Abstract Body (Do not enter title and authors here): Purpose:
After acute myocardial infarction (MI), lymphocytes play a pivotal role in the scar formation and remodeling of the remote myocardium. Activation of lymphocytes takes places in mediastinal lymph nodes (MLN). Therefore, imaging of MLN as a read-out of the adaptive immune response to MI may identify subjects at increased risk for cardiac functional decline.

Methods
The on-going prospective study (NCT05519735) enrolls patients with acute ST-elevation MI followed by complete reperfusion and multimodal imaging with C-X-C motif chemokine receptor 4 (CXCR4)-directed PET/CT and cardiac MRI (CMR) as baseline imaging. Follow-up (FU) CMR scans are repeated after 6 and 12 months. The CMR scans are analyzed regarding LV function, myocardial and LGE mass. Tracer uptake (SUVpeak) in the myocardium and MLN (defined as LN with most intense uptake) are determined. Infarct/remote myocardial (IRR), MLN/Remote LN (LNR) ratios and the overall LNR (including uptake from all LN) are calculated. Association of uptake with the function CMR parameters is tested.
Results
Currently, 41 patients (29 males, median age 59 yo) were enrolled in the study (6 months FU 27/41, 12 months FU 17/41). At baseline, the median CMR EF was 49% and improved with the FUs (6mo: 52.8%, 12 mo 53.2%). LGE mass was 30.3 g and declined to 13.8 g after 12 months (LGE/Myocardial 15.8%). SUV_peak from infarcted myocardium and mediastinal LN were consistently >1, indicating increased uptake relative to background.
Changes of LVEF correlated with LNR (6 mo FU: %LVEF, r= - 0.48; P = 0.01, 12 mo FU: %LVEF, r= - 0.55; P = 0.02) and overall LNR (6 mo FU: %LVEF, r= - 0.52; P< 0.01; 12 mo FU: %LVEF; r= - 0.61; P = 0.01), but not with IRR (P= 0.498).
LNR was increased in subjects with decreased LVEF. In logistic regression analysis, increasing LNR and overall LNR were significantly associated with decreased LVEF at the 12 months FU (LNR OR 1.32 (95% CL: 1.06-1.81, p = 0.03), Overall LNR OR 1.36 (95 % CL: 1.09-1.92, p = 0.03)).
Conclusion
CXCR4-directed imaging of MLN provides information on the extent of local and systemic tissue inflammation in patients after acute MI. Especially MLN CXCR4 uptake holds predictive potential for cardiac adverse remodelling during follow up (LVEF decline) and may be used to identify patients who benefit from a selective immune modulation after acute MI.
Funding: German Research Foundation (453989101).