Collagen Adenosine Diphosphate Closure Time Research Articles

The aptamer BT200 blocks von Willebrand factor and platelet function in blood of stroke patients

The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are blunted under high shear stress in the presence of increased levels of circulating von Willebrand factor (VWF). VWF is critically involved in thrombus formation at sites of stenotic extracranial/intracranial arteries. A third generation anti-VWF aptamer (BT200) has been generated which could be useful for secondary stroke prevention. To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke (LAA). Blood samples were obtained from 33 patients with acute stroke or transient ischemic attack to measure inhibition of VWF activity and VWF-dependent platelet function. Patients who received clopidogrel or dual antiplatelet therapy did not differ in VWF dependent platelet function tests from aspirin treated patients. Of 18 patients receiving clopidogrel with or without aspirin, only 3 had a prolonged collagen adenosine diphosphate closure time, and none of the patients had ristocetin induced aggregation in the target range. BT200 concentration-dependently reduced median VWF activity from 178 to < 3%, ristocetin induced platelet aggregation from 40U to < 10U and prolonged collagen adenosine diphosphate closure times from 93 s to > 300 s. Baseline VWF activity correlated (r = 0.86, p < 0.001) with concentrations needed to reduce VWF activity to < 20% of normal, indicating that BT200 acts in a target concentration-dependent manner. Together with a long half-life supporting once weekly administration, the safety and tolerability observed in an ongoing phase I trial, and the existence of a reversal agent, BT200 is an interesting drug candidate.

Variables that Influence Platelet Function Analyzer-100™ Closure Times in Healthy Algerian Adults.

Context:The Platelet Function Analyzer (PFA-100™) assesses primary hemostasis in vitro under high shear stress to simulate the conditions to which platelets are exposed at the site of an injured blood vessel wall.Aims:We investigated preanalytical variables in healthy Algerian adults, and we also assess the performance of the test.Subjects and Methods:Closure time (CT) was measured in 302 well-characterized healthy Algerian adults with the collagen/epinephrine (CEPI) and the collagen/adenosine diphosphate (CADP) cartridges.Results:Age and sex did not affect CT values. Blood group O was associated significantly with longer CEPI CT and CADP CT than non-O groups (P ≤ 0.0001 for both). CTs were shorter in samples collected in the morning vs the afternoon (P < 0.0001 for both). We found a strong positive correlation between CT CEPI and CT CADP with r = 0.72 and P < 0.001 and an inverse mean correlation between von Willebrand factor level and CT with r = −0.56, r = −0.45 for CT CEPI and CT CADP, respectively P < 0.001. Duplicate analysis of PFA-100™ CT revealed a mean difference of 3.6% ±19.1% for the CEPI cartridge and 1.5% ±10% for the CADP cartridge. The mean coefficient of variation was 7.4% for the CADP CT and 7.6% for the CEPI CT. No marked difference between test positions.Conclusions:The PFA-100™ showed good reproducibility. The variables influencing the test in healthy Algerian adults are similar to Western and Asian populations. Standardization of preanalytical and analytical conditions is essential for obtaining reliable PFA-100™ results.

Does Hemodialysis Need to be Initiated to Improve Platelet Function in CKD G5 Patients? A Pilot Prospective, Observational Cohort Study.

Introduction:We previously showed that patients with chronic kidney disease (CKD) Stage G4-5 have normal bleeding times. This made us question whether hemodialysis (HD) initiation was really necessary solely to improve platelet function.Methods: In this prospective observational study, two 5 ml citrated blood samples and one 2 ml EDTA blood sample were collected from incident HD patients fulfilling inclusion criteria prior to HD initiation (baseline sample) and after three sessions of short duration, low flow, counter-current HD. In each instance, one sample was used to perform Collagen adenosine diphosphate closure time (CADPCT) using the Platelet function analyzer (PFA 200, normal range 68-142 seconds) and the second for light transmission aggregometry (LTA) with ADP as agonist (normal ≥50%).Results: This study included 20 patients between October 2017 and February 2019. Overall, and in the subgroup with normal baseline CADPCT or LTA, there was no statistically significant improvement after HD. However, of the 30% of patients who had an abnormal baseline CADPCT, 50% attained a normal value after three HD sessions, and the overall reduction in CADPCT in this group was statistically significant (P = 0.02). Of those with a baseline normal CADPCT, 21% developed abnormal prolongation post HD.Conclusion: HD for the sole purpose of improving platelet function is only of benefit in the subgroup of patients with an abnormal CADPCT at baseline, with close to 50% normalizing their platelet function after three sessions of low flow, short duration, counter-current HD.

