Impedance Aggregometry Multiplate Research Articles

Factors that modulate platelet reactivity as measured by 5 assay platforms in 3429 individuals

BackgroundAssessment of platelet function is key in diagnosing bleeding disorders and evaluating antiplatelet drug efficacy. However, there is a prevailing “one-size-fits-all” approach in the interpretation of measures of platelet reactivity, with arbitrary cutoffs often derived from healthy volunteer responses. ObjectivesOur aim was to compare well-used platelet reactivity assays. MethodsBlood and platelet-rich plasma obtained from the Framingham Heart Study (N = 3429) were assayed using a range of agonists in 5 platelet assays: light transmission aggregometry, Optimul aggregometry, Multiplate impedance aggregometry (Roche Diagnostics), Total Thrombus-Formation Analysis System, and flow cytometry. Using linear mixed-effect models, we determined the contribution of preanalytical and technical factors that modulated platelet reactivity traits. ResultsA strong intra-assay correlation of platelet traits was seen in all assays, particularly Multiplate velocity (r = 0.740; ristocetin vs arachidonic acid). In contrast, only moderate interassay correlations were observed (r = 0.375; adenosine diphosphate Optimul Emax vs light transmission aggregometry large area under the curve). As expected, antiplatelet drugs strongly reduced platelet responses, with aspirin use primarily targeting arachidonic acid–induced aggregation, and explained substantial variance (β = −1.735; P = 4.59 × 10−780; variance proportion = 46.2%) and P2Y12 antagonists blocking adenosine diphosphate responses (β = −1.612; P = 6.75 × 10−27; variance proportion = 2.1%). Notably, female sex and older age were associated with enhanced platelet reactivity. Fasting status and deviations from standard venipuncture practices did not alter platelet reactivity significantly. Finally, the agonist batch, phlebotomist, and assay technician (more so for assays that require additional sample manipulation) had a moderate to large effect on measured platelet reactivity. ConclusionCaution must be exercised when extrapolating findings between assays, and the use of standard ranges must be medication-specific and sex-specific at a minimum. Researchers should also consider preanalytical and technical variables when designing experiments and interpreting platelet reactivity measures.

Functional Testing for Heparin-Induced Thrombocytopenia Using Whole Blood Multiplate Impedance Aggregometry.

Immune-mediated heparin-induced thrombocytopenia (HIT) occurs when heparin-dependent IgG antibodies bind to heparin/platelet factor 4 (H/PF4) complexes and activate platelets. There is a vast panoply of assays to investigate HIT which can be divided into two groups, antigen-based immunoassays that detect all antibodies against H/PF4 and are used as a first diagnostic step and functional assays that will identify only the antibodies capable of activating platelets and are mandatory to confirm a diagnosis of pathological HIT. The serotonin-release assay, known as SRA, has been the gold standard for decades, but in the last 10years, other easier alternatives have been described. The current chapter will focus on whole blood multiple electrode aggregometry, a validated method for the functional diagnosis of HIT.

Abstract 13538: Associations Between Circulating Liver Enzymes and Platelet Reactivity

Introduction: The liver plays an essential role in thrombopoiesis and coagulation, and circulating liver enzymes are associated with altered platelet counts. However, the role of liver enzymes in the modulation of platelet reactivity remains unclear. Methods: A total of 3,429 Framingham Heart Study participants were included in this study. Platelet reactivity to 8 agonists, including adenosine diphosphate (ADP), thromboxane A 2 mimetic (U46619) and arachidonic acid (AA), was measured using light transmission aggregometry (LTA), Multiplate impedance aggregometry and Optimul aggregometry. Platelet counts and platelet-red blood cell aggregates were enumerated using flow cytometry. Levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also measured. Associations of platelet reactivity phenotypes with liver circulating liver enzyme levels analyzed using linear mixed-effects models and adjusted for sex, age, relatedness, smoking, aspirin-, and statin-use. To correct for multiple testing, a Bonferroni-correction threshold of P<0.0011 was used to account for multiple comparisons. Results: Higher ALT levels were associated with platelet disaggregation in LTA to ADP (β=0.056, SE=0.02, P=3.54E-04), and with decreased platelet reactivity in response to U46619 in Optimul (EC 50 : β=0.064, SE=0.019, P=7.65E-04). Interestingly, higher AST levels were associated with decreased platelet counts (β=-0.082, SE=0.019, P=1.04E-05), platelet reactivity to U46619 (β=-0.069, SE=0.018, P=1.04E-04) and AA (β=-0.047, SE=0.013, P=3.12E-04), and circulating platelet-red blood cell aggregates (β=-0.062, SE=0.018, P=9.54E-04). Conclusion: Our findings suggest that ALT levels could alter primary platelet aggregation. AST may indirectly modulate platelet counts. In addition, lower AST levels may contribute to platelet hyperresponsiveness. Lastly, ALT and AST levels may have antagonistic effects on the formation of platelet and red blood cell aggregates, which may indirectly influence platelet margination within vessels. Additional studies are underway to examine whether liver fat, a marker of fibrosis associated with cardiovascular disease, is also associated with altered platelet function.

