Introduction
Worldwide, atrial fibrillation (AF) is one of the most prevalent cardiac arrhythmias in adults1. Owing to extended longevity and intensifying search for undiagnosed AF, approximately 4% experience AF in general population2 and a 2.3-fold rise is expected3. AF, which is associated heart failure4 and stroke5, worsens patient quality of life6 and increases significant burden to patients and societal health due to the high morbidity and mortality. Previous studies7-11 have shown that inflammation is associated with AF development and progression in general population and patients after cardioversion, cardiac surgery and catheter ablation. Increasing evidence supports the essential role of inflammatory factors10,12-14 in predicting the onset of AF and recurrence. Some inflammatory factors including platelet-to-lymphocyte ratio (PLR)15,16, IL-617, IL-1018 and high sensitivity C-reactive protein19, were proven to be simple biomarkers to predict the incidence of AF in patients with or without history of AF. However, these biomarkers only involve one or two types of immune- inflammatory cells and may not accurately reflect inflammation status.
The systemic immune-inflammation index (SII) is a novel and integrated inflammatory index based on neutrophil, platelet and lymphocyte counts. SII was initially demonstrated to be associated with prognosis of various cancers, such as prostate cancer20, hepatocellular carcinoma21 and gastric cancer22. Up to now, the relationships of SII and coronary artery disease23,24, heart failure25 were reported by many studies. SII is now considered to comprehensively reflect inflammation status. However, the association between SII and AF still remains unclear. Therefore, we conducted this study to investigate the association between SII levels and AF to determine the prognostic value of SII in patients with AF.