Changes in platelet maturity and reactivity following acute ST-segment elevation myocardial infarction.

Background: Reduced effect of antiplatelet therapy has been reported in patients with ST-segment elevation myocardial infarction (STEMI). This could partly be explained by an increase of highly reactive immature platelets.

Objectives: To investigate changes in platelet maturity and reactivity after acute STEMI.

Methods: Patients diagnosed with STEMI, admitted for primary percutaneous coronary intervention, and treated according to international guidelines, were included. Blood samples were obtained within 24 hours after admission and at 2- to 3-months follow-up. Platelet maturity and reactivity using multicolor flow cytometry with SYTO-13 to categorize platelet maturity, whole blood platelet aggregation, serum thromboxane B2 levels, and standard immature platelet markers (eg, immature platelet count and fraction, and mean platelet volume) were measured.

Results: A total of 44 STEMI patients were included. The reactivity of immature platelets was consistently higher at baseline and at follow-up when compared to the entire platelet population and the mature platelet population (all values < .05). The expression of CD63 (a dense granule marker) in immature platelets was consistently high compared to the entire platelet population and the mature platelet population and did not change from baseline to follow-up ( values > .24). Additionally, a positive significant correlation was found between standard immature platelet markers and the expression of CD63 on platelets both at baseline and follow-up (rho ranging from 0.32 to 0.62, all values < .05).

Conclusion: Immature platelets represent a highly reactive platelet subpopulation crucial for the overall platelet reactivity, partly due to a high expression of dense granules. Despite treatment with loading and maintenance doses of antiplatelet therapy, the reactivity of immature platelets remained high in STEMI patients.