Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 18 2 2023 04 30 87 93 EN Abdullah Kadir Dolu Department of Cardiology, Izmir Katip Çelebi University Ataturk Education and Research Hospital, Izmir, Turkey. Filiz Akyıldız Akçay Department of Cardiology, Izmir Katip Çelebi University Ataturk Education and Research Hospital, Izmir, Turkey. Murat Atalay Department of Cardiology, Izmir Katip Çelebi University Ataturk Education and Research Hospital, Izmir, Turkey. Mustafa Karaca Department of Cardiology, Izmir Katip Çelebi University Ataturk Education and Research Hospital, Izmir, Turkey. 2022 04 24 2023 04 10 Background: The systemic immune-inflammation index (SII) has recently been investigated for cardiovascular diseases. We aimed to evaluate the relationship between SII and left atrial thrombosis (LAT). Methods: This retrospective, case-control study recruited patients with nonvalvular atrial fibrillation (NVAF) who underwent transesophageal echocardiography (TEE) for LAT detection before cardioversion or catheter ablation at a tertiary hospital between 2012 and 2021. Demographic characteristics were obtained from the hospital data system. According to TEE findings, the patients were categorized into LAT (+) and (-) groups. Age, gender, history of chronic diseases, urea, creatinine, albumin, hemogram parameters, the neutrophil-lymphocyte ratio (NLR), the platelet-lymphocyte ratio (PLR), SII, the CHADS₂ score, the CHA₂DS₂-VASc score, echocardiographic parameters, antiaggregant-anticoagulant use, and non-paroxysmal atrial fibrillation were included and analyzed. Results: The study population consisted of 403 patients, including 228 men (56.6%), at a mean age of 60.84±12.26 years. A high white blood cell count (WBC) (OR, 1.26; 95% CI, 1.05 to 1.51; P=0.013), a high SII (OR, 1.00, 95% CI, 1.00 to 1.00; P=0.003), and a low ejection fraction (OR, 0.95; 95% CI, 0.90 to 0.99; P=0.018) were independent predictors of LAT (+). A spontaneous echo contrast (OR, 2.43; 95% CI, 1.35 to 4.39; P=0.003) was associated with LAT (+). SII values above 693.6 predicted LAT (+) with 71.6% sensitivity and 71.7% specificity (AUC, 0.77; P<0.001). The predictiveness of SII was similar to that of NLR (0.77 vs 0.74, P=0.093) but higher than PLR (0.77 vs 0.67; P<0.001) and WBC (0.77 vs 0.69; P=0.031). Conclusion: SII is an independent predictor of LAT in patients with NVAF. https://rhythm.tums.ac.ir/index.php/jthc/article/view/1646 https://rhythm.tums.ac.ir/index.php/jthc/article/download/1646/1060