Dual antiplatelet therapy unmasks distinct platelet reactivity in patients with coronary artery disease

Summary. Background: Platelet‐induced thrombosis is a major risk factor for recurrent ischemic events, although platelet function in patients with cardiovascular disease taking aspirin and clopidogrel is very poorly characterized. The aim of this study was to assess platelet reactivity in patients with cardiovascular disease taking aspirin and clopidogrel. Methods: We developed a rapid assay to measure platelet aggregation in response to arachidonic acid, collagen, adenosine diphosphate (ADP), epinephrine and thrombin receptor activating peptide (TRAP) in 80 healthy volunteers. We then recruited 200 consecutive patients from outpatient clinics and the cardiac catheterization laboratory and tested platelet function. Platelet aggregation induced by epinephrine is a marker of global platelet reactivity. We tested platelet function in 146 patients compliant with antiplatelet therapy. Platelet aggregation to epinephrine was divided into quartiles. The platelet response to the other agonists was analysed based on the response to epinephrine. Results: Platelet reactivity increased significantly across the quartiles in response to epinephrine in healthy volunteers and patients (P < 0.0001). A significant increase in response across quartiles was seen with all agonists in healthy volunteers (P < 0.001). In contrast, a significant increase in response across quartiles was only seen with ADP in patients (P < 0.0001). Hypertension, smoking and diabetes were significantly associated with increasing platelet reactivity to epinephrine (P < 0.05). Conclusion: This study shows that platelet response differs between healthy volunteers and patients on dual antiplatelet therapy. In patients with cardiovascular disease, dual antiplatelet therapy unmasks a distinct type of platelet reactivity in response to epinephrine and ADP but not other agonists.     

Enhanced antiplatelet effect of clopidogrel in patients whose platelets are least inhibited by aspirin: a randomized crossover trial

Summary. Objective: We aimed to determine whether adding clopidogrel to aspirin in patients at high risk of future cardiovascular events would suppress laboratory measures of the antiplatelet effects of aspirin; and have greater platelet inhibitory effects in patients with the least inhibition of platelets by aspirin. Methods: We performed a randomized, double‐blind, placebo‐controlled, crossover trial, comparing clopidogrel 75 mg day^?1 versus placebo, in 36 aspirin‐treated patients with symptomatic objectively confirmed peripheral arterial disease. Results: The addition of clopidogrel to aspirin did not suppress platelet aggregation induced by arachidonic acid, urinary 11 dehydro thromboxane B₂ concentrations, or soluble markers of platelet activation markers (P‐selectin, CD40‐ligand) and inflammation (high sensitivity serum C‐reactive protein, interleukin‐6). Clopidogrel significantly inhibited platelet aggregation induced by ADP (reduction 26.2%; 95% CI: 21.3–31.1%, P < 0.0001) and collagen (reduction 6.2%; 95% CI: 3.2–9.3%, P = 0.0003). The greatest inhibition of collagen‐induced platelet aggregation by clopidogrel was seen in patients with the least inhibition of arachidonic acid induced aggregation by aspirin [lower tertile of arachidonic acid‐induced platelet aggregation: 2.8% (95% CI: ?0.8 to 6.3%) reduction in mean collagen‐induced aggregation by clopidogrel; middle tertile: 4.0% (95% CI: 0.4–7.6%); upper tertile 12.6% (95% CI: 4.5–20.8%); P‐value for interaction 0.01]. Conclusions: The greatest platelet inhibitory effect of clopidogrel occurs in patients with the least inhibition of arachidonic acid‐induced platelet aggregation by aspirin. This raises the possibility that the clinical benefits of adding clopidogrel to aspirin may be greatest in patients whose platelets are least inhibited by aspirin. Confirmation in clinical outcome studies may allow these patients to be targeted with antiplatelet drugs that inhibit the ADP receptor, thereby overcoming the problem of laboratory aspirin resistance.     

