Statistical analysis
The sample size was estimated by the time to VA elimination since
ablation and ablation applications.7,10,13 The average
IA successful rate (𝜋) was assumed 85% and the difference (𝜹) was
assumed 20%. For a power of 90% (Z𝛽=1.28) at a
two-sided alpha level of 0.05 (Z𝛼=1.96), 134 patients
were needed. Assuming a dropout rate of 20%, 160 patients were planned
to be enrolled. Due to the significant subgroup effect, after reviewing
the data, the ethics committee and the leadership discontinued the trial
in July 2020.
The primary and secondary outcome was analyzed using the
intention-to-treat (ITT) principle. The logistic regression model using
frontward selection (Wald) was applied to test the multiplicative
interaction between the EVA sites and strategies. Their addictive
interaction of absolute excess risk due to interaction (AERI) was
calculated.14 Continuous variables were expressed as
mean ± standard deviation or median (interquartile range). Categorical
variables were expressed as number (frequency %). For comparison of
patient characteristics, differences of continuous variables were tested
using Student’s t-test if normally distributed; otherwise, Mann-Whitney
U test was used. Categorical variables were compared using Fisher exact
test. The VA recurrence was compared based on a time-to-first-event
analysis using the log-rank test. A two-tailed P value of less than 0.05
was considered statistically significant. For multiple comparisons of 6
contrasts among subgroups based on the EVA sites and IA strategies, a
two-tailed P value of less than 0.0083 was considered statistically
significant using Bonferroni correction. All statistical analysis was
performed using SPSS 26.