Statistical analysis
For continuous variables, the Shapiro-Wilk test was used to determine the normality of the data of the IPT and SPT groups. If the distribution was normal, Levene’s test was used to confirm equal variance between the two groups. When the distribution did not follow a normal distribution, the Mann-Whitney U test was used. If the variance was uniform, the Student’s t-test was used, and if not, the Welch t-test was used. In addition, Fisher’s exact probability test was used to compare categorical variables between the two groups. Furthermore, when statistically significant differences were found, a receiver operating characteristic (ROC) curve was generated to determine the cut-off value for assessing the pacing threshold increase. All analyses were performed using EZR version 1.42 (Saitama Medical Center, Jichi Medical University, Saitama, Japan), a graphical user interface for R 2.13.0 (R Foundation for Statistical Computing, Vienna, Austria). In all tests, the significance level was set at P  ≤ 0.05.