Reversal of the anti‐platelet effects of aspirin and clopidogrel

Summary. Background: Guidelines recommend stopping aspirin and clopidogrel 7 to 10 days before surgery to allow time for replacement of permanently inhibited platelets by newly released uninhibited platelets.Objectives: The purpose of the present study was to determine the rate of offset of the anti‐platelet effects of aspirin and clopidogrel after stopping treatment and the proportion of untreated donor platelets that are required to reverse their anti‐platelet effects.Methods: Cohort 1 consisted of 15 healthy subjects who received aspirin 81 mg day^?1 or clopidogrel 75 mg day^?1 for 7 days and underwent serial blood sampling until platelet function testing results normalized. Cohort 2 consisted of 36 healthy subjects who received aspirin 325 mg day^?1, clopidogrel 75 mg day^?1, aspirin 81 mg day^?1 plus clopidogrel 75 mg day^?1 or no treatment for 7 days and underwent a single blood sampling.Results: In cohort 1, arachidonic acid (AA)‐induced light transmission aggregation (LTA) returned to baseline levels in all subjects within 4 days of stopping aspirin, coinciding with the partial recovery of plasma thromboxane B₂ concentrations. ADP‐induced LTA did not return to baseline levels until 10 days after stopping clopidogrel. In cohort 2, AA‐induced LTA in patient treated with aspirin reached control levels after mixing with 30% untreated donor platelets whereas ADP‐induced LTA in patients treated with clopidogrel reached control levels only after the addition of 90% or more donor platelets.Conclusions: Platelet aggregation recovers within 4 days of stopping aspirin but clopidogrel must be stopped for 10 days to achieve a normal aggregatory response.     

A case–control study on platelet reactivity in patients with coronary stent thrombosis

Summary. Background: The pathophysiology of stent thrombosis (ST) has evolved from the identification of single causative factors to a complex multifactorial model. Objectives: The aim of the present study was to investigate whether patients with a history of ST exhibit heightened platelet reactivity to clopidogrel and aspirin. Patients/methods: Pretreatment and on‐treatment platelet reactivity to clopidogrel and aspirin, as well as dual antiplatelet therapy resistance, was determined in 84 patients with a history of definite ST (cases: 41 early ST; 43 late ST) and in 103 control patients with a previously implanted coronary stent but no ST after the index procedure. Platelet function was evaluated with optical aggregometry, the VerifyNow P2Y12 and aspirin assays, the PFA‐100 Innovance P2Y* cartridge, the flow cytometric vasodilator‐stimulated phosphoprotein assay and urine 11‐dehydrothromboxane B₂ measurement before and after the administration of a 600‐mg loading dose of clopidogrel and 100 mg of aspirin. The study was registered at ClinicalTrials.gov, number NCT01012544. Results: Patients with a history of early ST clearly demonstrated higher on‐clopidogrel platelet reactivity than controls. Patients with both early and late ST exhibited heightened on‐aspirin platelet reactivity status, and dual antiplatelet therapy resistance was more frequent. Conclusions: Patients with a history of early ST exhibit a poor response to clopidogrel. Furthermore, both early and late ST are strongly and independently associated with heightened on‐aspirin platelet reactivity, and dual antiplatelet therapy resistance is more frequent.     

Effect of preanalytical time-delay on platelet function as measured by multiplate,PFA-100 and VerifyNow

Background and aims: Platelet function testing may help to identify poor responders to antiplatelet drugs. The aim of this study was to compare three commonly used platelet function tests with special focus on the pre-analytical influence of time-delay on the tested parameters.

Methods: We assessed ADP-induced platelet function by the Multiplate, Platelet Function Analyzer-100 (PFA-100) and VerifyNow in nine healthy volunteers and 36 patients receiving clopidogrel or prasugrel 1 and 3?hours after sampling. Results: The PFA-100 demonstrated non-closure time in 23 patients. A more graded response could be detected with the two other devices. Aggregation in whole blood (Multiplate) decreased after 3?hours compared to 1?hour in all subjects (p?p?Conclusion: Responses to ADP are time-dependent after blood sampling for the Multiplate in all subjects and for the VerifyNow in patients on antiplatelet drugs. For both devices, platelet aggregation was reduced 3?hours after sampling which may affect data interpretation and clinical consequences.     

