Statistical Analysis
Pre-operative covariates were assessed for normal distribution using the Shapiro-Wilk test. Between group characteristics were assessed for statistical differences using the Student T-test or Wilcoxon Rank Test for non-parametric variables. Differences in discrete data was assessed using Pearson’s χ2 test. Multivariate logistic regression models were constructed to assess the influence of a variety of covariates on a composite end-point (moderate/severe aortic regurgitation, reintervention on the aortic root or valve and mortality).
Crude survival curves were estimated using the nonparametric Kaplan-Meier method, and log rank tests were used to compare the survival distribution among groups. Cox proportional hazard regression was conducted to calculate the adjusted hazards ratio with 95% confidence intervals. Stepwise selection was performed using age, sex, COPD, Euroscore, NYHA class and LV function in the model. Statistical analyses were conducted using the Stata 13.0 software (Stata Corp., College Station, TX, USA).