Abstract 13330: Cardiorespiratory Fitness is Associated With Decreased Platelet Reactivity

Introduction: Platelets are key mediators in atherosclerotic cardiovascular disease (CVD). Low cardiorespiratory fitness (CRF) is a major risk factor for atherosclerosis. However, little is known about the effects of CRF on platelet function. Methods: Platelet assays and cardiopulmonary exercise testing were conducted in the Framingham Heart Study (n= 3001). A linear mixed effects model was used to analyze associations between CRF (assessed by peak oxygen uptake [VO 2 ] in participants achieving a respiratory exchange ratio >= 1), and platelet reactivity traits from multiple platelet function assays: whole blood Multiplate impedance aggregometry (MP), Total-Thrombus Formation Analysis System (T-TAS), and light transmission aggregometry (LTA). Statistical models adjusted for relatedness, age, sex, and anti-platelet medications. Bonferroni correction for multiple statistical testing resulted in a significance threshold of p<7.35E-04. Results: Of 68 platelet traits analyzed, 31 traits passed the significance threshold, all with a direction of effect indicating higher CRF associated with decreased platelet reactivity. Significant traits spanned multiple platelet agonists. Our strongest associations were seen with MP after TRAP-6 (velocity, p=1.57E-26; AUC, p=2.33E-21; aggregation, p=5.30E-16) and ADP stimulation (velocity, p=1.63E-19; AUC, p=7.64E-17; aggregation, p=1.00E-11), and LTA after ristocetin stimulation (max aggregation, p=5.33E-11; AUC, p=1.11E-10). Conclusion: Our research adds to past work that shows CRF to be associated with reduced CVD by suggesting that decreased platelet reactivity may be involved mechanistically. We found significant associations with multiple platelet agonists, indicating higher CRF globally inhibits platelets; however, given the multiple strong associations after TRAP-6 and ADP stimulation, PAR-1 and purinergic signaling, respectively, may be most heavily involved. This is notable since each of these receptor pathways is directly or indirectly tied to anti-coagulant or anti-platelet therapies. Ultimately, our results suggest that CRF may be important for additional consideration in tailoring anti-platelet strategies.

Thrombelastography Compared with Multiple Impedance Aggregometry to Assess High On-Clopidogrel Reactivity in Patients with Atrial Fibrillation Undergoing Percutaneous Coronary Intervention.