The development and characterization of a long acting anti‐thrombotic von Willebrand factor (VWF) aptamer

BackgroundThrombus formation involves coagulation proteins and platelets. The latter, referred to as platelet‐mediated thrombogenesis, is predominant in arterial circulation. Platelet thrombogenesis follows vascular injury when extracellular von Willebrand factor (VWF) binds via its A3 domain to exposed collagen, and the free VWF A1 domain binds to platelet glycoprotein Ib (GPIb). ObjectivesTo characterize the antiplatelet/antithrombotic activity of the pegylated VWF antagonist aptamer BT200 and identify the aptamer VWF binding site. MethodsBT100 is an optimized aptamer synthesized by solid‐phase chemistry and pegylated (BT200) by standard conjugation chemistry. The affinity of BT200 for purified human VWF was evaluated as was VWF inhibition in monkey and human plasma. Efficacy of BT200 was assessed in the monkey FeCl3 femoral artery thrombosis model. ResultsBT200 bound human VWF at an EC50 of 5.0 nmol/L and inhibited VWF A1 domain activity in monkey and human plasma with mean IC50 values of 183 and 70 nmol/L. BT200 administration to cynomolgus monkeys caused a time‐dependent and dose‐dependent effect on VWF A1 domain activity and inhibited platelet function as measured by collagen adenosine diphosphate closure time in the platelet function analyzer. BT200 demonstrated a bioavailability of ≥77% and exhibited a half‐life of >100 hours after subcutaneous injection. The treatment effectively prevented arterial occlusion in an FeCl3‐induced thrombosis model in monkeys. ConclusionsBT200 has shown promising inhibition of human VWF in vitro and prevented arterial occlusion in non‐human primates. These data including a long half‐life after subcutaneous injections provide a strong rationale for ongoing clinical development of BT200.

Evaluation of platelet count and platelet function analyzer – 100 testing for prediction of platelet transfusion following coronary bypass surgery

Platelet transfusions are commonly administered to treat bleeding in cardiac surgery. The aim of this study was to compare platelet (PLT) count and values of collagen adenosine diphosphate closure time (cADP-CT) measured by Platelet Function Analyzer (PFA) for prediction of PLT transfusion therapy following coronary bypass surgery. For this prospective observational study, 66 patients scheduled for coronary artery bypass grafting (CABG) who received early PLT transfusions (within 60 min after the operation) were enrolled. To assess changes in platelets, count and function, two time points were selected: 15 min before and 30 − 60 min after the end of PLT transfusion. The patients were divided into transfused and non-transfused with further PLT in the 48 h postoperatively. We used the receiver operating characteristics (ROC) curve to investigate whether the PLT count and cADP-CT values were predictors of PLT transfusion. The positive predictive values (PPV) of PLT count and cADP-CT after PLT transfusion for further PLT transfusion were 33% and 86% respectively, with a PLT count threshold of ≤200 × 109/L and cADP-CT threshold of ≥118 s. The comparison among the ROC curves showed a statistical difference (p = .0002). In multiple regression analysis, cADP-CT was the strongest predictor for the number of PLT transfusion doses in the 48 h postoperatively. In CABG patients, the results of cADP-CT after PLT transfusion have a better predictive capacity for further PLT transfusions than the PLT count.

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

Abstract WP97: The Aptamer BT200 Blocks Von Willebrand Factor and Platelet Function in Blood of Stroke Patients

Background: The effect of conventional anti-platelet agents is limited in secondary stroke prevention, and their effects are further blunted under conditions of high shear stress in the presence of increased levels of circulating VWF. VWF mediates platelet adhesion to collagen under high shear stress and is thereby critically involved in thrombus formation at sites of stenotic extracranial intracranial arteries (reviewed by Buchtele et al. 2018). We have created a novel anti-VWF aptamer (BT200) which could be useful for secondary stroke prevention, because the anti-VWF aptamer ARC1779 effectively reduced cerebral embolization after carotid endarterectomy (Markus et al. 2011). Aims: To characterize the effects of BT200 in blood of patients with large artery atherosclerosis stroke. Methods: Blood samples were obtained from 30 patients with acute stroke Inhibition of VWF activity by BT200 was quantified by REAADS ELISA and VWF ristocetin cofactor activity (VWF:RCo), platelet function under high shear rates with the PFA-100, and ristocetin-induced platelet aggregation in whole blood. Results: The majority of stroke patients had elevated VWF:RCo levels (mean: 198%; range 55-330%). Of 15 patients receiving clopidogrel with or without aspirin, only two had a prolonged collagen adenosine diphosphate closure time (CADP-CT) &gt;123s, and only one patient had a ristocetin induced aggregation of &lt;20U. BT200 concentration dependently inhibited VWF activity to &lt;3% and VWF dependent platelet function (p&lt;0.001): BT200 invariably prolonged CADP-CT to target levels of &gt;300s, and decreased aggregation to &lt;20U in blood samples from all patients. Conclusions: BT200 effectively inhibits VWF activity and VWF-dependent platelet function in blood from patients with acute stroke. Results from this study proved useful for planning of the ongoing phase I and planned phase II trial.

