Statistical analysis
The statistical analysis was performed using the computer program STATISTICA v.13.3 (StatSoft, Inc., Tulsa, USA). P values less than 0.05 were considered significant.
For quantitative variables, basic descriptive statistics were calculated (M - average, SD - standard deviation, Me - median, Q1 - lower quartile, Q3 - upper quartile, Min - minimum value, Max - maximum value) and the compliance of their distributions with the theoretical normal distribution was checked using the Shapiro-Wilk’s W test. Comparisons were performed with the Students’ T test or Mann-Whitney U test for independent groups or Kruskal-Wallis ANOVA for multiple comparisons. Each categorical variables were presented as numbers and percentages. The comparisons were performed with the Chi-square test. The correlations between the studied parameters were performed using Spearman’s rank correlation coefficient according to statistical properties of the data.
The receiver operational curve (ROC) was used to assess the ability of P wave duration to classify disease status. Based on the results of examination and receiver operating characteristic (ROC) analysis, a cut-off threshold for P wave duration was calculated for AF and CV groups.