Labeled White Blood Cell SPECT-CT in the Diagnostic Workup of patients with suspected Infective Endocarditis in the Real-World

Objectives: Labeled white blood cell scintigraphy is used in various clinical conditions. When there is suspicion of an infectious process, especially for bacterial agents, it has high specificity. It can be used in several conditions such as fever of obscure or undetermined origin, osteomyelitis screening and, in cardiology, when there is suspicion of infective endocarditis (IE) associated with the prosthesis. In 2015 it was included in the assessment of suspected IE patient in the Guideline of the European Society of Cardiology (ESC) in 2015. Labeled white blood cell scintigraphy SPECT-CT (WBCS) has demonstrated to be able to reduce the rate of misdiagnosed cases of IE. Few studies are published in a real-world scenario because the technique is not broadly available. The goal of this study is to describe the use of WBCS in a series of consecutive patients in a reference cardiovascular hospital to evaluate the clinical impact in the diagnostic workup of suspected endocarditis.

Methods: WBCS was performed at the nuclear medicine service of our institution from January 2015 to August 2017. The clinical indication, type of radiotracer employed, demographic aspects and scintigraphic findings were analyzed. Exams were performed using the in vivo labeling technique with antigranulocyte Besilesomab antibody or with the in vitro labeling of autologous leukocytes with ^99mTc-HMPAO. The scintigraphic images were performed on SPECT-CT equipment (Symbia T2). Experienced nuclear medicine physicians performed the interpretation of the scans.

Results: A total of 138 WBCS were performed in this period, and the majority (108 patients) used the in vitro labeling of autologous leukocytes with HMPAO. Suspected infective endocarditis was responsible for 19% of the clinical indications. The mean age of the patients who underwent endocarditis WBCS was 70 years compared to patients with other indications that had a mean age of 66 years (p = 0.3). There was a predominance of males among patients with suspected endocarditis in relation to other indications (85% x 57%, p = 0.0001). Of the 26 exams requested for endocarditis, 13 (50%) were positive: 5 in prosthetic heart valves, 4 aortic endoprostheses, 2 in mechanical circulatory assist devices. In 2 other cases the examination showed the presence of a non-cardiovascular infectious focus: 1 pulmonary infection and another in the knee joint. Three patients with suspected infection of transcatheter aortic valve implant (TAVI) had negative labeled WBC scans that discarded the TAVI as the focus of infection.

Conclusions: The use of WBCS has proved to be useful in the identification of IE in real-world complex cases such as valvular prostheses and vascular endoprostheses. WBCS use should be incorporated in the diagnostic workup of patients with suspected IE when conventional techniques do not yield conclusive results as is recommended by ESC Guideline.