Abstract: Background:Metabolic syndrome (MS) is a risk factor for stroke and thromboembolism event.Left atrial or LA appendage (LA/LAA) thrombus is a surrogate of potential stroke.The relationship between MS and atrial thrombus remains unclear.In this study,we sought to investigate the effect of MS on risk stratification of LA/LAA thrombus formation in patients with nonvalvular atrial fibrillation (NVAF).Methods:This cross-sectional study enrolled 294 consecutive NVAF patients without prior anticoagulant and lipid-lowering therapies.LA/LAA thrombus was determined by transesophageal echocardiography.Risk assessment of LA/LAA thrombus was performed using the CHADS2,CHA2DS2-VASc,MS,CHADS2-MS,and CHA2DS2-VASc-MS scores.Logistic regression analyses were performed to determine which factors were significantly related to LA/LAA thrombus.Odds ratio (OR) including 95% confidence interval was also calculated.The predictive powers of different scores for the risk of LA/LAA thrombus were represented by C-statistics and compared by receiver operating characteristic (ROC) analysis.Results:LA/LAA thrombi were identified in 56 patients (19.0%).Logistic analysis showed that MS was the strongest risk factor for LA/LAA thrombus in NVAF patients (OR =14.698,P < 0.001).ROC curve analyses revealed that the C-statistics of CHADS2-MS and CHA2DS2-VASc-MS was significantly higher than those of CHADS2 and CHA2DS2-VASc scores (CHADS2-MS vs.CHADS2,0.807 vs.0.726,P=0.0019).Furthermore,MS was helpful for identifying individuals with a high risk of LA/LAA thrombus in the population with a low risk of stroke (CHADS2 or CHA2DS2-VASc score =0).Conclusions:MS is associated with LA/LAA thrombus risk in patients with NVAF.In addition to the CHADS2 and CHA2DS2-VASc scores,the CHADS2-MS and CHA2DS2-VASc-MS scores provide additional information on stroke risk assessment.