Elsevier

American Heart Journal

Volume 154, Issue 2, August 2007, Pages 385-390
American Heart Journal

Clinical Investigation
Outcomes, Health Policy, and Managed Care
Area socioeconomic status and mortality after coronary artery bypass graft surgery: The role of hospital volume

https://doi.org/10.1016/j.ahj.2007.04.052Get rights and content

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.

Section snippets

Setting and study population

Data were collected as part of the CCMRP.14, 15 This registry, based on the Society of Thoracic Surgeons Template, contains information collected from 75 California hospitals on 20 864 participants who underwent isolated CABG (ie, concomitant valve or aortic surgery was excluded) between January 1, 1999, and December 31, 2000. Trained abstractors performed a comprehensive and detailed clinical data extraction. Accuracy of the CCMRP data was assured through an independent, external audit of 1006

Results

Of the 18 961 patients in our sample, 501 (2.6%) died inhospital after their CABG surgery. Contrary to our hypothesis, in unadjusted analyses, SES was not associated with greater CABG mortality. Inhospital mortality was 2.66% (n = 167) among individuals residing in low-SES areas, 2.57% (n = 163) among individuals residing in medium-SES areas, and 2.70% (n = 171) among individuals residing in high-SES areas (P = .89).

Discussion

Improving socioeconomic disparities in cardiovascular health requires identification of mechanisms potentially amenable to improvement. We had hypothesized that one of these mechanisms could be hospital selection. We expected that individuals of low SES would have greater mortality after CABG, mediated through both a poorer clinical risk factor profile and reduced access to CABG at hospitals presumed to have higher quality. We confirmed that individuals residing in low-SES areas did indeed have

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This study was supported by a grant from the Robert Wood Johnson Health and Society Scholars Program, the American Diabetes Association, and NIDDK K23-DK071552.

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