Aspirin resistance is more common in lacunar strokes than embolic strokes and is related to stroke severity

Frequency of Aspirin Resistance in Ischemic Stroke Patients and Healthy Controls from Colombia

Objective

To evaluate the aspirin resistance prevalence in patients with previous ischemic cerebrovascular disease undergoing aspirin therapy for secondary prevention.

Materials and Methods

Three hundred fifty patients presenting ischemic strokes and 100 healthy controls under aspirin treatment were evaluated using the optic platelet aggregation test.

Results

Aspirin resistance was found in 7.4% of the patients with ischemic stroke and 4% of controls. Aspirin resistance was associated with stroke recurrence in univariate analysis (p = 0.004). Aspirin resistance was not associated with smoking, diabetes, or hypercholesterolemia.

Conclusion

Aspirin resistance is present in Colombian patients with ischemic stroke as well as in healthy controls.

Prevalence and Effect of Cerebral Small Vessel Disease in Stroke Patients With Aspirin Treatment Failure-A Hospital-Based Stroke Secondary Prevention Registry

Background: Breakthrough strokes during treatment with aspirin, termed clinical aspirin treatment failure (ATF), is common in clinical practice. The burden of cerebral small vessel disease (SVD) is associated with an increased recurrent ischemic stroke risk. However, the association between SVD and ATF remains unclear. This study investigated the prevalence and clinical characteristics of SVD in stroke patients with ATF.

Methods: Data from a prospective, and multicenter stroke with ATF registry established in 2018 in Taiwan were used, and 300 patients who developed ischemic stroke concurrent with regular use of aspirin were enrolled. White matter lesions (WMLs) and cerebral microbleeds (CMBs) were identified using the Fazekas scale and Microbleed Anatomical Rating Scale, respectively. Demographic data, cardiovascular comorbidities, and index stroke characteristics of patients with different WML and CMB severities were compared. Logistic regression analyses were performed to explore the factors independently associated with outcomes after ATF.

Results: The mean patient age was 69.5 ± 11.8 years, and 70.0% of patients were men. Among all patients, periventricular WML (PVWML), deep WML (DWML), and CMB prevalence was 93.3, 90.0, and 52.5%, respectively. Furthermore, 46.0% of the index strokes were small vessel occlusions. Severe PVWMLs and DWMLs were significantly associated with high CMB burdens. Patients with moderate-to-severe PVWMLs and DWMLs were significantly older and had higher cardiovascular comorbidity prevalence than did patients with no or mild WMLs. Moreover, patients with favorable outcomes exhibited significantly low prevalence of severe PVWMLs (p = 0.001) and DWMLs (p = 0.001). After logistic regression was applied, severe WMLs predicted less favorable outcomes independently, compared with those with no to moderate PVWMLs and DWMLs [odds ratio (OR), 0.47; 95% confidence interval (CI), 0.25–0.87 for severe PVWMLs; OR, 0.40; 95% CI, 0.21–0.79 for severe DWMLs].

Conclusions: SVD is common in stroke patients with ATF. PVWMLs and DWMLs are independently associated with functional outcomes in stroke patients with ATF. The burden of SVD should be considered in future antiplatelet strategies for stroke patients after ATF.

The Prognostic Value of High Platelet Reactivity in Ischemic Stroke Depends on the Etiology: A Pilot Study

Background: Reduced aspirin response may result in a worse prognosis and a poor clinical outcome in ischemic stroke. The aim of this prospective pilot study was to assess the relationship between platelet reactivity and early and late prognosis, and the clinical and functional status in ischemic stroke, with the role of stroke etiology. Methods: The study involved 69 subjects with ischemic stroke, divided into large and small vessel etiological subgroups. Platelet function testing was performed with two aggregometric methods—impedance and optical—while the clinical condition was assessed using the National Institute of Health Stroke Scale (NIHSS) and the functional status was assessed using the modified Rankin Scale (mRS) on the first and eighth day (early prognosis) and the 90th day of stroke (late prognosis). Results: The initial platelet reactivity was found to be higher in patients with severe neurological deficits on the 90th day after stroke, than in the group with mild neurological deficits (median, respectively, 40 area under the curve (AUC) units vs. 25 AUC units, p = 0.033). In the large vessel disease group, a significant correlation between the platelet reactivity and the functional status on the first day of stroke was found (correlation coefficient (R) = 0.4526; p = 0.0451), the platelet reactivity was higher in the subgroup with a severe clinical condition compared to a mild clinical condition on the first day of stroke (p = 0.0372), and patients resistant to acetylsalicylic acid (aspirin) had a significantly greater possibility of a severe neurological deficit on the first day of stroke compared to those who were sensitive to aspirin (odds ratio (OR) = 14.00, 95% confidence interval (CI) 1.25–156.12, p = 0.0322). Conclusion: High on-treatment platelet reactivity in ischemic stroke was associated with a worse late prognosis regardless of the etiology. We demonstrated a significant relationship between high platelet reactivity and worse early prognosis and poor clinical and functional condition in the large vessel etiologic subgroup. However, due to the pilot nature of this study, its results should be interpreted with caution and further validation on a larger cohort is required.

