2-6 Statistical analysis
Descriptive statistics were reported as mean (± SD) or median (interquartile range) values for continuous variables, and as frequency (percentage) for the categorical variables. To compare continuous variables between two groups, the independent t-test or Mann-Whitney U test was used. The categorical variables were compared between groups using the chi-squared test. Friedman test was used to compare the distributions of 3 or more dependent variables. Multivariate analysis was conducted to identify the predictors of study endpoints by including significant covariates (i.e., age, sex, atrial fibrillation, admission INR, functional class, size of thrombus, elapsed time since valve surgery, redo-operation, recurrent episodes, and treatment types) into multiple logistic regression analyses. The survival plot and freedom from recurrence were estimated using the Kaplan-Meier method. The p <0.05 was considered statistically significant. All statistical analyses were performed using the SPSS version 21 (IBM, Armonk, NY).