Background: High on-clopidogrel platelet reactivity (HPR) following percutaneous coronary intervention (PCI) is associated with increased ischemic risk. It is unclear whether conventional definitions of HPR apply to patients with concomitant oral anticoagulation (OAC). This study aimed to compare the performance of multiple platelet aggregometry (MEA) and thrombelastography (TEG) to detect HPR in patients with atrial fibrillation (AF) and indication for an OAC. Methods: In this observational single-center cohort study, MEA and TEG were performed in patients with AF with an indication for OAC on day 1 to 3 after PCI. The primary outcome was HPR as assessed by MEA (ADP area under the curve ≥ 46 units [U]) or TEG (MAADP ≥ 47 mm), respectively. The secondary exploratory outcomes were a composite of all-cause death, myocardial infarction (MI) or stroke and bleeding, as defined by the International Society on Thrombosis and Hemostasis, at 6 months. Results: Platelet function of 39 patients was analyzed. The median age was 78 (interquartile range [IQR] was 72–82) years. 25 (64%) patients were male, and 19 (49%) presented with acute coronary syndrome. All patients received acetylsalicylic acid and clopidogrel prior to PCI. Median (IQR) ADP-induced aggregation, MAADP, TRAP-induced aggregation, and MAthrombin were 9 (6–15) U, 50 (43–60) mm, 54 (35–77) U and 65 (60–67) mm, respectively. The rate of HPR was significantly higher if assessed by TEG compared with MEA (25 [64%] vs. 1 [3%]; p < 0.001). Within 6 months, four (10%) deaths, one (3%) MI and nine (23%) bleeding events occurred. Conclusion: In patients with AF undergoing PCI, the rates of HPR detected by TEG were significantly higher compared with MEA. Conventional cut-off values for HPR as proposed by consensus documents may need to be re-evaluated for this population at high ischemic and bleeding risk. Further studies are needed to assess the association with outcomes.

Platelet reactivity is higher in e-cigarette vaping as compared to traditional smoking

IntroductionVaping emerges as alternative to standard tobacco smoking. However, there is evidence for critical cardiovascular, gastrointestinal and respiratory side effects. Nevertheless, long-term vaping effects on thrombocyte reactivity have not been investigated. Therefore, we investigated the influence of vaping on thrombocyte reactivity in comparison to standard smoking and non-smoking. MethodsPlatelet function was measured by Multiplate Impedance Aggregometry as area under the curve (AUC). Smoking habits and characteristics were assessed by questionnaire. Results were analyzed using inverse probability of treatment weighting (IPTW) and conventional t-tests to test for robustness. ResultsAfter IPTW adjustment, participants in all groups were balanced by age, gender, body height and weight. Collagen-induced aggregation was higher in vapers compared to non-smokers (non-smokers 52.55 ± 23.97 vs. vapers 66.63 ± 18.96 AUC, p = 0.002) and to smokers (vapers vs. smokers 49.50 ± 26.05 AUC, p < 0.0001). ADP-induced aggregation in vapers was higher compared to non-smokers (non-smokers 33.16 ± 16.61 vs. vapers 45.27 ± 18.67 AUC, p = 0.001) and was numerically increased compared to smokers (vapers vs. smokers 40.09 ± 19.80 AUC, p = 0.08). These findings remained robust in t-test analysis. ConclusionThis study provides first evidence that vaping leads to enhanced platelet reactivity compared to standard smoking and non-smoking. This suggests health effects of vaping might be more severe than previously assumed. Whether this effect translates to clinical outcome with a higher incidence of major cardiovascular events, should be evaluated in large-scaled clinical studies.

Resistance to Antiplatelet Therapy Is Associated With Symptoms of Cerebral Ischemia in Carotid Artery Disease.

Background:Platelet inhibitory therapy is prescribed to prevent arterial thromboembolism in patients with atherosclerotic disease. Although taken by millions of people, around 30% are resistant to the treatment they are being prescribed.Aims:To determine whether symptoms of cerebral ischemia, or pre-operative cerebral emboli, in patients admitted for a carotid endarterectomy were associated with resistance to aspirin or clopidogrel.Methods:Venous blood from 133 patients immediately before carotid endarterectomy (CEA) was analyzed for resistance to aspirin and clopidogrel by multiplate impedance aggregometry. The number of emboli/hour entering the ipsilateral middle cerebral artery was counted by transcranial Doppler (TCD) on the day before surgery in 33 of these patients.Results:Resistance was found in 21 (26.3%) of 100 patients taking aspirin and 14 (42%) of 33 taking clopidogrel. Mean (sd) residual platelet aggregation was significantly higher at 41.9(32) Au in patients who had suffered recent symptoms of cerebral ischemia compared with 30.8(16) Au in asymptomatic patients (p = 0.012). Residual platelet aggregation also correlated significantly with the number of emboli/hour counted by TCD in the ipsilateral middle cerebral artery (r = 0.45, p = 0.009).Conclusion:Antiplatelet resistance was associated with the frequency of cerebral emboli and recent symptoms of cerebral ischemia in patients with carotid disease. Definitive clinical studies are needed to explore whether testing for antiplatelet resistance should be undertaken routinely in patients starting platelet inhibitory therapy for cardiovascular disease.

