Statistical analysis
Normally and non-normally distributed variables were expressed as mean and median, respectively. Differences between groups were assessed using independent samples t-test and Chi-square test for continuous and categorical variables, respectively. Proportional-hazards Cox regression was used to identify predictors of time to VT or death. Variables with a P-value (P) ≤ 0.10 in univariate analysis were entered simultaneously in the multivariate regression model and deemed as statistically significant if P<0.05. Multicollinearity was excluded by assessing Pearson’s correlation coefficient between pairs of continuous variables. Kaplan-Meier curves were used to report VT-free survival for the NC-ABL and C-ABL groups, while differences in their survival curves were assessed with the log-rank test. Annual relapse rates were obtained by dividing the total numbers of first events by the total number of person-years of follow-up for each group. The propensity score (PS) for an individual is the probability of receiving a particular treatment based on a particular set of individual covariates7. A PS matching was assessed for the ablation strategy (C-ABL vs NC-ABL) by multivariable logistic regression, with the inclusion of the covariates identified as independent predictors of VT recurrence and mortality: age; IHD etiology; left ventricular ejection fraction (LVEF); New York Heart Association (NYHA) functional class III or IV; ES at presentation. The resulting scores were matched in a 1:1 ratio to the best corresponding patient, with a maximal allowable difference of 0.05 (caliper width of 0.05 of the standard deviation of the logit of the PS). Any remaining differences between matched pairs were assessed by standardized difference of the means (level of significance <0.05). Statistical analysis was performed using Statistical Package for Social Sciences (SPSS) version 23.0 (SPSS Inc., Chicago, USA) for Windows OS. Statistical significance was set at P<0.05 (two-sided tailed).