High post-treatment platelet reactivity identified low-responders to dual antiplatelet therapy at increased risk of recurrent cardiovascular events after stenting for acute coronary syndrome

Summary.  Background and objectives: Low response to antiplatelet therapy may be a risk factor for the development of ischemic complications in patients with non-ST segment elevation acute coronary syndrome (NSTE ACS) undergoing coronary stenting. Methods: We prospectively studied the platelet response to both clopidogrel and aspirin in 106 NSTE ACS consecutive patients undergoing percutaneous coronary intervention (PCI) with stenting. A single post-treatment blood sample was obtained just before PCI and analyzed by platelet aggregometry using both ADP and arachidonic acid (AA) as agonists to explore the responses to clopidogrel and aspirin, respectively. Patients were divided into quartiles according to the ADP or AA induced maximal intensity of platelet aggregation. Patients of the highest quartile (quartile 4) were defined as the 'low-responders'. Results: Twelve recurrent cardiovascular (CV) events occurred during the 1-month follow-up. Clinical outcome was significantly associated with platelet response to clopidogrel [Quartile 4 vs. 1, 2, 3: OR (95% CI) 22.4 (4.6–109)]. Low platelet response to aspirin was significantly correlated with clopidogrel low response ( P  = 0.003) but contributed less to CV events [OR (95%CI): 5.76 (1.54–35.61)]. Conclusions: A post-treatment ADP-induced platelet aggregation performed just before PCI identifies low responders to dual antiplatelet therapy with an increased risk of recurrent CV events.     

Earlier recovery of platelet function after discontinuation of treatment with ticagrelor compared with clopidogrel in patients with high antiplatelet responses

Summary. Background: The rate of recovery of platelet function after discontinuation of P2Y₁₂ inhibitors depends on the reversibility of the antiplatelet effect and the extent of the on‐treatment response. P2Y₁₂ inhibition increases the bleeding risk in patients requiring surgery. Objectives: To evaluate recovery of platelet function after discontinuation of ticagrelor vs. clopidogrel in stable coronary artery disease (CAD) patients with high levels of platelet inhibition (HPI) during the ONSET/OFFSET study. Methods: Patients received aspirin 75–100 mg per day and either ticagrelor 90 mg twice‐daily or clopidogrel 75 mg daily for 6 weeks. This subanalysis included patients with HPI after the last dose of maintenance therapy, defined as: inhibition of platelet aggregation (IPA) > 75% 4 h post‐dose (ADP 20 μm , final extent); < 120 P2Y₁₂ reaction units 8 h post‐dose (VerifyNow P2Y₁₂ assay); or platelet reactivity index < 50% 8 h post‐dose (VASP‐P assay). Results: IPA > 75% was observed in 39 out of 47 ticagrelor‐treated and 17 out of 44 clopidogrel‐treated patients. The rate of offset of IPA over 4–72 h was greater with ticagrelor (IPA %/hour slope: ?1.11 vs. ?0.67 for clopidogrel; P < 0.0001). Mean IPA was significantly lower with ticagrelor than clopidogrel between 48 and 168 h post‐dose (P < 0.01). Similar findings were observed with the other assays. The average time for IPA to decline from 30% to 10% was 50.8 h with ticagrelor vs. 110.4 h with clopidogrel. Conclusions: In patients with HPI, recovery of platelet function was more rapid after discontinuation of ticagrelor than clopidogrel leading to significantly greater platelet reactivity by 48 h after the last dose in the ticagrelor group.     

