Bedside Evaluation of Thienopyridine Antiplatelet Therapy

Effect of cytochrome P450 2C19 (CYP2C19) gene polymorphism and clopidogrel reactivity on long term prognosis of patients with coronary heart disease after PCI

Objective

To investigate the impact of CYP2C19 gene polymorphism on clopidogrel reactivity and its association with long-term clinical outcome in patients with coronary heart disease (CHD) undergoing percutaneous coronary intervention (PCI).

Methods

In total, 675 patients were enrolled. Based on the platelet inhibition rate, patients were categorized into two groups: clopidogrel low responsiveness (CLR) and normal clopidogrel responsiveness (NCR). The CLR group was divided into ticagrelor and clopidogrel group based on the antiplatelet drugs used in the follow-up treatment. Patients were classified into three groups (normal metabolizer, intermediate metabolizer, and poor metabolizer) based on the CYP2C19 genotype. We aimed to evaluate the impact of CYP2C19 gene polymorphism on clopidogrel reactivity. The cumulative rates of 12-month all-cause deaths, major adverse cardiovascular events (MACCEs), and bleeding events were calculated.

Results

CLR was observed in 44.4% of the overall population. Significant differences were observed in the platelet inhibition rate of clopidogrel among the three metabolic genotypes (P < 0.05). At the 12-month follow-up, 13 patients (1.9%) died and 96 patients (14.2%) experienced MACCEs. Patients with CLR (9.6% vs. 11.7% vs. 22.1%, P < 0.05) or poor metabolizer (10.7% vs. 16.4% vs. 22.6%, P = 0.026) experienced a higher rate of MACCEs. A MACCEs risk score between zero and two was calculated. The highest incidence of MACCEs significantly increased with the 2-positive results, and the area under the curve (AUC) was 0.712 (95% CI: 0.650-0.774, P < 0.05). There was no significant difference between the group with a score of one and the occurrence of MACCEs (P > 0.05).

Conclusions

Low response to clopidogrel in CHD patients is correlated with CYP2C19 gene polymorphism. CYP2C19 genotyping combined with platelet reactivity is an independent predictor of 12-months MACCEs in patients with clopidogrel treatment after PCI, which is better than either test alone.

An alternative reduced dose regimen of ticagrelor for neuroendovascular patients

OBJECTIVE

There is a growing use of ticagrelor in patients undergoing neuroendovascular procedures, especially those who demonstrate clopidogrel resistance. While multiple dosages are studied in the cardiology literature, the optimal dose for patients with neurological pathology has yet to be established. Here, we describe a single center experience involving 39 patients who underwent neuroendovascular procedures that then received an adjusted lower dose of ticagrelor.

METHODS

A retrospective chart review was performed between 2013 and 2017 for patients on dual anti-platelet therapy (DAPT) for either cervical or intracranial vascular pathologies, as well as stenting of the neurovasculature, including carotid arteries. Patients were placed on ticagrelor if their measured P2Y12 reaction units (PRU) responses to clopidogrel were outside the expected range in our center using the VerifyNow™ P2Y12 test. All patients were maintained on a dose of 45 mg twice daily except for one patient who received 22.5 mg twice daily. Responsiveness to ticagrelor were measured utilizing the VerifyNow™ P2Y12 test.

RESULTS

The mean number of days for follow-up post treatment initiation was 532 days. A total of 39 patients were included in the analysis. Of these, 8 patients (21%) received implantation of intracranial stents (5 patients received pipeline embolization devices, 1 patient received stent-assisted coiling, and 2 patients received intracranial stents for atherosclerotic disease). Fourteen patients (35%) received carotid angioplasty and stenting. Seventeen patients (44%) did not receive permanent implantation of a stent. All patients on the lower dose ticagrelor of 45 mg twice daily achieved responsiveness (i.e., PRU < 194). Hemorrhagic transformation of ischemic stroke occurred in one patient (2.5%). No other hemorrhagic complications were encountered. No thromboembolic events were recorded aside from one patient (2.5%) with intracranial atherosclerotic disease who had an ischemic event.

CONCLUSIONS

A lower dose of ticagrelor (45 mg twice daily) appears to be safe and effective in this small cohort of patients who are resistant to clopidogrel per P2Y12 testing and who have increased risk of ischemic or hemorrhagic strokes due to neurovascular pathologies and implants. Further randomized studies are required to confirm these findings.

Antiplatelet Therapy in End-stage Renal Disease Patients on Maintenance Dialysis: a State-of-the-art Review

Patients with end-stage renal disease (ESRD) on maintenance dialysis have an increased risk of ischaemic events, such as recurrent myocardial infarction (MI) and stroke. Potent antiplatelet therapy may help mitigate this risk. Nonetheless, ERSD patients are also at increased risk of bleeding due to their complex vascular milieu, which limits the routine use of potent P2Y12 inhibitors. Moreover, these patients are often underrepresented or excluded from major clinical trials leaving a significant gap in existing knowledge. Understanding the mechanisms of this paradox may serve as a benchmark for the development of ESRD trials. The present review aims to provide an overview of the pathophysiological nature of increased bleeding and ischaemic risks in ERSD patients as well as summarize available evidence of antiplatelet use and propose new concepts to guide physicians in selecting appropriate drug regimes for this high-risk cohort.

Platelets and Their Role in Hemostasis and Thrombosis-From Physiology to Pathophysiology and Therapeutic Implications

Hemostasis is a physiological process critical for survival. Meanwhile, thrombosis is amongst the leading causes of death worldwide, making antithrombotic therapy one of the most crucial aspects of modern medicine. Although antithrombotic therapy has progressed tremendously over the years, it remains far from ideal, and this is mainly due to the incomplete understanding of the exceptionally complex structural and functional properties of platelets. However, advances in biochemistry, molecular biology, and the advent of 'omics' continue to provide crucial information for our understanding of the complex structure and function of platelets, their interactions with the coagulation system, and their role in hemostasis and thrombosis. In this review, we provide a comprehensive view of the complex role that platelets play in hemostasis and thrombosis, and we discuss the major clinical implications of these fundamental blood components, with a focus on hemostatic platelet-related disorders and existing and emerging antithrombotic therapies. We also emphasize a number of questions that remain to be answered, and we identify hotspots for future research.

Pharmacological Difference Between Platelet Aggregations in Cardioembolic Stroke Patients with Direct Oral Anticoagulants: A Pilot Study

Background Selecting the appropriate direct oral anticoagulants (DOACs) for embolic ischemic stroke patients, especially on concurrent antiplatelet therapy, is important. However, a limited number of studies have reported on the pharmacological differences in platelet aggregation of each DOAC. We aimed to evaluate the antiplatelet effects of selected DOACs, by comparing dabigatran (a direct oral thrombin inhibitor) and factor Xa (FXa) inhibitors (apixaban and rivaroxaban) in patients who had suffered a cardioembolic stroke. Methods We retrospectively evaluated 12 patients diagnosed with a cardioembolic stroke who took any DOAC without an antiplatelet drug and underwent platelet aggregation tests within 60 days from the onset of symptoms. The platelet aggregation tests were analyzed by both light transmission aggregometry and VerifyNow®. Results Six patients (50%) took dabigatran, while the other six (50%) took an FXa inhibitor (n = 4 for apixaban and n = 2 for rivaroxaban). From the light transmission aggregometry analysis, it was found that the maximal extent of aggregation for adenosine diphosphate (ADP) was significantly higher with dabigatran than with FXa inhibitors, and the ED₅₀ value of ADP on platelet aggregation was significantly lower with dabigatran than with FXa inhibitors. Moreover, the VerifyNow® analyses revealed that P2Y₁₂ reaction units were significantly higher with dabigatran than with FXa inhibitors. Conclusions Dabigatran had little impact on platelet aggregation compared to FXa inhibitors in patients who had suffered a cardioembolic stroke with atrial fibrillation, and who took DOACs for secondary prevention within 60 days from the onset.

Candidate Gene of NOS3, MMP3, AGT, and AGT1R and Pathway Analyses for Platelet Reactivity and Clinical Outcomes of Repeat Revascularization After First PCI in Chinese Patients

PURPOSE

Major disadvantages of the percutaneous coronary intervention (PCI) are the high occurrence of repeat revascularization due to restenosis and disease progression. The current study aimed to identify indicators that can predict the risk of repeat revascularization.

METHODS

A total of 143 patients who underwent PCI and had genetic test results were enrolled. We retrospectively reviewed their medical records after the first PCI. P2Y12 reaction unit (PRU) test results were obtained by VerifyNow; 4 candidate genes (NOS3, MMP3, AGT, and AGT1R) and 380 genes related to platelet activation-related processes and clopidogrel activity were selected for analysis. Repeat revascularization and in-stent restenosis (ISR) were used as clinical outcomes, and PRU and ADP aggregation rates were used as platelet function outcomes in analysis.

RESULTS

After the first PCI, the incidence of repeat revascularization at 18, 30, and 42 months was 14.1% (20/142), 17.5% (24/137), and 39.7% (31/78), respectively. In the candidate gene analysis, rs7830 (NOS3) was associated with both ADP aggregation rate and 18- and 30-month ISR, and rs 62,275,847 (AGTR1) was associated with both ADP aggregation rate and 30-month ISR. In the pathway, gene-set analysis, the linkage rs471683 and rs7785386 of GNAI1|GNAT3 were associated with PRU and ADP aggregation rate, 18-month and 30-month ISR, and repeat revascularization within 30 months. Rs1715389 of GNAI1|GNAT3 was associated with both PRU and ADP aggregation rate, 18-month and 30-month ISR, and repeat revascularization within 30 months. Rs7313458 of ITPR2 was associated with PRU and ADP aggregation rate, 18-month and 30-month ISR, and repeat revascularization within 18 months.

CONCLUSIONS

The genetic polymorphisms of rs7830 (NOS3), rs62275874 (AGTR1), linkage rs471683 and rs7785386 (GNAI1|GNAT3), rs1715389 (GNAI1|GNAT3), and rs7313458 (ITPR2) may lead to an increased risk of in-stent restenosis and revascularization after the first PCI in Chinese patients by affecting the efficacy of clopidogrel. The above six SNP may be used as potential genetic biomarkers for high risk of in-stent restenosis and revascularization after the first PCI in Chinese patients.

An optimal window of platelet reactivity by LTA assay for patients undergoing percutaneous coronary intervention

Objective

This study was aimed to determine how platelet reactivity (PR) on dual antiplatelet therapy predicts ischemic and bleeding events in patients underwent percutaneous coronary intervention (PCI).

Design

A total of 2768 patients who had received coronary stent implantation and had taken aspirin 100 mg in combination with clopidogrel 75 mg daily for > 5 days were consecutively screened and 1885 were enrolled. The recruited patients were followed-up for 12 months. The primary end-point was the net adverse clinical events (NACE) of cardiovascular death, nonfatal myocardial infarction (MI), target vessel revascularization (TVR), stent thrombosis (ST) and any bleeding.

Result

1709 patients completed the clinical follow-up. By using the receiver operating characteristic (ROC) curve analysis, the optimal cut-off values were found to be 37.5 and 25.5% respectively in predicting ischemic and bleeding events. Patients were classified into 2 groups according to PR: inside the window group (IW) [adenosine diphosphate (ADP) induced platelet aggregation (PL_ADP) 25.5–37.4%)] and outside the window group (OW) (PL_ADP < 25.5% or ≥ 37.5%). The incidence of NACE was 16.8 and 23.1% respectively in the IW and OW group. The hazard ratio of NACE in IW group was significantly lower [0.69 (95% CI, 0.54–0.89, P = 0.004)] than that in the OW group during 12-month follow-up.

Conclusion

An optimal therapeutic window of 25.5–37.4% for PL_ADP predicts the lowest risk of NACE, which could be referred for tailored antiplatelet treatment while using LTA assay.

Trial registration

Trial registration number: ClinicalTrials.govNCT01968499. Registered 18 October 2013 - Retrospectively registered.

Can we think of a TAT, that is a "tailored antiplatelet therapy"?

What can be seen from the case report by Verzelloni et al. has a double value, beyond the case itself. First of all, the use of platelet aggregation assessment tests, such as TEG-PM, allows clinicians to verify the exact timing between the suspension of thienopyridines and the possibility of surgery without further temporal delays and is also able to favor the evolution of ischemic problems or hemodynamic instability not easily treatable. It, therefore, allows clinicians to optimize the bleeding/thrombosis matching. Second, the use of point of care methodologies for the evaluation of platelet aggregation allows us to evaluate the adequacy of the antiaggregation, facilitating, where resistance or percentages of antiaggregation are lower than expected, modification of the therapeutic regimen.

Intensified P2Y12 inhibition for high-on treatment platelet reactivity

High on treatment platelet reactivity (HPR) during treatment with clopidogrel has been consistently found to be strong risk factor for recurrent ischemic events after percutaneous coronary intervention (PCI). Insufficient P2Y12 receptor inhibition contributes to HPR measured by the VerifyNow (VN) assay. Prasugrel and ticagrelor are more potent P2Y12 inhibitors than clopidogrel and commonly substituted for clopidogrel when HPR is documented, however benefit of VN guided intensified antiplatelet therapy is uncertain. We identified patients who had undergone platelet reactivity testing after PCI with VN after pretreatment with clopidogrel (n = 252) in a single center observational analysis. Patients who had HPR defined as PRU > 208 were switched to alternate P2Y12 inhibitors. Primary clinical endpoint was 1-year post PCI combined cardiovascular death, myocardial infarction (MI), and stent thrombosis. One hundred and eight (43%) subjects had HPR and were switched to prasugrel (n = 60) and ticagrelor (n = 48). Risk of recurrent 1-year primary endpoint remained higher for HPR patients switched to either ticagrelor or prasugrel as compared to subjects who had low on treatment platelet reactivity (n = 144) (LPR) on clopidogrel [Hazard Ratio: 3.5 (95% CI 1.1-11.1); p = 0.036)]. Propensity score matched analysis demonstrated higher event rates in patients with HPR on alternate P2Y12 inhibitor as compared to patients with LPR (log-rank: p = 0.044). The increased risk of recurrent events associated with HPR measured by VN is not completely attenuated by switching to more potent P2Y12 inhibitors. Non-P2Y12 mediated pathways likely contribute to increased incidence of thrombotic events after PCI in subjects with HPR.

Effects of switching from clopidogrel to prasugrel at the chronic phase after coronary stenting on antiplatelet action and vascular endothelial function: Switch-Pras study

Compared to clopidogrel, prasugrel has a lower incidence of ischemic events following percutaneous coronary intervention (PCI) because of an early reduction during the acute phase in P2Y12 reaction units (PRU). The objective of this study was to compare the antiplatelet effect and vascular endothelial function of both drugs during the chronic phase after PCI. Patients who had undergone PCI and were confirmed to have no restenosis by follow-up coronary angiography under dual anti-platelet therapy with clopidogrel (75 mg/day) and aspirin (100 mg/day) were randomized to either continue clopidogrel or switch to prasugrel (3.75 mg/day). At baseline, prior to randomization we determined the CYP2C19 genotype. At the baseline and 24 weeks after randomization, the P2Y12 reactivity unit (PRU) was measured using the VerifyNow™ P2Y12 assay. Endothelial function was evaluated by flow-mediated vasodilation (FMD) and reactive hyperemia peripheral arterial tonometry (RH-PAT), while and circulating CD34+/CD133+/CD45^low progenitor cells were measured by flow cytometric analysis. Serum high-sensitivity C-reactive protein (hsCRP) level was also measured. The PRU was reduced significantly in the prasugrel group (P = 0.0008), especially in patients who were intermediate or poor metabolizers based on the CYP2C19 genotype (P < 0.0001). This reduction was not observed in the clopidogrel group. The number of CD34+/CD133+/CD45^low cells increased in the clopidogrel group (P = 0.008), but not in the prasugrel group. The hsCRP, FMD and reactive hyperemia index measured by RH-PAT did not change in either group. Prasugrel is potentially better than clopidogrel for preventing thrombotic events, although clopidogrel may have an advantage over prasugrel in terms of preventing atherosclerotic events. Proper use of thienopyridine drugs based on the CYP2C19 genotype has promising clinical potential.

Platelet Function Testing in Patients on Antiplatelet Therapy before Cardiac Surgery

Based on variable pharmacodynamic responsiveness and platelet reactivity recovery after discontinuation of P2Y12 receptor inhibitors, preoperative platelet function testing may individualize discontinuation and be a part of transfusion algorithm triggering targeted postpump hemostatic management.

Open-label multicenter registry on the outcomes of peripheral arterial disease treated by balloon angioplasty with optical frequency domain imaging in superficial femoral artery and popliteal artery (OCEAN-SFA study)

Although balloon angioplasty for femoropopliteal artery lesions has been associated with restenosis rates of up to 60% at 12 months, the mechanism of restenosis has not been fully evaluated. The aim of this study was to evaluate the relationship between the vascular features observed on optical frequency domain imaging (OFDI) before and after balloon angioplasty of femoropopliteal artery lesions, and restenosis at 6 months. This study was a prospective multicenter single arm study. OFDI was performed before and after balloon angioplasty and plaque characteristics and vascular features, along with de novo lesions, were assessed. The primary outcome was the presence or absence of restenosis 6 months after balloon angioplasty. Residual platelet reactivity was assessed according to VerifyNow platelet reactivity units (PRUs). The number of patients completing 6 months of follow-up was 47, of which 14 had developed restenosis. Maximum thickness of the dissection flap (odds ratio (OR) 2.71; 95% confidence interval [0.9-8.0]; p = 0.071) and lesion length were identified as risk factors for restenosis (OR 1.015; 95% confidence interval [0.001-0.029]; p = 0.039). The mean PRU at the time of treatment in patients with restenosis was significantly higher than in those without restenosis (286.3 ± 82.6 vs. 208.5 ± 03.6, p = 0.026). Long lesions and major dissection on OFDI after balloon angioplasty for femoropopliteal artery lesions increase restenosis at 6 months. In addition, high residual platelet reactivity at the time of EVT may also be a risk factor for restenosis.Clinical Trial Registration Number UMIN000021120.

Impact of Routine Platelet Reactivity Testing with VerifyNow Assay on Antiplatelet Choice After Percutaneous Coronary Intervention

Background

High on-treatment ADP platelet reactivity (HPR) measured by VerifyNow P2Y12 assay (VN) is an established risk factor for ischemic events after percutaneous coronary intervention (PCI). We hypothesized that routine use of VN at time of PCI in clinical practice may affect choice of P2Y12 antiplatelet therapy at discharge.

Methods

In a single center retrospective analysis, we examined the influence of VN testing on choice of P2Y12 inhibitor post PCI in routine clinical practice. Assessment of HPR was used routinely in clinical care during the time period of analysis at discretion of clinical providers. Subjects with PRU>208 after the loading dose of clopidogrel or during clopidogrel steady state were switched to alternate P2Y12 inhibitors.

Results

We identified 1001 patients with PCI during the time period specified. A total of 252 subjects underwent VN testing. Among those, 43% were found to have HPR on clopidogrel and were switched to alternate therapies (prasugrel [n=60], ticagrelor [n=48]). Patients who had VN platelet function testing were more likely to be discharged on clopidogrel as compared to those who did not have VN assay done (57% vs. 50%, p=0.039). There was no significant difference in 1-year net-MACE (CVD, MI, stent thrombosis, BARC 2 or higher bleeding) using tailored antiplatelet therapy (VN testing) as compared to standard of care group (adjusted HR:0.92, 95% CI: 0.54-1.5, p=0.74).

Conclusion

Routine use of VN assay in personalized antiplatelet treatment decision-making after PCI is associated with lower likelihood of using novel P2Y12 inhibitors.

Safety and Efficacy of Prasugrel in Elderly/Low Body Weight Japanese Patients with Ischemic Stroke: Randomized PRASTRO-II

INTRODUCTION

The safety of prasugrel in elderly and/or low body weight Japanese patients with ischemic stroke who have a relatively high bleeding risk with antiplatelet therapy remains unknown.

OBJECTIVE

We aimed to investigate the safety and efficacy of long-term prasugrel monotherapy for stroke prevention compared with clopidogrel in elderly and/or low body weight Japanese patients with non-cardioembolic ischemic stroke.

METHODS

In this randomized, double-blind, comparative, phase III study, elderly (age ≥75 years) and/or low body weight (≤50 kg) Japanese patients with a previous history of non-cardioembolic ischemic stroke were assigned to a prasugrel 3.75 mg (PRA3.75) group, a prasugrel 2.5 mg (PRA2.5) group, or a clopidogrel 50 mg (CLO50) group and followed up for 48 weeks. The primary safety endpoint was the combined incidence of primary safety events, defined as life-threatening, major, and other clinically relevant bleeding. The efficacy endpoint was a composite of ischemic stroke, myocardial infarction, and death from other vascular causes.

RESULTS

A total of 654 patients (age 76.4 ± 7.3 years, body weight 55.6 ± 9.3 kg, women 43.9%) from 74 medical institutions within Japan were enrolled. The combined incidence (95% CI) of primary safety events was 4.2% (1.9-7.8%), 1.9% (0.5-4.7%), and 3.6% (1.6-6.9%) in the PRA3.75 group (n = 216), PRA2.5 group (n = 215), and CLO50 group (n = 223), respectively (hazard ratios [HR] PRA3.75/CLO50, 1.13 [0.44-2.93]; PRA2.5/CLO50, 0.51 [0.15-1.69]). The incidences of bleeding leading to treatment discontinuation (95% CI) were 2.3% (0.8-5.3%), 0.9% (0.1-3.3%), and 2.2% (0.7-5.2%) in the PRA3.75, PRA2.5, and CLO50 groups, respectively (HRs PRA3.75/CLO50, 1.01 [0.29-3.48]; PRA2.5/CLO50, 0.41 [0.08-2.12]). There was no significant difference in all bleeding events between groups. The incidence of ischemic stroke, myocardial infarction, and death from other vascular causes was lower, but not significantly so, in patients treated with prasugrel than in patients treated with clopidogrel: PRA3.75, 0.0% (0/216); PRA2.5, 3.3% (7/215); and CLO50, 3.6% (8/223; HRs PRA3.75/CLO50, 0.00 [0.00-0.00]; PRA2.5/CLO50, 0.90 [0.32-2.47]).

CONCLUSIONS

Elderly and/or low body weight -Japanese patients with previous non-cardioembolic ischemic stroke who received PRA3.75 showed similar results in terms of primary safety endpoint, and a numerically lower incidence of ischemic stroke, myocardial infarction, and death from other vascular causes, compared with those who received CLO50.

Intravenous cangrelor as a peri-procedural bridge with applied uses in ischemic events

Cangrelor is a relatively new antiplatelet drug that has been approved for use as an adjunct therapy to percutaneous coronary intervention (PCI) to decrease peri-procedural myocardial infarction (MI), coronary revascularization, and stent thrombosis. Cangrelor is an adenosine triphosphate analogue with a pharmacokinetic mechanism based on a reversible, dose-dependent inhibition adenosine diphosphate (ADP)-induced platelet aggregation. This drug has lately been in the spotlight as a possible bridge therapy for anti-platelet medication prior to cardiac and non-cardiac surgeries. Platelet function is usually restored within sixty minutes of cessation of therapy, thereby decreasing the risk of bleeding while providing adequate pre-procedural coverage to reduce ischemic events. This manuscript reviews the literature on cangrelor and summarizes its role as a peri-procedural bridge.

Cardiovascular Risk Reduction: A Pharmacotherapeutic Update for Antiplatelet Medications

This update presents evidence for new antiplatelet therapies including modified P2Y₁₂ inhibitors and a new class of thromboxane antagonists. Discussed are emerging data on established antihyperlipidemic medications that support an additional antiplatelet effect. Current information about the effectiveness of several bleeding reversal agents is discussed, and the concept of personalized antiplatelet therapy, wherein selection of an antiplatelet therapy is based on genetic factors or laboratory testing that predict response to therapy and risk of adverse effects. Finally, future drug targets are introduced and drug interactions that can be leveraged to design more effective and safe antiplatelet therapies are described.

Platelet inhibition to target reperfusion injury trial: Rationale and study design

BACKGROUND

In ST-segment elevation myocardial infarction (STEMI) patients treated with primary percutaneous coronary intervention (PPCI), current oral P2Y12 platelet inhibitors do not provide maximal platelet inhibition at the time of reperfusion. Furthermore, administration of cangrelor prior to reperfusion has been shown in pre-clinical studies to reduce myocardial infarct (MI) size. Therefore, we hypothesize that cangrelor administered prior to reperfusion in STEMI patients will reduce the incidence of microvascular obstruction (MVO) and limit MI size in STEMI patients treated with PPCI.

METHODS

The platelet inhibition to target reperfusion injury (PITRI) trial, is a phase 2A, multi-center, double-blinded, randomized controlled trial, in which 210 STEMI patients will be randomized to receive either an intravenous (IV) bolus of cangrelor (30 μg/kg) followed by a 120-minute infusion (4 μg/kg/min) or matching saline placebo, initiated prior to reperfusion (NCT03102723).

RESULTS

The study started in October 2017 and the anticipated end date would be July 2020. The primary end-point will be MI size quantified by cardiovascular magnetic resonance (CMR) on day 3 post-PPCI. Secondary endpoints will include markers of reperfusion, incidence of MVO, MI size, and adverse left ventricular remodeling at 6 months, and major adverse cardiac and cerebrovascular events.

SUMMARY

The aim of the PITRI trial is to assess whether cangrelor administered prior to reperfusion would reduce acute MI size and MVO, as assessed by CMR.

Management of antiplatelet therapy in patients undergoing neuroendovascular procedures

Neuroendovascular techniques for treating cerebral aneurysms and other cerebrovascular pathology are increasingly becoming the standard of care. Intraluminal stents, aneurysm coils, and other flow diversion devices typically require concomitant antiplatelet therapy to reduce thromboembolic complications. The variability inherent with the pharmacodynamic response to common antiplatelet agents such as aspirin and clopidogrel complicates optimal selection of antiplatelet agents by clinicians. This review serves to discuss the literature related to antiplatelet use in neuroendovascular procedures and provides recommendations for clinicians on how to approach patients with variable response to antiplatelet agents, particularly clopidogrel.

Lower on-treatment platelet reactivity during everolimus-eluting stent implantation contributes to the resolution of post-procedural intra-stent thrombus: serial OCT observation in the PRASFIT-Elective study

Intra-stent thrombus (IS-Th) formed immediately after percutaneous coronary intervention (PCI) is associated with subsequent adverse coronary events. However, the impact of on-treatment platelet reactivity on IS-Th is unknown. PRASFIT-Elective is a multicenter study of PCI patients receiving prasugrel (20/3.75 mg, loading/maintenance dose) or clopidogrel (300/75 mg), with aspirin (100 mg). Among the 742 study patients, 111 were pre-specified for the OCT sub-study. Of these, 82 underwent OCT immediately after PCI to assess IS-Th and at an 8-month follow-up to evaluate the fate of the IS-Th. Lesions were considered resolved when IS-Th were detected after PCI but not on the follow-up or persistent when IS-Th were observed on both scans. The P2Y12 Reactive Unit (PRU) value was determined at the initial PCI and 4 and 48 weeks post-PCI. In 76 patients (86 lesions), we detected 230 IS-Th initially, and 196 IS-Th (85.2%) were resolved at the 8-month OCT. At PCI, but not 4 or 48 weeks after, the resolved IS-Th group had a lower PRU than the persistent IS-Th group (199 ± 101 vs. 266 ± 102, p = 0.008). Multivariate logistic regression analyses revealed that lower PRU at PCI and less calcified lesions were independent predictive factors for the resolution of IS-Th. Local lesion-related factors and lower on-treatment platelet reactivity at the time of PCI may contribute to the resolution of IS-Th after EES implantation, potentially improving clinical outcome.

Antiplatelet and anticoagulation therapy during percutaneous coronary interventions: A review for the interventionalist

Pharmacotherapy for percutaneous coronary interventions is essential to optimize the balance between thrombosis and bleeding. Currently, choices abound for the selection of antiplatelet and anticoagulation therapies during percutaneous intervention (PCI). This review article discusses the mechanisms, pharmacokinetics/dynamics, and clinical data behind the various pharmacotherapies including; aspirin, thienopyridines, glycoprotein IIb/IIIa inhibitors, vorapaxar, heparin, direct thrombin inhibitors, and factor Xa inhibitors.

Platelet reactivity in human immunodeficiency virus infected patients on dual antiplatelet therapy for an acute coronary syndrome: the EVERE2ST-HIV study

Aim

To explore platelet reactivity on dual antiplatelet therapy (DAPT) of acute coronary syndrome (ACS) patients infected with HIV.

Methods and results

Acute coronary syndrome patients infected with HIV (n = 80) were matched to ACS patients without HIV (n = 160) on age, sex, diabetes, and DAPT (aspirin 100%, clopidogrel 68%, prasugrel 31%, ticagrelor 1%). Platelet reactivity was evaluated after ACS (>30 days) by measuring residual platelet aggregation (RPA) to aspirin and to P2Y12 inhibitors with light transmission aggregometry (LTA), VerifyNow aspirin assay (ARU), and P2Y12 assay (PRU) and with the VASP platelet reactivity index (VASP-PRI). Proportion of patients with high residual platelet reactivity (HPR) was evaluated. HIV-infected ACS patients had higher levels of platelet reactivity in response to P2Y12 inhibitors (RPA: 23.8 ± 2.7% vs. 15.3 ± 1.3%; P = 0.001; PRU: 132 ± 10 vs. 107.4 ± 6.6; P = 0.04; and VASP-PRI: 45.2 ± 2.6% vs. 32.0 ± 2.0%; P < 0.001) and to aspirin (RPA: 3.6 ± 1.5% vs. 0.4 ± 0.1%; P = 0.004 and ARU: 442 ± 11 vs. 407 ± 5; P = 0.002) compared with non-HIV. HIV-infection was independently associated with increased platelet reactivity regardless of the test used (RPA: P = 0.005; PRU: P < 0.001 and VASP-PRI: P < 0.001) and a higher proportion of HPR (OR = 7.6; P < 0.001; OR = 2.06; P = 0.06; OR = 2.91; P = 0.004, respectively) in response to P2Y12 inhibitors. Similar results were found with aspirin. Protease inhibitors use was associated with increased platelet reactivity and higher rate of HPR.

Conclusions

Acute coronary syndrome patients infected with HIV have increased levels of platelet reactivity and higher prevalence of HPR to P2Y12 inhibitors and aspirin than non-HIV patients. These results could provide potential explanations for the observed increase risk of recurrent ischemic events in the HIV-infected population.

Haemodialysis impairs clopidogrel but not aspirin responsiveness in patients with end-stage renal disease

Dual antiplatelet therapy (DAPT) with aspirin (ASA) and clopidogrel (Clp) is the standard treatment to reduce ischaemic coronary events, but in patients with end-stage renal disease (ESRD) the efficacy of Clp remains unclear. Patients with ESRD are at higher risk for coronary artery disease (CAD) and also their post-interventional outcome is worse compared to patients with normal renal function. Little is known about the influence of haemodialysis (HD) on ASA and Clp responsiveness. To assess the effect of HD on ASA- and Clp-responsiveness in patients with documented CAD and ESRD, 31 patients with ESRD (mean age 66.5 ± 1.8 years, 23 male ) on DAPT were evaluated for their ASA and Clp responsiveness with the Verify Now System (Accumetrics Inc.) We measured the antiplatelet effect in all ESRD patients at three time points: T1: just before HD; T2: directly after HD; T3: steady state on a HD free day one week after T1. In our study at baseline 10 (32.3%) patients were ASA-low responder (ASA-LR) and 14 (45.2%) patients Clp-low responder (Clp-LR). There was a significant difference in the PRU values before ( T1) and immediately after HD (T2) [PRU T1=234 (169; 274) vs PRUT2= 247 (199; 278); pT1,2=0.036; ]. Results were shown as median ARU T1 (25th, 75th percentile) or median PRU T1 (25th, 75th percentile). Hence HD seems to impair responsiveness to Clp, resulting in an increase of 6.5 % Clp-LR. No significant differences in the ARU values at the different time-points were found.

Clopidogrel non-responsiveness in patients undergoing percutaneous coronary intervention using the VerifyNow test: frequency and predictors

Objectives

Stent thrombosis and death after percutaneous coronary intervention (PCI) can be caused by a phenomenon known as clopidogrel non-responsiveness which has been shown to occur in approximately 5%–44% of patients. We investigated the responsiveness of clopidogrel in an Iraqi series of cases. Our aim was to determine for the first time the frequency and predictors of clopidogrel non-responsiveness among Iraqi patients with ischaemic heart disease undergoing PCI.

Methods

The study was conducted at the Cardiac Catheterization Center, Baghdad Teaching Hospital, Medical City, from January to May 2014, and included patients who presented for PCI. A platelet aggregation test was performed for those patients using the VerifyNow system.

Results

A total of 115 patients (mean age: 58.3±10.1 years; male sex: 73.9%) were included in the study. 18.3% of the study population were clopidogrel non-responders, which was comparable with the results of a Chinese study (20.28%, P=0.796) but contrasted with other reports from Jordan, Brazil and Thailand. The major independent predictive factor for non-responsiveness in our report was diabetes mellitus (OR 5.96, 95% CI 2.23 to 13.71; P=0.001), followed by hypertension (OR 4.135, P=0.035), obesity (OR 3.44, P=0.037) and male sex (OR 3.039, P=0.045). Previous use of clopidogrel (OR 0.17, P=0.02) and younger age (OR 0.72, P=0.026) were identified as protective factors.

Conclusions

In this study, 18.3% of patients were non-responders to clopidogrel and the major independent predictive factors for non-responsiveness were diabetes mellitus, hypertension, obesity and male sex.

Use of Aspirin and P2Y12 Response Assays in Detecting Reversal of Platelet Inhibition With Platelet Transfusion in Patients With Traumatic Brain Injury on Antiplatelet Therapy

BACKGROUND

At present, guidelines are lacking on platelet transfusion in patients with a traumatic intracranial bleed and history of antiplatelet therapy. The aspirin and P2Y 12 response unit (ARU and PRU, respectively) assays detect the effect of aspirin and P2Y 12 inhibitors in the cardiac population.

OBJECTIVE

To describe the reversal of platelet inhibition after platelet transfusion using the ARU and PRU assays in patients with traumatic brain injury.

METHODS

Between 2010 and 2015, we conducted a prospective comparative cohort study of patients presenting with a positive head computed tomography and a history of antiplatelet therapy. ARU and PRU assays were performed on admission and 6 hours after transfusion, with a primary end point of detection of disinhibition after platelet transfusion.

RESULTS

One hundred seven patients were available for analysis. Seven percent of patients taking aspirin and 27% of patients taking clopidogrel were not therapeutic on admission per the ARU and PRU, respectively. After platelet transfusion, 51% of patients on any aspirin and 67% of patients on any clopidogrel failed to be reversed. ARU increased by 71 ± 76 per unit of apheresis platelets for patients taking any aspirin, and PRU increased by 48 ± 46 per unit of apheresis platelets for patients taking any clopidogrel.

CONCLUSION

A significant percentage of patients taking aspirin or clopidogrel were not therapeutic and thus would be unlikely to benefit from a platelet transfusion. In patients with measured platelet inhibition, a single platelet transfusion was not sufficient to reverse platelet inhibition in almost half.

Utility of the Aspirin and P2Y12 Response Assays to Determine the Effect of Antiplatelet Agents on Platelet Reactivity in Traumatic Brain Injury

BACKGROUND

Premorbid antithrombotic medication may worsen intracranial injury and outcome after traumatic brain injury (TBI). Routine laboratory tests are insufficient to evaluate platelet activity.

OBJECTIVE

To profile the spectrum of platelet inhibition, as measured by aspirin and P2Y12 response unit assays, in a TBI population on antiplatelet therapy.

METHODS

This single-center, prospective cohort study included patients presenting to our institution between November 2010 and January 2015 with a clinical history of TBI. Serum platelet reactivity levels were determined immediately on admission and analyzed using the aspirin and P2Y12 response unit assays; test results were reported as aspirin response units and P2Y12 response units. We report congruence between assay results and clinical history as well as differences in assay results between types of antiplatelet therapy.

RESULTS

A sample of 317 patients was available for analysis, of which 87% had experienced mild TBI, 7% moderate, and 6% severe; the mean age was 71.5 years. The mean aspirin response units in patients with a history of any aspirin use was 456 ± 67 (range, 350-659), with 88% demonstrating therapeutic platelet inhibition. For clopidogrel, the mean P2Y12 response unit was 191 ± 70 (range, 51-351); 77% showed therapeutic response.

CONCLUSION

Rapid measurement of antiplatelet function using the aspirin and P2Y12 response assays indicated as many as one fourth of patients on antiplatelet therapy do not have platelet dysfunction. Further research is required to develop guidelines for the use of these assays to guide platelet transfusion in the setting of TBI.

High On-Treatment Platelet Reactivity to Adenosine Diphosphate Predicts Ischemic Events of Minor Stroke and Transient Ischemic Attack

BACKGROUND

This study aimed to evaluate the relationship between thromboelastography adenosine diphosphate maximum amplitude (TEG-ADP_MA) and recurrent ischemic events in patients with minor ischemic stroke or high-risk transient ischemic attack (TIA).

METHODS

A total of 265 patients received dual antiplatelet therapy were consecutively enrolled. High on-treatment platelet reactivity (HTPR) to ADP was assessed by TEG-ADP_MA and detected the CYP2C19 genotype; recurrent ischemic events were followed up for 90 days after onset. The difference of recurrent ischemic events was analyzed with or without HTPR to ADP by the Kaplan-Meier, and further to determine the difference of recurrent ischemic events in each group according to TEG-ADP_MA-based tertile distribution.

RESULTS

A total of 23 (8.6%) patients had recurrent ischemic events. TEG-ADP_MA greater than or equal to 48 mm had good predictive value. Whether these patients were divided into 2 groups or 3 groups, the HTPR to ADP group had higher risk of recurrent ischemic events than the normal on-treatment platelet reactivity to ADP group by the Kaplan-Meier (all, P < .05). The tertile distribution map showed that the results of recurrent ischemic events were statistically significant in the third tertile group compared with the other two groups (all, P < .03); also, the third tertile group had a higher rate of carriers of at least 1 CYP2C19 reduced-function allele than the other two groups (P < .05).

CONCLUSIONS

In patients with minor ischemic stroke and high-risk TIA, the TEG-ADP_MA could predict recurrent ischemic events and has auxiliary effect on clinical decision-making.

Head to Head Comparison of Two Point-of-care Platelet Function Tests Used for Assessment of On-clopidogrel Platelet Reactivity in Chinese Acute Myocardial Infarction Patients Undergoing Percutaneous Coronary Intervention

Background:

Platelet function tests are widely used in clinical practice to guide personalized antiplatelet therapy. In China, the thromboelastography (TEG) test has been well accepted in clinics, whereas VerifyNow, mainly used for scientific research, has not been used in routine clinical practice. The aim of the current study was to compare these two point-of-care platelet function tests and to analyze the consistency between the two tests for evaluating on-clopidogrel platelet reactivity in Chinese acute myocardial infarction patients undergoing percutaneous coronary intervention (PCI).

Methods:

A total of 184 patients admitted to Fuwai Hospital between August 2014 and May 2015 were enrolled in the study. On-clopidogrel platelet reactivity was assessed 3 days after PCI by TEG and VerifyNow using adenosine diphosphate as an agonist. Based on the previous reports, an inhibition of platelet aggregation (IPA) <30% for TEG or a P2Y12 reaction unit (PRU) >230 for VerifyNow was defined as high on-clopidogrel platelet reactivity (HPR). An IPA >70% or a PRU <178 was defined as low on-clopidogrel platelet reactivity (LPR). Correlation and agreement between the two methods were analyzed using the Spearman correlation coefficient (r) and kappa value (κ), respectively.

Results:

Our results showed that VerifyNow and TEG had a moderate but significant correlation in evaluating platelet reactivity (r = −0.511). A significant although poor agreement (κ = 0.225) in identifying HPR and a significantly moderate agreement in identifying LPR (κ = 0.412) were observed between TEG and VerifyNow. By using TEG as the reference for comparison, the cutoff values of VerifyNow for the Chinese patients in this study were identified as PRU >205 for HPR and PRU <169 for LPR.

Conclusions:

By comparing VerifyNow to TEG which has been widely used in clinics, VerifyNow could be an attractive alternative to TEG for monitoring on-clopidogrel platelet reactivity in Chinese patients.

Effects of clopidogrel therapy on whole blood platelet aggregation, the Plateletworks® assay and coagulation parameters in cats with asymptomatic hypertrophic cardiomyopathy: a pilot study

BACKGROUND

Although scientific evidence is limited, clopidogrel is frequently used as prophylaxis for arterial thromboembolism in cats with hypertrophic cardiomyopathy (HCM).

OBJECTIVES

Evaluating effects of clopidogrel therapy in asymptomatic cats with HCM on (1) conventional whole blood aggregation (WBA), (2) alternative platelet aggregation assessed with tubes of the Plateletworks® assay and (3) standard coagulation parameters.

ANIMALS AND METHODS

Prospective, randomized, double-blind, placebo-controlled pilot study. Fourteen asymptomatic HCM cats were randomly allocated to receive placebo (n = 5) or clopidogrel (18.75 mg/cat q24h, n = 9) as part of a larger study. Aggregation responses (to 20 µM adenosine diphosphate (ADP) and 10 µg/ml collagen) in WBA and the Plateletworks® assay and standard coagulation parameters were evaluated at baseline and after seven days of therapy.

RESULTS

Clopidogrel therapy significantly reduced aggregation responses to ADP and collagen in the Plateletworks® agonists tubes (ADP and collagen: P < 0.001), but did not significantly reduce aggregation responses to ADP and collagen in the WBA technique (ADP: P = 0.07, collagen: P = 0.30). Clopidogrel therapy did not show a significant effect on prothrombin time, activated partial thromboplastin time, antithrombin, D-dimers and fibrinogen concentrations.

CONCLUSION AND CLINICAL IMPORTANCE

Clopidogrel therapy at a dose of 18.75 mg/cat q24h for seven days causes a significant decrease in in vitro platelet aggregation evaluated with the Plateletworks® assay, without affecting standard coagulation parameters in cats with asymptomatic HCM.

Ticagrelor versus prasugrel in patients with high on-clopidogrel treatment platelet reactivity after PCI: The ISAR-ADAPT-PF study

Patients with high on-treatment platelet reactivity (HTPR) on clopidogrel are at high risk for adverse cardiovascular events after percutaneous coronary intervention (PCI). The aim of the ISAR-ADAPT-PF study was to assess the antiplatelet efficacy of ticagrelor versus prasugrel in patients with HTPR on clopidogrel. In a prospective and randomized clinical study, 70 patients with HTPR on clopidogrel loading dose (LD) within 24 h post PCI were assigned to receive either ticagrelor [180 mg LD followed by 90 mg maintenance dose (MD) twice daily] or prasugrel (60 mg LD followed by 10 mg MD once daily). The adenosine diphosphate-induced platelet aggregation assessed on the Multiplate analyzer on day 2 after randomization (primary end point) was as follows: the mean difference between the two treatment groups was 6 aggregation units (AU) × min with an upper 95% confidence interval (CI) of 41 AU × min, which was greater than the predefined noninferiority margin of 18 AU × min (P for noninferiority = 0.29). However, no significant differences in absolute platelet reactivity levels between ticagrelor- versus prasugrel-treated patients at that time point were observed (138 ± 100 AU × min vs. 132 ± 64 AU × min, P for superiority = 0.77). In conclusion, neither drug was statistically more effective for inhibition of platelet aggregation in patients with HTPR on clopidogrel post PCI, although the study could not formally demonstrate the assumed noninferiority of ticagrelor versus prasugrel.

A randomised trial of the pharmacodynamic and pharmacokinetic effects of ticagrelor compared with clopidogrel in Hispanic patients with stable coronary artery disease

The objective was to compare the pharmacodynamic (PD) and pharmacokinetic (PK) effects of ticagrelor with clopidogrel among subjects of Hispanic ethnicity, as the PD and PK effects of antiplatelet agents among Hispanics are not specifically known. This was a randomised, open-label, crossover PD/PK study of 40 Hispanic subjects with stable coronary artery disease (CAD). Subjects were allocated to either ticagrelor 180 mg loading dose (LD)/90 mg twice-daily maintenance dose (MD) followed by clopidogrel 600 mg LD/75 mg once-daily MD with an intervening washout period, or vice versa. The primary endpoint was on-treatment reactivity (OTR) at 2 h post-LD according to the VerifyNow P2Y12 test. OTR was significantly lower at 2 h post-LD with ticagrelor compared with clopidogrel (34 PRU vs. 201 PRU, least square means difference = −167 PRU [95 % CI, −197, −137], P < 0.001). OTR was also lower with ticagrelor at 30 min and 8 h post-LD (P < 0.001). The greater magnitude of antiplatelet effect with ticagrelor persisted after 7 days of MD (52 PRU [95 % CI, 30, 73] vs. 182 PRU [95 % CI, 160, 205], P < 0.001). Mean plasma concentration of ticagrelor and its active metabolite were greatest at 2 h post-LD, with similar levels at 2 h post-MD after 7 days of MD. Among Hispanic subjects with stable CAD, ticagrelor provides a more rapid onset of platelet inhibition and a significantly greater antiplatelet effect compared with clopidogrel during both the loading and maintenance phases of treatment.

A pharmacodynamic study of the optimal P2Y12 inhibitor regimen for East Asian patients with acute coronary syndrome

BACKGROUND/AIMS

Newer P2Y12 inhibitors, such as prasugrel and ticagrelor, have greater antiplatelet efficacy but may increase the risk of bleeding. In this study, we compared the pharmacodynamic efficacy of prasugrel and ticagrelor in East Asian patients with acute coronary syndrome (ACS).

METHODS

We selected 83 ACS patients undergoing percutaneous coronary intervention who were discharged with 90 mg ticagrelor twice daily (n = 24), 10 mg prasugrel daily (n = 39) or 5 mg prasugrel daily (n = 20). After 2 to 4 weeks, on-treatment platelet reactivity (OPR) was assessed in terms of P2Y12 reaction units (PRUs) using the VerifyNow P2Y12 assay (Accumetrics). We compared East Asian (85 < PRU ≤ 275) and Caucasian (85 < PRU ≤ 208) criteria for assessing the therapeutic window of OPR.

RESULTS

OPR was lowest in the ticagrelor group, followed by the 10 mg prasugrel and 5 mg prasugrel groups (49.1 ± 29.9 vs. 83.7 ± 57.1 vs. 168.5 ± 60.8, respectively; p < 0.001). The 5 mg prasugrel group had the highest proportion of patients with OPR values within the therapeutic window, followed by the 10 mg prasugrel and ticagrelor groups (90.0% vs. 46.2% vs. 12.5%, respectively; p < 0.001 for East Asian criteria; 60.0% vs. 43.6% vs. 12.5%, respectively; p < 0.001 for Caucasian criteria).

CONCLUSIONS

Short-term administration of 5 mg prasugrel facilitated maintenance within the therapeutic window of OPR compared with the 10 mg prasugrel and ticagrelor groups. Thus, 5 mg prasugrel daily may be the optimal antiplatelet regimen for stabilized East Asian ACS patients.

Increased platelet inhibition after switching from maintenance clopidogrel to prasugrel in Japanese patients with stable coronary artery disease

BACKGROUND

The pharmacodynamic effects of changing from standard-dose clopidogrel to low-dose (3.75 mg) prasugrel in Japanese patients are largely unknown.

METHODS AND RESULTS

A total of 53 consecutive Japanese patients with stable coronary artery disease (CAD) who received aspirin and clopidogrel were enrolled. Clopidogrel was switched to 3.75 mg prasugrel. At day 14, prasugrel was switched to 75 mg clopidogrel. Platelet reactivity was measured using the VerifyNow assay at baseline, day 14, and day 28. VerifyNow P2Y12 reaction units (PRU) >208 was defined as high on-treatment platelet reactivity (HPR). The prevalence of HPR (18.9% vs. 41.5% vs. 44.2%, P<0.001) and the PRU level (154.3±54.2 vs. 196.2±55.5 vs. 194.6±55.8, P<0.001) were significantly lower on prasugrel maintenance therapy compared with the clopidogrel therapy before and after switching. The CYP2C19 genotypes that account for the 3 phenotypes (ie, extensive metabolizer, intermediate metabolizer, and poor metabolizer) had a significant impact on platelet reactivity with clopidogrel (174.9±54.0 vs. 193.1±56.5 vs. 240.6±25.4 PRU, P<0.001) but not prasugrel (147.0±51.9 vs. 147.5±58.3 vs. 184.4±38.3 PRU, P=0.15).

CONCLUSIONS

Low-dose prasugrel achieves stronger platelet inhibition than clopidogrel in Japanese patients with stable CAD.

Comparison of Aggregometry with Flow Cytometry for the Assessment of Agonists´-Induced Platelet Reactivity in Patients on Dual Antiplatelet Therapy

Data on the agreement between aggregometry and platelet activation by flow cytometry regarding the measurement of on-treatment platelet reactivity to arachidonic acid (AA) and adenosine diphosphate (ADP) are scarce. We therefore sought to compare three platelet aggregation tests with flow cytometry for the assessment of the response to antiplatelet therapy. Platelet aggregation in response to AA and ADP was determined by light transmission aggregometry (LTA), the VerifyNow assays, and multiple electrode aggregometry (MEA) in 316 patients receiving aspirin and clopidogrel therapy after angioplasty with stent implantation. AA- and ADP-induced P-selectin expression and activated glycoprotein (GP) IIb/IIIa were determined by flow cytometry. LTA, the VerifyNow P2Y₁₂ assay and MEA in response to ADP correlated significantly (all p<0.001), and the best correlation was observed between LTA and the VerifyNow P2Y₁₂ assay (r = 0.63). ADP-induced platelet reactivity by all aggregation tests correlated significantly with ADP-induced P-selectin expression and activated GPIIb/IIIa (all p<0.001). The best correlation was seen between the VerifyNow P2Y₁₂ assay and activated GPIIb/IIIa (r = 0.68). The platelet surface expressions of P-selectin and activated GPIIb/IIIa in response to ADP were significantly higher in patients with high on-treatment residual platelet reactivity (HRPR) to ADP by all test systems (all p<0.001). A rather poor correlation was observed between AA-induced platelet reactivity by LTA and the VerifyNow aspirin assay (r = 0.15, p = 0.007), while both methods did not correlate with MEA. AA-induced platelet reactivity by all aggregation tests correlated significantly, but rather poorly with AA-induced P-selectin expression (all p<0.05), while only AA-induced platelet reactivity by LTA correlated significantly with AA-induced activated GPIIb/IIIa (r = 0.21, p<0.001). The platelet surface expression of P-selectin in response to AA was significantly higher in patients with HRPR by LTA AA and MEA AA (both p<0.02). In contrast, P-selectin expression in response to AA was similar in patients without and with HRPR by the VerifyNow aspirin assay (p = 0.5), and platelet surface activated GPIIb/IIIa in response to AA did not differ significantly between patients without and with HRPR to AA by all test systems (all p>0.1). In conclusion, ADP-induced platelet reactivity by aggregometry translates partly into flow cytometry. In contrast, AA-induced platelet reactivity correlates poorly between different platelet aggregation tests, and between aggregometry and flow cytometry. Overall, both approaches capture different aspects of platelet function and are therefore not interchangeable in the assessment of agonists´-induced platelet reactivity. Clinical outcome data are needed to determine which test systems and settings are associated with different in vivo consequences.

An Assay of Measuring Platelet Reactivity Using Monoclonal Antibody against Activated Platelet Glycoprotein IIb/IIIa in Patients Taking Clopidogrel

Background and Objectives

Residual platelet reactivity in patients who are taking clopidogrel is commonly measured with VerifyNow assay, which is based on the principle of light transmission aggregometry. However, to evaluate the residual platelet reactivity, it would be more accurate if the reactivity of platelet glycoprotein (GP) IIb/IIIa is directly monitored. In this study, PAC1, a monoclonal antibody against activated platelet GP IIb/IIIa, was used to measure the residual platelet reactivity.

Subjects and Methods

Twenty seven patients with coronary artery disease taking clopidogrel were enrolled. Platelets in whole blood were stained with fluorescein isothiocyanate (FITC)-conjugated PAC1. Mean fluorescence intensity (MFI) and % positive platelets (PP) were measured with flow cytometry, and the binding index (BI; MFI × %PP/100) was calculated. P2Y12 reaction unit (PRU) and % inhibition of VerifyNow assay were also measured in the usual manner.

Results

PRU of VerifyNow assay correlated significantly with MFI, %PP, and BI at 10 µM (r=0.59, 0.73, and 0.60, respectively, all p<0.005) and 20 µM of adenosine diphosphate (ADP; r=0.61, 0.75, and 0.63, respectively, all p<0.005). The % inhibition also correlated significantly with MFI, %PP, and BI at 10 µM (r=-0.60, -0.69, and -0.59, respectively, all p<0.005) and 20 µM of ADP (r=-0.63, -0.71, and -0.62, respectively, all p<0.005).

Conclusion

Direct measurements of the reactivity of platelet GP IIb/IIIa were feasible using PAC1 and flow cytometry in patients taking clopidogrel. Further clinical studies are required to determine the cut-off values which would define high residual platelet reactivity in patients on this treatment protocol.

Point-of-care platelet function testing predicts bleeding in patients exposed to clopidogrel undergoing coronary artery bypass grafting: Verify pre-op TIMI 45--a pilot study

BACKGROUND

Guidelines recommend delaying coronary artery bypass grafting (CABG) for 5 days after discontinuing clopidogrel. However, platelet function may recover quicker in certain individuals.

HYPOTHESIS

We hypothesized that perioperative measurement of platelet function with a point-of-care P2Y12 inhibitor assay could predict bleeding during CABG in patients exposed to clopidogrel.

METHODS

Verify Pre-Op TIMI 45 was a prospective pilot study of 39 patients on clopidogrel who subsequently underwent CABG. Preoperative on-treatment platelet reactivity was assessed with VerifyNow P2Y12 Reaction Units (PRU), with higher PRU indicating more reactive platelets. Outcomes were stratified by PRU quartiles, as well as prespecified cutpoints for the lowest quartile (PRU 173), a cutpoint for major bleeding determined by the Youden index using receiver operator curve analysis (PRU 207), and clopidogrel resistance (PRU 230).

RESULTS

Patients in higher PRU quartiles experienced smaller decreases in hemoglobin and hematocrit (P < 0.05 for all comparisons), less major bleeding (P = 0.021), and less major or minor bleeding (P = 0.003). Patients above the PRU 207 and 230 cutpoints had less chest-tube output (P = 0.041 and P = 0.012, respectively), less major bleeding (P = 0.005 and P = 0.036, respectively), and less major or minor bleeding (P = 0.013 and P < 0.001, respectively). By receiver operator curve analysis, preoperative PRU ≤ 207 discriminated between patients with and without major bleeding during surgery (area under the curve: 0.76, 95% confidence interval: 0.59-0.94, P = 0.018).

CONCLUSIONS

In this pilot study, we found that point-of-care platelet function assessment could predict bleeding in patients recently exposed to clopidogrel undergoing CABG.