BACKGROUND: Primary percutaneous coronary intervention (pPCI) has been the national reperfusion strategy for patients with ST-segment elevation myocardial infarction (STEMI) in Denmark since 2003. We recently reported a gradual reduction in 1-year mortality in patients with pPCI-treated STEMI. To elucidate potential causes of this reduction, we examined trends in major adverse cardiovascular events (MACE). OBJECTIVES: The purpose of this study was to examine trends in 1-year risk of MACE following pPCI-treated STEMI from 2003 to 2017. METHODS: The Western Denmark Heart Registry was used to identify first-time PCI-treated patients undergoing pPCI for STEMI from 2003 to 2017. Patients were categorized into 4 time periods (2003-2006, 2007-2010, 2011-2014, and 2015-2017) and the main outcome was 1-year MACE, defined as recurrent myocardial infarction, ischemic stroke, or cardiovascular death. Temporal changes were compared to those of an age- and sex-matched general population. RESULTS: We included 18,540 first-time pPCI-treated STEMI patients between 2003 and 2017. The 1-year risk of MACE decreased from 13.0% in 2003-2006 to 8.7% in 2015-2017 (adjusted HR: 0.67
95% CI: 0.58-0.76). Similar relative reductions were observed for the individual components of MACE. Cardiovascular death was the most common outcome and the largest contributor to the absolute reduction in MACE. Compared to the matched general population, STEMI patients had 11% higher 1-year risk of MACE in 2003 to 2006, a risk difference that decreased to 7% in 2015 to 2017. CONCLUSIONS: In Western Denmark, with a fully implemented pPCI strategy, the 1-year risk of MACE and its individual components declined gradually by one-third in pPCI-treated STEMI patients from 2003 to 2017.