Standardization of light transmittance aggregometry for monitoring antiplatelet therapy: an adjustment for platelet count is not necessary

Summary. Background: Light transmittance aggregometry (LTA) is considered to be the ‘gold standard’ of platelet function testing. As LTA has been poorly standardized, we analyzed the results of LTA in healthy subjects and patients with antiplatelet therapy using different concentrations of agonists and performing tests in non‐adjusted and platelet count‐adjusted platelet‐rich plasma (PRP). Methods: LTA was performed in 20 healthy subjects and in patients treated with aspirin (n = 30) or clopidogrel (n = 30) monotherapy, as well as in patients on combination therapy (n = 20), using arachidonic acid (ARA 0.25 and 0.5 mg mL⁻¹) and adenosine diphosphate (ADP 2 and 5 μm ) as agonists and performing platelet function tests in non‐adjusted and platelet count (250 nL⁻¹ ± 10%)‐adjusted PRP. Results: The overall platelet aggregation response is decreased after adjusting the PRP for platelet count compared with measurements in unadjusted PRP. The variability of aggregation results is high in adjusted PRP in the subgroup of healthy subjects, ranging from 9.2–95.3% (5th–95th percentile) relative to 77.6–95.5% in non‐adjusted PRP when determining maximum aggregation to ARA 0.5 mg mL⁻¹. Late aggregation using ADP 2 μm ranges from 3.8–89.9% in adjusted PRP compared with 42.9–92.5% in non‐adjusted PRP. Maximum aggregation using ARA 0.5 mg mL⁻¹ in non‐adjusted PRP differentiates between aspirin‐treated patients and healthy controls well, whereas late aggregation using ADP 2 μm in non‐adjusted PRP offers the best discrimination between clopidogrel‐treated patients and healthy controls. Conclusion: Adjustment of PRP for platelet count does not provide any advantage and therefore the time‐consuming process of platelet count adjustment is not necessary.     

比浊法血小板聚集试验的影响因素研究

目的 在不同的实验条件下,观察影响比浊法血小板聚集试验的因素.方法 选择30例健康对照组和204例病例组,观察不同的血小板计数及诱导剂浓度对糖尿病患者餐前与餐后、采血后的检测时间、诱导剂的种类互补等不同试验条件下的血小板聚集率.结果 随着血小板计数的减少或增加,血小板聚集率相应的减少或增加;二磷酸腺苷(ADP)、胶原(COL)、花生四烯酸(AA)浓度增加,血小板最大聚集率增大,相应的阿司匹林抵抗(AR)或氯吡格雷抵抗(CR)的检出率增高;服用不同的抗血小板药物,糖尿病患者对以ADP、COL、AA为诱导剂测定的血小板聚集率,其影响不同;未空腹及检测时间超过3 h重复性较差;服药2周后,COL、AA诱导的血小板聚集率下降不明的患者,随着时间的延长,6个月后易重新出现CR.结论 血小板计数、诱导剂浓度、糖尿病疾病、空腹状态、检测时间与比浊法检测血小板聚集率相关,以ADP、COL、AA作诱导剂检测血小板聚集率较单一的ADP更全面、准确.     

Adenosine diphosphate-inducible platelet reactivity shows a pronounced age dependency in the initial phase of antiplatelet therapy with clopidogrel

Summary.  Background:  Until recently, there were hardly any data on the antiplatelet effect of clopidogrel in advanced age. Like other metabolic processes, the conversion of clopidogrel to its active metabolite may be impaired in older patients, leading to high on-treatment residual ADP-inducible platelet reactivity. Objective:  To investigate the age dependency of clopidogrel-mediated platelet inhibition. Patients and methods:  This was a prospective observational study. We determined adenosine 5'-diphosphate (ADP)-inducible platelet reactivity using light transmission aggregometry (LTA) and the VerifyNow P2Y12 assay in 191 patients on dual antiplatelet therapy after angioplasty and stenting for cardiovascular disease. Results:  ADP-inducible platelet reactivity increased linearly with age after adjustment for cardiovascular risk factors, type of intervention, medication, C-reactive protein (CRP) and renal function [using LTA 0.36% of maximal aggregation per year, 95% CI 0.08–0.64%, P  = 0.013; using the VerifyNow P2Y12 assay 3.2 P2Y12 reaction units (PRU) per year, 95% CI 1.98–4.41 PRU, P  < 0.001]. ADP-inducible platelet reactivity was significantly higher in patients aged 75 years or older compared with younger patients ( P  = 0.003 for LTA and P  < 0.001 for the VerifyNow P2Y12 assay). Further, high on-treatment residual ADP-inducible platelet reactivity was significantly more common among patients aged 75 years or older ( P  = 0.02 for LTA and P  < 0.001 for the VerifyNow P2Y12 assay). Conclusion:  ADP-inducible platelet reactivity shows a pronounced age dependency in the initial phase of antiplatelet therapy with clopidogrel. The clinical implications of these findings need to be addressed in future trials.     

