or where there is concern about internal malignancy as a cause for acute pericarditis.41 As well as confirming inflammation and assessing disease activity, this may also identify lymph nodes or other structures to target for biopsy where histologic data is lacking.
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