Abstract 20209: Risk Factors for 'Microsize' versus Usual Myocardial Infarctions in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) Study

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Introduction: Increasingly sensitive troponin assays allow detection of very small elevations of troponin. Microsize MI is a recently described phenomenon consisting of events that meet rigorous criteria for MI, but with very low peak troponin elevations (<0.05 ng/mL). Emerging evidence shows that these events are common and carry increased risk of all-cause mortality, but risk factors for microsize vs. usual MI have not been examined.

Objectives: To compare risk factors for microsize vs. usual MIs in the national REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort (n=30,239).

Methods: Among 24,470 REGARDS participants free of coronary heart disease at baseline, heart-related hospitalizations were expert adjudicated for MI using published guidelines. MIs were classified as microsize MI (peak troponin <0.5 ng/ml) or usual MI (peak troponin ≥0.5 ng/ml). Competing risk analyses assessed associations between baseline risk factors and incident microsize vs. usual MI.

Results: The 891 included MIs occurred between 2003-2013; 279 were microsize MI and 612 were usual MI. Older age, male gender, diabetes, impaired kidney function, and functional status were associated with both microsize and usual MI (Table 1). Black race, current smoking, and Southeastern residence were associated with usual but not microsize MI.

Conclusions: Microsize MI and usual MI share many well-known CHD risk factors, suggesting a possible common etiology. The similarities in risk profiles should encourage clinicians to both treat reversible risk factors for microsize MI and to initiate secondary prevention strategies post-MI until this emerging clinical entity is better understood.

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