Is the measurement of cerebral microembolic signals a good surrogate marker for evaluating the efficacy of antiplatelet agents in the prevention of stroke?

Stroke is difficult to treat with few treatment options. Until such time as appropriate therapeutic regimens are established, prevention, both in the primary and in the secondary setting, is of paramount importance. Evaluation of pharmacological agents for the prevention of stroke in conventional clinical studies has the advantage that the outcome parameter is a direct measure of efficacy, and the disadvantage that many patients must be recruited and many evaluations performed over an extended period to provide adequate statistical power, making such studies lengthy and costly. Measurement of cerebral microembolic signals (MES) using transcranial Doppler ultrasonography has been proposed as a useful surrogate end point to investigate new antiplatelet agents and to evaluate further the benefits of existing antiplatelet therapies. MES measurements may provide a means of more directly evaluating the pharmacological activity of an antiplatelet agent. However, does measurement of MES accurately predict efficacy in stroke prevention? This review evaluates recent studies where the relationship between MES and cerebral ischaemic events has been explored and studies where the effects of antiplatelet agents on MES rates have been investigated. Overall, there is a growing body of evidence to suggest that MES may be used as a surrogate marker for cerebral infarction and clinical events, thus allowing quick appraisal of the efficacy of antiplatelet agents. Studies currently in progress should provide further insight into the value of the measurement of MES in clinical studies in stroke prevention.