Hemostatic potential of cold-stored non-leukoreduced whole blood over time: An assessment of platelet function and thrombin generation for optimal shelf life.

Cold-stored low-titer whole blood (WB) is becoming increasingly used as the preferred product for initial hemorrhagic shock resuscitation. The purpose of this study was to identify whether the current 21-day shelf life is the optimal duration for storage of WB, maintaining hemostatic efficacy. Five units of fresh low-titer group O WB (non-leukoreduced) were acquired from our regional blood center. These units were stored at 4°C for up to 21 days as per current clinical storage guidelines in our emergency department. Hemostatic parameters were measured in vitro at 0 days, 7 days, 14 days, and 21 days. Assessments of hemostatic potential included cell count, rapid thrombelastography (r-TEG) and kaolin thrombelastography (TEG), multiplate impedance aggregometry, and calibrated automated thrombogram (CAT). Univariate analysis, including one-way analysis of variance with repeated measures, was performed (STATA 12.1). Compared with baseline product (0 days), both platelet count and platelet function of WB showed sharp decreases at 7 days and again at 14 days. Platelet function deterioration was noted by r-TEG c (MA), TEG-MA, and multiplate arachidonic acid and adenosine diphosphate (all p < 0.001). With respect to clot initiation, r-TEG ACT and TEG R-time were similar over the 21-day shelf life (p = 0.058 and p = 0.620, respectively). Thrombin generation assessed by CAT demonstrated stable endogenous thrombin potential over the course of storage (p = 0.162), but increased peak thrombin generation and quicker time to peak generation after 7 days. While the platelet function of WB degrades significantly at 7 days (and again at 14 days), clot initiation remains stable over time, and thrombin generation appears to be improved at 7 days. This study supports a current storage limit for cold-stored, low-titer WB of 14 days.

Prevalence and predictors of high-on treatment platelet reactivity during prasugrel treatment in patients with acute coronary syndrome undergoing stent implantation

BackgroundADP-antagonists such as prasugrel have reduced but yet not overcome the phenomenon of high-on treatment platelet reactivity (HRPR), that has been shown to increase the rate of major cardiovascular events after an acute coronary syndrome (ACS) or percutaneous coronary intervention (PCI). However, the exact prevalence and the principal determinants of suboptimal platelet inhibition in patients treated with dual antiplatelet therapy (DAPT) with prasugrel have not been completely clarified and were therefore the aim of the present study. MethodsWe included patients (<75 years and >60kg) treated with DAPT (aspirin+prasugrel) after PCI, mainly for an ACS. Platelet function test evaluation was performed at 1–3 months from discharge. HRPR was assessed by multiplate impedance aggregometry and defined for results above upper limit of normal after ADP stimulation. ResultsWe included 190 post-ACS patients. HRPR with prasugrel was observed in 19 patients (10%). The prevalence of HRPR was stable in different high-risk subgroups of patients (female gender, hypercholesterolemic, and chronic kidney disease) whereas it was increased in diabetic patients (p=0.045), with a significant interaction between diabetic status and HRPR (p=0.04). However, at multivariate analysis, an impaired metabolic status, with higher levels of glycosylated hemoglobin and low-density lipoprotein (LDL) cholesterol, but not diabetic status, emerged as independent predictors of HRPR with prasugrel [OR (95% CI)=2.1 (1.32–3.33), p=0.002 and OR (95% CI)=1.03 (1.01–1.05), p=0.003, respectively], with a stronger linear relationship between ADP-mediated platelet aggregation and glycosylated hemoglobin levels (r=0.24, p=0.002), than for LDL-cholesterol (r=0.13, p=0.09). ConclusionsIn post-ACS patients treated with PCI and receiving DAPT with prasugrel, HRPR is observed in about 10% of patients. Impaired metabolic status, and especially elevated glycosylated hemoglobin, emerged as independent predictors of the suboptimal effectiveness of prasugrel.

