Determination of platelet aggregation inhibition during percutaneous coronary intervention with the platelet function analyzer PFA-100

Silica nanoparticles induced the pre-thrombotic state in rats via activation of coagulation factor XII and the JNK-NF-κB/AP-1 pathway

The pre-thrombotic state induced by SiNPsviathe interaction between platelet activation, coagulation hyperfunction, anti-coagulation and fibrinolytic resistance.

The platelet-function analyzer (PFA-100 ® ) for evaluating primary hemostasis

The platelet-function analyzer, PFA-100, is a relatively novel method for rapid in vitro global evaluation of primary hemostasis. The aim of this review is to summarize the published studies reporting on the utility of the PFA-100 device as a screening tool for primary hemostasis. Data were identified by searches of the published literature, including PubMed, references from reviews and abstracts from the most important meetings on this topic. The literature data support the use of the PFA-100 as a useful screening tool for the investigation of von Willebrand's disease and other acquired and congenital intrinsic platelet function disorders. Moreover, it is useful for evaluating primary hemostasis before surgical procedures and for monitoring desmopressin therapy in both von Willebrand's disease and platelet function disorders. Given its high sensitivity, speed and simplicity of use, we conclude that the PFA-100 could replace the in vivo bleeding time as a screening test for primary hemostasis in routine clinical practice.

Glycoprotein IIb/IIIa inhibitors: an update on the mechanism of action and use of functional testing methods to assess antiplatelet efficacy

The human glycoprotein (GP)IIb/IIIa belongs to a large family of cation-dependent adhesion molecules known as integrins, which share a common heterodimeric structure. The primary function of GPIIb/IIIa is to aid platelet aggregation by transmitting bidirectional signals across the plasma membrane. Since the GPIIb/IIIa receptor is among the key integrins involved in platelet aggregation and, therefore, thrombus formation, the development of GPIIb/IIIa antagonists (e.g., abciximab, eptifibatide and tirofiban) has become an attractive strategy for antiplatelet therapy with an expected strong and specific effect. All three drugs are administered intravenously, and large-scale clinical trials have demonstrated a clear clinical benefit and good safety profile in high-risk patients, especially those undergoing percutaneous coronary intervention. However, the adverse events related to thrombosis or bleeding are still reported in patients undergoing therapy with GPIIb/IIIa antagonists and reflect a variable interindividual responsiveness. Therefore, some form of laboratory monitoring is required to optimize the effects of a drug or to indicate that it needs replacing with other antithrombotic agents, as well as for identifying and enhancing the platelet inhibition in this subgroup of patients to improve the clinical outcome and reduce bleeding complications. As such, the aim of this article is to provide an update on the mechanism of action and use of functional testing methods to assess antiplatelet efficacy in patients undergoing therapy with GPIIb/IIIa antagonists.

Point-of-care assessment of antiplatelet agents in the perioperative period: a review

The aim of this paper was to review the strengths and limitations of current 'point-of-care' techniques for the detection of antiplatelet drug effects. The review was based on a Medline search for articles with key words related to "platelet function tests", "point-of-care", and "anaesthesia", published in English between January 1996 and September 2008. It was found that global assessments of 'haemostasis', such as the standard thrombelastograph, Sonoclot, Clot Signature Analyser and Hemodyne, are not specific for platelet function and are essentially insensitive to cyclooxygenase inhibitors (aspirin, non-steroidal anti-inflammatory drugs) and P2Y12 antagonists (ticlopidine, clopidogrel). Global assessments of 'platelet function', such as the PFA-100 and PlateletWorks, are more specific for platelet function, but also have limited sensitivity for cyclooxygenase inhibitors and P2Y12 antagonists. The newer devices developed specifically for the assessment of antiplatelet drugs, such as Platelet Mapping, the Impact Cone and Platelet Analyser and the VerifyNow, are more promising, but are not as sensitive as laboratory platelet aggregometry. All three categories of devices detect G(p)II(b)/III(a) antagonists (abciximab, tirofiban, eptifibatide) activity, but not all provide quantitative assessments for monitoring therapy. The limitations appeared to be related to the complexity of platelet function, the multiple pathways of platelet activation, the wide interpatient variability in platelet responses and the interdependence between platelets and other aspects of coagulation. The strengths and limitations of point-of-care devices should be appreciated before they are used to assist clinical decision-making in the perioperative period.

