2.3 Statistical analysis
The baseline characteristics of patients with internal and external BiVAD were compared using the χ2 test for categorical variables and analysis of variance for continuous variables. The Poisson regression model was used to assess the change in estimated quarterly volumes of internal, external, and all BiVADs. Finally, we sought to explain the national trends using exploratory subgroup analyses. The total population was divided into patients who survived the index hospitalization and those who died during the hospitalization. We performed regression analyses using comorbidities and complications as covariates. STATA was used to perform all analyses. Statistical significance was considered to be p < 0.05.