My approach to Nuclear Medicine in the evaluation of prosthetic valve and cardiac implantable electronic device endocarditis

Nuclear medicine has played an increasing role in the evaluation of patients with a suspected or confirmed diagnosis of infective endocarditis. Scintigraphy with marked leukocytes (ML) is a method widely used in clinical practice to detect sites of infection, being especially indicated in patients with suspected infective endocarditis (IE) in prosthetic valves or implantable cardiac devices (ICD) when other conventional imaging methods studies are not conclusive. The technique involves labeling the patient's own leukocytes with a radiotracer, such as 99m Tc-HMPAO, maintaining its biological properties. Upon injection into the bloodstream, leukocytes actively mark sites of active inflammation, allowing detection of infection. Blood collection for ML scintigraphy requires a sufficient amount of leukocytes, which can be a major limiting factor in patients with neutropenia. Another point of limitation is that the leukocyte labeling process and the start of obtaining scintigraphic images can take about 2 hours. The images are acquired at different times, and the presence of capture in the 4-hour and 24-hour images is important to confirm the presence of active infection. ML scintigraphy has been recommended as part of the diagnostic algorithm for IE in patients with prosthetic valves or implantable cardiac devices such as pacemakers who suspect the disease, being considered a major modified Duke criterion when positive. It is indicated when the echocardiogram is inconclusive or doubtful, and may change the categorization of IE from possible to defined in up to 25% of patients. In addition, it can also be used in the investigation of embolic events in extracardiac sites, such as the lung, spleen and bone/joint tissue. Positron Emission Tomography coupled with Computed Tomography (PET-CT) is a molecular imaging technique that has shown great importance in the management of IE. PET-CT uses a radiopharmaceutical labeled with a short-lived radioactive substance, such as ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG), which is captured by cells with high metabolism, such as inflammatory cells present in areas of active infection. This allows for accurate, non-invasive detection of areas of inflammation, including the lesions, vegetations and abscesses associated with IE. The use of PET-CT in IE has shown promise in the early detection of infection, providing important information for diagnosis and treatment planning. Additionally, PET-CT can help differentiate between active infection and post-surgical complications, as well as identify areas of infection in extracardiac sites, which can be useful in evaluating more complex cases. The high sensitivity and specificity of PET-CT in detecting active inflammation make it a valuable tool in the clinical management of IE, especially in cases of moderate clinical suspicion or when conventional imaging methods are inconclusive. However, it is important to consider the limitations of PET-CT, such as its availability in some health centers, cost and exposure to ionizing radiation, and to use PET-CT findings in conjunction with other clinical and laboratory data for an proper diagnosis and management of IE. (author)