Statistical analysis
Results are presented as mean with standard deviation, median with interquartile range or frequency. The mean values were compared using paired t -test. Analysis of the receiver operating characteristic curve was used to assess the ability of ΔLVEF during dobutamine infusion for detecting improvement of post-operative LVEF. The optimal cut-off point was calculated by determining the ΔLVEF during dobutamine infusion that provided the greatest sum of sensitivity and specificity. In all analyses, two-tailed P values of <0.05 were considered statistically significant. All analyses were performed with R statistical software (R software, version 3.3.0; R Foundation for Statistical Computing, Vienna, Austria).