Aspirin resistance predicts unfavorable functional outcome in acute ischemic stroke patients

OBJECTIVE

To investigate the prognostic value of aspirin reaction units (ARU) in a 3-month follow-up study in a cohort of Chinese patients with first-ever ischemic stroke.

METHODS

Prospective single-center survey of acute ischemic stroke patients receiving aspirin therapy. Two hundred and seventy-five Chinese patients with first-ever ischemic stroke who previously received aspirin therapy were enrolled. ARU was measured using the VerifyNow system. A cutoff of 550 ARU was used to determine the presence of aspirin resistance (AR).

RESULTS

Median age at study entry was 67 years (IQR: 59-75) and 142(51.6%) were male. A total of 52 of 275 enrolled patients (18.9%) were AR. Median regression estimated a statistically significant increase in NIHSS score of 0.033 point for every 1-point increase in ARU (95% CI, 0.024 to 0.068; P < 0.001). The unfavorable outcomes distribution across the ARU quartiles ranged between 11.8% (first quartile) to 64.8% (fourth quartile). After adjusting for other established risk factors, in multivariate models comparing the third and fourth quartiles against the first quartile of the ARU, levels of ARU were associated with unfavorable outcome, and the adjusted risk of unfavorable outcome increased by 145% (OR = 2.45 [95% CI 1.46-3.87], P = 0.011) and 317% (4.17[2.76-6.15], P < 0.001), respectively. Similarly, the adjusted risk of mortality increased by 215% (OR = 3.15 [95% CI 1.98-4.73], P = 0.008) and 429% (5.29[4.02-8.17], P < 0.001), respectively.

CONCLUSIONS

The results suggest that AR is a meaningful and independent marker to predict short-term functional outcome in patients with ischemic stroke.

Biochemical aspirin resistance is associated with increased stroke severity and infarct volumes in ischemic stroke patients

To explore the correlation of aspirin resistance (AR) with clinical stroke severity and infarct volume using diffusion-weighted imaging (DWI) in 224 Chinese ischemic stroke patients who were taking aspirin before stroke onset. In those patients, the median age was 64 years (IQR, 56-75 years), and males accounting for 54.9%(123)of the total subjects. Fifty of 224 enrolled patients (22.3%; 95% confidence interval (CI), 16.9% to 27.7%) showed AR. In the median regression model, significant increase was estimated in NIHSS score of 0.04 point for every 1-point increase in aspirin reaction units (ARU) (95% CI, 0.02 to 0.06; P<0.001). Diffusion-weighted MRI (DWI)-measured infarct volume were significantly higher in patients with AR as compared with those with AS [13.21 (interquartile ranges [IQR], 8.51-23.88) vs.4.26 (IQR, 1.74-11.62); P<0.001). Furthermore, a statistically significant increase was also measured in NIHSS score of 0.05 point for every 1-point increase in ARU in the median regression model (95% CI, 0.03 to 0.08; P<0.001). The median DWI infarct volume was significantly larger in the highest ARU quartile when compared to that in the low 3 quartiles (P<0.001). In conclusion, stroke patients with AR indicated higher risk of severe strokes and large infarcts compared to patients in the aspirin-sensitive group.

Platelet Function Testing in Patients with Acute Ischemic Stroke: An Observational Study

BACKGROUND

The measurement of platelet reactivity in patients with stroke undergoing antiplatelet therapies is not commonly performed in clinical practice. We assessed the prevalence of therapy responsiveness in patients with stroke and further investigated differences between patients on prevention therapy at stroke onset and patients naive to antiplatelet medications. We also sought differences in responsiveness between etiological subtypes and correlations between Clopidogrel responsiveness and genetic polymorphisms.