Platelet function testing: dead or alive

Background High on-treatment platelet reactivity (HTPR) to antiplatelet medication leads to ischemic events, whereas low on-treatment platelet reactivity (LTPR) increases bleeding risk. However, various trials have failed to demonstrate superiority of tailored antiplatelet regimens (ARCTIC, ANTARCTIC, Trigger-PCI, and GRAVITAS). TROPICAL-ACS was the first study that demonstrated the benefit of tailoring antiplatelet medication according to platelet function analysis. A potential reason may be that different platelet function assays were used in these trials. Objectives To evaluate whether the results of platelet function tests are comparable. Patients/Methods We tested three commonly used assays - light transmission aggregometry (LTA), (Multiplate impedance aggregometry [MP]), and vasodilator-stimulated phosphoprotein phosphorylation assay (VASP) - in 23 patients receiving dual antiplatelet therapy with aspirin and clopidogrel. Results With LTA, HTPR occurred in 57% of patients; with VASP, it occurred in 43% of patients; and with MP, it occurred in 13% of patients. According to LTA, only 35% of patients were in the therapeutic window; according to VASP, 57% of patients were in the therapeutic window; and according to MP, 48% of patients were in the therapeutic window. With LTA, LTPR occurred in 9% of patients; with VASP, it occurred in 0% of patients; and with MP, it occurred in 39% of patients. Therefore, the prevalences of HTPR and LTPR differed significantly between assays. Remarkably, in 17% of patients, one assay showed HTPR whereas another showed LTPR. Conclusions The results of different platelet function assays differ substantially. Up to now, only TROPICAL-ACS had demonstrated a benefit of tailoring antiplatelet medication according to platelet function analysis. Future trials are needed to evaluate whether the platelet function assay used in TROPICAL-ACS is the 'correct' one and revives platelet function testing.

P-034: Multiple impedance aggregometry (Multiplate®) in healthy women during normal pregnancy – a prospective and longitudinal study

P-034: Multiple impedance aggregometry (Multiplate®) in healthy women during normal pregnancy – a prospective and longitudinal study

Platelet reactivity in thromboelastometry. Revision of the FIBTEM test: a basic study

This study aimed to investigate modifications to the FIBTEM test to better assess fibrinogen levels and the quality of fibrin polymerization in citrated blood using Multiplate impedance aggregometry to verify platelet inhibition. Blood samples from 26 healthy volunteers were subjected to thromboelastometry studies (EXTEM/FIBTEM tests) in accordance with the standard study protocol (cytochalasin D) and according to a modified protocol (synthetic IIbIIIa receptor antagonist vs. acetylsalicylic acid [ASA] + synthetic IIbIIIa receptor antagonist instead of cytochalasin D). Independent of thromboelastometry, Multiplate impedance aggregometry was used to assess the degree of restriction by the platelet blocked with the following treatments: (1) cytochalasin D, (2) synthetic IIbIIIa antagonist or (3) ASA + synthetic IIbIIIa antagonist to assess the aggregation response to activation with an agonist (ADP, collagen, thrombin receptor activating peptide-6 [TRAP-6], and arachidonic acid). Via aggregometry, cytochalasin D more weakly inhibited platelet aggregation than simultaneous administration of the -IIbIIIa receptor antagonist with ASA. However, total platelet aggregation inhibition was observed after simultaneous administration of cytochalasin D combined with a synthetic IIbIIIa receptor antagonist. In the thromboelastometry, a significant decrease of the A10, A20 and MCF parameters were observed in the EXTEM/FIBTEM tests after they were modified by the addition of a synthetic IIbIIIa receptor antagonist alone or in combination with ASA. In conclusion, in this Multiplate- and ROTEM-based laboratory approach, a two-way blockade (IIbIIIa-antagonist + cytochalasine D) was sufficient to completely inhibit procoagulant platelet function as observed by aggregometry and thromboelastometry.

Preoperative hemostatic testing and the risk of postoperative bleeding in coronary artery bypass surgery patients.

