The Association between Dual Antiplatelet Responsiveness and the Level of Platelets in Acute Coronary Syndrome

This study was designed to demonstrate the association between dual antiplatelet therapy responsiveness to the level of platelets and hospital outcome in acute coronary syndrome patients. Background: Dual antiplatelet therapy, namely, Aspirin and Clopidogrel, is the mainstay for the early treatment regimen in acute coronary syndrome patients. However, some patients have had an unfavorable outcome due to antiplatelet non- responsiveness. In animal models, the platelet level has some influence on the aggregation of platelets. Methods: A descriptive prospective study was used to investigate acute coronary syndrome patients who presented at Phramongkutklao Hospital Thailand, from May 2010 to January 2011. Patients who had a platelet level more than 100,000 per cubic milliliter and a creatinine clearance more than 15 milliliter per minute were included. Patients were measured for platelet aggregation using platelet aggregometry within 6 hours after an aspirin and a clopidogrel loading dose. The clinical outcomes were observed during hospitalization. Non-responsiveness to the dual antiplatelet regimen was defined as Platelet aggregation by 10 micromoles of ADP ≥ 70% or platelet aggregation by collagen ≥ 50%. Results: 102 patients were enrolled into this study. Sixty two patients (60.8%) were male. The mean age was 68.18 ± 10.16 years. Non-responsiveness to the two antiplatelet agents was observed in forty- four (43.1%) patients. The association pattern between the reponsiveness to the two antiplatelet agents and the level of platelets illustrated a U-shaped pattern. The responsiveness of platelets was good when their level was between 200,000-300,000 per cubic millilitre. Non-responsiveness to the dual antiplatelet regimen was independently associated with an increased incidence of in- hospital heart failure (OR = 3.42; p-value = 0.006) and in-hospital minor bleeding (OR = 2.76; p-value = 0.039) when compared to the responsive group. Conclusion: This is a pioneering study that demonstrates an association pattern between responsiveness of the dual antiplatelet regimen to the level of platelets and hospital outcome in acute coronary syndrome patients. Among acute coronary syndrome patients, the lack of responsiveness to the dual antiplatelet treatment had a strong impact on in-hospital heart failure and minor bleeding. Keywords: Platelet aggregation test, Dual antiplatelet non-responsiveness