Inflammation, platelet aggregation and prognosis in acute myocardial infarction

Abstract: The incidence of stroke and re-infarction is noticeably high in the first few days following acute myocardial infarction. This finding has raised questions whether the systemic inflammatory reaction secondary to myocardial necrosis is involved. The inflammation might affect the activation of platelets leading to insufficient effect of the antiplatelet treatment given. Furthermore, the importance of platelet reactivity and inflammation in terms of long-term prognosis is not fully understood. The prognostic importance of C-reactive protein (CRP) in relation to clinical variables also needs to be clarified.The present studies are aimed at describing the dynamics of platelet function during the first days of an acute myocardial infarction, in relation to diabetes and inflammation. We also investigated whether increased platelet reactivity or the increased concentration of CRP in blood were related to a worse outcome. Finally, we examined if CRP levels contributed to a predictive model using clinical variables known to affect outcome in patients with AMI. We used two novel platelet function tests to measure platelet reactivity; the PA-200 (a laser light aggregometer) and the PFA-100 (measures primary haemostasis in whole blood).Platelet aggregation increased during the initial course of an acute myocardial infarction. The increase in platelet aggregation was most pronounced in diabetics and in patients showing higher systemic inflammatory reaction, assessed by measuring the concentration of CRP in blood. The pronounced platelet aggregation occurred despite ongoing antiplatelet and antithrombotic treatment.There was a significant association between the levels of CRP and the degree of platelet reactivity. However, while the CRP levels were associated with a worse outcome (AMI, stroke and death), the results of the platelet function tests were not. The importance of CRP in predicting prognosis depended on which adjustments were made for confounding factors.CRP and prognostic variables in a statistical model predicting death, however, showed that CRP was excluded. Thus CRP did not predict outcome beyond clinical prognostic variables.The results of these studies reinforce the importance of clinical variables such as heart failure, age, atrial fibrillation, smoking status, diabetes and impaired kidney function - all of which were associated with worse prognosis in multivariable analysis.