Serum Brain-Derived Neurotrophic Factor is Related to Platelet Reactivity and Metformin Treatment in Adult Patients With Type 2 Diabetes Mellitus.

The aim of this study was to investigate the association of serum brain-derived neurotrophic factor (BDNF) levels with platelet reactivity and antidiabetes treatment, as well as serum adipocytokine concentrations. This observational, open-label study enrolled 149 patients. Serum BDNF, hematologic, biochemical parameters and platelet reactivity were measured. Blood samples were taken after the last acetylsalicylic acid dose. Patients with high BDNF levels were younger (65.60±8.956 vs. 68.59±8.516) and smoked cigarettes more frequently (14.6% vs. 4.1%); they were more commonly being treated by metformin (77.3% vs. 54%); had higher platelet counts (245.81±68.85 103/mm3 vs. 206.61±44.48 103/mm3); had shorter collagen-adenosine diphosphate closure time (CADP-CT) values (104.88±69.73 s vs. 140.93±86.63 s); had higher triglyceride concentrations (140.73±67.5 vs. 121.76±60.49) and had higher concentrations of serum thromboxane B2 (0.938±1.59 vs. 0.364±0.76). In univariate linear regression analyses, predictive factors for serum BDNF levels above the median were metformin treatment, current smoking, platelet count, triglyceride concentration, total cholesterol concentration and CADP-CT >74 s. In multivariate backward stepwise analysis CADP-CT >141 s; adiponectin concentration >4.22 µg/mL; total cholesterol and low-density lipoprotein levels were independently associated with serum BDNF levels above the median. Our results suggest that BDNF may be associated with lipid metabolism and that increased production of BDNF may be related to metformin treatment. Moreover, we showed an association between BDNF levels and platelet reactivity; we found that serum BDNF levels in patients with type 2 diabetes who had high platelet reactivity were higher than in subjects with normal platelet reactivity despite antiplatelet therapy.

Variables That Affect Results of PFA-100 in a Group of Healthy Blood Donors in the Slovak Population

Abstract Background: The platelet function analyzer (PFA-100) is a system analyzing platelet function determined for detection of the functional inherited and acquired platelet disorders, screening of von Willebrand disease (vWD) and recently also considered as useful for monitoring of antiplatelet treatment. The PFA-100 test uses a high shear flow system to simulate in vitro the conditions to which platelets are subjected at the site of a damaged blood vessel wall. Aim of study: We decided to establish the reference intervals of PFA closure time (CT) in the Slovak population of healthy blood donors. Patients and methods: Fifty age and gender matched healthy blood donors were enrolled in the study. We investigated the relationships between PFA-100 CT, gender and ABO blood groups. Results: The reference intervals for CT measured on CEPI (collagen/epinephrine) and CADP (collagen/adenosine diphosphate) cartridge in 3.2% citrated blood were 86 - 199 sec. and 42 - 119 sec., respectively. Blood group O was associated with significantly longer CEPI CT (p&lt;0.05) compared to non - O groups. The prolongation of CADP CT in blood donors with blood group O was without significance. The influence of gender as another variable analyzed with CT has not been evaluated as statistically significant. Conclusion: PFA-100 CT should be interpreted carefully with consideration of both the patient’s clinical presentation and laboratory variables such as ABO blood group.

A Comparison of Von Willebrand Factor Indexes in Heartmate II Compared to Heartware Left Ventricular Assist Devices

