Statistical Methods and Analysis
Primary stratification was between males and females who underwent ATAAD repair. Continuous variables were presented as mean ± standard deviation for normally distributed data, or median and interquartile range (IQR) for non-normally distributed data. Categorical data were reported by frequency and percentage. Normally distributed continuous variables were analyzed using the student’s t-test, while non-normally distributed continuous variables were analyzed with the nonparametric Mann-WhitneyU test. The Chi-squared or Fisher’s exact test was used to compare categorical variables between groups, as appropriate. Unadjusted survival estimates were generated using Kaplan-Meier methods and compared using log-rank statistics. A Cox proportional hazards regression model was used for the multivariable analysis of mortality. The assumption of proportional hazards was validated using Schoenfeld residuals, and, for covariates other than sex in the model, the method of stepwise selection was employed with a threshold of inclusion in the model of p<0.020.
Supplementary propensity score matched analyses were performed using greedy nearest neighbor caliper matching, with calipers of width setting at 0.2 of standard deviation. Propensity score matching incorporated the following variables: patient age, history of hypertension, history of chronic lung disease, performance of hemiarch replacement, and performance of total arch replacement. All statistical analyses were performed using SAS/STAT Version 15.2 (SAS Institute Inc., Cary, NC, USA). All tests were 2-sided with an alpha level of 0.05 designated to indicate statistical significance.