Objectives Recent studies in acute coronary syndrome (ACS) have reported mixed results for trends in ACS subtypes. The All New Zealand Acute Coronary Syndrome Quality Improvement (ANZACS-QI) 31 study evaluated trends in ACS event rates, invasive management and mortality of ST-elevation myocardial infarction (STEMI), non-STEMI (NSTEMI) and unstable angina (UA) in New Zealand.

Methods All ACS hospitalisations between 2006 and 2016 were identified from routinely collected national data and categorised into STEMI, NSTEMI, UA and MI unspecified (MIU). Annual hospitalisation, coronary procedure, 28-day and 1-year mortality rates were calculated and trends tested using Poisson regression adjusting for age and sex.

Results Over the 11-year study period, there were 188 264 ACS admissions, of which 16.0% were STEMI, 54.5% NSTEMI, 25.7% UA and 3.8% MIU. Event rates of all ACS subtypes fell: STEMI by 3.4%/year, NSTEMI by 5.9%/year and UA by 8.5%/year, while the proportion of patients with ACS receiving angiography and revascularisation increased by 5.6% per year. Rates of percutaneous coronary intervention rose for STEMI, NSTEMI and UA, but coronary artery bypass grafting increased only for NSTEMI and UA. Mortality at 28 days and 1 year was higher for STEMI than NSTEMI and lowest for UA. There was a relative 1.6%/year decline in 1 year mortality for NSTEMI (p<0.001), but no significant change for STEMI and UA.

Conclusions We observed declines in the event rates of all ACS subtypes and increases in revascularisation rates. The finding that mortality declined in patients with NSTEMI, but not in patients with STEMI and UA, despite increases in invasive procedures, requires further investigation.