METHODS

A total of 624 stroke patients on antiplatelet therapy were included. Two different groups were identified: "non-naive patients", and "naive patients". Platelet function was measured with multiple electrode aggregometry, and genotyping assays were used to determine CYP2C19 polymorphisms.

RESULTS

Aspirin (ASA) responsiveness was significantly more frequent in naive patients compared with non-naive patients (94.9% versus 82.6%, P < .0010). A better responsiveness to ASA compared with Clopidogrel or combination therapy was found in the entire population (P < .0010), in non-naive patients (P < .0253), and in naive patients (P < .0010). Multivariate analysis revealed a strong effect of Clopidogrel as a possible "risk factor" for unresponsiveness (odds ratio 3.652, P < .0001). No difference between etiological subgroups and no correlations between responsiveness and CYP2C19 polymorphisms were found.

CONCLUSION

In our opinion, platelet function testing could be potentially useful in monitoring the biological effect of antiplatelet agents. A substantial proportion of patients with stroke on ASA were "resistant", and the treatment with Clopidogrel was accompanied by even higher rates of unresponsiveness. Longitudinal studies are needed to assess whether aggregometry might supply individualized prognostic information and whether it can be considered a valid tool for future prevention strategies.

[Prevalence and prognosis of aspirin resistance in critical limb ischemia patients]

OBJECTIVES

To assess the prevalence and the association between aspirin resistance in critical limb ischemia patients using the VerifyNow^® bed-side platelet test, and occurrence of cardiovascular morbidity and/or death at one year.

MATERIALS AND METHODS

National multicenter prospective observational study related to COPART II centers. From 2010 through 2014, 64 subjects hospitalized for critical limb ischemia and already treated by aspirin before the VerifyNow^® test were included. A VerifyNow^® test>550 ARU was defined as aspirin resistance. Critical limb ischemia was defined according to the TASC I criteria. The primary outcome was a composite including death, acute coronary syndrome, stroke and major amputation during the one-year follow-up period.

RESULTS

In all, 9/64 patients were aspirin resistant, the status was confirmed in one case. The prevalence of aspirin resistance was 14.06%. There was no significant difference between aspirin resistant and aspirin non-resistant groups in terms of cardiovascular history and glycemia status. Neither was there significant difference between the two groups in terms of survival.

CONCLUSION

Aspirin resistance was not predictive of poorer survival in critical limb ischemia patients. However, our population was limited. Considering that a clear definition of aspirin resistance and standardized diagnostic tests are lacking, complementary studies might be useful.

Aspirin resistance is associated with increased stroke severity and infarct volume

OBJECTIVES

To investigate whether aspirin resistance is associated with initial stroke severity and infarct volume, using diffusion-weighted imaging (DWI) in patients with acute ischemic stroke that occurred while taking aspirin.

METHODS

We studied a total of 310 patients who were admitted within 48 hours of acute ischemic stroke onset. All patients had been taking aspirin for at least 7 days before stroke onset. Aspirin resistance, defined as high residual platelet reactivity (HRPR) on aspirin treatment, was measured using the VerifyNow assay and defined as an aspirin reaction unit ≥550. Initial stroke severity was assessed using the NIH Stroke Scale (NIHSS) score. Infarct volume was measured using DWI.

RESULTS

HRPR occurred in 86 patients (27.7%). The initial NIHSS score (median [interquartile range]) was higher in patients with HRPR than in the non-HRPR group (6 [3-15] vs 3 [1-8], p < 0.001). DWI infarct volumes were also larger in the HRPR group compared to the non-HRPR group (5.4 [0.8-43.2] vs 1.7 [0.4-10.3], p = 0.002). A multivariable median regression analysis showed that HRPR was significantly associated with an increase of 2.1 points on the NIHSS (95% confidence interval 0.8-4.0, p < 0.001) and an increase of 2.3 cm(3) in DWI infarct volume (95% confidence interval 0.4-3.9, p < 0.001).

CONCLUSIONS

Aspirin resistance is associated with an increased risk of severe stroke and large infarct volume in patients taking aspirin before stroke onset.

