Objective To assess the left ventricular dyssynchrony in coronary artery disease(CAD) without visual segmental wall motion abnormalities using strain delay index (SDI).Methods A total of 135 patients under suspicion of CAD were recruited in this study.Two-dimensional cchocardiography was performed to collect dynamic images of left ventricular apical long axis views,tow-chamber views,four chamber views and parasternal short axis mitral views,papillary views and apical views.The time to minimal systolic longitudinal,radial,circumferential strain (Tssl,Tssr and Tssc) were measured from the start point of QRS wave in electrocardiogram.The left ventricular segmental standard deviation (Tssl-SD,Tssr-SD,Tssc-SD),maximal difference (Tssl-Dif,Tssr-Dif,Tssc-Dif) and longitudinal,radial,circumferential SDI (LSDI,RSDI,CSDI) of 18 left ventricular segments were calculated.Results According to coronary angiography results,patients were divided into three groups:severe stenosis group,mild stenosis group and control group.Compared with the other two groups,SDI and Tssl-SD,Tssl-Dif were decreased in severe stenosis group (P ＜0.001 or P ＜0.05).However,there were not significant differences between the mild stenosis group and the control group except Tssr-SD.The receiver operating characteristic (ROC) curves analysis demonstrated that LSDI had the highest accuracy and Tssl-SD had the lowest accuracy for detecting severe CAD (areas under the curve were 0.891,0.797,0.666,0.580 and 0.556 respectively).High sensitivity and specificity (80.6％ and 86.7％,respectively) were shown when using-12.67％ as a cutoff point of LSDI to diagnose severe CAD.Conclusions SDI can be helpful for assessing the left ventricular dyssynchrony in patients without visual segmental wall motion abnormalities,and LSDI is the most effective parameter to detecting severe CAD.