Area socioeconomic status and mortality after coronary artery bypass graft surgery: the role of hospital volume.
BACKGROUND
Individuals of low socioeconomic status (SES) have reduced access to coronary artery bypass graft surgery (CABG). It is unknown if low-SES CABG patients have reduced access to hospitals with better outcomes.


METHODS
We conducted a retrospective cohort analysis of the California CABG Mortality Reporting Program, consisting of individuals with zip code information who underwent CABG at participating hospitals in 1999-2000 (n = 18,961). Primary outcome measures were inhospital mortality after CABG; primary independent variables of interest were area-level SES, clinical risk factors, and hospital volume. We used 2-level hierarchical random-effects logit models to estimate the relationship between explanatory variables and inhospital mortality.


RESULTS
Within high-volume hospitals, patients of low-SES areas had greater mortality than those of mid- and high-SES areas (2.5% vs 1.5% vs 1.8%, P = .024). However, there was no relationship between SES and mortality in lower-volume hospitals. Contrary to expectations, individuals of high-SES areas (42%) underwent surgery at low-volume hospitals more often than patients of low-SES areas (28%, P < .001), although mortality at low-volume hospitals was greater than that at high-volume facilities (P < .001). Discrepancies were not explained by distance traveled.


CONCLUSIONS
Mortality after CABG is modified by both SES and hospital volume. Within high-volume hospitals, patients of low-SES areas fared worse than patients of higher-SES areas. Patients of high SES tended to have CABG surgery at low-volume hospitals where mortality was greater and therefore had higher mortality than expected.
Kim
Catherine
C
Division of General Internal Medicine, Department of Medicine, University of Michigan, Ann Arbor, MI, USA. cathkim@umich.edu
Diez Roux
Ana V
AV
Hofer
Timothy P
TP
Nallamothu
Brahmajee K
BK
Bernstein
Steven J
SJ
Rogers
Mary A M
MA
D000368:Aged; D000369:Aged, 80 and over; D002140:California / Q000453:epidemiology; D001026:Coronary Artery Bypass / Q000401:mortality* / Q000706:statistics & numerical data; D005260:Female; D017052:Hospital Mortality; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012923:Social Class