Evolving role of FDG-PET/CT in the workup of infective endocarditis

Introduction: 1. Review the current workup for infective endocarditis (IE). 2. Introduce recent data regarding the use of FDG-PET/CT in IE diagnosis and explain the indications of FDG-PET/CT for this application.

Methods: IE is a devastating infection with substantial mortality risk. Based on the modified Duke criteria, blood cultures and echocardiogram are the cornerstones of IE diagnosis. However, the diagnosis of IE remains challenging because of the heterogeneity of its clinical presentation and multiorgan involvement. The diagnosis is further complicated by the presence of prosthetic valves (PV) and implantable cardiac electronic devices (ICED), including pacemakers and implantable cardioverter defibrillators (ICD) which could decrease the sensitivity and specificity of echocardiography. Recently, additional imaging modalities have been discussed in both American and European guidelines, such as the inclusion of FDG-PET/CT imaging as a major criterion in the 2015 European Society of Cardiology (ESC) guidelines. In addition to IE, FDG-PET/CT has been proven beneficial in diagnosing other infectious diseases due to its ability to show the presence of macrophages and inflammatory cells at the sites of infection or inflammation. Apart from diagnosing intracardiac infections, FDG-PET/CT is also able to detect clinically silent disseminated IE.

Results: The diagnostic performance of FDG-PET/CT in IE depends on the presence of native valves, prosthetic valves, or ICED. Negative FDG-PET/CT findings cannot rule out native valve endocarditis (NVE) due to its low sensitivity in NVE; however, if there is evidence of intracardiac infection in patients with native valves, it is highly predictive for IE because of its high specificity. For patients with prosthetic valve endocarditis (PVE), the sensitivity and specificity of FDG-PET is high. This is important as the diagnostic value of echocardiography is affected by prosthetic valve-related artifacts. Although PDG-PET/CT has high sensitivity and specificity for cardiac device-related IE (CDRIE), studies have found that the sensitivity of FDG-PET/CT is better in pocket infections than lead infections; hence, for patients with suspected CDRIE-lead infections, the results should be interpreted cautiously. The ability to detect disseminated disease will greatly impact the management of the patients, making it a superior diagnostic imaging modality. To date, echocardiograms remain the first-line imaging modality as they are widely available and cost-effective. FDG-PET/CT is recommended to be performed as soon as possible after an echocardiogram, especially in patients with suspected PVE and CDRIE to allow for timely management and to prevent false-negative findings due to the effects of antibiotics on inflammation.

Conclusions: FDG-PET/CT is a useful adjunctive diagnostic tool in the evaluation of challenging cases of IE, especially in those cases of possible IE involving prosthetic valves when an echocardiogram is inconclusive.