Background: Von Willebrand factor (VWF) is a multimeric glycoprotein synthesized in endothelium and megakaryocytes. Elevated total VWF antigen has been associated with arterial thrombosis, while in patients with left ventricular assist devices (LVAD), loss of high molecular weight multimers is associated with spontaneous bleeding. We hypothesized that the lower rotational speed of the Heartware LVAD would be associated with less severe disruption of VWF.Methods: A total of 22 patients were included. We compared samples from a) 17 patients with Heartmate II LVAD (HM II), 76% male, median age 67 (54-73) years, 24% non-white, 45 (33-59) months after implant, with b) 5 patients with Heartware (HW) LVAD, all male, age 64 (59-65) years, 20% non-white, 27 (14-29) months after implant. All patients received warfarin. All HW patients took aspirin, while 82% of HM II patients took aspirin. Samples were analyzed for VWF antigen, activity, platelet function analyzer-100 collagen adenosine diphosphate closure time (PFA) and VWF multimers by gel electrophoresis. Multimers were assessed qualitatively and quantitatively by dividing mers > 15 by mers 2-15 (multimer ratio) and with a normalized multimer ratio (multimer ratio of patient / normal plasma control from the same gel).Results: Although flow rates did not differ significantly between HM II and HW, 5.2 (4.6-6.5) versus 4.3 (4.2-5.4) liters per minute respectively, rotational speeds were very different, mean 9472 versus 2680 rpms, p<0.0001). There were no differences in hemoglobin, hematocrit, or platelet count at the time of sampling. Qualitative VWF multimers were abnormal in all patients, and PFA was non-clotting in 88% of HM II patients and 80% of HW patients. VWF activity to antigen ratio was not different: HM II 0.68 (0.63-0.74) versus HW 0.70 (0.63-0.71). However, VWF antigen was significantly higher in HM II patients, 199 (174-227) compared to HW, 139 (122-160), p=0.039 and the normalized VWF multimer ratio was significantly lower, suggesting greater loss of high molecular weight multimers in HM II, 0.43 (0.41-0.48) compared to HW, 0.53 (0.48-0.56), p=0.0025 (figure).Conclusion: The lower rotational speed associated with the Heartware LVAD appears to produce less elevation of VWF antigen, and slightly less loss of VWF high molecular weight multimers compared to the Heartmate II LVAD. Additional studies are needed to describe whether or not lower pump thrombosis rates and rates of spontaneous bleeding are associated with these differences. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Patients With Severe Aortic Valve Stenosis and Impaired Platelet Function Benefit From Preoperative Desmopressin Infusion

Patients 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. In this double-blind, randomized placebo controlled trial, 43 patients undergoing aortic valve replacement (due to severe aortic valve stenosis with CADP-CT>170 seconds) were given desmopressin 0.3 μg/kg or saline intravenously after induction of anesthesia. Measurement of CADP-CT, factor VIII activity, von Willebrand factor antigen, GpIb binding activity, ristocetin cofactor activity, collagen-binding activity, and multimers were performed after induction of anesthesia, one hour after desmopressin infusion, and 24 hours postoperatively. In the majority of patients, baseline values of von Willebrand factor related indices were normal, but increased one hour after infusion of desmopressin by 73% to 90% as compared with placebo. Selective loss of high molecular weight multimers was seen only in a minority of patients. The CADP-CT was greater than 170 seconds in 92% of screened patients, and desmopressin shortened CADP-CT by 48% versus baseline and reduced postoperative blood loss by 42% (p<0.001). Prolonged CADP-CT indicates platelet dysfunction in severe aortic valve stenosis, and can guide the use of desmopressin as an effective prohemostatic agent in patients with severe aortic valve stenosis.

Residual platelet reactivity after aspirin and clopidogrel treatment predicts 2-year major cardiovascular events in patients undergoing percutaneous coronary intervention

Background Studies on the prognostic significance of residual platelet reactivity despite the use of dual anti-platelet agents are limited and seldom extend beyond 1 year. Methods This study enrolled 144 patients treated with standard-dose aspirin and clopidogrel and undergoing percutaneous coronary intervention (PCI). Platelet reactivity was measured by the Platelet Function Analyzer-100 (PFA-100) just before PCI and presented as collagen/epinephrine closure time (CEPI-CT) and collagen/adenosine diphosphate closure time (CADP-CT). Primary endpoint included cardiovascular death, myocardial infarction, and stroke. Secondary endpoint was the primary endpoint plus hospitalization due to unstable angina or urgent target vessel revascularization. Results During the 24-month follow-up, 14 patients (9.7%) developed the primary endpoint events and 33 had the secondary endpoints. After controlling possible confounding factors, both CEPI-CT < 193 s and CADP-CT < 95 s were independently predictive of the primary endpoint (hazard ratio = 3.5; 95% confidence interval: 1.04–11.7; p = 0.044 and 5.3; 1.4–20.1; p = 0.015, respectively). Only CADP-CT < 95 s remained significantly predictive of secondary endpoints in the follow-up periods of 0–9 and 9–24 months, during which clopidogrel was mostly discontinued. Conclusion This study demonstrates that increased residual platelet reactivity measured by PFA-100 CADP-CT consistently predicts the occurrence of cardiovascular events following PCI throughout the 24-month follow-up period, irrespective of the changes in anti-platelet use.

Effects of Aspirin Responsiveness and Platelet Reactivity on Early Vein Graft Thrombosis After Coronary Artery Bypass Graft Surgery

The purpose of this study was to determine if an incomplete response to or inadequate antiplatelet effect of aspirin, or both, contribute to saphenous vein graft (SVG) occlusion after coronary artery bypass graft (CABG) surgery. Thrombosis is the predominant cause of early SVG occlusion. Aspirin, which inhibits cyclooxygenase-1 activity and thromboxane generation in platelets, reduces early SVG occlusion by one-half. Aspirin responsiveness and platelet reactivity were characterized 3 days and 6 months after coronary artery bypass graft surgery in 229 subjects receiving aspirin monotherapy by platelet aggregation to arachidonic acid, adenosine diphosphate, collagen and epinephrine, Platelet Function Analyzer-100 (Siemens Healthcare Diagnostics, Newark, Delaware) closure time (CT) using collagen/epinephrine agonist cartridge and collagen/adenosine diphosphate (CADP) agonist cartridge, VerifyNow Aspirin assay (Accumetrics, Inc., San Diego, California), and urine levels of 11-dehydro-thromboxane B(2) (UTXB(2)). SVG patency was determined 6 months after surgery by computed tomography coronary angiography. Inhibited arachidonic acid-induced platelet aggregation, indicative of aspirin-mediated cyclooxygenase-1 suppression, occurred in 95% and >99% of subjects 3 days and 6 months after surgery, respectively. Despite this, 73% and 31% of subjects at these times had elevated UTXB(2). Among tested parameters, only UTXB(2) and CADP CT measured 6 months after surgery correlated with outcome. By multivariate analysis, CADP CT of ≤88 s (odds ratio: 2.85, p = 0.006), target vessel diameter of ≤1.5 mm (odds ratio: 2.38, p = 0.01), and UTXB(2) of ≥450 pg/mg creatinine (odds ratio: 2.59, p = 0.015) correlated with SVG occlusion. CADP CT and UTXB(2) in combination further identified subjects at particularly high and low risk for SVG occlusion. Aspirin-insensitive thromboxane generation measured by UTXB(2) and shear-dependent platelet hyper-reactivity measured by Platelet Function Analyzer-100 CADP CT are novel independent risk factors for early SVG thrombosis after coronary artery bypass graft surgery.

Enhanced ex vivo inhibition of platelet function following addition of dipyridamole to aspirin after transient ischaemic attack or ischaemic stroke: First results from the TRinity AntiPlatelet responsiveness (TrAP) study

Ex vivo dipyridamole 'non-responsiveness' has not been extensively studied in ischaemic cerebrovascular disease. Platelet surface marker expression, leucocyte-platelet complex formation and inhibition of platelet function at high shear stress as detected by the PFA-100® Collagen-Adenosine-diphosphate (C-ADP) and Collagen-Epinephrine cartridges was assessed in 52 patients within 4 weeks of transient ischaemic attack (TIA) or ischaemic stroke on aspirin, and then 14 d (14 d) and >90 d (90 d) after adding dipyridamole. A novel definition of 'Dipyridamole non-responsiveness' was used. The median C-ADP closure time increased following addition of dipyridamole, remained elevated at 90 d (P ≤ 0·03), and was unaffected by aspirin dose. 59% at 14 d and 56% at 90 d were 'dipyridamole non-responders' on the PFA-100. The proportion of non-responders at 14 and 90 d was similar (P= 0·9). Compared with baseline (4·6%), median monocyte-platelet complexes increased at 14 d (5·0%, P= 0·03) and 90 d (4·9%, P= 0·04). Low C-ADP closure times were associated with increased monocyte-platelet complexes at 14 d (r= -0·32, P= 0·02) and 90 d (r= -0·33, P = 0·02). Monocyte-platelet complexes increased in the subgroup of dipyridamole non-responders on the PFA-100 (P≤ 0·045), but not in responders (P ≥ 0·5), at 14 and 90 d versus baseline. Additional inhibition of platelet function has been detected with the PFA-100 when dipyridamole is added to aspirin. Elevated monocyte-platelet complexes may contribute to ex vivo dipyridamole non-responsiveness.

