Discussion
This study mainly investigated the association between SII level and adverse outcomes in patients with AF, and tried to evaluate the prognostic value of SII as a new inflammatory factor in AF. The major finding was that high SII level was strongly associated with adverse outcomes and was an independent predictor for death from all causes and death from cardiovascular diseases in patients with AF. Our study is the first study to report the association and prognostic value of SII in patients with AF. This finding adds to current knowledge regarding the predictive relationship between SII and adverse outcomes in AF patients.
Previous studies13,14,17,27 have established that inflammation plays a key role in development and progression of AF. Inflammatory factors, such as PLR15, IL-617, IL-1018 and CRP19, were proven to be risk factors in AF and were potential predictors of prognosis in patients developed AF. As for SII, which combined neutrophil, lymphocyte and platelet count, serving as a detectable biomarker for systemic inflammatory activity and reflecting the inflammatory state28. Previously, SII emerged as a reliable and powerful predictor in various malignant diseases, including hepatocellular carcinoma21, gastric cancer22 and renal cell cancer29. Evidence is accumulating that SII level, apart from their well-known predictive value in cancer, were close related with in-hospital mortality in infective endocarditis30 and the incidence of major cardiovascular events in coronary artery disease23,31,32. Until now, the association between SII level and AF is still unknown. Therefore, we utilized a novel predictor, SII, which was demonstrated to be significantly related to adverse outcomes in AF patients.
SII was measured based on the counts of three types of circulating immune cells: platelets, lymphocytes, and neutrophils. Our study showed that AF patients with high SII level had increased risk for mortality. Neutrophils, which constitute the largest proportion of leukocyte, are of great importance for initiating and modulating immune processes33,34. Lymphocytes are also an important component of white blood cells, mediate adaptive immunity and function in innate immunity. Both neutrophils and lymphocytes can mediate adaptive and innate immunity. Platelets could be considered as aspecific first line inflammatory biomarkers which bind to leukocytes, influencing the function of inflammatory elements of these cells35. In several clinical studies, mediators of the inflammatory response were supported to be associated with remodeling of AF36,37. Inflammation can initiate AF, which subsequently generates an inflammatory response that further enhances atrial electrical and structural remodeling and perpetuates the arrhythmia.
Our study had several strengths. The sample size was relatively large to identify the significant association between SII and adverse outcomes in patients with AF. Moreover, we adjusted the potential confounders which might influence the prognostic value of SII in patients with AF. However, some limitations on this study also should be mentioned. First, because of the retrospective study design, results of our study need to be verified by multicenter, prospective studies. In addition, we only collected the baseline data of SII, rather than collecting data at multiple times.