3.6 Statistical analysis
Categorical values are expressed as absolute values and relative
frequencies. Continuous variables are expressed as mean ± SD. Tests for
significance were conducted using the unpaired t-test or nonparametric
test (Mann-Whitney U-test) for continuous variables and the chi-squared
test or Fisher’s exact test for categorical variables. The cutoff value
of the voltage in each region was examined using the Receiver Operating
Characteristic (ROC) curve. The score below the cutoff value was set as
1 point each, and the relationship with the recurrence of atrial
fibrillation was examined by a chi-square test. Clinical factors
associated with AF recurrence were determined using univariate and
multivariate Cox proportional hazard models and logistic regression
analyses. All statistical analyses were performed using commercial
software (SPSS version 25 ®, SPSS, Chicago, IL, USA), and statistical
significance was defined as p <0 .05.