has acknowledged the lack of consensus guidelines for antiplatelet therapy in the periprocedural setting. Their website recommendations were compiled from consensus expert opinion in 2007 but have not been formally published. The recommendations were released in an effort to spark a debate over appropriate guidelines. As yet, no such guidelines exist.
Pandya et al. (2010
) recently reported the largest prospective trial to evaluate pre-procedure dosing regimens and antiplatelet resistance in neurointerventional procedures. Data was collected from 216 consecutive patients including all neurointerventional procedures. Thirteen percent of patients taking aspirin were found to be resistant (>550 ARU) while 66% of patients taking clopidogrel were resistant (<50% inhibition of P2Y12/ADP receptor). Patients taking clopidogrel 75
mg for ≥7
mg for 24
h, and 600
mg same day load had a mean P2Y12/ADP inhibition of 45%, 35% (P
0.09), and 16%, respectively (P
0.005). The authors suggested this data may reflect an inferiority with same day loading when compared to longer loading periods to achieve adequate platelet inhibition.
Lee et al. (2008
) applied point-of-care tests to assess antiplatelet response prior to neurointerventional procedures. One-hundred six consecutive patients were assessed in a single center from 2006 to 2007. Antiplatelet regimen included aspirin (325
mg daily) and clopidogrel (75
mg for 5–10
days pre-procedure). Two percent of patients demonstrated aspirin poor response (<550 ARU) and 42.9% of patients demonstrated clopidogrel poor response (>40% inhibition). Three cases were complicated by intraprocedural thrombosis, with all three cases observed in the poor responders group. The authors commented that frequency of poor responders appears high in a population undergoing neurointerventional procedures. Routine monitoring with point-of-care tests may be helpful for early identification of non-responders.
Prabhakaran et al. (2008
) conducted a similar single center prospective evaluation in 76 patients undergoing cerebrovascular stenting. Aspirin resistance was detected in 4.2% of patients (ARU
550) and clopidogrel resistance in 51.9% of patients (>40% inhibition). Outcomes were not assessed in relation to rates of resistance in this group. Interestingly, a significant inverse relationship was demonstrated between dose of aspirin and rate of resistance, with lower weekly doses of aspirin correlating to higher rates of resistance (r
0.01). The authors highlighted the need for further investigation of ideal dosing, timing and duration of antiplatelet therapy for neurointerventional stent procedures.
The existence of aspirin and clopidogrel resistance appears certain. Less clear is the true prevalence and appears dependent on factors including choice of test, dose of antiplatelet agent, age of patient, and presence of comorbidities including hypertension and hyperlipidemia. The use of point-of-care tests such as the VerifyNow RPFA and P2Y12 enable rapid testing and may assist in clinical decision making but more data are needed for validation. In assessing platelet function, the P2Y12 is well correlated to LTA, which has been shown in large trials to be associated with loss-of-function genetic CYP2C19 expression and significantly poorer cardiovascular outcomes in patients taking clopidogrel. It is likely, but not yet tested, that similar associations with stroke will exist in populations that undergo neurointerventional procedures. The most significant impact on future risk of ischemic event in poor responders to clopidogrel was detected in patients with a history of coronary stenting. Whether similar conclusions can be drawn for patients with intracranial or extracranial stents remains to be seen. Use of point-of-care tests in patients undergoing carotid stenting has been described (Maruyama et al., 2011
), with addition of an extra agent showing improved platelet aggregation inhibition.
A risk of thromboembolism exists in coiling procedures. Stroke associated with coiling occurs in between 2 and 9% of patients despite antiplatelet therapy, and may be as high as 25% when considering silent ischemia on MRI diffusion restriction. There is a suggestion that antiplatelet agents may reduce the risk of thromboembolism without increasing the risk of hemorrhage, but this question needs to be studied in a prospective trial. Risk of thromboembolism may increase with wide necked aneurysms. The increased prevalence of antiplatelet resistance in older populations that have increased comorbidities should be taken into account when pursuing neurointerventional procedures in this group. Poorer outcomes in carotid stenting may be related to increased rates of antiplatelet resistance in this group and requires further investigation. Point-of-care testing in these groups may be warranted. Meta-analysis evidence provides support that higher doses of aspirin lead to lower levels of resistance. This may be a treatment option in patients shown to have aspirin resistance.