We sought to assess predictability of excessive bleeding using thrombelastography (TEG), multiplate impedance aggregometry, and conventional coagulation tests including fibrinogen in patients undergoing coronary artery bypass graft (CABG) surgery. A total of 170 patients were enrolled in this prospective observational study. TEG, Multiplate aggregometry, and coagulation tests were sampled on the day before surgery. Excessive bleeding was defined as >1000 mL over 18 hours. Multiplate-adenosine diphosphate (ADP) measurements were significantly lower in patients with excessive bleeding, 85.5AU ± 32.8 versus 108.5AU ± 30.0, p = 0.012. Bivariate analysis revealed body mass index, myocardial infarction, and multiplate-ADP as predictors of bleeding. In multivariable linear regression analysis, multiplate-ADP remained a significant predictor of bleeding (β: -6.2 [confidence interval: -12.0 to -0.3], p = 0.035). The lowest interval of multiplate-ADP (<50 AUC) was associated with significantly more bleeding and need for platelet concentrate transfusion. Fibrinogen levels <2.5 g/L were also found to be associated with excess bleeding (p = 0.020). Multiplate impedance aggregometry identified patients at risk for excessive bleeding after CABG. Low fibrinogen levels were associated with increased bleeding. Neither routine TEG parameters nor conventional coagulation tests were correlated with bleeding.

Impact of atorvastatin or rosuvastatin co-administration on platelet reactivity in patients treated with dual antiplatelet therapy

BackgroundResidual high-on treatment platelet reactivity (HRPR) still represents a challenging matter in patients with coronary artery disease. Drug-to-drug interaction has been suggested between some statin and antiplatelet agents, despite their co-administration is mandatory in patients after an acute cardiovascular event or coronary stenting. Therefore, the aim of the current study was to investigate any impact of rosuvastatin or atorvastatin co-administration on platelet reactivity in patients receiving dual antiplatelet therapy (DAPT). MethodsOur population is represented by patients on DAPT (ASA and either clopidogrel 75 mg or ticagrelor 90 mg b.i.d) after an ACS or percutaneous revascularization, and receiving rosuvastatin or atorvastatin. Platelet function was assessed by Multiplate Impedance Aggregometry (Roche Diagnostics AG). ResultsWe included a total of 374 patients, 240 (64.2%) receiving atorvastatin, 134 (35.8%) rosuvastatin. Rosuvastatin treated patients were more often using beta-blockers (p = 0.05), diuretics (p = 0.04) and displayed higher HDL (p < 0.001) and lower LDL cholesterol (p < 0.001). The prevalence of HRPR for ASA was low, with no difference according to statin type (0.8% vs 1.5%, p = 0.62, adjusted OR[95%CI] = 2[0.23–16.6], p = 0.52). Concerning ADP-antagonists, in the 163 patients treated with clopidogrel, rosuvastatin co-administration was associated with a significantly increased rate of HRPR (55.6%vs 32%, p = 0.01, adjusted OR[95%CI] = 2.69[1.22–5.96], p = 0.015) with higher ADP-mediated platelet reactivity (p = 0.01) and TRAP-test results (p = 0.04). On the contrary, in the 211 ticagrelor treated patients, statin type did not affect mean platelet reactivity or the prevalence of HRPR with ticagrelor (10.5% vs 11.2%, p = 0.99, adjusted OR[95%CI] = 0.86[0.34–2.22], p = 0.76) ConclusionsAmong patients receiving DAPT, rosuvastatin but not atorvastatin is associated with an increased rate of HRPR for clopidogrel, without any influence on the antiplatelet effect of ASA or ticagrelor. Therefore, cautiousness should be exerted for clopidogrel and rosuvastatin therapeutic association.

Hantavirus infection-induced thrombocytopenia triggers increased production but associates with impaired aggregation of platelets except for collagen

