1. The incidence of having reduced antiplatelet activity to aspirin (ALR) increased after vascular procedures.
Evidence Rating Level: 1 (Excellent)
Though clinical guidelines often recommend antiplatelet therapy in secondary and tertiary prevention of thromboembolic events, studies investigating their efficacy have shown variable results. Moreover, while vascular surgery patients are at high risk of these events, few studies have evaluated the prevalence of reduced antiplatelet activity of aspirin (ALR) or clopidogrel (CLR) in this population, and any changes in ALR or CLR which may occur after their procedures. In this prospective, observational, single-centre study, 176 patients taking either aspirin 100 mg daily, aspirin 300 mg daily, or clopidogrel 75 mg daily with symptomatic PAD (peripheral arterial disease) or internal carotid stenosis were included. They had the activity of their antiplatelet medication measured by impedance aggregometry (using Multiplate®) before and after their vascular procedure. Prior to vascular treatment, prevalence rates of ALR and CLR were 13.1% and 32% respectively. Post-operatively, the overall ALR increased significantly by approximately two-fold (27.5%, p=0.0006), while no significant change in CLR was detected. Due to low numbers of cases in the other groups, risk factor analysis was only performed in patients taking aspirin 100 mg daily. In this cohort, concomitant insulin medication (p=0.0006) and elevated C-reactive protein (p=0.0021) were found to be potential risk factors for having a low response rate to antiplatelet therapy. Overall, this study showed ALR prevalence in vascular surgery patients to be at the lower end of values reported in literature; however, the comparability of these results are limited as there is no preferred diagnostic test in detecting low antiplatelet response. How these reduced antiplatelet response rates may or may not affect clinical outcomes will require gathering long-term data and whether other potential risk factors may contribute to ALR and CLR will require studying larger vascular surgery populations.
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