Declining severity of myocardial infarction from 1987 to 2002: the Atherosclerosis Risk in Communities (ARIC) Study

Death rates for coronary heart disease have been declining in the United States, but the reasons for this decline are not clear. One factor that could contribute to this decline is a reduction in the severity of acute myocardial infarction (MI). We hypothesized that for those patients hospitalized in the Atherosclerosis Risk in Communities (ARIC) Study with acute incident MI, there was a decline in MI severity from 1987 to 2002.

The community surveillance component of the ARIC Study consisted of tracking residents 35 to 74 years of age with hospitalized MI or fatal coronary heart disease in 4 diverse communities. For incident, hospitalized MI, a probability sample of hospital discharges was validated and an MI classification was assigned according to an algorithm consisting of chest pain, ECG evidence, and cardiac biomarkers. Severity indicators were chosen from abstracted hospital charts validated as a definite or probable MI. With few exceptions, the MI severity indicators suggested a significant decline in the severity of MI during the period of 1987 to 2002. The percent of MI cases with major ECG abnormalities decreased as evidenced by a 1.9%/y (P=0.002) decline in the proportion of those with initial ST-segment elevation, a 3.9%/y (P<0.001) decline in those with subsequent Q-waves, and a 4.5%/y (P<0.001) decline in those with any major Q wave. Maximum creatine kinase and creatine kinase-MB values declined (5.2% and 7.6%; P<0.001, P<0.001 per year, respectively), although in the later years, maximum troponin I values remained stable (1.1%/y decline; P=0.66). The percent with shock declined (5.7%/y; P<0.001), although those with congestive heart failure remained stable. A combined severity score, the Predicting Risk of Death in Cardiac Disease Tool (PREDICT) score, also declined (0.2%/y; P<0.001). Results for blacks paralleled those of the entire group, as did results for women.

Evidence from ARIC community surveillance suggests that the severity of acute MI has declined among community residents hospitalized for incident MI. This reduction in severity may have contributed, along with other factors, to the decline in death rates for coronary heart disease.