Why have temporal trends in STEMI and NSTEMI incidence and short-term mortality changed in recent years? A nationwide 35-year cohort study in Iceland.

Abstract

Temporal trends in the incidence of ST-elevation myocardial infarction (STEMI) have been declining in many countries, while the incidence of non-ST elevation myocardial infarction (NSTEMI) has reached a plateau or even increased. The reasons for these changing trends have yet to be explained. We analysed these trends and short-term mortality from acute coronary syndromes in a nationwide cohort study over 35 years in Iceland. Retrospective cohort study using a national MI registry. Iceland. All cases of myocardial infarction in individuals aged 25-74 years in Iceland 1981-2015. Each case was classified as STEMI, NSTEMI or no ECG taken. ECG recordings were classified according to Minnesota criteria. Trends of STEMI and NSTEMI incidence and 1-day and 28-day mortality were obtained from the National Death Registry. A total of 10 348 cases were identified (mean age 61 years, 76.4% male). These were categorised as STEMI (32.7%), NSTEMI (45.8%) and no ECG taken (21.5%). We detected a significant 3.7% annual decline in the incidence of first MI. The age-adjusted incidence of STEMI showed an 83.2% decline, most pronounced after 1994, while for NSTEMI the decline was 66.5%, reaching a plateau from the year 1989 onwards. In Iceland, the uptake of highly sensitive biomarkers was initiated in 1997 (cardiac troponin T) and 2012 (high-sensitive troponin T), respectively. The different temporal trends in the incidence of STEMI and NSTEMI cannot be explained only by the uptake of highly sensitive biomarkers in 1997 and 2012. The change in population-level risk factor exposure is likely to have influenced atherosclerotic plaque burden and thrombotic mechanisms. Finally, increasing uptake of cardioprotective pharmacological and interventional therapy may have resulted in a primary preventive effect on plaque rupture and thrombosis and thus on the rates of STEMI and NSTEMI disproportionally.