Aspirin withdrawal in patients treated with ticagrelor presenting with non‐ST elevation myocardial infarction

Essentials

• Strong P2Y₁₂ blockade may cause platelet inhibition that is only minimally enhanced by aspirin.
• We evaluated aspirin withdrawal on platelet reactivity in ticagrelor treated patients.
• Aspirin withdrawal resulted in increased platelet reactivity to arachidonic acid.
• Aspirin withdrawal caused little difference in adenosine diphosphate‐induced platelet aggregation.

Summary

Background

Recent studies have shown that the thromboxane A₂‐dependent pathway is dependent on the ADP–P2Y₁₂ pathway, and that strong P2Y₁₂ receptor blockade alone causes inhibition of platelet aggregation that is minimally enhanced by aspirin. Data from the PLATO trial suggested that, among ticagrelor‐treated patients, high‐dose versus low‐dose (< 100 mg day^?1) aspirin is associated with an increased risk fof ischemic events.

Objectives

To evaluate the impact of aspirin withdrawal on platelet reactivity in acute coronary syndrome (ACS) patients treated with a potent P2Y₁₂ blocker.

Patients/Methods

This was a current prospective, randomized, placebo‐controlled, double‐blind, cross‐over study. The study population comprised 22 consecutive ACS patients who underwent percutaneous coronary intervention and were treated with aspirin (100 mg day^?1) and ticagrelor. Thirty days post‐ACS, open‐label aspirin was stopped, and patients were randomized to either blinded aspirin or placebo for 2 weeks, with each patient crossing over to the other arm for an additional 2 weeks. Platelet reactivity to arachidonic acid and ADP determined with light‐transmission aggregometry (LTA) and VerifyNow was evaluated at baseline, and 2 weeks and 4 weeks later.

Results

Aspirin withdrawal resulted in an increase in arachidonic‐acid induced platelet reactivity as determined with both LTA (77.0% ± 11.3% versus 20.8% ± 4.4%) and VerifyNow (607.7 ± 10.6 aspirin reaction units [ARU] versus 408.5 ± 14.4 ARU). Platelet response to ADP, as determined with both LTA and VerifyNow, did not differ with either aspirin or placebo (32.9% ± 2.6% versus 35.8% ± 3.6%, and 33.5 ± 6.4 P2Y₁₂ reaction units (PRU) versus 29.6 ± 5.7 PRU, respectively).

Conclusions

Aspirin withdrawal early post‐ACS results in increased platelet reactivity in response to arachidonic acid, despite concomitant treatment with the potent P2Y₁₂ blocker ticagrelor.

     

