Racial differences in the incidence of femoral bypass and abdominal aortic aneurysmectomy in Massachusetts: relationship to cardiovascular risk factors.

PURPOSE: Atherosclerotic disease appears to be more severe in black patients than in white patients, but abdominal aortic aneurysms, which have traditionally been believed to have an atherosclerotic cause, are reported to be less common in black patients than in white patients. Our goals were to compare and contrast factors associated with the development of abdominal aortic aneurysms and clinically significant atherosclerotic occlusive disease (1) to determine whether these diseases share a common cause and (2) to explore their association with race.
METHODS: Dual case-control studies were conducted with multivariate analysis to compare cases (patients undergoing aneurysmectomy or patients undergoing femoral bypass) with a comparison group consisting of patients who had undergone appendectomy. Two data sources were used: (1) hospital discharge data for Massachusetts from 1984 through 1988 and (2) medical records at University Hospital of Boston and Boston City Hospital. For both the Massachusetts database and the hospital chart review, records were obtained for all patients discharged between January 1984 and December 1988 with an International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) procedure code for abdominal aortic aneurysm resection (38.44) or aneurysmorrhaphy (38.34) or with a procedure code for femoral artery bypass/reconstruction (39.29). To conduct a nested case-control study, records were also obtained for a control group consisting of patients between the ages of 50 and 84 years who had undergone appendectomy during the same 5-year period.
RESULTS: Black patients had higher rates of femoral bypass than did white patients after adjustment for age and sex (odds ratio = 1.97; 95% confidence interval: 1.49, 2.61; p < 0.0001). However, femoral bypass was also associated with hypertension, diabetes, and low household income. After adjusting for these additional factors in the statewide data set, the black/white odds ratio for femoral bypass was only 1.44 (95% confidence interval: 1.08, 1.92). The parallel case-control study at University Hospital and Boston City Hospital, which provided information about smoking status and more accurate ascertainment of coexisting hypertension and diabetes, indicated that there was no racial difference in rates of femoral bypass after correcting for these additional risk factors (odds ratio = 0.94; 95% confidence interval: 0.40, 2.22; p = 0.90). In contrast, abdominal aortic aneurysmectomy occurred predominantly in white men. Aneurysmectomy was also associated with smoking and hypertension, but aneurysmectomy was not significantly associated with diabetes mellitus or family income. The black/white odds ratio for aneurysm was 0.29; (95% confidence interval: 0.07, 1.23; p = 0.09 after adjustment for other variables).
CONCLUSIONS: Hypertension, smoking, and male sex are risk factors for the development of femoral atherosclerosis and abdominal aortic aneurysm formation. However, abdominal aortic aneurysms occur predominantly in white men and do not appear to be associated with diabetes mellitus or income. In contrast, the higher rate of femoral artery bypass in black patients is probably the result of greater prevalence among black patients of hypertension, diabetes, smoking, and perhaps by other ill-defined factors associated with socioeconomic status.