The Interplay between Stroke Severity, Antiplatelet Use, and Aspirin Resistance in Ischemic Stroke

BACKGROUND

The issue of whether prior antiplatelet use favorably affects stroke severity is currently unresolved. In this study, we evaluated the effect of antiplatelet use on clinical stroke severity and ischemic lesion volume, and assessed the confounding effect of laboratory-defined aspirin resistance on this relationship.

METHODS

Admission National Institutes of Health Stroke Scale (NIHSS) score, ischemic lesion volumes on diffusion-weighted imaging (DWI), and in vitro aspirin resistance, in addition to other pertinent stroke features, were determined in a series of ischemic stroke patients. Univariate and multivariate analyses were performed to compare clinical and imaging markers of stroke severity among patients with and without prior antiplatelet use, taking into consideration the presence or absence of aspirin resistance.

RESULTS

Antiplatelet users experienced more severe strokes, per NIHSS score, in comparison to antiplatelet-naive patients (P = .007). No significant difference was observed with respect to admission DWI lesion volume. When analyses were repeated after adjustment for stroke subtype and other confounders, no association was observed between antiplatelet use and stroke severity. On the other hand, NIHSS scores were significantly higher in aspirin-unresponsive patients than in both aspirin responders (P = .049) and aspirin nonusers (P = .005).

CONCLUSION

We were unable to demonstrate a substantial positive influence of prestroke antiplatelet usage on stroke severity. Although the presence of more severe strokes among patients with laboratory resistance suggests a protective influence of aspirin sensitivity on stroke severity, the hypothesis could not be validated as no difference was observed among aspirin-naive and aspirin-sensitive patients with respect to admission NIHSS score or DWI lesion volume.

Antiplatelet strategies for secondary prevention of stroke and TIA

Stroke is a major public health issue, and stroke recurrence accounts for a quarter of all events. Antiplatelet therapy has been extensively studied for secondary stroke prevention and is established as effective in this high-risk population. Several agents have been evaluated in this setting, both in isolation and combination. The most widely used antiplatelet medications are aspirin, clopidogrel, and aspirin plus extended-release dipyridamole. However, new agents and combinations continue to be evaluated. A detailed review of the evidence supporting various antiplatelet regimens for secondary stroke prevention is outlined with special focus on recent developments that may impact clinical management of patients with stroke or TIA.

Searching for factors associated with resistance to acetylsalicylic acid used for secondary prevention of stroke

INTRODUCTION

The aim of the study was to evaluate the prevalence of resistance to acetylsalicylic acid (ASA), used for secondary prevention of stroke, including the assessment of risk factors associated with the lack of ASA anti-aggregatory action.

MATERIAL AND METHODS

Patients after a transient ischaemic attack (TIA) or ischaemic stroke in the acute (n = 111) and chronic phase (n = 87) were enrolled in the study. The assessment of platelet function was performed by whole blood impedance aggregometry using a multi-channel platelet function analyser (Multiplate).

RESULTS

A proper response to ASA was found in 121 patients (61.1%) (ASA responders), a partial response to ASA in 59 patients (29.8%) (ASA partial responders), and ASA resistance in 18 patients (9.1%) (ASA non-responders). Acetylsalicylic acid resistance was observed more frequently in the chronic phase. The mean low-density lipoprotein (LDL) concentration was higher in ASA non-responders (p = 0.02). The mean heart rate (p = 0.03) and the mean haematocrit (p = 0.03) were higher in the group of ASA partial responders and ASA non-responders. Angiotensin II receptor antagonists were more often used in the group of ASA partial responders and ASA non-responders (p = 0.04). Diuretics were more rarely used by ASA non-responders, whereas fibrates were more rarely used by ASA partial responders.

CONCLUSIONS

The method enabled the detection of ASA resistance in some patients with cerebrovascular disease. The study revealed some possible risk factors of ASA resistance: long ASA therapy, increased heart rate, higher LDL concentration, and higher haematocrit value. The relationship between the effect of ASA and other medications (angiotensin II receptor blockers, fibrates, diuretics) requires further study. Platelet function monitoring should be considered in patients at a greater risk of ASA resistance.