Normalization of platelet reactivity in clopidogrel-treated subjects

BACKGROUND: Aspirin (ASA) + clopidogrel are commonly used in acute coronary syndrome (ACS), but persistent antiplatelet effects may complicate surgery. METHODS AND RESULTS: To study the possibility of normalizing platelet reactivity after ASA + clopidogrel treatment, 11 healthy subjects received a 325-mg ASA + clopidogrel loading dose (300 or 600 mg dependent on study arm), followed by 81 mg of ASA + 75 mg of clopidogrel daily for 2 days. Platelet reactivity was assessed by light transmittance aggregometry (LTA) [challenged by adenosine diphosphate (ADP), arachidonic acid (AA), collagen, and thrombin receptor activating peptide (TRAP)] and flow cytometry for platelet activation by GPIIb/IIIa receptor exposure pretreatment, 4 and 72 h postload. To normalize platelet reactivity, increasing amounts of pooled platelets from five untreated volunteers [volunteers (V)-platelet-rich plasma (PRP)] were added ex vivo to the subject's PRP (S-PRP). At both 4 and 72 h, 40% and 50% V-PRP were needed to overcome platelet disaggregation in the 300 or 600 mg arms, respectively, after ADP challenge; an additional 10% V-PRP fully normalized aggregation. Recovery of function was linear with each incremental increase of V-PRP. ADP-induced GPIIb/IIIa activation showed the same pattern as LTA (r = 0.74). Forty percent V-PRP was required to normalize platelet function to AA, collagen, and TRAP. CONCLUSION: Our results suggest that the pre-operative transfusion of 10 platelet concentrate units (the equivalent of 40% V-PRP) after a 300-mg clopidogrel loading or 12.5 units (50% V-PRP) after a 600 mg loading may adequately reverse clopidogrel-induced platelet disaggregation to facilitate postoperative hemostasis. An additional 2.5 units fully normalized platelet function. The potential clinical implications of our observations could include shorter hospitalizations and reduced bleeding complications. But these observations should be fully explored in an in vivo clinical setting with clopidogrel-treated patients before and after surgery.     

The greater in vivo antiplatelet effects of prasugrel as compared to clopidogrel reflect more efficient generation of its active metabolite with similar antiplatelet activity to that of clopidogrel''s active metabolite

BACKGROUND AND METHODS: Prasugrel is a novel orally active thienopyridine prodrug with potent and long-lasting antiplatelet effects. Platelet inhibition reflects inhibition of P2Y(12) receptors by its active metabolite (AM). Previous studies have shown that the antiplatelet potency of prasugrel is at least 10 times higher than that of clopidogrel in rats and humans, but the mechanism of its higher potency has not yet been fully elucidated. RESULTS: Oral administration of prasugrel to rats resulted in dose-related and time-related inhibition of ex vivo platelet aggregation, and its effect was about 10 times more potent than that of clopidogrel. The plasma concentration of prasugrel AM was higher than that of clopidogrel AM despite tenfold higher doses of clopidogrel, indicating more efficient in vivo production of prasugrel AM than of clopidogrel AM. In rat platelets, prasugrel AM inhibited in vitro platelet aggregation induced by adenosine 5'-diphosphate (ADP) (10 microm) with an IC(50) value of 1.8 microm. Clopidogrel AM similarly inhibited platelet aggregation with an IC(50) value of 2.4 microm. Similar results were also observed for ADP-induced (10 microm) decreases in prostaglandin E(1)-stimulated rat platelet cAMP levels. These results indicate that both AMs have similar in vitro antiplatelet activities. CONCLUSIONS: The greater in vivo antiplatelet potency of prasugrel as compared to clopidogrel reflects more efficient in vivo generation of its AM, which demonstrates similar in vitro activity to clopidogrel AM.     

Comparison of collagen versus adenosine diphosphate in detecting antiplatelet effect in patients with coronary artery disease

Widely varying methods of assessing platelet aggregation have resulted in the absence of an established standard approach to assess the effects of antiplatelet drugs. The objective of this study was to compare the roles of collagen and adenosine diphosphate (ADP) in the assessment of effects of aspirin or clopidogrel on platelet aggregation. Sixty patients with documented coronary artery disease were assigned to receive aspirin alone (ASA 100 mg/d) (n = 30) or aspirin-plus-clopidogrel (ASA 100 mg/d + C 75 mg/d) (n = 30). Platelet aggregation assessment by the use of whole blood aggregation tests with collagen or ADP was performed in these patients and 30 age- and gender-matched normal volunteers. When compared with the control group, therapy with ASA or ASA + C resulted in significant inhibition of collagen-induced platelet aggregation (P < 0.001 for each), but there was no statistically significant difference in the results between the ASA and ASA + C groups. When platelet aggregation was induced by ADP, the combined therapy with aspirin and clopidogrel decreased platelet aggregation significantly when compared with aspirin alone (P < 0.001), and no significant difference in the results between the ASA and normal groups was observed. In conclusion, collagen may prove useful to study the effect of aspirin and ADP may be appropriate for assessing the inhibitory effect of clopidogrel.     