Monitoring antiplatelet therapy during peripheral vascular and coronary interventions

Platelets play a central role in the initiation and propagation of thrombus formation. The use of antiplatelet and antithrombotic medications during peripheral vascular and coronary interventions helps reduce the likelihood of intravascular thrombus formation and adverse ischemic events. As formation of intravascular thrombus and subacute stent thrombosis are thrombin- and platelet-mediated phenomenon, achieving optimal activated clotting time and platelet inhibition (PI) during the interventional procedure is critical. However, as a quick and easy measure of platelet function has previously not been available in the interventional laboratory, cardiovascular interventions are routinely performed after administration of oral or intravenous antiplatelet agents without evaluating platelet function. Recently, point-of-care rapid platelet function assays have become available that allow quick and reproducible measure of platelet function in the interventional laboratory after administration of aspirin, thienopyridines, and glycoprotein IIb/IIIa inhibitors. Though PI can now be routinely measured during vascular interventions, considerable inconsistencies exist in the management of patients based on these results. We present an algorithm for the management of antiplatelet therapy during cardiovascular interventions based on rapid evaluation of platelet function in the interventional laboratory.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Measuring antiplatelet drug effects in the laboratory

This review discusses the advantages and disadvantages of currently available tests for the monitoring of antiplatelet therapy (especially aspirin and clopidogrel). Many tests of platelet function are now available for clinical use, and some of these tests have been shown to predict clinical outcomes after antiplatelet therapy. However, in most of these studies, the number of major adverse clinical events was low. No published studies address the clinical effectiveness of altering therapy based on the results of monitoring antiplatelet therapy. Therefore, the correct treatment, if any, of "resistance" to antiplatelet therapy is unknown and, other than in research trials, monitoring of antiplatelet therapy in patients is not generally recommended. A clinically meaningful definition of "resistance" to antiplatelet drugs needs to be developed, based on data linking drug-dependent laboratory tests to clinical outcomes in patients.

Value of Platelet Reactivity in Predicting Response to Treatment and Clinical Outcome in Patients Undergoing Primary Coronary Intervention

OBJECTIVES

The purpose of this study was to evaluate the value of platelet reactivity (PR) in predicting the response to treatment and outcome in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention assisted by glycoprotein (GP) IIb/IIIa inhibition.

BACKGROUND

There is limited prognostic information on the role of spontaneous or drug-modulated PR in STEMI patients.

METHODS

The PR was measured with Platelet Function Analyzer (PFA)-100 and light transmission aggregometry (LTA) using adenosine diphosphate as agonist in 70 consecutive STEMI patients at entry (PR-T0), 10 min after GP IIb/IIIa bolus (PR-T1), and discharge (PR-T2) and in 30 stable angina (SA) patients (PR-SA). Complete platelet inhibition (CPI) was based on closure time >300 s by PFA-100 and percentage inhibition of platelet aggregation >95% by LTA. Clinical, electrocardiographic, and angiographic responses to treatment during 1-year follow-up were collected.

RESULTS

According to both techniques, PR-T0 was higher than: 1) PR-T2 and PR-SA; 2) in those without CPI at T1; and 3) in patients with final Thrombolysis In Myocardial Infarction (TIMI) flow grade <3. The PR-T0 assessed with PFA-100 correlated with: 1) corrected TIMI frame count (r = -0.6, p < 0.001); 2) ST-segment resolution (r = 45, p < 0.001); and 3) creatine kinase-MB (r = -0.47, p < 0.001). At 1 year, patients with high PR-T0 showed an adjusted 5- to 11-fold increase in the risk of death, reinfarction, and target vessel revascularization (hazard ratio [HR] 11, 95% confidence interval [CI] 1.5 to 78 [p = 0.02] in PFA-100; HR 5.2, 95% CI 1.1 to 23 [p = 0.03] in LTA).

CONCLUSIONS

The PR at entry affects response to GP IIb/IIIa inhibition, mechanical treatment, and long-term outcome in STEMI patients undergoing primary intervention.

