The impact of the health care system on socioeconomic inequalities in coronary heart disease in Australia : a population-level study of 45-74 year olds

Socioeconomic inequalities are a substantial problem in relation to Australia's biggest killer and area of health expenditure, coronary heart disease (CHD). They have been well documented for mortality, but little is known about whether they are due to differing chances of having a major coronary event (the event rate) or of dying when one occurs (the case-fatality rate). Nor does very much detail exist on whether these inequalities have changed over time. This study aims to fill these gaps, and also to examine the role the health care system plays in generating inequalities by analysing inequalities in the use of relevant services, and whether levels of use match levels of need for these services. A large, national dataset was constructed. It contains information on all major coronary events (essentially heart attacks) in Australia over a period of 10 years, 1996-2005, both fatal and non-fatal. Similarly, all 'services' provided for up to 10 years in the form of cholesterol-lowering medications (statins), a diagnostic procedure (angiography) and two types of revascularisation (coronary artery bypass grafts (CABGs) and percutaneous coronary interventions (PCls)) are included. In addition, a measure of need for services was developed. The dataset was then linked to census information on the socioeconomic characteristics of small areas to enable analysis of differences in outcomes and services across socioeconomic groups. The majority of the analysis was carried out using negative binomial regression to derive relative and absolute measures of inequality, including in particular the relative index of inequality and the slope index of inequality. The study clearly shows that nearly all of the socioeconomic inequality in CHD mortality in Australia comes from event rates rather than case-fatality rates. This indicates that the health care system's efforts to reduce these inequalities need to focus on preventing major coronary events, including by encouraging improvements in behavioural risk factors for them and treating risk factors when present (such as with medications), diagnosing problems early, and using surgery and other procedures (such as CABGs and PCls). Differential access to emergency care appears not to contribute to these inequalities. Time series analysis shows that inequalities in event rates have been increasing in relative terms, and even in absolute terms for males. Analysis of the use of statins, angiography and revascularisations shows substantial inequity -that is, use relative to need is much higher among the most well-off compared with the least well-off. The former are over twice as likely as the latter to receive these services for a given level of need. The largest inequities were found for the newer service (PCl rather than CABG) and for care provided earlier in the disease process (through medications and angiography). The study also shows that differential use of private health care plays a significant role in this inequity, and rural or remote locations play a smaller role. This study clearly demonstrates that socioeconomic inequalities in CHD are a major problem in Australia, and the gap is widening-improvements over time are benefiting the most well-off more than the least well-off. Inequalities largely derive from differential chances of having a major coronary event, rather than of dying when one occurs. The health care system appears to also contribute to the inequalities, and therefore has the potential to help reduce them by becoming more equitable