Prediction of postoperative atrial fibrillation with the systemic immune-inflammation index in patients undergoing cardiac surgery using cardiopulmonary bypass: a retrospective, single-center study

The systemic immune-inflammation index (SII, platelet count × neutrophil–lymphocyte ratio) is a novel parameter for systemic inflammation. Cardiopulmonary bypass (CPB) is associated with systemic inflammatory responses. This retrospective study aimed to determine whether SII could predict postoperative atrial fibrillation (POAF) after cardiac surgery using CPB. Patients who underwent cardiac surgery using CPB between January 2020 and July 2021 were included. The primary outcome was POAF incidence within 7 days. Receiver-operating characteristic (ROC) curve analysis was used to evaluate SII ability in predicting POAF. Multivariable analysis was used to estimate the independent association between SII and POAF development. The study included 212 patients, and 90 (43%) developed POAF. The preoperative SII cutoff of 545 × 10⁹/L predicted a poor outcome with 71% sensitivity and 81% specificity. The area under the ROC curve was 0.80 (95% confidence interval [CI] 0.73–0.86). Multivariable analysis showed that SII ≥ 545 × 10⁹/L was associated with the development of POAF (odds ratio 10.2; 95% CI 5.1–20.2, P < 0.001). SII predicted POAF with a curve of 0.91 (95% CI 0.82–1.00) in patients with coronary artery bypass grafting (CABG); the corresponding value in patients without CABG was 0.75 (95% CI 0.67–0.83). Preoperative SII may be a useful prognostic biomarker for POAF in patients undergoing cardiac surgery using CPB. Moreover, preoperative SII may play an important role in predicting POAF in patients undergoing CABG.