氯吡格雷抵抗的发生率、影响因素及干预策略研究

目的通过检测冠心病患者二磷酸腺苷（adenosine diphosphate,ADP）诱导的血小板聚集、血浆P选择素（CD62P）浓度及可溶性CD40配体（sCD40L）的浓度,了解氯吡格雷抵抗在冠心病患者的发生率及影响因素,探讨氯吡格雷抵抗的干预策略。方法130例受选对象在服用氯吡格雷75mg／d前、服药5天后,测定血小板聚集（platelet aggregation）、CD62P浓度及sCD40L的浓度。根据ADP诱导的血小板聚集降低程度分为氯吡格雷抵抗组和非氯吡格雷抵抗组。对氯吡格雷抵抗患者随机分为氯吡格雷剂量加倍（150mg／d）和维持原有剂量两组,5天后重复测定血小板聚集率、血浆CD62P浓度及sCD40L浓度。结果服用氯吡格雷5天后测得氯吡格雷抵抗的发生率分别为16．2％（ADP10μmol／L）和14．6％（ADP20μmol／L）。对氯吡格雷抵抗患者剂量加倍干预5天后测得剂量加倍组的血小板聚集为（8．1±3．1）Ω,较服氯前（10．9±3．6）Ω有所降低（P〈0．05）;维持剂量组的血小板聚集为（7．4±5．7）Ω,较服氟前（9．9±5．1）Ω有所降低,但差异无统计学意义（P〉0．05）。剂量加倍组中氯吡格雷抵抗患者由10例降低为3例（30．0％）,维持原剂量组中氯吡格雷抵抗患者由9例降低为5例（55．6％）。结论氯吡格雷的抗血小板作用存在时间和剂量依赖性。     

反复脑梗死患者服阿司匹林后血小板聚集功能的变化

目的比较反复脑梗死患者同一次脑梗死患者服用阿司匹林后血小板聚集功能的差异，来探讨阿司匹林预防脑血管方面的作用。方法40名至少二次脑梗死的患者和28名一次脑梗死的患者服用阿司匹林（100mg／d）至少7天以上，用二磷酸腺苷和花生四烯酸作诱导剂，测定血小板聚集功能。结果花生四烯酸作诱导剂时，反复脑梗死患者同一次脑梗死患者的血小板聚集功能有显著差异（P〈0．01）。结论服用阿司匹林需检测血小板聚集功能，反映阿司匹林能否有效预防脑梗死复发。     

Determinants of high on-treatment platelet reactivity and agreement between VerifyNow and Multiplate assays

Dual antiplatelet therapy with clopidogrel is a regimen used before and after drug-eluting stent (DES) implantation. Point-of-care platelet reactivity assays are easy-to-use methods to determine adequate response to the drug. The aim of this study was a comparison of the two platelet reactivity assays: Multiplate^® and VerifyNow^® and an identification of factors potentially influencing the results of these tests, including common genetic polymorphisms. The study included 39 patients receiving 75?mg clopidogrel daily before angioplasty with DES implantation. Platelet reactivity was measured with Multiplate and P2Y₁₂ VerifyNow assays. Genetic polymorphisms of CYP2C19*2, ABCB1 3435C?>?T, and CYP3A4*1G were determined with PCR-RFLP method and CYP2C19*17 was determined by means of an allele-specific PCR. Agreement between Multiplate and VerifyNow assays was poor (Cohen’s κ?=?0.056, p?=?.273). Hematocrit significantly negatively correlated with VerifyNow assayed platelet reactivity (r?=??.487, p?=?.002). Female sex was significantly associated with higher VerifyNow assay results after adjustment to hematocrit (253.2?±?47.6 PRU vs. 195.9?±?56.9 PRU, p?=?.013) and the prevalence of high-on-treatment platelet reactivity (OR: 8.50; 95% CI 1.13–77.60, p?=?.024). Reactivity measured with Multiplate was lower in women (82.3 vs. 175.6?AU·min, p?=?.037) and in patients who received calcium channel blockers (74.7 vs. 191.7?AU·min, p?=?.002). None of the studied polymorphisms significantly influenced platelet aggregation measurements. In conclusion, different aspects modify between-patient variability of the Multiplate and VerifyNow assays and agreement between those two assays was poor.     

