Statistical analysis
We ranked patients by national ADI percentile, and divided them into 4
equal-sized quartiles, where the lowest quartile (Q1) represents least
socioeconomically deprived status, and highest quartile (Q4) represents
most deprived.10 To compare differences in
demographics and comorbidities between ADI quartiles, we used
Kruskal-Wallis rank sum test for continuous variables and Pearson
chi-squared test or Fisher’s exact test for categorical variables, as
appropriate. Pairwise chi-squared test with nominal independence and
Bonferroni correction was used for between-group differences. Two-sided
Cochrane-Armitage test was used to compare occurrence of clinical and
imaging follow-up between ADI quartiles.
Bivariate and multivariate generalized logistic regression were used to
determine factors associated with occurrence of surveillance imaging (CT
chest or echocardiogram) at or before 24 months following index CT scan.
Variables with p-value <0.1 on bivariate analysis were
included in the multivariate model.
Competing risks analysis, as described by Fine et
al.,17, 18 was used to model the effect of ADI
quartile on time from index CT scan to first encounter with a
cardiologist or cardiac surgeon for ATAA aneurysm, with the competing
risk of death. Time to follow-up was defined as 0 for patients who were
already established with either of these specialties. This methodology
allows for visual representation of the subset of patients with
pre-established follow-up prior to index scan, in which new first-time
encounters do not apply. We performed competing risks regression
adjusted for ADI quartile, age, sex, race, and ATAA size on index scan,
factors which may influence a provider’s decision to refer patients to a
cardiovascular specialist. We defined statistical significance asp <0.05. All data analysis was performed in R version
3.6.3 (R Foundation for Statistical Computing).
The Yale University Institutional Review Board approved this study and
individual consent was waived (IRB 2000027551). The study followed the
Strengthening the Reporting of Observational Studies in Epidemiology
(STROBE) reporting guidelines for cohort studies.