IntroductionWe evaluated the mechanisms of thrombocytopenia encountered in hantavirus disease by studying platelet production together with platelet aggregation and deposition to collagen surface. Patients and methodsThe study group consisted of 31 prospectively recruited, consecutive, hospitalized patients having acute Puumala hantavirus infection. Blood samples were collected acutely and at the control visit and subjected to analysis in Sysmex® XE-5000 to capture mean platelet volume (MPV) and immature platelet fraction (IPF%). Platelet aggregation under low shear rate conditions was assessed with impedance aggregometry Multiplate®, whereas platelet function analyzer (PFA)-100® was applied under blood flow of high shear forces. ResultsIPF% was 3.1-fold higher acutely compared with the control (median 7.4%, range 2.0–23.8% vs. median 2.4%, range 1.4%–5.2%, p<0.001) tightly associating with the low platelet count (r=−0.76, p<0.001). Accordingly, acute MPV was high (median 11.4fl, range 9.4–13.1fl vs. median 10.5fl, range 9.0–12.0fl, p=0.003). Acute platelet aggregation in Multiplate® was decreased to all agonists compared with the later control (p<0.05 for all agonists). Aggregation capacity associated with thrombocytopenia (for all agonists r≥0.81, p<0.001), but impaired aggregation occurred also among patients with a nearly normal platelet count. Triggered by collagen, 20% of values were below reference range, while 73% of responses were low with thrombin receptor activating peptide. Significantly, under high shear platelet deposition to collagen surface was normal despite thrombocytopenia. ConclusionsDuring acute hantavirus disease, platelet aggregation is impaired especially when induced with thrombin. Platelet adhesive mechanisms on collagen are intact despite thrombocytopenia while thrombopoiesis is active.

Hypercoagulability after energy drink consumption

BackgroundEnergy drink consumption in the United States has more than doubled over the last decade and has been implicated in cardiac arrhythmias, myocardial infarction, and even sudden cardiac death. We hypothesized that energy drink consumption may increase the risk of adverse cardiovascular events by increasing platelet aggregation, thereby resulting in a relatively hypercoagulable state and increased risk of thrombosis. MethodsThirty-two healthy volunteers aged 18–40 y were given 16 oz of bottled water or a standardized, sugar-free energy drink on two separate occasions, 1-wk apart. Beverages were consumed after an overnight fast over a 30-min period. Coagulation parameters and platelet function were measured before and 60 min after consumption using thrombelastography and impedance aggregometry. ResultsNo statistically significant differences in coagulation were detected using kaolin or rapid thrombelastography. In addition, no differences in platelet aggregation were detected using ristocetin, collagen, thrombin receptor–activating peptide, or adenosine diphosphate–induced multiple impedance aggregometry. However, compared to water controls, energy drink consumption resulted in a significant increase in platelet aggregation via arachidonic acid–induced activation (area under the aggregation curve, 72.4 U versus 66.3 U; P = 0.018). ConclusionsEnergy drinks are associated with increased platelet activity via arachidonic acid–induced platelet aggregation within 1 h of consumption. Although larger clinical studies are needed to further address the safety and health concerns of these drinks, the increased platelet response may provide a mechanism by which energy drinks increase the risk of adverse cardiovascular events.

Prevalence and predictors of high-on treatment platelet reactivity with ticagrelor in ACS patients undergoing stent implantation

BackgroundResidual high-on treatment platelet reactivity (HRPR) predicts outcomes and major cardiovascular events. Ticagrelor has provided pharmacological and clinical evidence of more predictable and more potent antiplatelet effect as compared to clopidogrel. However, so far, few data have investigated the prevalence and predictors of HRPR in unselected patients treated with ticagrelor, that is therefore the aim of the current study. Methods and resultsOur population is represented by 195 patients undergoing coronary stenting for ACS and receiving ASA and ticagrelor. Platelet function was assessed by multiplate impedance aggregometry (MEA) between 1 and 3months after stenting. Main clinical features and biochemistry parameters were collected. HRPR for ticagrelor was defined for aggregation>417 AUC after MEA-ADP stimulation. A total of 26 patients, (13.3%), displayed HRPR with ticagrelor. Older age (≥70years, p=0.002), hypertension (p=0.02) previous myocardial infarction (p=0.04), therapy with nitrates and beta-blockers (p=0.02), diuretics (p=0.03) and fasting glycaemia (p=0.05) were associated to HRPR with ticagrelor. By multivariate analysis, age≥70years (OR [95%CI]=4.6[1.55–13.8], p=0.006), concomitant therapy with beta-blockers (OR [95%CI]=3.2[1.06–9.6], p=0.04) and platelets count (OR[95%CI]=1.0007 [1–1.016], p=0.05) were identified as independent predictors of HRPR with ticagrelor. ConclusionThe present study firstly demonstrates that the occurrence of HRPR in patients treated with ticagrelor is not so futile, as it was observed in 13% of patients treated with ticagrelor. Older age, beta-blockers administration and platelets count are independent predictors of HRPR with ticagrelor.

