Abstract
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Introduction: Activation of extra-cardiac immune cells and organs like the spleen and bone marrow has been demonstrated after acute myocardial infarction (AMI). This extra-cardiac response may play a role in recovery after AMI and, thus, characterizing its activation may lay the groundwork for novel therapies that directly target immune cells or organs. A novel high-sensitivity high spatial-resolution molecular imaging modality, the EXPLORER PET/CT, can provide high resolution 3-dimensional imaging of the entire human body in a single scan, permitting the assessment of the multi-organ inflammatory response to AMI. Using 18F-FDG total-body PET/CT, our study examined the metabolic activity of multiple lymphoid tissues simultaneously, particularly the bone marrow, spleen, and regional lymph nodes (LNs), in subjects after AMI compared to healthy controls.
Methods: Ten subjects who were treated for AMI with percutaneous coronary intervention (PCI) and guideline-directed medical therapy were evaluated with static total-body 18F-FDG PET/CT after 7-12 days of initial presentation and compared to 15 controls. Analysis of standardized uptake value (SUV) in the regional LNs, spleen, and bone marrow, was performed to assess multi-organ metabolic activity; static PET images were acquired 90-110 minutes post-injection, using AMIDE software. The LNs were categorized into 3 broad regions - head and neck, axillary and inguinal. The bone marrow was represented by the first to fifth lumbar vertebrae. The mean 18F-FDG dose administered to the control group was 10.1 ± 0.5 mCi, compared to 5.2 ± 0.2 mCi in the AMI group. This difference was adjusted for during PET analysis.
Results: The mean age, sex, weight, and fasting blood glucose levels were not significantly different between the AMI and control groups. As shown in Table 1 and Figure 1, the SUVmax in the LNs was increased by 1.9-fold in the right and 2.3-fold in the left head and neck regions, 2.1-fold in the right and 2.3-fold in the left axillary regions, and 2.8-fold in the right and 2.2-fold in the left inguinal regions in AMI subjects compared to controls. Additionally, the SUVmax was increased by 1.3-fold in the bone marrow and 1.5-fold in the spleen in AMI subjects compared to controls.
Conclusions: This study evaluated the metabolic activity of three extra-cardiac lymphoid organs simultaneously in subjects after AMI using a total-body 18F-FDG PET/CT. In addition to increased metabolic activity in the bone marrow and spleen, shown in previous studies, we found that subjects with AMI had significantly increased metabolic activity in the head and neck, axillary and inguinal lymph nodes. Seven out of the 10 AMI patients received PCI via the right femoral artery, possibly accounting for the higher signal noted on the right inguinal region. Additional studies are needed to further characterize this multi-organ lymphoid activation and the risk of future adverse cardiovascular events post AMI.
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