Thrombelastography maximal clot strength could predict one-year functional outcome in patients with ischemic stroke

BACKGROUND

Elevated maximal clot strength, measured by thrombelastography (TEG) maximum amplitude (MA) has been associated with a higher risk for ischemic events in patients with coronary artery diseases. However, it has not been investigated in patients with cerebrovascular diseases. In the current study, we aimed to evaluate the predictive ability of TEG-MA in assessing the risk for ischemic event recurrence and the functional outcome after index ischemic stroke.

METHODS

This was a prospective observational study. Consecutive eligible patients with acute ischemic stroke were included and followed up for one year. Patients were stratified into tertile groups based on MA levels. TEG-hypercoagulability was defined as an MA of ≥ 69 mm. Ischemic events were defined as a composite of ischemic stroke, myocardial infarction, or vascular death (excluding hemorrhagic death). The functional outcome was evaluated by modified Rankin Scale (mRS). Unfavorable functional outcome was defined as mRS ≥ 2.

RESULTS

Two hundred and eleven patients were enrolled with 27 lost to follow-up at one year contact. At baseline, 38 (18.0%) patients were TEG-hypercoagulopathy after the treatment of antiplatelets. Patients with higher tertile of MA were more likely to be females, and had lower hemoglobin levels, higher platelet counts, higher fibrinogen levels, higher white blood cell counts, as well as higher ESR and hsCRP levels. Patients in the third tertile group were more likely to have intracranial artery stenosis and large-vessel subtype stroke than those in the other two groups. Higher tertile of MA was also related to stroke severity in acute phase (higher NIHSS scores on admission and longer in-hospital stay). At one year of follow-up, a higher percentage of unfavorable functional outcome and a non-significant trend of higher ischemic event rate were observed in higher MA tertile groups. Multivariate logistic analysis revealed that higher MA level (OR = 1.192, p = 0.022) was an independent predictor for unfavorable one-year functional outcome. Other independent predictors included old age (OR = 1.119, p = 0.001), diabetes mellitus (DM) (OR = 4.280, p = 0.014), previous ischemic stroke/TIA history (OR = 4.953, p = 0.008), and higher NIHSS scores on admission (OR = 1.437, p = 0.001).

CONCLUSIONS

We found that higher TEG-MA levels could predict an unfavorable functional outcome after index ischemic stroke. Further, large-scale studies are required to investigate the relationship between MA levels and risk of recurrent ischemic events in ischemic stroke patients.

Clinical and biochemical aspirin resistance in patients with recurrent cerebral ischemia

BACKGROUND AND AIM

Stroke recurrence is an important public health concern. One half of survivors remain disabled, and one seventh requires institutional care. Aspirin remains the cornerstone of primary and secondary stroke prevention; meanwhile, aspirin resistance is one of the possible causes of stroke recurrence. We aimed to evaluate the clinical and biochemical aspirin resistance in patients with recurrent ischemic stroke.

PATIENTS AND METHODS

We studied demographic characteristics, vascular risk factors, stroke subtypes, radiologic findings and biochemical aspirin resistance tests using both arachidonic acid (AA) and adenosine diphosphate (ADP)-induced light transmittance aggregometry (LTA) on admission and 24 h after observed aspirin ingestion.

RESULTS

Of the 82 patients with recurrent cerebral ischemia included in this study, 37 (45%) patients were poor compliant with aspirin. There were no statistically significant differences between the two groups regarding the demographic characteristics, stroke severity, laboratory tests, radiological findings or vascular risk factors. On admission, 19.6% and 4.8% of patients showed aspirin resistance, while 24 h after supervised 300 mg single aspirin dose ingestion, it was 9.8% and 2.4% using ADP and AA-induced LTA respectively. Of the eight aspirin resistant patients, two only showed resistance using both AA and ADP. Aspirin resistance was statistically significantly higher in the male gender, older age, hyperlipidemia, smokers and in all lacunar strokes using AA.

CONCLUSION

Biochemical aspirin resistance in one's series was rather rare (2.4%) and was more prevalent in patients with lacunar strokes. Clinical aspirin failure may often be contributed to poor compliance with aspirin intake.

Frequency, risk factors, prognosis, and genetic polymorphism of the cyclooxygenase-1 gene for aspirin resistance in elderly Chinese patients with cardiovascular disease

BACKGROUND

Cardiovascular disease (CVD) is an important cause of mortality in elderly patients worldwide. Aspirin resistance has been well reported in CVD.

