To determine the prevalence of aspirin resistance and/or platelet hypersensitivity as determined by platelet aggregometry in Caucasian patients who have suffered one or more atherothrombotic cerebro-vascular accidents (CVAS) and/or transient ischaemic attacks (TIAS) as compared with control subjects

Bernstein, Penelope Lizetta
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Objective: Stroke is the second most common cause of death in most countries.1 In South Africa, which has a population undergoing demographic and epidemiological transition, stroke is the third most common cause of death.2 Platelet response to therapeutic doses is not uniform, although aspirin remains an essential part of treatment. Some patients exhibit aspirin resistance and develop secondary thrombotic events. It was decided to determine the prevalence of aspirin resistance and/or platelet hypersensitivity, as determined by platelet aggregometry, in sixty Caucasian patients who have suffered one or more strokes and/or Transient Ischaemic Attacks (TIAs) as compared with sixty control subjects. Methods: Aspirin resistance was determined by platelet aggregation (>20%) to one or more of the four agonists, namely arachidonic acid (1.5mM), adrenaline (0.05mg/ml), collagen (0.2mg/ml) or ADP (0.1x10-5 M). Results: Two patients demonstrated ‘complete aspirin resistance’ (non-responder to aspirin) with resistance to arachidonic acid (high concentration) noted. Three patients demonstrated ‘partial aspirin resistance’ (semi-responder to aspirin). One control subject showed ‘complete aspirin resistance’. There is a 1.67% chance of a control subject being resistant to aspirin in a general South African Caucasian population. A history of prior stroke or transient ischaemic attack was associated with a statistically significant increase in risk of aspirin resistance with an odds ratio of 5.36. Conclusion: These results essentially concur with those of the studied literature in showing an 8.3% prevalence (statistically significant) of aspirin resistance (complete and partial) in South vi African Caucasian patients with previous atherothrombotic cerebrovascular events i.e.CVAs and/or TIAs. The current study shows an increased prevalence of aspirin resistance in people who have had prior strokes / TIAs and raises the question whether people who have had these events are somehow predisposed to vascular events or indeed recurrent vascular events. ‘Aspirin resistant’ patients or ‘poor responders’ to aspirin must be considered at heightened risk of atherothrombotic events and laboratory monitoring of antiplatelet therapy may become clinically useful.
MMed, Haematology, Faculty of Health Sciences, University of the Witwatersrand, 2009