Incidence of Myocardial Infarction

Posted by Graham McMahon • June 11th, 2010

Yeh et al. identified 46,086 patients 30 years of age or older who were hospitalized for incident myocardial infarction between 1999 and 2008 (representing a period of 18,691,131 person-years).

Clinical Pearls

Has the incidence of myocardial infarction changed over time?

The age- and sex-adjusted incidence of myocardial infarction increased from 274 cases per 100,000 person-years in 1999 to a peak of 287 cases per 100,000 person-years in 2000, and then decreased each year thereafter, to 208 cases per 100,000 person-years in 2008 (relative decrease between 1999 and 2008, 24%).

Is there a difference in the incidence trends between ST-elevation and non-ST-segment elevation myocardial infarctions?

The age- and sex-adjusted incidence of ST-segment elevation myocardial infarction decreased each year, from 133 cases per 100,000 persons in 1999 to 50 cases per 100,000 persons in 2008 (relative decrease between 1999 and 2008, 62%; P<0.001 for linear trend), whereas the incidence of non-ST-segment elevation myocardial infarction increased from 155 cases per 100,000 persons in 1999 t0 202 cases per 100,000 persons in 2004 before  decreasing thereafter.

Morning Report Questions

Q: Has the case-fatality rate for ST-segment elevation myocardial fallen over time?

A: Adjusted mortality decreased significantly over time among patients with non-ST-segment elevation myocardial infarction (adjusted odds ratio for the comparison of 2008 with 1999, 0.82; 95% CI, 0.67 to 0.99), with the decrease occurring primarily after 2005. In contrast, adjusted mortality did not change significantly among patients with ST-segment elevation myocardial infarction (adjusted odds ratio for the comparison of 2008 with 1999, 0.93; 95% CI, 0.71 to 1.20).

Q: What accounts for the increased relative prevalence of non-ST-segment elevation myocardial infarction over time?

A: The increasing detection of less severe infarctions with troponin testing would contribute to artifactual declines in case fatality rates. Thus, observed reductions in case fatality rates could be attributable to secular trends in ascertainment of myocardial infarction and decreasing severity on presentation, as well as any improvements in acute management. The observation that mortality after ST-segment elevation myocardial infarction (which is less dependent on the use of highly sensitive biomarkers) did not decrease over time provides support for this hypothesis.

Figure 2. Previous Use of Medication on an Outpatient Basis.

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