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).