Current options in platelet function testing

The variable response to antiplatelet therapy has led to the use of platelet function tests to monitor the effects of antiplatelet drugs in cardiovascular diseases. The goal is to guide antiplatelet therapy to the optimal dose for the prevention or treatment of thrombosis while minimizing hemorrhagic side effects. The bleeding time is no longer recommended for use because of its nonspecificity and lack of clinical correlations. The current de facto "gold standard" test of platelet function is turbidometric platelet aggregometry. Although this method has been successful in measuring the aggregation of platelets in a glycoprotein (GP) IIb/IIIa (integrin alpha(IIb)beta(3))-dependent manner, it has several limitations, including poor reproducibility, high sample volume, requirement for sample preparation, length of assay time, requirement for a skilled technician, and cost. Therefore, new options for platelet function testing have been developed to address these disadvantages and to meet the need for point-of-care testing that can be performed at or near a patient's bedside without requiring a high degree of technical expertise. The new tests include VerifyNow (Accumetrics, San Diego, CA); Plateletworks (Helena Laboratories, Beaumont, TX); Thrombelastograph PlateletMapping System (Haemoscope Corporation, Niles, IL); Impact cone and plate(let) analyzer (DiaMed, Cressier, Switzerland); and Platelet Function Analyzer 100 (PFA-100; Dade Behring, Newark, DE). In patients treated with antiplatelet drugs, the degree of platelet inhibition, as determined by several of these new platelet function assays, has been shown to predict major adverse cardiac events.

Single high-dose bolus tirofiban with high-loading-dose clopidogrel in primary coronary angioplasty

Glycoprotein IIb/IIIa inhibitor therapy during primary percutaneous coronary intervention (PCI) decreases the incidence of major adverse cardiac events. These effects directly result from the level of platelet inhibition. It was shown that standard dosing of tirofiban is insufficient for optimal platelet inhibition. We sought to determine the efficacy and safety of single high-dose bolus (HDB) tirofiban with high-dose clopidogrel loading in primary PCI in acute ST elevation myocardial infarction. A total of 100 patients (mean age 55.2 +/- 9.9 years, male/female = 86/14) undergoing primary PCI, pretreated with clopidogrel (450 mg) and aspirin (325 mg), were consecutively randomized into two groups. Group I (n = 50) received a standard dose bolus of tirofiban (10 microg/kg/3 min) with 24-h infusion at a rate of 0.15 microg/kg/min. Group II received single HDB tirofiban (25 microg/kg/3 min). The assessed angiographic, clinical, and echocardiographic endpoints were: initial and final Thrombolysis in Myocardial Infarction (TIMI) grade flow (TGF), corrected TIMI frame count (CTFC), ST-segment resolution (STR) at 90 min, in-hospital bleeding complications, echocardiographic left ventricular ejection fraction (LVEF), death, reinfarction, and repeat target vessel revascularization at 1 month. Platelet function inhibition was measured using PFA-100 (Behring-Dade, Liederbach, Germany) with a test cartridge unit containing a membrane coated with 2 microg of equine Type I collagen and 50 microg adenosine diphosphate before, and 10 min, 2, 4, 6, 12, and 24 h after the bolus of the tirofiban in the first 10 cases of each group. There were no significant differences in baseline characteristics between groups. Initial TGF III was more frequent (24% vs 8%, P = 0.029) and the value of CTFC was lower (75 +/- 34 vs 89 +/- 25, P = 0.03) in group II. Postprocedural TGF, CTFC, STR, bleeding complications, and LVEF at 1 month were not different between the two groups. There was a higher rate of reinfarction in group II (8%) compared with group I (2%), but this difference was not statistically significant (P > 0.05). The results of platelet function analyses showed that group II patients had significantly prolonged platelet function assay closure times (299 +/- 6 s) compared with group patients (236 +/- 97 s) at 10 min after the bolus dose (P = 0.04). However, after the first dose between 2 and 24 h, PFA closure times were significantly prolonged in patients with tirofiban infusion. High-dose bolus of tirofiban seems to be safe and more effective than conventional dose at the periprocedural time, whereas continuous infusion of tirofiban may be necessary in the first 24 h before stable and safe antiplatelet status is reached with clopidogrel. However, safety and efficacy of HDB tirofiban and high-loading-dose clopidogrel together with tirofiban infusion requires further studies with a larger population.

Platelet function analyzer (PFA)-100 closure time in the evaluation of platelet disorders and platelet function

BACKGROUND

Closure time (CT), measured by platelet function analyzer (PFA-100) device, is now available to the clinical laboratory as a possible alternative or supplement to the bleeding time test.

AIM

On behalf of the Platelet Physiology Subcommittee of the Scientific and Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH-SSC), a working Group was formed to review and make recommendations on the use of the PFA-100 CT in the evaluation of platelet function within the clinical laboratory.

METHODS

The Medline database was searched to review the published information on the PFA-100 CT in the evaluation of platelet disorders and platelet function. This information, and expert opinion, was used to prepare a report and generate consensus recommendations.

RESULTS

Although the PFA-100 CT is abnormal in some forms of platelet disorders, the test does not have sufficient sensitivity or specificity to be used as a screening tool for platelet disorders. A role of the PFA-100 CT in therapeutic monitoring of platelet function remains to be established.