Pronounced platelet hyperfunction in patients with cardiac arrest achieving restoration of spontaneous circulation*

Markers of platelet activation are increased in patients undergoing cardiopulmonary resuscitation. Hyperfunctional platelets may contribute to impairment of microcirculatory function and overall poor outcome despite restoration of spontaneous circulation (ROSC). Patients with myocardial infarction have hyperfunctional platelets, which predict the degree of myocardial necrosis. Thus, we hypothesized that platelets may be even more activated in patients whose myocardial infarction leads to cardiac arrest and compared them with patients whose cardiac arrest was due to a noncardiac origin. Prospective observational study. Emergency department of a tertiary care hospital. One hundred four patients with witnessed cardiac arrest who achieved ROSC. Blood sampling. We assessed collagen adenosine diphosphate closure time with the platelet function analyzer-100, and measured plasma levels of von Willebrand factor: ristocetin cofactor activity levels by turbidometry. Independent physicians diagnosed the origin of cardiac arrest. The majority of cardiac arrests were caused by myocardial ischemia. Invariably, collagen adenosine diphosphate closure time values (55 seconds; 95% confidence interval: 52-58 seconds) were much shorter in these patients compared with patients with other causes of cardiac arrest (110 seconds; 95% confidence interval: 84-135 seconds, p < 0.001). von Willebrand factor: ristocetin cofactor activity plasma levels were more than three-fold above normal values in both groups. Patients with myocardial ischemia-triggered cardiac arrest had the highest degree of platelet hyperfunction under high shear rates, which was not solely due to increased von Willebrand factor. Future trials are necessary to clarify whether rapid, more aggressive antiplatelet therapy improves outcome after cardiac arrest.

Platelet Dysfunction in Outpatients With Left Ventricular Assist Devices

Thromboembolic and bleeding complications in outpatients with a left ventricular assist device are common and can be detrimental. A meticulous balance between anticoagulant and procoagulant factors is therefore crucial. However, in contrast to routinely performed plasmatic coagulation tests, platelet function is hardly ever monitored although recent reports indicated platelet dysfunction. We therefore differentially evaluated platelet function with four commonly used point-of-care devices. In a cross-sectional design platelet function was assessed in 12 outpatients and 12 healthy matched volunteers using thrombelastography platelet mapping, thromboelastometry, platelet function analyzer, and a new whole blood aggregometer (Multiplate). Phenprocoumon produced an international normalized ratio of 3.5. It was associated with a twofold prolongation in the thromboelastometry clotting time (p < 0.001). Platelet function under high shear was severely compromised: collagen adenosine diphosphate closure times were 2.5-fold longer in patients than in volunteers (p < 0.001), and 50% of patients had maximal collagen adenosine diphosphate closure time values. Although antigen levels of von Willebrand factor were 80% higher in patients (p < 0.001), von Willebrand factor-ristocetin was subnormal in 5 of 12 patients. Ristocetin-induced aggregation was also threefold higher in volunteers (p < 0.001), indicating an additional functional defect of platelets affecting the glycoprotein Ib-von Willebrand factor axis. The von Willebrand factor multimer pattern in patients also appeared abnormal. Multimodal antiplatelet monitoring showed markedly impaired platelet function in patients with a left ventricular assist device. Platelet dysfunction under high shear rates and abnormal ristocetin-induced aggregation is only partly attributable to low von Willebrand factor activity. These findings resemble the acquired von Willebrand syndrome that is associated with microaggregate formation and enhanced bleeding.

Laboratory Response to Intranasal Desmopressin in Women with Menorrhagia and Underlying Platelet Dysfunction.

