There is very limited information on disparities in cardiac procedure use among AIAN, a population that is culturally diverse and dispersed throughout the United States, but AIAN have one of the highest prevalence rates of cardiovascular disease.1,2,25
We found that during hospitalizations for ischemic heart disease AIAN had similar rates of the cardiac procedures, cardiac catheterization and percutaneous coronary intervention, both before and after adjustment for covariates as non-Hispanic whites. However, for coronary artery bypass graft surgery, we found higher rates among AIAN as compared to non-Hispanic whites hospitalized for ischemic heart disease in unadjusted analyses that then attenuated and were no longer significant after adjustment for age, sex, comorbidities, and hospitalization payer source.
Our results differ from a previous study that found AIAN less likely to receive a cardiac catheterization or percutaneous coronary intervention in the setting of an acute myocardial infarction as compared to whites in specific geographic regions of the U.S.14
This same study also found that AIAN with diabetes were less likely to get a coronary artery bypass surgery, but there was no difference among those without diabetes as compared to whites.14
California was not included in that study, because it was done using an Indian Health Service hospitalization database and California does not have any an Indian Health Service funded hospital, and California has the lowest per capita Indian Health Service funds for financing hospitalizations in other hospitals.14,18,26
It is possible that the availability of the Tribal Health Programs in the California counties we studied contributed to our finding of no disparities in cardiac procedures during a hospitalization for ischemic heart disease between AIAN and non-Hispanic whites. Even though the Tribal Health Programs are severely limited in the amount of specialist or hospital care they can purchase for their users, it may be that these programs play a significant role in informing and empowering AIAN about their health care choices. Alternatively, our findings may reflect a difference in the practice patterns between Indian Health Service hospitals previously studied outside of California and the use of non Indian Health Service hospitals by AIAN in California. While we do not have data outside of California, it is worth noting that our findings are also consistent with a separate study that used a voluntary national registry and found that AIAN hospitalized for acute ischemic heart disease were as likely as whites to receive a cardiac catheterization and percutaneous coronary intervention.15
The administrative data in our study lacked key clinical information, such as the number of coronary vessels found to be atherosclerotic during cardiac catheterization or number of vessels bypassed during coronary artery bypass graft surgery. However, the Strong Heart Study, a longitudinal cardiovascular cohort conducted among AIAN in the Southwest, Northern Plains, and Oklahoma, showed that the majority of coronary artery disease found was related to diabetes.2
Given that patients with diabetes tend to have more severe three-vessel coronary artery disease, it maybe that AIAN had more severe coronary artery disease than non-Hispanic whites that we were unable to account for in adjustments and this may explain why our data showed higher rates of coronary artery bypass graft surgery among the AIAN group.
Though our study did not show a disparity in cardiac procedures during ischemic heart disease hospitalizations for AIAN compared to non-Hispanic whites in California, it has several limitations that are important to note. First, our analysis is based on administrative data. The reliability of racial coding in administrative databases is a concern especially for races other than white, and AIAN are often misclassified.1,18,19
However, we were able to overcome some of those challenges in our study by linking a file of AIAN active users of Indian Health Service funded care through Tribal Health Programs that operate in 37 counties with a statewide hospital discharge database.18
Second, the unit of analysis and denominator for our analyses is hospitalizations and not individuals. We might have found a different result had we been able to study individuals. If for example, non-Hispanic whites were more likely than AIAN to have multiple hospitalizations to manage an episode of ischemic heart disease this could create the appearance of a similarity in the use of cardiac procedures between AIAN and non-Hispanic whites when an analysis at the person level might suggest a disparity. We were unable to analyze the data using the individual as the unit of analysis because we were not provided with individual identifiers in the OSHPD hospital discharge file that was linked with users of the Tribal Health Program. However, we did limit our sample to those acute ischemic heart disease admissions that had a 5th digit of “1” to signify initial episode of care in an attempt to minimize influence from multiple hospitalizations.
Third, we cannot account for clinical appropriateness using the hospitalization administrative data, and thus even though we have found a similarity in the use of cardiac procedures between AIAN and non-Hispanic whites hospitalized for ischemic heart disease, the rates we observed per hospitalization may reflect underuse in one group and overuse in the other.27,28
Research on health care disparities among other racial and ethnic groups has tended to find greater degrees of underuse in minority populations and overuse in non-Hispanic whites.29,30
Also we cannot account for patients who may have been offered a cardiac procedure and subsequently refused.31,32
Further work is needed to elucidate the mechanisms of high mortality among AIAN from ischemic heart disease. We need to understand the prevalence of cardiac risk factors, the incidence of the disease, and the factors that influence the receipt of and continued adherence to beneficial treatments. These include specialty referral patterns and patients’ treatment preferences, both as inpatients and outpatients. We will need new and continued cooperation among tribes, agencies, and academic institutions to address these critical health care issues and questions.