title: Platelet aggregation at discharge: a useful tool in acute coronary syndromes?
abstract: BACKGROUND
  Inhibition of platelet aggregation appears two hours after the first dose of clopidogrel, becomes significant after the second dose, and progresses to a steady-state value of 55% by day seven. Low response to clopidogrel has been associated with increased risk of stent thrombosis and ischemic events, particularly in the context of stable heart disease treated by percutaneous coronary intervention.
  
  
  OBJECTIVE
  To stratify medium-term prognosis of an acute coronary syndrome (ACS) population by platelet aggregation.
  
  
  METHODS
  We performed a prospective longitudinal study of 70 patients admitted for an ACS between May and August 2009. Platelet function was assessed by ADP-induced platelet aggregation using a commercially available kit (Multiplate(®) analyzer) at discharge. The primary endpoint was a combined outcome of mortality, non-fatal myocardial infarction, or unstable angina, with a median follow-up of 136.0 (79.0-188.0) days.
  
  
  RESULTS
  The median value of platelet aggregation was 16.0U (11.0-22.5U) with a maximum of 41.0U and a minimum of 4.0U (normal value according to the manufacturer: 53-122U). After ROC curve analysis with respect to the combined endpoint (AUC 0.72), we concluded that a value of 18.5U conferred a sensitivity of 75.0% and a specificity of 68% to that result. We therefore created two groups based on that level: group A - platelet aggregation <18.5U, n=44; and group B - platelet aggregation ≥18.5U, n=26. The groups were similar with respect to demographic data (age 60.5 [49.0-65.0] vs. 62.0 [49.0-65.0] years, p=0.21), previous cardiovascular history, and admission diagnosis. There were no associations between left ventricular ejection fraction, GRACE risk score, or length of hospital stay and platelet aggregation. The groups were also similar with respect to antiplatelet, anticoagulant, proton pump inhibitor (63.6 vs. 46.2%, p=0.15) and statin therapy. The variability in platelets and hemoglobin was also similar between groups. Combined event-free survival was higher in group A (96.0 vs. 76.7%, log-rank p<0.01). Platelet aggregation higher than 18.5U was an independent predictor of the combined event (HR 6.75, 95% CI 1.38-32.90, p=0.02).
  
  
  CONCLUSIONS
  In our ACS population platelet aggregation at discharge was a predictor of medium-term prognosis.
authors.affiliation: Serviço de Cardiologia, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal. rogeriopteixeira@gmail.com
authors.forename: Rogério
authors.initials: R
authors.lastname: Teixeira
authors.forename: Pedro
authors.initials: P
authors.lastname: Monteiro
authors.forename: Gilberto
authors.initials: G
authors.lastname: Marques
authors.forename: João Mariano
authors.initials: JM
authors.lastname: Pego
authors.forename: Margarida
authors.initials: M
authors.lastname: Lourenço
authors.forename: Carlos
authors.initials: C
authors.lastname: Tavares
authors.forename: Alda
authors.initials: A
authors.lastname: Reboredo
authors.forename: Sílvia
authors.initials: S
authors.lastname: Monteiro
authors.forename: Francisco
authors.initials: F
authors.lastname: Gonçalves
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Ferreira
authors.forename: Mário
authors.initials: M
authors.lastname: Freitas
authors.forename: Graça
authors.initials: G
authors.lastname: Ribeiro
authors.forename: Luís A
authors.initials: LA
authors.lastname: Providência
mesh_terms: D054058:Acute Coronary Syndrome / Q000097:blood / Q000188:drug therapy*; D000077144:Clopidogrel; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010351:Patient Discharge; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D010979:Platelet Function Tests; D011446:Prospective Studies; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine