Platelet Function Analyzer PFA-100 Research Articles

Correlation between PlateletWorks® and PFA-100® for Measuring Platelet Function before Urgent Surgery in Patients with Chronic Antiplatelet Therapy.

Hemostasis is crucial for reducing bleeding during surgical procedures. The points-of-care based on the platelet function test could be useful to minimize the complications related to chronic antiplatelet therapy during surgery. The present study is aimed at comparing two point-of-care platelet function devices—Platelet Function Analyzer PFA-100® (Siemens Canada, Mississauga, ON, Canada) and Plateletworks®(Helena Laboratories, Beaumont, TX, USA). Our objective is to evaluate if they provide comparable and useful information to manage anti-aggregate patients before surgery. We included patients with a femoral fracture receiving chronic antiplatelet therapy and a median age of 89 years (range from 70 to 98). A platelet function evaluation was performed on all patients before surgery using both devices—Plateletworks® and PFA-100®. The correlation between Plateletworks® and PFA-100® was performed using Cohen’s Kappa coefficient. Twenty consecutive patients participated in the trial; 16 patients were under treatment with 75 mg/day of clopidogrel, three with >300 mg/day of acetylsalicylic acid (ASA), and only one was in treatment with both antiplatelet agents. Cohen’s Kappa coefficient was 0.327 comparing PFA-100®-ADP (adenosine diphosphate) and Plateletworks® and, 0.200 comparing PFA-100®-EPI (epinephrine) and Plateletworks®. In conclusion, we found a weak concordance comparing PFA-100® and Plateletworks®. This could partially be due to the advanced age of the included patients. However, given the limited sample size, more studies are necessary to confirm these results.

Effects of electronic cigarette on platelet and vascular function after one month of use

Abstract Background and aims Smoking is a major factor that contributes to the development of cardiovascular disease. Smoking cessation delays progress of coronary artery disease. Electronic cigarette is proposed as a bridge to smoking cessation. We examined its effects on platelet function after 1 month of use compared to tobacco smoking. Patients and methods 40 current smokers (mean age 48 years±5) without cardiovascular disease were randomized to smoke either a conventional cigarette (conv-cig) or an electronic cigarette (e-cig) (electronic cigarette fluid with nicotine concentration of 12 mg/dL) for one month. All subjects smoked an electronic cigarette with nicotine concentration 12 mg/dL for one month. Measurements were performed at baseline and after one month of smoking the conventional or electronic cigarette. We measured a) perfused boundary region (PBR) of the sublingual arterial micro vessels (range 5–25 micrometers), a marker inversely related with glycocalyx thickness, b) pulse wave velocity (PWV), central systolic blood pressure (cSBP) and augmentation index (AIx), c) platelet function by two different methods, namely the novel Platelet Function Analyzer PFA-100 and the traditional Light Transmission Aggregometry (LTA) d) the exhaled CO level (parts per million-ppm) as a smoking status marker; and e) the plasma malondialdehyde (MDA) levels, as an oxidative stress burden index. Results After 1 month of electronic smoking, we did not observe any significant change in platelet function and arterial stiffness (p>0.05 for all markers) with the exception of a reduction of MDA (1.22±0.1 vs 1.09±0.1 μmol/L, p=0.03) and exhaled CO; 14.9±0.7 vs 5.9±0.7 ppm, p<0.001. Conversely, after continuation of conventional cigarette smoking for a month, platelet function was further impaired as assessed by PFA [125,5±31,1 vs 152,35±51,4 U, p=0.047) and by LTA (epinephrine as stimulator) [59,8%±16,1 vs 35,6%±19.1, p<0.001] and markers of arterial stiffness were deteriorated, as assessed by PWV (9,5±2,8 vs 10,3±2,9, p=0,028) and by Aixc (8,36±35,9 vs 30,4±21,6, p=0,004). Conclusions Electronic Cigarette smoking has a neutral effect on platelet function and arterial stiffness markers compared to conventional tobacco smoking which further deteriorates platelet and vascular function during one moth of use. Funding Acknowledgement Type of funding source: None

Effects of electronic cigarette on platelet and vascular function after four months of use

We examined the effects of electronic cigarette on platelet and vascular function after 4 months of use compared to tobacco smoking. Forty smokers without cardiovascular disease were randomized to smoke either conventional cigarettes or an electronic cigarette (nicotine concentration of 12 mg/ml). At baseline and after four months, we measured a) platelet function by Platelet Function Analyzer PFA-100 and Light Transmission Aggregometry, b) pulse wave velocity, c) plasma malondialdehyde levels as oxidative stress index and d) the exhaled CO level. After 4 months, continuation of conventional cigarette smoking further impaired platelet function compared to vaping as assessed by PFA (mean increase 27.1 vs 11.6 s, p for interaction = 0.048) and by LTA (decline 24.1 vs 9.4%, p for interaction = 0.045). Conversely, compared to smoking, vaping resulted in greater reduction of exhaled CO (6.9 ppm vs 2.6, p for interaction < 0.001), improvement of PWV (decrease of 0.8 m/s vs increase of 0.8 m/s, p for interaction = 0.020) and reduction of MDA (reduction 0.13 vs increase 0.19 nmol/L, p for interaction = 0.035). Switching to electronic cigarette for 4 months has a neutral effect on platelet function while it reduces arterial stiffness and oxidative stress compared to tobacco smoking.

Corrigendum to “Patients With Severe Aortic Valve Stenosis and Impaired Platelet Function Benefit From Preoperative Desmopressin Infusion” [Ann Thorac Surg 91 (2011) 1420-1426

The senior author, Dr Bernd Jilma, apologizes for having overlooked the contribution of Martin Dworschak, MD, to aspects of developing relevant study documents and conducting the trial, and thus for not having included him among the co-authors in the originally published article. The correct and final version with updated author list and respective affiliations follows. Patients With Severe Aortic Valve Stenosis and Impaired Platelet Function Benefit From Preoperative Desmopressin InfusionThe Annals of Thoracic SurgeryVol. 91Issue 5PreviewPatients with severe aortic valve stenosis have a markedly reduced platelet function as measured by a prolonged collagen adenosine diphosphate closure time (CADP-CT) determined by the platelet function analyzer PFA-100. We hypothesized that such patients may benefit from desmopressin when they present with prolonged CADP-CT due to the specific action of desmopressin on von Willebrand factor (VWF) and CADP-CT. Full-Text PDF Corrigendum to “Patients With Severe Aortic Valve Stenosis and Impaired Platelet Function Benefit From Preoperative Desmopressin Infusion” [Ann Thorac Surg 91 (2011) 1420-1426]The Annals of Thoracic SurgeryVol. 109Issue 3PreviewPatients with severe aortic valve stenosis have a markedly reduced platelet function as measured by a prolonged collagen adenosine diphosphate closure time (CADP-CT) determined by the platelet function analyzer PFA-100. We hypothesized that such patients may benefit from desmopressin when they present with prolonged CADP-CT due to the specific action of desmopressin on von Willebrand factor (VWF) and CADP-CT. Full-Text PDF

External Quality Assurance of Platelet Function Assays: Results of the College of American Pathologists Proficiency Testing Program.

The College of American Pathologists (CAP) developed proficiency testing for platelet function assays by using blood collected by the participant added to challenge tubes containing either saline (normal) or tirofiban (abnormal). To analyze platelet function proficiency testing for Platelet Function Analyzer PFA-100, platelet aggregation, PlateletWorks, and PlateletMapping. Proficiency testing data from 2012-2016 were analyzed. For PFA-100, a total of 1200 laboratories participated; the coefficient variation (CV) of cartridge closure times was 22% (saline); 44,952 of 45,616 survey responses (99%) provided an interpretation, and 42,934 of 44,952 (96%) were correct. For optical platelet aggregation, 190 laboratories participated; the CV was 17% (saline), 7444 of 7813 survey responses (95%) provided an interpretation, and 7015 of 7444 (94%) were correct. For PlateletWorks, 60 laboratories participated; the CV was 3% to 11% (saline); 2412 of 2454 survey responses (98%) provided an interpretation, and 1207 of 1276 (95%) were correct for adenosine diphosphate (ADP) and 936 of 1136 (82%) for collagen. For PlateletMapping, 200 laboratories participated. For ADP, 1128 of 2697 survey responses (42%) provided an interpretation, but only 927 of 1128 (82%) were correct. For arachidonic acid, 1139 of 2604 survey responses (44%) provided an interpretation and 964 of 1139 (85%) were correct. CAP is the first to provide proficiency testing for platelet aggregation, PlateletWorks, and PlateletMapping. Platelet aggregation, PFA-100, and PlateletWorks using ADP as an agonist performed well with more than 90% of laboratories providing an interpretation and a similar number providing correct results. PlateletWorks using collagen and PlateletMapping showed worse interpretive accuracy than the other methods.

136. A cohort study utilising a biochemical assessment of aspirin compliance vs resistance in high-risk pregnant women

Introduction The benefit of low-dose aspirin in preventing preeclampsia is well established. Despite prescription of aspirin, 30–40% of women still develop preeclampsia. Aspirin-resistance or non-compliance and their effects on clinical outcomes has not been examined in high-risk pregnant women and could explain the observed lack of clinical response. Objective We aimed to examine for aspirin non-compliance and resistance through biochemical analysis and compare against self-reported compliance. We also examined clinical outcomes against biochemical compliance. Methods Sequential recruitment of women in a high-risk pregnancy clinic was undertaken in a metropolitan hospital. Demographic and clinical data, together with a 3-point questionnaire and plasma collection was undertaken at 8 time-points (12, 16, 20, 24, 28, 32, 36, 38 weeks gestation). Blood samples were assessed for PFA100 (platelet function analyser) and plasma salicylate acid (SA) detection through liquid-chromatography, mass-spectrometry (LCMS). Non-compliance was defined as normal PFA100 and non-detectable plasma SA in Results Seventy-one women completed the protocol. Biochemical non-compliance was identified in 22(31%) women and only 45(63%) of women’s self-reported compliance corresponded biochemically (kappa coefficient = 0.65). No women were aspirin resistant. The clinical outcomes of compliance and non-compliance with aspirin were significantly different. Compliant women had a lower incidence of late-onset preeclampsia (4.1% vs 59%, p 90% compliance. Discussion Aspirin non-compliance is more likely than aspirin resistance and self-reporting is not a reliable measure. Women who are non-compliant have worse clinical outcomes.

Effects of immunosuppressive agents on the hemostatic system in normal dogs.

BackgroundIn dogs, the effects of immunosuppressive medications on hemostasis are not well known.Hypothesis/ObjectivesThe objective was to determine the effects of immunosuppressive medications on primary and secondary hemostasis. Our hypothesis was that cyclosporine and prednisone would increase markers of hypercoagulability and thromboxane synthesis, while azathioprine, mycophenolate mofetil, and leflunomide would have minimal effects on hemostasis.AnimalsEight healthy dogs.MethodsA randomized, cross‐over study used aggregometry, the PFA‐100 platelet function analyzer, viscoelastometry, platelet count, and prothrombin and activated partial thromboplastin times to evaluate hemostasis during the administration of prednisone, azathioprine, cyclosporine, mycophenolate mofetil, and leflunomide for 1 week each at standard oral doses. Urine 11‐dehydro‐thromboxane‐B2 (11‐dTXB2) and 6‐keto‐prostaglandin‐F1α (6‐keto‐PGF1α) concentrations, normalized to urine creatinine concentration, were measured.ResultsThe aggregometry amplitude decreased from 51 ± 21 to 27 ± 14 (P = .002) during leflunomide treatment (ADP activation), but there were no differences in amplitude (P = .240) for any medications when platelets were activated with collagen. For all medications, there were no significant differences in viscoelastometry indices (ACT, P = .666; ClotRate, P = .340; and platelet function, P = .411) and platelet count (P = .552). Compared with pretreatment values, urinary 11‐dTXB2‐to‐creatinine ratio increased (P = .001) after drug administration (from 3.7 ± 0.6 to 5.6 ± 1.1). Cyclosporine was associated with an increase (P < .001) in the 6‐keto‐PGF1α‐to‐creatinine ratio (from 10.3 ± 4.6 to 22.1 ± 5.3).Conclusions and Clinical ImportanceMost immunosuppressive drugs do not enhance platelet function or coagulation in healthy dogs, suggesting that these medications might not predispose hypercoagulable dogs to thromboembolism. The results of our study need to be correlated with the clinical outcomes of hypercoagulable dogs.

Influence of a low dosage of clopidogrel on platelet function in cats as measured by the platelet function analyser PFA-100 and the multiplate analyser

The antiplatelet drug clopidogrel is widely used for prophylaxis of arterial thromboses in cats in a standard dosage of 18.75mg per cat once daily. The aim of the study was to verify if a reduced daily dose of 10mg clopidogrel per cat has a similar antiplatelet effect as the standard dosage. Platelet function was measured with the platelet function analyser PFA-100® and a novel impedance aggregometer.Suitability of the platelet function analyser was tested in citrated blood samples of 59 healthy cats and reference ranges were established. In addition, agonist concentrations for impedance aggregometry were optimised. In the main experiment two groups of 6 healthy cats received clopidogrel either in a dosage of 10 or 18.75mg per cat over a period of seven days. Analyses were performed on days 1, 2, 3, 5, and 7.In comparison to baseline both clopidogrel dosages showed an inhibitory effect on results of the platelet function analyser and velocity of ADP-induced platelet aggregation. Values at all times were different from baseline, with the exception of day 1 in cats receiving 10mg clopidogrel where the closure time of the platelet function analysis and part of ADP-induced aggregation did not show a significant difference. Significant differences were not found between the two doses.In conclusion, our study indicates that 10mg clopidogrel per day may be as effective as 18.75mg although the latter may be advantageous as an initial loading dosage to achieve effective levels more rapidly.

Evaluation of platelet function using PFA-100® in patients treated with Acetylsalicylic acid and qualified for Trauma and Orthopedic surgery procedures

The phenomenon of high on-acetylsalicylic acid (ASA) treatment platelet (PLT) reactivity – HATPR – and its clinical implications have not been fully understood. Little data is available on assessing PLT activity based on the severity of intra- and postoperative bleeding in a population of orthopedic patients with normal closure time (CT) measured by a PLT function analyzer PFA-100®, despite being given long-term ASA therapy. The aim is to assess PLT function using PFA-100® in patients with ASA therapy and qualified for trauma and orthopedic surgery procedures. The retrospective analysis covered 384 patients whose PLT reactivity was assessed using PFA-100®. Out of those, 198 had been taking ASA with a 75 mg dose until hospital admission. In addition, a group of 70 patients with a proximal femoral fracture surgically treated using the dynamic hip screw (DHS) was selected, in whom severity of bleeding was assessed by HIP ASA (+). The reference group comprised 52 patients (without ASA therapy) who were operated on due to the same indications. Normal CT was found in 37% of ASA-receiving patients. Patients with normal CT, despite ASA therapy, exhibited significantly more intense bleeding after DHS surgery. A similar number of patients required red blood cells (RBCs) transfusion in HIP ASA (+) and HIP ASA (-). Increased risk of complications in HIP ASA (+) group was not found.Conclusions: Normal PLT function assessed using PFA-100® is a common phenomenon in patients with long-term ASA treatment and who are qualified for trauma and orthopedic surgery procedures. In many cases, it seems that inadequate response to ASA is only a laboratory phenomenon.

The In vitro Effects on Thrombocyte Functions and Coagulation of Different Prime Solutions Used in Cardiopulmonary by Pass

Purpose: To investigate the in vitro effect of human albumin (HA) and fresh frozen plasma (FFP) added to prime solution on platelet functions and coagulation in patients undergoing cardiopulmonary bypass (CPB) surgery. Methods: Sixty consecutive patients receiving elective cardiopulmonary bypass with open heart surgery were enrolled in the study. Patients were divided into three equal groups. Group 1: with 2 units of fresh frozen plasma added to prime solution. Group 2: With 100 cc 25% human albumins added to prime solution. Group 3: (control group) with no FFP or HA added to prime solution. PFA100 platelet function analyzer and platelet aggregation tests were investigated pre-induction, during and after CPB and on the 1 st day postoperatively.

Role of sodium tungstate as a potential antiplatelet agent

PurposePlatelet inhibition is a key strategy in the management of atherothrombosis. However, the large variability in response to current strategies leads to the search for alternative inhibitors. The antiplatelet effect of the inorganic salt sodium tungstate (Na2O4W), a protein tyrosine phosphatase 1B (PTP1B) inhibitor, has been investigated in this study.MethodsWild-type (WT) and PTP1B knockout (PTP1B−/−) mice were treated for 1 week with Na2O4W to study platelet function with the platelet function analyzer PFA-100, a cone-and-plate analyzer, a flat perfusion chamber, and thrombus formation in vivo. Human blood aliquots were incubated with Na2O4W for 1 hour to measure platelet function using the PFA-100 and the annular perfusion chamber. Aggregometry and thromboelastometry were also performed.ResultsIn WT mice, Na2O4W treatment prolonged closure times in the PFA-100 and decreased the surface covered (%SC) by platelets on collagen. Thrombi formed in a thrombosis mice model were smaller in animals treated with Na2O4W (4.6±0.7 mg vs 8.9±0.7 mg; P<0.001). Results with Na2O4W were similar to those in untreated PTP1B−/− mice (5.0±0.3 mg). Treatment of the PTP1B−/− mice with Na2O4W modified only slightly this response. In human blood, a dose-dependent effect was observed. At 200 μM, closure times in the PFA-100 were prolonged. On denuded vessels, %SC and thrombi formation (%T) decreased with Na2O4W. Neither the aggregating response nor the viscoelastic clot properties were affected.ConclusionNa2O4W decreases consistently the hemostatic capacity of platelets, inhibiting their adhesive and cohesive properties under flow conditions in mice and in human blood, resulting in smaller thrombi. Although Na2O4W may be acting on platelet PTP1B, other potential targets should not be disregarded.

Can the Previous Therapeutic Control of the Main Risk Factors of Cerebrovascular Disease Influence the Acetylsalicylic Acid–Nonresponsive Status in Acute Ischemic Stroke Patients? Results from a Portuguese Prospective Cohort Study

Acute ischemic stroke (AIS) is a complex disease, and the therapeutic control of its risk factors may influence the efficacy of acetylsalicylic acid (ASA) and the occurrence of new vascular events. The aim of this study was to investigate the potential invivo properties of a previous treatment controlling the main risk factors of cerebrovascular disease, in the ASA-nonresponsive status in a Portuguese population. We conducted a prospective cohort study with the recruitment of 90 patients diagnosed with AIS and a follow-up protocol was set up with recurrent stroke as the main clinical end point under evaluation. At admission, PFA-100 (platelet function analyzer) test was evaluated in blood samples from AIS patients treated with 100mg/day of ASA and previously treated with antihypertensive, antidiabetic, or statin drugs. We observed that 30% of patients were ASA nonresponders. Multivariate regression analysis indicated that the previous treatment with antihypertensive drugs emerged with a significant risk reduction of anASA-nonresponsive status (odds ratio, .119; 95% confidence interval, .026-.538; P=.006). Furthermore, our results indicated an influence of ASA-nonresponsive status in a decreased period to a new recurrent stroke event in the time frame of24months (P=.005, log-rank test). ASA is an important part oftreatment of AIS, and its efficacy may be improved in previous high-riskcerebrovascular patients, particularly with antihypertensive therapeutic control.

Pro-thrombotic effect of exercise in a polluted environment: a P-selectin- and CD63-related platelet activation effect.

Exposure to diesel exhaust is an important cardiovascular risk factor and may promote atherothrombotic events. Some data suggest that polluted air exposure could affect haemostasis through platelet activation. The aim of the study was to investigate the effects of acute exposure to diesel exhaust on platelet activation and platelet function. We tested the hypothesis in a randomised, crossover study in 25 healthy men exposed to ambient and polluted air; 11 of the subjects also performed exercise during exposure sessions. Platelet activation was evaluated by surface expression of CD62P (P-selectin) and CD63 (dense granule glycoprotein) using flow cytometry of labelled platelets. Platelet function was measured using the PFA-100 platelet function analyser and by Multiplate whole blood impedance platelet aggregometry. Acute diesel exhaust exposure had no effect on platelet activation at rest, but exercise in polluted air increased the collagen-induced expression of CD62P and CD63 (both p< 0.05). The increase in the expression of CD62P and CD63 was related to the total amount of PM2.5 inhaled during the exercise sessions (r=+0.58 and +0.60, respectively, both p< 0.05). Platelet aggregation was not impaired after polluted air exposure at rest or during exercise. In conclusion, in healthy subjects, diesel exhaust exposure induces platelet activation as illustrated by a dose-response increase in the release of CD62P and CD63. This platelet priming effect could be a contributor to the triggering of atherothrombotic events related to air pollution exposure.

Von Willebrand Factor As a Biological Sensor of Blood Flow in Percutaneous Cardiac Procedures

▪Background:Acquired deficiency of von Willebrand Factor (VWF) characterized by a quantitative loss of high molecular weight (HMW) multimers of VWF is associated with cardiovascular disorders such as aortic stenosis. It has been shown that HMW-multimers defect is usually corrected after surgical aortic valve replacement. However, the initial time course of loss/recovery of VWF HMW-multimers following acute changes in blood flow in-vivo has not yet been studied. We hypothesized that recovery of HMW-multimers could occur within minutes following correction of the underlying “high shear” condition and as such could be used to monitor acute changes in flow induced by cardiac interventions. We further investigated the potential underlying mechanisms.Methods:We investigated the time course of HMW-multimers loss/recovery in an animal model of instantaneous and reversible aortic stenosis (AS) specifically developed for that purpose. This model allowed the evaluation, in the same rabbit, of the dynamic time course of loss and recovery of HMW-multimers. We further investigated the time course of HMW-multimers loss/recovery and its related bedside whole blood assessment (PFA-100 analyzer) in 28 patients included in the WITAVI (Willebrand-TAVI) registry and undergoing 1) implantation of an axial-continuous-flow-LVAD (HeartMate-IIÒ, n=8) and 2) transcatheter aortic valve procedures, either BAV (n=10) or TAVI (n=10). VWF antigen (VWF:Ag) and VWF propeptide (VWFpp) levels were measured by ELISA. VWF multimeric analysis was performed as previously described in patients and newly developed for rabbits. PFA-CADP was assessed by platelet-function analyzer PFA-100® using ADP cartridges.Results:In the rabbit model, induction of aortic stenosis was associated with a HMW-multimers defect (normalized ratio = 0.74±0.07; p<0.01 versus no stenosis). Partial recovery of HMW-multimers (0.89±0.12 versus AS baseline; p<0.01) occurred within 5 minutes of stenosis reversion. Thirty minutes after reversion, a complete recovery of HMW-multimers was observed (0.98±0.10). In patients with AS (n=18) a VWF HMW-multimers defect was observed at baseline (0.50±0.18). Among patients with AS, those treated with TAVI experienced an acute decrease in shear stress (4.47±0.41 m.s-1 to 1.81±0.43 m.s-1, p<0.0001, n=10) after treatment while those undergoing BAV alone experienced a modest improvement in shear stress conditions (4.47±0.25m.s-1 to 3.88±0.65m.s-1; p=0.03, n=8). In patients undergoing TAVI (n=10), similar to what was observed in the rabbit model, recovery of HMW-multimers defect was observed within minutes of valve implantation (p<0.001, Table1). By contrast, in patients undergoing BAV (n=8) no recovery of HMW-multimers defect was observed (p=0.21,Table1). A potential role of the vascular endothelium in the HMW-multimers recovery was also evaluated by measuring the VWFpp levels during TAVI and BAV procedures. In TAVI procedures, VWFppsignificantly increased 5 minutes after valve implantation, and further after 30 and 180 minutes when compared to baseline. In BAV procedures, VWFpp did not increase significantly overtime.The time course of PFA-CADP time mimicked the recovery of HMW-multimers defect both in TAVI in patients, in whom a rapid correction of PFA-CADP was observed (p<0.001, Table1), and BAV patients, in whom no correction was observed (p=0.69;Table1). Results are expressed as mean±SD, p values are for overall time course comparison (repeated Anova).Abstract 474. TableTranscatheter aortic valve implantion(TAVI, n=10)Balloon Aortic Valvuloplasty(BAV, n=8)T0T5T30T180pT0T5T30T180pHMW-multimers(ratio vs NP)0.47(±0.14)0.87(±0.24)0.93(±0.17)0.99(±0.16)<0.0010.52(±0.21)0.58(±0.20)0.66(±0.25)0.63(±0.10)nsVWFpp(UI/dL)168(±71)195(±63)215(±100)429(±195)p<0.01256(±121)234(±106)290(±96)275(±136)nsPFA-CT ADP(sec)252(±68)193(±51)116(±40)94(±26)<0.001201(±46)212(±61)204(±71)219(±76)nsConclusion:These results demonstrate that variations in the multimeric pattern of VWF are highly dynamic, occurring within minutes of changes in shear stress status. They further demonstrate that VWF multimeric pattern changes could be used in clinical practice as a tool to monitor the quality of the result of percutaneous aortic valve procedures procedures using a bedside analyzer. DisclosuresNo relevant conflicts of interest to declare.

Assessment Methods for Aspirin-mediated Platelet Antiaggregation in Type 2 Diabetic Patients

Impaired response to antiplatelet therapy in diabetic patients results in a higher incidence of drug-eluting stent thrombosis. This study determined the prevalence of high on-aspirin (AS) platelet reactivity in type 2 diabetic patients treated with percutaneous coronary intervention (PCI) using the VerifyNow Aspirin Assay (VN) and platelet function analyzer PFA-100 (PFA-100) and analyzed the correlation between both methods. Type 2 diabetic patients (100) with non-ST-elevation acute coronary syndrome who underwent PCI and Xience V drug-eluting stent implantation were included in this study. After PCI, platelet antiaggregation mediated by acetylsalicylic acid was assessed by VN and PFA-100. The degree of correlation and concordance was then determined. When assayed with VN, 7% of the patients were nonresponders to aspirin (aspirin reaction units >550), and when assayed with PFA-10, 41% were nonresponders (closure time <193 seconds). Of the patients, 4% were nonresponders to aspirin according to VN but were sensitive to aspirin according to PFA-100, and 38% were sensitive to aspirin according to VN and nonresponders according to PFA-100. Overall, 55% of the patients were aspirin-sensitive in both methods. The Spearman's coefficient between VN and PFA-100 results was r = 0.09 (P = 0.35). The kappa index value was 0.0062 (P = 0.91). There is no concordance or correlation between the VN and PFA-100 results. Therefore, the use of these analyses should be restricted to clinical research, which limits its application in clinical practice.

Laboratory Investigation of Platelet Function in Patients with Thalassaemia

The aim of this study was to investigate platelet function in patients with thalassaemia and to detect any relation to chelation treatment (deferasirox or deferiprone/deferiprone plus desferioxamine). Thirty-three transfusion-dependent patients with thalassaemia were included. The investigation consisted of aggregation testing of platelet-rich plasma by light transmission aggregometry (LTA) with the use of 5 agonists as well as the global test of haemostasis by means of the PFA-100 platelet function analyser. In 66.67% of the patients, there was reduced LTA to at least one agonist and in 18.18% there was reduced LTA to two or more agonists. The PFA-100 test was prolonged in 60.6% of the cases. An abnormal LTA and a prolonged PFA-100 time were recorded in 33.3% of the patients and 27.4% had a normal aggregation and PFA-100 test. No correlation between chelation regimen and either LTA or PFA-100 test was found. The abnormal LTA can be explained either by the release of ADP from the haemolysed red blood cells, which leads to defective platelet aggregation, or by the presence of two platelet populations. An in vitro effect without an in vivo impact could be an alternative explanation. In patients with thalassaemia, the reduced LTA and the prolonged PFA-100 closure time could be an in vitro effect and has a close correlation to the bleeding phenotype of each patient.

Cocaine in high concentrations inhibits platelet aggregation in vitro

Complications of cocaine administration are acute vascular occlusions such as myocardial infarction and stroke. We have studied the influence of cocaine on platelet function in vitro. For that purpose, citrated blood from healthy volunteers was incubated with cocaine concentrations of 0 (control), 10, 100, 1000, 2500, and 10'000 μmol/l plasma. Platelet aggregation was measured in whole blood under high shear flow conditions with a platelet function analyzer PFA-100 using either epinephrine (EPI) or ADP as a platelet activator, as well as in non-flowing blood measuring the change of impedance after the addition of either collagen or ADP (Chronolog-700 Aggregometer). In addition, platelet aggregation was measured by the change in light transmission in platelet rich plasma containing the same cocaine concentrations (Chronolog-700). Platelet aggregation in flowing whole blood (PFA-100) was not affected by cocaine up to 1000 μmol/l, partially inhibited by 2500 μmol/l and completely inhibited by 10'000 μmol/l cocaine. In non-flowing blood, platelet aggregation was decreased already at cocaine concentrations of 1000 μmol/l with ADP and 2500 μmol/l with collagen as a platelet activator. In platelet-rich plasma, aggregation was partially inhibited by 1000 and 2500 μmol/l and completely inhibited by 10'000 μmol/l cocaine. We conclude that platelet aggregation is inhibited by cocaine in vitro. This occurs, however, at concentrations above those measurable in vivo. These observations make it very unlikely that a direct platelet activation plays a role in vascular events complicating cocaine consumption.

High On‐Aspirin Platelet Reactivity and Clinical Outcome in Patients With Stable Coronary Artery Disease: Results From ASCET (Aspirin Nonresponsiveness and Clopidogrel Endpoint Trial)

BackgroundPatients with stable coronary artery disease on single-antiplatelet therapy with aspirin are still at risk for atherothrombotic events, and high on-aspirin residual platelet reactivity (RPR) has been suggested as a risk factor.Methods and ResultsIn this randomized trial, the association between platelet function determined by the PFA100 platelet function analyzer system (Siemens Healthcare Diagnostics, Germany) and clinical outcome in 1001 patients, all on single-antiplatelet therapy with aspirin (160 mg/d) was studied. Patients were randomized to continue with aspirin 160 mg/d or change to clopidogrel 75 mg/d. A composite end point of death, myocardial infarction, ischemic stroke, and unstable angina was used. At 2-year follow-up, 106 primary end points were registered. The prevalence of high RPR was 25.9%. High on-aspirin RPR did not significantly influence the primary end point in the aspirin group (13.3% versus 9.9%, P=0.31). However, in post hoc analysis, patients with von Willebrand factor levels or platelet count below median values and high on-aspirin RPR had a statistically significant higher end point rate than that of patients with low RPR (20% versus 7.5%, P=0.014, and 18.2% versus 10.8%, P=0.039, respectively). The composite end point rate in patients with high on-aspirin RPR treated with clopidogrel was not different from that of patients treated with aspirin (7.6% versus 13.3%, P=0.16).ConclusionsIn stable, aspirin-treated patients with coronary artery disease, high on-aspirin RPR did not relate to clinical outcome and did not identify a group responsive to clopidogrel. Post hoc subgroup analysis raised the possibility that high on-aspirin RPR might be predictive in patients with low von Willebrand factor or platelet count, but these findings will require confirmation in future studies.Clinical Trial RegistrationURL: http://www.clinicaltrials.gov Unique identifier: NCT00222261. (J Am Heart Assoc. 2012;1:e000703 doi: 10.1161/JAHA.112.000703.)

Antiplatelet and antithrombotic effect of F 16618, a new thrombin proteinase‐activated receptor‐1 (PAR1) antagonist

New antithrombotic agents with the potential to prevent atherothrombotic complications are being developed to target receptors on platelets and other cells involved in plaque growth. The aim of this study was to investigate the antiplatelet effects of F 16618, a new non-peptidic PAR1 (thrombin receptor) antagonist. We investigated the inhibitory effect of F 16618 on human platelet aggregation ex vivo, in whole blood and washed platelets, by using a multiple-electrode platelet aggregometer based on impedance and an optical aggregometer, respectively. Its effects on whole-blood haemostasis (clot parameters) were analysed with the ROTEM thromboelastometry device and the platelet function analyser PFA-100. A guinea-pig model of arterial thrombosis was used to investigate its effects on thrombus formation in vivo. F 16618 inhibited PAR1 agonist peptide (SFLLR-peptide)-induced washed platelet aggregation ex vivo. This effect was concentration-dependent and exhibited a competitive inhibition profile. Washed platelet aggregation, as well as P-selectin expression induced by thrombin, were significantly inhibited by 10 µM F 16618. In whole-blood experiments, 20 µM F 16618 inhibited SFLLR-induced platelet aggregation by 49%. In contrast, it had no effect on whole-blood haemostasis. In the guinea-pig model of carotid thrombosis, 0.32 mg·kg(-1) F 16618 doubled the occlusion time. F 16618 was shown to have strong antithrombotic activity in vivo and moderate antiplatelet effects ex vivo. As these effects were not associated with major effects on physiological haemostasis, this molecule is a good antiplatelet drug candidate for use either alone or in combination with current treatments.

Inhibition of Von Willebrand Factor (VWF) by ARC1779 Normalizes Von Willebrand Factor/FVIII Levels and Corrects Thrombocytopenia in VWD Type 2b Patients,

Abstract 3377 Introduction:Infusion of the anti-VWF aptamer ARC1779 effectively elevated platelet counts in some patients with congenital thrombocytopenic purpura, and blunted the platelet drop induced by desmopressin in patients with type 2b von Willebrand disease (VWD). Thus, we hypothesized that ARC1779 may increase VWF levels and correct thrombocytopenia by blocking the hyperactive VWF A1 domain in type 2b VWD. Methods:Thrombocytopenic patients suffering from type 2b VWD received intravenous infusions of ARC1779 (4 mcg/kg/min) for 72 hours in a prospective clinical trial. Patients were monitored using previsouly published assays (Thromb Haemost. 2010;104:563–70). Data are provided as median and the range and were tested for significance by repeated measures analysis of variance. Results:All patients had moderate thrombocytopenia, low levels of VWF:RCo, VWF:CBA, FVIII:C, and collagen/ADP closure times >300s (platelet function analyzer PFA-100). ARC1779 was well tolerated and safe even in a patient who suffered from active chronic gastrointestinal bleeding due to angiodysplasias before start of infusion. Plasma concentrations of ARC1779 increased to 76 mcg/mL (59–130) which suppressed free VWF A1 domains in the REAADS assay to a minimum of <3 to 5%. Consistent with the estimated in vivo half-life of VWF, VWF/FVIII levels increased as early as 12h after start of infusion, peaked near the end of infusion, and returned to baseline at follow-up. That was best exemplified by VWF:RCo levels which increased from 32% (26–45%) 10-fold to 367% (215–418%) 8h after end of infusion, and decreased again to 33% (20–40%) during follow up. Similarly VWF:CBA levels increased 16-fold (8 to 69-fold), VWF: Ag levels 5.2 fold (3 to 27-fold), and FVIII levels 4.3 fold (3 to 6-fold). Most importantly inhibition of hyperactive VWF rapidly increased platelet counts from 40/nL (38–58/nL) to a maximum of 146/nL (107–248/nL). This was observed although patients were suffering from chronic liver disease due to hepatitis C infection or associated immune thrombocytopenia, which could have blunted the platelet response. All changes were statistically significant (p<0.007). Conclusion:This clinical trial underscores the therapeutic efficacy of the VWF A1 antagonist aptamer ARC1779. ARC1779 significantly increases VWF/FVIII levels and most importantly improves or even corrects thrombocytopenia in VWD type 2b patients. This could facilitate (i) the collection of autologous platelets for platelet transfusions pre-operatively or (ii) interferon therapy in patients whose HCV therapy could not be initiated or had to be stopped due to thrombocytopenia. As angiodysplasias may be caused by defective or deficient VWF (Blood 2011;117:1071–80), it may also be tempting to further investigate the potential of chronic anti-VWF aptamer therapy to treat angiodysplasia. Disclosures:Knoebl:Archemix Corp.: Consultancy. Pabinger:Archemix Corp.: Consultancy. Gilbert:Archemix Corp.: previous employment. Schaub:Archemix Corp.: Consultancy, previous employment. Jilma:Archemix Corp.: Consultancy, Research Funding.