Rates of percutaneous coronary interventions and bypass surgery after acute myocardial infarction in Indigenous patients

Indigenous Australians have high rates of coronary artery heart disease1 and die from this condition at more than twice the rate of other Australians.2 Ensuring equal access to optimal care is a key objective of the free public hospital system in Australia, but good information about the extent to which this is being achieved in Indigenous Australians is scarce, in particular as regards optimal care for acute coronary syndromes — percutaneous coronary intervention (PCI) and bypass surgery.

Cunningham found that Indigenous patients admitted to public hospitals for circulatory disease were 47% less likely than other patients to have a diagnostic or therapeutic procedure.3 The only other published information, a recent report by the Australian Institute of Health and Welfare (AIHW), found that for the period 1998–2001, population-based PCI rates were 40% lower among Indigenous men than non-Indi-genous men, but were 20% higher among Indigenous women than non-Indigenous women.4 For bypass surgery, the corresponding figures were 7% lower for men and 50% higher for women.

One limitation of the AIHW report was that, in calculating the rates, Indigenous status identification in the numerator (number of PCIs and bypass operations) may be different from Indigenous status identification in the denominator (population data from the Australian Bureau of Statistics). This problem is not unique to comparisons of Indigenous and non-Indi-genous Australians; it hinders interpretation of race-specific rates around the world.5,6

Here, we report a cohort study based on linkage of computerised discharge abstracts. The two cohorts for comparison were Indigenous and non-Indigenous patients treated in the public sector for acute myocardial infarction (AMI). We followed up each patient for 1 year to determine whether they had an invasive coronary procedure. Because the comparisons are based on data from a single source, they are not affected by differential classification of Indigenous status in the numerator and denominator.

Our study is the first Australian analysis, based on administrative data, examining racial differences in coronary procedure rates. More than 25 such studies have been published in the United States.10 We found relatively low rates of PCI for Indigenous patients with AMI, even after adjusting for age, sex, remoteness, socioeconomic status, hospital characteristics and comorbidities. Adjusted rates for bypass surgery were more equitable, but adjusted rates for any cor-onary procedure (ie, PCI or bypass surgery) were 22% lower among Indigenous patients.

Moreover, the case-fatality rates for Indi-genous people show that they are a group at high risk of further coronary events. There are particularly strong indications for revascularisation procedures in such patients.17 Consequently, the lower rates of revascularisation procedures in Indigenous patients may indicate a greater inequity than suggested by our analyses, which do not take into account the potential benefit from the procedure.

There are at least four possible reasons why Indigenous patients with AMI have relatively low rates of coronary procedures in the public hospital sector, despite their clinical need. First, relative contraindications such as comorbidities, smoking and obesity might be more common. Second, Indigenous people might prefer not to have a procedure. Third, Indigenous people might have less access to coronary pro-cedures because they are more likely to live in remote areas or attend small hospitals. Fourth, there might be discrimination against them, albeit subtle, in the public hospital system.10

Like similar studies based on administrative data in the United States, our linked data set contained some of these factors, but not others. Specifically, we had data on socioeconomic status, remoteness, hospital characteristics, and comorbid conditions. Like similar studies in the United States, we adjusted for these covariates in the analysis to obtain the most valid estimates of differences in procedure rates, given the available data. However, we did not have data on potentially important variables such as severity of AMI, smoking status, and patient preferences for intervention. Consequently, we could not (and did not attempt to) untangle the possible causes of the disparity in procedure rates. We stress that the variables we did consider are not confounders in the traditional sense of being nuisance variables that should be ignored after being accounted for in a statistical model. Instead, they are of intrinsic interest because they lie on the causal pathway,18 providing clues about ways to address the problem.

Along these lines, the results for comorbidities are particularly helpful. Diabetes, chronic renal failure and pneumonia were at least twice as common among Indigenous patients with AMI as among non-Indigenous patients with AMI; and chronic bronchitis and emphysema and heart failure were at least 60% more common (Box 4). If a patient had at least one comorbidity, then their probability of having a coronary pro-cedure was reduced by 40% (Box 7). High levels of comorbidities have also been found among African Americans in the United States, and commentators there have suggested that improved access to primary care would allow for better management of comorbidites and, consequently, increased rates of revascularisation.19

There is some evidence that primary care can reduce the prevalence and severity of comorbidities among Indigenous Australians. A study in the Northern Territory showed significant improvements in rates of progression to renal failure by implementing evidence-based secondary prevention in a primary health care setting,20 and there have been similar encouraging results from an evaluation of a primary care program for diabetes in North Queensland.21

Two other features of our data are of particular interest. First, Indigenous patients hospitalised for AMI were 14 years younger than their non-Indigenous counterparts. This is consistent with data from other sources, which show that Indigenous people aged in their 50s have rates of chronic disease similar to non-Indigenous Australians aged in their 60s or 70s.2

Second, Indigenous patients who survive long enough to be admitted to hospital and receive medical treatment have case-fatality rates that are nearly twice as high as their non-Indigenous counterparts. Possible reasons include more severe disease or more life-threatening comorbidities. Our data set is not suited to the task, but further investigation is warranted to untangle the possible causes, because each is potentially amenable to modification. In particular, more accessible and culturally appropriate primary health care might enable Indigenous people with coronary artery disease to be identified earlier in the course of their illness and have any comorbidities treated. For example, mortality is 30 times higher in patients on dialysis than for other patients with AMI, even after adjusting for age, sex and the presence of diabetes.22 Also, Indigenous patients are known to be under-represented at cardiac rehabilitation programs,23 which can reduce cardiac deaths by up to 31%.24 In hospitals, previous work in Queensland has shown that low-cost quality improvement interventions can reduce mortality rates for AMI and might be especially effective in small hospitals where many Indi-genous patients are treated.25

Advances in technology, and in particular the use of stents for PCI, have improved success rates and increased the range of people who can benefit from coronary revascularisation.26 Therefore, increasing the capacity of the public sector to perform revascularisation might allow more Indi-genous patients with AMI and comorbidities to have these procedures, thereby delaying death, relieving symptoms and improving quality of life. However, there is no guarantee that Indigenous people would specifically benefit from this approach, especially if their prevalence of comorbidities remains high. For example, there is some evidence from Canada that physicians there generally select lower-risk patients for procedures after AMI.27 Also, in spite of a more than twofold increase in coronary revascularisation procedures in Finland between 1988 and 1996, inequalities remained, especially for the disadvantaged groups with a relatively high prevalence of comorbdities.28

Therefore, the extra capacity might be taken up treating more non-Indigenous patients with fewer comorbidities. What is needed is high-quality, integrated primary health care that complements the tertiary sector. The available data from the AIHW show that there is underfunding of primary care services for Indigenous Australians,29 and recent work done by Access Economics suggests that the underfunding is of the order of $300 million per year.30 The high rates of comorbidities found among the Indigenous patients in this study, and the effect of this on procedure rates, suggest that adequate primary health care is a pre-requisite for effective specialist care.

1 Definition of public and private sector patients

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* Includes patients who were transferred to a private hospital during their index admission

3 Age standardised* prevalence of comorbidities† by Indigenous status

*To improve statistical precision, the much larger non-Indigenous cohort (mean age, 68 years) was age standardised to the age distribution of the Indigenous cohort (mean age, 54 years). †We used comorbidities from a study based on administrative hospital data in Ontario,12 and then checked it against Queensland data to confirm that no other comorbidities were commonly reported for Queensland patients with AMI. Dementia and liver disease were not considered, as only three Indigenous patients had either of these conditions.

5 Age-adjusted survival* by Indigenous status

* Estimated using a proportional hazards model.