Precision and reliability of 5 platelet function tests in healthy volunteers and donors on daily antiplatelet agent therapy.

Anticoagulation protocols used during mechanical circulatory support call for titration of antiplatelet agents. We compared the precision and reliability of 5 platelet function tests in healthy volunteers and donors on daily antiplatelet therapy to distinguish their efficacy for titrating antiplatelet therapy. We assessed arachidonic acid-induced platelet function by light transmission aggregometry (LTA), Multiplate impedance aggregometry, VerifyNow, and platelet mapping by thromboelastography (TEG PM). We assessed ADP-induced platelet function by the same methods and flow cytometry. Forty healthy volunteers and 10-13 volunteers on daily aspirin and/or clopidogrel therapy were evaluated. We compared tests for intraassay precision, interassay precision (samples from 2 separate blood draws), and reliability coefficient. For arachidonic acid-induced platelet aggregation in healthy volunteers, intra- and interassay CVs were ≤ 10% for all methods. Intra- and interassay precision among donors on daily aspirin was ≤ 30% for all methods except LTA (38% interassay CV) and TEG PM (95% intraassay and 104% interassay CV). For ADP-induced platelet function, intra- and interassay precision was ≤ 10% and ≤ 30% for all methods. Only Multiplate demonstrated moderate or greater (R > 0.40) reliability coefficients for arachidonic acid-induced platelet function among all subjects. All methods of ADP-induced platelet function, except TEG PM, demonstrated substantial or greater (R > 0.60) reliability among all subjects. TEG PM is least suited to monitor effects of antiplatelet agents. Multiplate impedance aggregometry was the only method to demonstrate an acceptable reliability coefficient among healthy volunteers and donors on both aspirin and clopidogrel therapy.

PlA1/PlA2 polymorphism does not influence response to Gp IIb-IIIa inhibitors in patients undergoing coronary angioplasty

Glycoprotein IIb-IIIa (Gp IIb-IIIa), a fibrinogen receptor located on platelet surface, is a key point in the pathway leading to platelet aggregation. Therefore, great interest has emerged in the last decades on its pharmacological block, both by irreversible binding of abciximab or by competitive small molecules (tirofiban and eptifibatide). Gp IIb-IIIa inhibitors, in fact have demonstrated to provide benefits in clinical outcome among patients with acute myocardial infarction and in complex elective percutaneous coronary intervention (PCI) procedures. Still unclear is whether the genetic Leu 33Pro substitution in Gp IIIa may affect the extent of platelet aggregation inhibition by these drugs. Therefore, the aim was to evaluate whether this polymorphism (PlA) may influence inhibition of platelet aggregation after Gp IIb-IIIa administration in patients undergoing coronary angioplasty. We analyzed 80 patients undergoing nonurgent coronary revascularization and receiving Gp IIb-IIIa inhibitors (bolus and endovenous infusion; 40 patients with Abciximab and 40 patients with eptifibatide or tirofiban). The aggregation tests were performed at baseline and after 10 min, 1 h and 4 h, through multiplate impedance aggregometry. The PlA polymorphic variant was found in 26 patients (32.5%). The PlA carriers did not differ significantly from wild-type subjects for main clinical and angiographic features, except for in-stent restenosis that was more frequent among PlA carriers (P = 0.003). Therapy and aggregation values at baseline were similar in the two groups. The Leu33Pro substitution did not influence platelet response after Gp IIb-IIIa administration, which was confirmed for both abciximab and small molecules. This study showed that Leu33Pro polymorphism of Gp IIIa does not affect the extent of inhibition of platelet aggregation by Gp IIb-IIIa inhibitors.

In vitro platelet function of platelet concentrates transfused to high risk cardiac surgery patients as determined bedside by the Multiplate impedance aggregometry

In vitro platelet function of platelet concentrates transfused to high risk cardiac surgery patients as determined bedside by the Multiplate impedance aggregometry