Effect of platelet turnover on whole blood platelet aggregation in patients with coronary artery disease

Summary. Background: Previous studies have demonstrated considerable variation in the antiplatelet effect of aspirin. Objectives: To investigate the impact of platelet turnover on the antiplatelet effect of aspirin in patients with stable coronary artery disease (CAD) and to identify determinants of platelet turnover. Methods: Platelet turnover was evaluated by measurements of immature platelets and thrombopoietin in 177 stable CAD patients on aspirin monotherapy, including 85 type 2 diabetics and 92 non‐diabetics. Whole blood platelet aggregation was determined using the VerifyNow^® Aspirin test and multiple electrode aggregometry (MEA, Multiplate^®) induced by arachidonic acid (AA) (1.0 mm ), adenosine diphosphate (ADP) (10 μm ) and collagen (1.0 μg mL^?1). Results: Immature platelet levels significantly correlated with MEA (r = 0.31–0.36, P‐values < 0.0001) and the platelet activation marker sP‐selectin (r = 0.19, P = 0.014). Contrary to the VerifyNow^® test, MEA significantly correlated with variations in platelet count (r = 0.45–0.68, P‐values < 0.0001). Among patients with residual platelet reactivity according to AA, there were significantly more diabetics (61% vs. 41%, P = 0.027) and higher levels of sP‐selectin (77.7 ± 29 vs. 70.2 ± 25 ng mL^?1, P = 0.070) and serum thromboxane B₂ (0.81 [0.46; 1.70] vs. 0.56 [0.31; 1.12] ng mL^?1, P = 0.034). In a multivariate regression analysis, immature platelet levels were determined by thrombopoietin levels (P < 0.001), smoking (P = 0.020) and type 2 diabetes (P = 0.042). Conclusions: The antiplatelet effect of aspirin was reduced in CAD patients with an increased platelet turnover. Once‐daily dosing of aspirin might not suffice to adequately inhibit platelet aggregation in patients with an increased platelet turnover.     

Flow cytometric analysis of intraplatelet VASP phosphorylation for the detection of clopidogrel resistance in patients with ischemic cardiovascular diseases

Interindividual variability of the inhibitory effect of clopidogrel on platelet functions leading to clopidogrel resistance has been described in some patients with ischemic cardiovascular disease. A reliable laboratory test is therefore needed to identify patients insufficiently protected by this antiplatelet treatment. The phosphorylation of vasodilator-stimulated phosphoprotein (VASP), an intraplatelet actin regulatory protein, is dependent on the level of activation of the platelet P2Y12 receptor, which is targeted by clopidogrel. The aim of this study was to use a flow cytometric VASP phosphorylation assay to evaluate the efficacy of clopidogrel therapy. The platelet reactivity index (PRI), expressed as a percentage, is the difference in VASP fluorescence intensity between resting (+PGE1) and activated (+ADP) platelets. In vitro, the PRI was strongly correlated with the inhibition of platelet aggregation induced by specific blockade of the P2Y12 receptor by the competitive antagonist AR-C69931MX (R = 0.72, P < 0.0001). Ex vivo, the PRI was 78.3 +/- 4.6% in 47 healthy donors, 79.0 +/- 4.1% in 34 patients not receiving clopidogrel and 61.1 +/- 17.0% in 33 patients treated with clopidogrel (P < 0.0001). In the clopidogrel group, the PRI values were widely dispersed (from 6.6 to 85.8%) and more than 30% of these patients had a PRI equivalent of values in patients not receiving clopidogrel. The flow cytometric analysis of VASP phosphorylation seems to be a suitable test to evaluate the efficacy of clopidogrel treatment. This assay demonstrated a wide interindividual variability of the inhibitory response of platelets to clopidogrel and showed that one-third of the patients treated appeared to be 'unprotected' by this therapy.