Systemic Immune-Inflammation Index as a Predictor of Left Atrial Thrombosis in Nonvalvular Atrial Fibrillation

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.