Differences in cardiovascular mortality between Australia and New Zealand according to socioeconomic status: findings from the Long-Term Intervention with Pravastatin in Ischaemic Disease (LIPID) Study

Abstract

Background: Cardiovascular mortality is higher in New Zealand compared to Australia, but reasons for this difference are uncertain. This study describes differences in cardiovascular risk factors and cardiovascular mortality in Australians and New Zealanders with stable coronary artery disease stratified by socioeconomic status. Methods: Socioeconomic status was estimated from the residential area of 5949 Australians and 2784 New Zealanders with a history of myocardial infarction or unstable angina who participated in the Long-Term Intervention with Pravastatin in Ischaemic Disease (LIPID) Study. Socioeconomic and international differences in cardiovascular risk factors, medical treatments, and cardiovascular mortality during a median follow-up period of 7.8 years were evaluated. Results: Cardiovascular mortality increased as the median residential-area income decreased in both Australia (hazard ratio [HR]/income tertile 1.20, 95% confidence interval [CI] 1.08–1.32) and New Zealand (HR 1.16, 95%CI 1.02–1.31), but was higher in New Zealand across all socioeconomic groups (HR 1.42, 95%CI 1.25–1.61). Obesity, smoking, and a high white blood cell count at baseline were associated with higher cardiovascular mortality and were more common in lower-income areas in both countries. The total:HDL cholesterol ratio was higher in New Zealand, but similar across all socioeconomic groups. In both countries there were socioeconomic gradients in openlabel usage of cholesterol-lowering medication, percutaneous coronary intervention, and coronary artery bypass surgery. However, Australians in all socioeconomic groups were more likely than New Zealanders to receive these treatments. Conclusions: Although there is an important socioeconomic gradient in cardiovascular mortality in both Australia and New Zealand, cardiovascular mortality is higher in New Zealanders than Australians with stable coronary disease from all socioeconomic groups.