CONCLUSIONS

The PFA-100 closure time should be considered optional in the evaluation of platelet disorders and function, and its use in therapeutic monitoring of platelet function is currently best restricted to research studies and prospective clinical trials.

In vitro effects of gelatin solutions on platelet function: a comparison with hydroxyethyl starch solutions

The aim of this study was to investigate the effects of various gelatin and hydroxyethyl starch solutions on platelet reactivity. Citrated whole blood was obtained from 20 healthy volunteers. Expression of glycoprotein (GP) IIb-IIIa and p-selectin were determined using whole blood flow cytometry on both resting and agonist-activated platelets before and after in vitro haemodilution (20% and 40%) using oxypolygelatin, modified gelatin, urea-linked gelatin, hydroxyethyl starch (HES) 130 (mean molecular weight in kDa), HES 200, HES 450 and HES 550. High degrees of haemodilution using oxypolygelatin had no significant effect, similar to HES 130, whereas modified gelatin inhibited GP IIb-IIIa expression, similar to HES 200 and HES 450. Urea-linked gelatin significantly increased the expression of GP IIb-IIIa, similar to HES 550. p-selectin expression remained unchanged in all samples. The present in vitro study indicates that chemical characteristics of colloidal solutions modulate their influence on platelet reactivity.

Platelet function predicts myocardial damage in patients with acute myocardial infarction

BACKGROUND

Platelet activation is a hallmark of acute coronary syndromes. Numerous lines of evidence suggest a mechanistic link between von Willebrand factor or platelet hyperfunction and myocardial damage in patients with acute coronary syndromes. Thus, we assessed whether platelet function under high shear rates (collagen adenosine diphosphate closure times [CADP-CTs]) measured with the platelet function analyzer (PFA-100) may be enhanced in patients with myocardial infarction (MI) and whether it may predict the extent of myocardial damage as measured by creatine kinase (CK-MB) or troponin T (TnT) levels.

METHODS AND RESULTS

Patients with acute chest pain or symptoms suggestive of acute coronary syndromes (n=216) were prospectively examined at an emergency department. CADP-CT was significantly shorter in patients with MI, particularly in those with an ST-segment-elevation MI (STEMI) compared with the other patient groups (unstable angina, stable coronary artery disease, or controls). Furthermore, CADP-CT and collagen epinephrine-CT at presentation were independent predictors of myocardial damage as measured by CK-MB or TnT. Patients with MI whose CADP-CT values fell in the first quartile had 3-fold higher CK-MB and TnT levels than those in the fourth quartile.

CONCLUSIONS

Patients with STEMI have significantly enhanced platelet function when measured under high shear rates. CADP-CT is an independent predictor of the severity of MI, as measured by markers of cardiac necrosis. Measurement of platelet function with the PFA-100 may help in the risk stratification of patients presenting with MI.

Variable inhibition of high-shear-induced platelet plug formation by eptifibatide and tirofiban under conditions of platelet activation and high von Willebrand release: a randomized, placebo-controlled, clinical trial

BACKGROUND

Glycoprotein (GP) IIb/IIIa antagonists have become a mainstay for the treatment of acute coronary syndromes. Yet, they have rarely been evaluated under relevant pathophysiologic conditions, for example, high shear rates in the presence of physiologic calcium concentrations. We compared the efficacy of eptifibatide and tirofiban versus placebo on high shear-induced platelet plug formation in a model in which healthy subjects exhibit von Willebrand factor concentrations and platelet activation comparable to patients with acute coronary syndromes.

METHODS

Thirty male volunteers received 2 ng/kg endotoxin and standard doses of eptifibatide, tirofiban, or placebo over a period of 5 hours in a randomized, double-blinded, placebo-controlled, double-dummy parallel-group trial. Platelet inhibition was measured with the Platelet Function Analyzer-100 (PFA-100) and the Ultegra method.

RESULTS

Although bolus infusion of both GPIIb/IIIa antagonists inhibited high shear-induced platelet plug formation, continuous infusion of eptifibatide prolonged closure times more effectively than did tirofiban (P <.008). Interestingly, tirofiban had only placebo-like effects on platelet plug formation after 2 hours. However, when additional drug was exogenously added, closure time values were maximally prolonged in all cases.

CONCLUSIONS

Standard doses, particularly of tirofiban, have limited impact on high shear-induced platelet plug formation at physiologic Ca(2+) concentrations.