The changing epidemiology of myocardial infarction in Olmsted County, Minnesota, 1995-2012

Abstract

Background: Contemporary data on the epidemiology of myocardial infarction in the population are limited and derived primarily from cohorts of hospitalized myocardial infarction patients. We assessed temporal trends in incident and recurrent myocardial infarction, with further partitioning of the rates into prehospital deaths and hospitalized events, in a geographically defined community.

Methods: All myocardial infarction events recorded among Olmsted County, Minnesota residents aged 25 years and older from 1995-2012, including prehospital deaths, were classified into incident and recurrent. Standardized rates were calculated and temporal trends compared.

Results: Altogether, 5258 myocardial infarctions occurred, including 1448 (27.5%) recurrences; 430 (8.2%) prehospital deaths were recorded. Among hospitalized events, recurrent myocardial infarction was associated with greater mortality risk than incident myocardial infarction (age-, sex-, and year-adjusted hazard ratio, 1.49; 95% confidence interval, 1.37-1.61). Although the overall rate of myocardial infarction declined over time (average annual percent change, -3.3), the magnitude of the decline varied widely. Incident hospitalized myocardial infarction rate fell 2.7%/y, compared with decreases of 1.5%/y in recurrent hospitalized myocardial infarction, 14.1%/y in prehospital fatal incident myocardial infarction, and 12.3%/y in prehospital fatal recurrent myocardial infarction (all P for diverging trends < .05). These trends resulted in an increasing proportion of recurrences among hospitalized myocardial infarctions (25.3% in 1995-2000, 26.8% in 2001-2006, and 29.0% in 2007-2012, Ptrend = .02).

Conclusions: Over the past 18 years, a heterogeneous decline in myocardial infarction rates occurred in Olmsted County, resulting in transitions from incident to recurrent events and from prehospital deaths to hospitalized myocardial infarctions. Recurrent myocardial infarction confers a worse prognosis, thereby stressing the need to optimize prevention strategies in the population.

Keywords: Epidemiology; Myocardial infarction; Population; Prevention; Trends.

Figure 1

Adjusted survival curves for incident and recurrent events. Age-, sex-, and year-adjusted survival among Olmsted County, Minnesota, residents with myocardial infarction in 1995–2012. Survival probabilities were estimated with the direct adjustment method based on a stratified Cox model. MI = myocardial infarction.

Figure 2

Temporal trends in myocardial infarction rates. Myocardial infarction rates according to incident/recurrent and hospitalization status in Olmsted County, Minnesota, 1995 to 2012. Yearly rates (smoothed using 3-year moving average) per 100,000 persons have been standardized by the direct method to the age and sex distribution of the US population in 2010. MI = myocardial infarction.

Figure 3

Changes over time in absolute and relative contribution of myocardial infarction categories to overall rates. Temporal trends in myocardial infarction rates (per 100,000 persons) in Olmsted County, Minnesota, from 1995 to 2012 partitioned into incident/recurrent status and prehospital death/hospitalized myocardial infarction. Rates have been standardized by the direct method to the age and sex distribution of the US population in 2010 and are shown in 6-year intervals. The labels represent the relative percentage of the myocardial infarction categories at each time interval. MI = myocardial infarction.

Figure 4

Temporal trends in prehospital coronary heart disease (CHD) death rates. CHD mortality rates partitioned into myocardial infarction and other coronary heart disease diagnoses in Olmsted County, Minnesota, 1995 to 2012. Yearly rates (smoothed using 3-year moving average) per 100,000 persons have been standardized by the direct method to the age and sex distribution of the US population in 2010. CHD = coronary heart disease; MI = myocardial infarction.