Intranasal desmopressin (IN-DDAVP) is used for home treatment of menorrhagia in women with inherited bleeding disorders. The effect of IN-DDAVP on laboratory hemostatic parameters in women with menorrhagia and associated platelet dysfunction is unknown. We evaluated the effects of IN-DDAVP on hemostatic parameters in women with menorrhagia and platelet dysfunction and correlated them with menstrual blood flow. Eleven women (aged 18–45) with menorrhagia and abnormal platelet aggregation and/or platelet adenosine tri-phosphate (ATP) release had determination of factor VIII coagulant activity (FVIII: C), von Willebrand factor antigen (VWF: Ag), von Willebrand factor ristocetin cofactor (VWF: RCo) activity, platelet aggregation, and platelet ATP release pre and 60 minutes post IN-DDAVP. Eight of eleven women underwent Platelet Function Analyzer (PFA-100) closure time determination with collagen/epinephrine (CEPI) and collagen/adenosine diphosphate (CADP) cartridge pre and post treatment. IN-DDAVP was administered during two consecutive menstrual cycles. Menstrual blood flow was assessed during each cycle using a pictorial blood assessment chart (PBAC). Following administration of IN-DDAVP there was a 2–3 fold increase in FVIII: C, VWF: Ag, and VWF: RCo observed in most patients over baseline levels. Mean FVIII:C increased from 130% ± 34.8% to 218% ± 96.5% (P < 0.007), VWF: Ag increased from 86.9% ± 35.1% to 128.7% ± 64.3% (P < 0.011), and VWF: RCo increased from 89.8% ± 42.8% to 139.6% ± 86.5% (P < 0.02). The median baseline PBAC score of 235 decreased to 136 following IN-DDAVP. In addition, there were significant inverse correlations between changes in PBAC score and changes in VWF: Ag (rs= − 0.85, p = 0.02), VWF: RCo (rs= −0.81, p = 0.029), and FVIII:C (rs= 0.92, p = 0.003) with IN-DDAVP. Mean PFA-100 closure time with the CEPI cartridge shortened from 166.8sec ± 85sec to 90.9sec ± 49.3sec (p< 0.02), and the closure time with the CADP cartridge shortened from 104.5sec ± 34.3sec to 64.8sec ± 40.4sec (p <0.007). There were significant inverse correlations between post IN-DDAVP PFA-100 CADP closure time and post IN-DDAVP FVIII:C (rs= −0.86, p = 0.005), VWF: Ag (rs= −0.72, p = 0.04), and VWF: RCo (rs= −0.80, p = 0.01). In addition there were also significant inverse correlations between post IN-DDAVP PFA-100 CEPI closure time and post IN-DDAVP FVIII:C (rs= −0.73, p = 0.03), and VWF: RCo (rs= −0.74, p = 0.03), but not VWF: Ag (rs= −0.66, p = 0.07). In-vitro platelet aggregation and platelet ATP release response did not correct and did not correlate with changes in menstrual blood flow. Our results demonstrate a correlation between VWF parameters and menstrual blood flow following IN-DDAVP in women with menorrhagia and underlying platelet dysfunction.

Abstract 2223: Shear Induced Platelet Function Is Highly Increased In Patients With Cardiac Arrest Undergoing Cardio-pulmonary Resuscitation (CPR)

Background: The prognosis of patients with cardiac arrest is still poor, and hardly any specific therapeutic options exist to improve outcome. Platelet activation has been observed in patients undergoing cardiopulmonary resuscitation (CPR). This may contribute to impairment of microcirculatory function and overall poor outcome despite return of spontaneous circulation. Data on direct platelet function in cardiac arrest are scarce. Platelets of patients with myocardial infarction are hyperfunctional, which predicts the degree of myocardial necrosis. Thus, we hypothesized that platelets may be even more hyper-functional in patients whose myocardial infarction causes cardiac arrest. We determined platelet function under high shear rates of patients with cardiac arrest and were further interested whether this may be related to the cause of cardiac arrest. Methods: We conducted a prospective study in 77 cardiac arrest patients at the Emergency Department of a tertiary care hospital. Collagen adenosine diphosphate closure time (CADP-CT) was assessed by the FDA-approved platelet function analyzer (PFA-100). In addition, plasma levels of von Willebrand factor (vWf:RiCo) were measured by turbidometry. Independent staff members of the emergency department not otherwise involved in this trial diagnosed the origin of cardiac arrest. Results: More than half of cardiac arrests were caused by myocardial ischemia. CADP-CT values (54s; 95%CI: 48–60s in 3.8% citrate) were much shorter in these patients as compared to patients with other causes of cardiac arrest (110s; 95%CI: 84–135s, p&lt;0.001). This is substantially less than the 87s (95%CI: 80–94s) in patients with ST-elevation myocardial infarction as previously published. vWf:RiCo levels were substantially increased above the upper normal limit (180 U/dL) in all patient groups. Conclusion: Patients with myocardial ischemia triggered cardiac arrest displayed the highest degree of platelet hyper-function under high shear rates, which was not solely due to increased vWF. Those patients may benefit from a rapid, more aggressive anti-platelet therapy than currently performed or an anti-vWF targeted therapy.

Baseline platelet reactivity in acute myocardial infarction treated with primary angioplasty—Influence on myocardial reperfusion, left ventricular performance, and clinical events

