Objective To compare population-level trends in 30-day case fatality following incident myocardial infarction (MI) in people with diabetes and those without diabetes.

Methods We identified all hospitalised incident MIs in 35–84 year olds from the Western Australian Data Linkage System for 1998–2010, stratified by diabetes status. Crude and age- and sex-standardised 30-day case fatality were estimated, and age- and sex-adjusted trends were calculated from logistic regression. We calculated the trend in risk of 30-day death associated with diabetes from multivariable logistic regression, adjusting for demographics, comorbidities and MI type.

Results 26 610 hospitalised incident MI cases were identified, 24.8% of whom had diabetes. The prevalence of heart failure fell in people with diabetes, concurrent with increasing chronic kidney disease and prior coronary heart disease and increasing levels of evidence-based therapies. Case fatality in people with diabetes fell from 11.65%, in 1998–2001, to 3.96% by 2008–2010. Age- and sex-standardised case fatality declined at a greater rate in those with diabetes (−10.6%/year, 95% CI −12.8% to −8.2%) compared to non-diabetics (−6.9%/year, 95% CI −8.3% to −5.3%; interaction p=0.005). The adjusted risk of 30-day death after incident MI was 1.23 times higher in diabetics than non-diabetics in 1998–2001 (95% CI 1.01 to 1.50), but was lower by 2008–2010 (OR 0.64, 95% CI 0.46 to 0.88).

Conclusions Greater improvements in 30-day case fatality following incident MI in people with diabetes during the 13-year study period has led to diabetes no longer being an independent predictor of early death following incident MI by 2008–2010.