Statistical Analysis 
All statistical analyses were performed using SPSS software (version 23.0, SPSS Inc., Chicago, Illinois). Continuous variables were expressed as mean±SD and compared using an unpaired Student t-test or the nonparametric Mann-Whitney test. Categorical variables were presented as counts and percentages and compared using chi-square statistics or the Fisher exact test. Binary logistic regression analysis was performed to identify the independent determinants of AVD progression. Variables for inclusion were carefully chosen to ensure the parsimony of the final models. Candidate variables that were considered clinically relevant (based on clinical experience and previous literature) or showed a univariate relationship with outcom (p<0.20) were included in the multivariable model. P value<0.05 was considered statistically significant.