Platelet reactivity is believed to play a key role in the pathophysiology of ST-segment elevation myocardial infarction (STEMI). We sought to determine whether platelet reactivity predicts impaired myocardial reperfusion, left ventricular (LV) dysfunction, and clinical events in an unselected group of patients with STEMI. Platelet reactivity was measured before primary angioplasty in 125 consecutive patients with the use of Platelet Function Analyzer-100. Six-month follow-up was performed. Patients were stratified into 4 quartiles according to the collagen adenosine diphosphate closure time (CADP-CT), with the fourth quartile (CADP-CT < or = 55 seconds; n = 32) defined as high reactivity. There was an increasing rate of diabetes across quartiles: 6% in the first and 38% in fourth (P < .0001). Myocardial Blush Grade 0 or 1 and the absence of ST-segment resolution (< or = 50%) were observed more often in the fourth quartile than in quartiles 1 through 3 (84% vs 22%, 27%, 35% and 81% vs 16%, 17%, 26%, respectively; P < .0001 for all). In logistic regression, high reactivity was an independent predictor of Myocardial Blush Grade 0 or 1 (odds ratio [OR], 22.7; 95% confidence interval [CI], 6.5-78.8; P < .0001), ST-segment resolution < or = 50% (OR, 28.6; 95% CI, 8.6-95.2; P < .0001), LV remodeling (OR, 10.4; 95% CI, 3.3-32.7; P < .0001), lack of early (OR, 7.9; 95% CI, 2.8-22.3; P < .0001) and late LV functional recovery (OR, 7.3; 95% CI, 2.9-18.8; P < .0001), and clinical events (OR, 7.8; 95% CI, 2.5-24.9; P = .0005). Platelet reactivity is an independent predictor of myocardial reperfusion. Moreover, CADP-CT being a marker of myocardial reflow may also provide early prognostic information concerning LV performance and adverse clinical events after STEMI.

Perioperative Monitoring of Primary and Secondary Hemostasis in Coronary Artery Bypass Grafting

On-pump cardiac surgery is accompanied by complex alterations of hemostasis. The excessive postoperative bleeding has been attributed to acquired platelet dysfunction, impaired plasmatic coagulation, and increased fibrinolysis. The characterization of the hemostatic defects responsible for bleeding is crucial for specific treatment and optimal clinical management of the patient. For rapid determination of platelet-dependent primary hemostatic capacity (PHC), the Platelet Function Analyzer PFA-100 system is available. To evaluate the PFA performance in perioperative monitoring, a study was performed in 49 patients selected for low bleeding risk undergoing selective primary coronary artery bypass grafting (CABG). We compared PHC with Simplate bleeding time (BT) and platelet aggregometry. Furthermore, we analyzed global hemostasis by thromboelastography (TEG) and plasmatic coagulation by standard clotting tests prothrombin time (PT, Quick), activated partial thromboplastin time (aPTT), thrombin time (TT) and clotting factors and fibrinolysis by batroxobin (reptilase) time (RT). In all patients BT was postoperatively increased by 1.5- to 2-fold irrespective of perioperative complications and decreased to mildly prolonged values on the first postoperative day (1st day). In patients without complications, PHC in both collagen-adenosine diphosphate closure time (CADP-CT: 83 seconds preop, 78 seconds postop, and 74 seconds 1st day) and collagen-epinephrine closure time (CEPI-CT: 98 seconds preop, 95 seconds postop, 85 seconds 1st day) remained nearly stable. Apart from a patient with postoperative moderate thrombocytopenia, in bleeding patients no other significant defect of postoperative platelet hemostatic capacity was observed. However, on 1st day, the PHC of those patients was significantly reduced compared with non-bleeding patients. In patients with postoperative myocardial ischemia, increased PHC was identified by significantly shorter postoperative CADP-CT (66 seconds vs. 83 seconds) than in uncomplicated patients. By aggregometry, partial platelet dysfunction was observed in some patients without correlation to bleeding complications. In seven of 9 patients the postoperative bleeding complication was attributed to prolonged heparin anticoagulation and/or mildly enhanced fibrinogenolysis/fibrinolysis by TEG and standard plasmatic coagulation tests (TEG: k time 18 minutes vs. 8 minutes; aPTT: 47 seconds vs. 32 seconds; TT: 18.0 seconds vs. 12.3 seconds) and (RT: 19.5 seconds vs. 17.7 seconds). The impairment of PHC, platelet aggregation, and clotting factors observed on the 1st day in bleeding and in intra-aortic balloon pump (IABP) patients are most likely secondary effects, for example, loss of active platelets and clotting factors, to the primary postoperative bleeding or implantation of the IABP. In conclusion, our data indicate that in standard CABG procedures highly variable alterations of the hemostatic system occur after cardiopulmonary bypass (CPB) even in patients with assumed low operative risks. For identification of post-CPB bleeding complications, thromboelastography, aPTT, and TT and heparin and batroxobin (reptilase) time as fibrinolysis-sensitive assays are useful. Platelet function appears to be rapidly restored in uncomplicated CABG. PHC determination by PFA-100 demonstrates a high specificity for adequate platelet function and, therefore, could be beneficial in improved transfusion of platelet concentrates. PHC testing by PFA-100 may help identify postoperative platelet hyper-reactivity associated with myocardial lesion.