OBJECTIVE

The frequency, risk factors, prognosis, and genetic polymorphism of the cyclooxygenase-1 (COX-1) gene for aspirin resistance have not been reported in elderly patients with CVD. We therefore undertook this study to evaluate these associations among elderly Chinese patients with CVD.

METHODS

Four hundred thirty-one elderly Chinese patients with CVD receiving daily aspirin therapy (≥75 mg) over 1 month were enrolled. Platelet aggregation was measured by light transmission aggregometry (LTA) and thromboelastography platelet mapping assay (TEG) using arachidonic acid (AA) as a stimulus. The median follow-up was 1.8 years.

RESULTS

After the median follow-up, aspirin-resistant patients were at an increased risk of the composite endpoint compared to nonresistant patients by LTAAA + TEGAA (23.7 vs. 9.2%, p = 0.025). Additionally, Cox proportional hazards regression modeling demonstrated that aspirin resistance and cerebrovascular disease were associated with major adverse long-term outcomes (HR for aspirin resistance = 2.31, 95% CI 1.11-4.81, p = 0.026). The variant G-allele of COX-1 rs1330344 (-1676 A/G) significantly increased the risk of aspirin resistance defined by LTAAA + TEGAA (OR = 1.82, 95% CI 1.13- 2.92, p = 0.01).

CONCLUSIONS

Aspirin resistance, evaluated by LTAAA + TEGAA, is associated with an increased risk of adverse clinical events in elderly Chinese patients with CVD. The variant G-allele of COX-1 rs1330344 is significantly associated with aspirin resistance defined by LTAAA + TEGAA.

Antiplatelet therapy: aspirin resistance and all that jazz!

Platelets play a crucial role in the pathogenesis of atherosclerosis, thrombosis, and stroke. Aspirin used alone or in combination with other antiplatelet drugs has been shown to offer significant benefit to patients at high risk of vascular events. Resistance to the action of aspirin may decrease this benefit. Aspirin resistance has been defined by clinical and/or laboratory criteria; however, detection by laboratory methods prior to experiencing a clinical event will likely provide the greatest opportunity for intervention. Numerous laboratory methods with different cutoff points have been used to evaluate the resistance. Noncompliance with aspirin treatment has also confounded studies. A single assay is currently insufficient to establish resistance. Combinations of results to confirm compliance and platelet inhibition may identify "at-risk" individuals who truly have aspirin resistance. The most effective strategy for managing patients with aspirin resistance is unknown; however, studies are currently underway to address this issue.

Monitoring the effectiveness of antiplatelet therapy: opportunities and limitations

Previous clinical studies have shown heterogeneity in individual patient responses to antiplatelet therapy and high residual platelet reactivity is associated with increased risk of adverse clinical events. Monitoring response to antiplatelet therapy and tailoring treatment accordingly is currently not recommended in routine clinical practice largely due to the lack of a standardized definition of antiplatelet therapy hyporesponse and the need for a widely accepted point-of-care platelet function test that can be reliably utilized in frontline clinical practice. Recent data have shown that titrating the dose of clopidogrel in patients undergoing percutaneous coronary intervention significantly reduces the incidence of major adverse cardiovascular events and large-scale clinical trials are currently underway to investigate whether individually tailored treatment based on results of platelet function testing leads to improved clinical outcome. Furthermore, genetic testing has demonstrated a link between CYP2C19 genetic polymorphisms, altered clopidogrel metabolite concentrations and adverse clinical events. Clinical studies are currently underway to investigate the potential clinical benefit associated with genotype-guided tailoring of antiplatelet therapy. With the advent of newer, more potent antiplatelet agents and their associated increased bleeding risks, it will become imperative in the future to select the most appropriate, safe and effective drug.

Ischemic stroke in patients receiving aspirin

BACKGROUND

The widespread use of aspirin-driven vascular prevention strategies does not impede the occurrence of first and recurrent ischemic strokes in numerous subjects. It is not clear what factors are associated with aspirin failure beyond the functional diagnosis of aspirin resistance in selected subjects. Current management guidelines provide little or no recommendations on the proper strategy for subjects who had a stroke while receiving aspirin. We assessed clinical features of subjects who had a first or recurrent stroke while taking aspirin.

METHODS

We studied demographic characteristics, vascular risk factors, stroke subtypes, and concomitant medication use in subjects with first or recurrent ischemic strokes. Patients receiving antiplatelet medications other than aspirin and/or oral anticoagulants were excluded from this analysis.

