Optical aggregometry and aspirin resistance

Optical aggregometry and aspirin resistanceDear Editor, We have read with great enthusiasm the recently published article by Dr Sztriha and his coworkers entitled ÔOptical platelet aggregometry does not appear useful as a means of assessing the risk of recurrent vascular events in aspirin-treated patientsÕ (1).In this retrospective analysis, they concluded that the results of optical platelet aggregometry were not indicative of the risk of recurrent vascular events and the role of conventional risk factors (age was independently associated with worsening outcome) appeared to be more important.In their analysis, vascular event occurred prior to testing and retrospectively analyzed the parameters of the included patients.A recent study including healthy volunteers showed that the platelet function measured with the PFA-100 is not inhibited significantly after a single dose of 100 mg of aspirin, is thereafter inhibited consistently in the majority, but not in all individuals during a 4-week treatment, and returns to normal in 48-72 h (2).Furthermore, Poulsen et al. showed that the prevalence of aspirin resistance varies with the clinical status of the patients, and indeed an acute MI is associated with temporary aspirin resistance; it did not affect 1-year clinical outcome (3).These results suggest that a retrospective analysis may not reflect the previous platelet function (prior to the testing).Furthermore, there is platelet inhibition beyond traditional antiplatelet agents; statins, angiotensin receptor blockers and selective serotonin reuptake inhibitors, etc. inhibit platelets by different pathways (4).These results suggest that the definition of resistance should be based on the difference of platelet aggregation values between the pre-treated stage (baseline values) and the aspirin-treated stage.Compliance is also an important factor in the development of vascular events.A recent metaanalysis showed the hazards of discontinuing aspirin (5).