Risk factors for 'microsize' vs. usual myocardial infarctions in the REasons for Geographic and Racial Differences in Stroke (REGARDS) study

AIMS

A recently described phenomenon is that of myocardial infarction (MI) events that meet criteria for MI, but that have very low peak troponin elevations, so-called 'microsize MI'. These events are very common and associated with increased risk of all-cause mortality. Our aim is to compare risk factors for microsize MI vs. usual MI events.

METHODS AND RESULTS

Among 24 470 participants of the Reasons for Geographic and Racial Differences in Stroke (REGARDS) cohort free of coronary heart disease at baseline, heart-related hospitalizations were expert adjudicated for MI using published guidelines. Myocardial infarctions 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. Between 2003 and 2013 there were 891 MIs; 279 were microsize MI and 612 were usual MI. Risk factors for both usual MI and microsize MI include age, gender, diabetes, and urinary albumin to creatinine ratio. Risk factors for only usual MI include Residence in the Stroke Belt and Buckle regions and current smoking. Black race was associated with a uniquely lower risk of usual MI.

CONCLUSION

The similarities in risk profiles suggest a possible common aetiology and should encourage clinicians to both treat reversible risk factors for microsize MI and to initiate secondary prevention strategies following these events until this emerging clinical entity is better understood. Future studies should further assess the clinical outcomes of these two entities and their effect on future management.