RESULTS

Seven hundred and nine patients with first (n = 552) or recurrent (n = 157) ischemic stroke were evaluated. Aspirin was being taken by 29% of first and 48% of recurrent stroke subjects. There was a higher prevalence of hypertension, hypercholesterolemia, and smoking in aspirin users with first and recurrent stroke (P < .05). Diabetes and coronary artery disease were more frequent in aspirin users with first ischemic strokes (P < .003), but not in those who had recurrent ischemic strokes. Aspirin users were more likely to be also receiving statins and antihypertensive drugs (P < .001).

CONCLUSIONS

Aspirin failure in ischemic stroke prevention may exceed functional resistance to aspirin and could be associated with a higher prevalence of lacunar stroke, comorbidities, and/or adverse interactions with other drugs. These patients may require a different approach regarding prevention strategies.

Aspirin resistance in patients with acute coronary syndrome. Part 2

Aim.In patients with acute coronary syndrome (ACS), to investigate the prevalence of aspirin resistance, its clinical features, prognostic effects, and potential correction.Material and methods.The study included 100 ACS patients receiving aspirin. Aspirin resistance was diagnosed if at Day 7 of aspirin therapy, the level of platelet aggregation (PLA) with arachidonic acid was ≥20%. In addition, a thromboxane A2 (ТхА2) metabolite – 11-dehydro-thromboxane B2 (11DHTxB2), as well as inflammation markers and genetic polymorphisms (sub-unit IIIa – Leu33Pro and cyclooxygenase-2 (COG) genes) were studied.Results.Aspirin resistance was diagnosed in 11% of ACS patients, receiving aspirin in a standard dose of 100 mg/d. The majority of aspirin-resistant patients had ACS with ST segment elevation (STE-ACS). In all aspirin-resistant ndividuals, the resistance was pharmacokinetic. The level of 11DHTxB2, increased at baseline in ACS patients and especially in those with STE-ACS, was reduced during aspirin therapy. The combination of high PLA and high 11DHTxB2 levels was typically associated with true aspirin resistance. In patients with metabolite levels >438 ng/ mmol creatinine, prognosis was significantly worse than in those with lower levels of this parameter. In aspirinresistant patients, the levels of interleukin-6 (IL-6), IL-10, and C-reactive protein (CRP) at baseline and throughout the study were significantly higher than in aspirin-sensitive subjects. There was no significant association between aspirin resistance and Leu33Pro or А842G polymorphisms, while А842G polymorphism was more common in aspirin-resistant patients.Conclusion.In aspirin-resistant patients, the level of ТхА2 metabolite is increased (true resistance). In ACS individuals with high levels of 11DHTxB2, the prognosis was worse. Aspirin resistance could be linked to inflammation activation. There was no consistent association between aspirin resistance and studied genetic polymorphisms.

Antiplatelet resistance in stroke

Although the exact prevalence of antiplatelet resistance in ischemic stroke is not known, estimates about the two most widely used antiplatelet agents - aspirin and clopidogrel - suggest that the resistance rate is high, irrespective of the definition used and parameters measured. Inadequate antiplatelet responsiveness correlates with an increased risk of recurrent ischemic vascular events in patients with stroke and acute coronary syndrome. It is not currently known whether tailoring antiplatelet therapy based on platelet function test results translates into a more effective strategy to prevent secondary vascular events after stroke. Large-scale clinical trials using a universally accepted definition and standardized measurement techniques for antiplatelet resistance are needed to demonstrate whether a 'platelet-function test-guided antiplatelet treatment' strategy translates into improved stroke care. This article gives an overview of the clinical importance of laboratory antiplatelet resistance, describes the challenges for platelet-function test-guided antiplatelet treatment and discusses practical issues about the management of patients with aspirin and/or clopidogrel resistance.

Aspirin resistance

The development of adverse cardiovascular events despite aspirin use has established an interest in a possible resistance to the drug. Several definitions have been set and various laboratory testing modalities are available. This has led to a wide range of prevalence reports in different clinical entities. The etiologic mechanism has been related to clinical, genetic, and other miscellaneous factors. The clinical implications of this phenomenon are significant and warrant concern. Management strategies are currently limited to dosing alteration and introduction of other anitplatelet agents. However, these measures have not met the expected efficacy or safety.