The use of activated clotting times to monitor heparin therapy during and after interventional procedures

Construction of a highly sensitive detection platform for heparin based on a "turn-off" cationic fluorescent dye

A highly sensitive detection platform for heparin was constructed via the utilization of a commercially available cationic fluorescent dye (cresyl violet acetate, CV) as a fluorescence probe. The electrostatic binding between CV and heparin quenched the fluorescence in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic (HEPES) buffer solution (10 mM, pH 7.1). CV was highly selective towards heparin over other potential inferring substances. The detection limit of heparin detection was 5.19 ng/mL, and the linear working range was 0 ∼ 1 μg/mL in HEPES solution. In 1 % serum, the detection platform based on the fluorescence "turn-off" behavior of CV was also successfully constructed with a detection limit of 5.86 ng/mL in the linear range of 0 ∼ 0.8 μg/mL. Moreover, the CV-heparin complex was considered a potential sensor platform for the detection of protamine because of its stronger affinity for heparin and protamine.

Percutaneous Coronary Intervention with Procedural Unfractionated Heparin without Activated Clotting Time Guidance: A Unique Opportunity to Assess Thrombotic and Bleeding Events

Background

Rates of major bleeding and intraprocedural thrombotic events (IPTE) in the setting of percutaneous coronary intervention (PCI) using weight-adjusted unfractionated heparin (UFH) without activated clotting time (ACT) monitoring are not known.

Methods

We reviewed 2,748 consecutive patients who underwent coronary angiography at our tertiary care university hospital between January 2017 and December 2020. All patients who underwent PCI with weight-adjusted UFH without ACT guidance were considered for further analysis. Major bleeding complications occurring within 48 hours of PCI were collected from patients' medical records. IPTE were collected independently by two interventional cardiologists after review of coronary angiograms.

Results

There were 718 patients included in the analysis (65.4 ± 12.2 years old; 81.3% male). In total, 45 patients (7.8%) experienced a major bleed or IPTE. The most common IPTE were slow/no reflow (1.5%) and coronary artery dissection with decreased flow (1.1%). Other IPTE occurred in <1% of cases. Major bleeding occurred in 11 patients (1.5%), of whom 8 required blood transfusion and 3 required vascular intervention. Bleeding complications were more common with femoral compared with radial access (6.6% vs. 0.2%, P < 0.001).

Conclusion

Weight-adjusted UFH use during PCI without ACT monitoring was related to low rates of major bleeding or IPTE.

The Evolution of Anticoagulation for Percutaneous Coronary Intervention: A 40-Year Journey

The selection of antithrombotic strategies continue to be of utmost importance during percutaneous coronary intervention (PCI) and have evolved over the past 40 years. Although the backbone of therapy during PCI continues to be a combination of oral antiplatelets and parenteral anticoagulants, a variety of different approaches have been tested over time. In particular, different choices of anticoagulation management have been tested in the stable ischemic heart disease and acute coronary syndrome setting. Evaluation of alternative regimens in the quest to balance ischemic and bleeding risk have undoubtedly improved patient care with PCI. In the current review we highlight the evolution of evidence-based therapeutic options over the past 40 years from the beginning of coronary angioplasty to contemporary PCI. We provide insight into future therapeutic options and provide a contemporary overview of anticoagulation choices for patients who require PCI on the basis of up-to-date evidence balancing ischemic and bleeding risk and according to clinical presentation.

Optimization of Heparin Monitoring with Anti-FXa Assays and the Impact of Dextran Sulfate for Measuring All Drug Activity

Heparins, unfractionated or low molecular weight, are permanently in the spotlight of both clinical indications and laboratory monitoring. An accurate drug dosage is necessary for an efficient and safe therapy. The one-stage kinetic anti-FXa assays are the most widely and universally used with full automation for large series, without needing exogenous antithrombin. The WHO International Standards are available for UFH and LMWH, but external quality assessment surveys still report a high inter-assay variability. This heterogeneity results from the following: assay formulation, designed without or with dextran sulfate to measure all heparin in blood circulation; calibrators for testing UFH or LMWH with the same curve; and automation parameters. In this study, various factors which impact heparin measurements are reviewed, and we share our experience to optimize assays for testing all heparin anticoagulant activities in plasma. Evidence is provided on the usefulness of low molecular weight dextran sulfate to completely mobilize all of the drug present in blood circulation. Other key factors concern the adjustment of assay conditions to obtain fully superimposable calibration curves for UFH and LMWH, calibrators' formulations, and automation parameters. In this study, we illustrate the performances of different anti-FXa assays used for testing heparin on UFH or LMWH treated patients' plasmas and obtained using citrate or CTAD anticoagulants. Comparable results are obtained only when the CTAD anticoagulant is used. Using citrate as an anticoagulant, UFH is underestimated in the absence of dextran sulfate. Heparin calibrators, adjustment of automation parameters, and data treatment contribute to other smaller differences.

Coagulation and heparin requirements during ablation in patients under oral anticoagulant drugs

BACKGROUND

Anticoagulation during catheter ablation should be closely monitored with activated clotting time (ACT). However vitamin K antagonists (VKA) or direct oral anticoagulant drugs (DOAC) may act differently on ACT and on heparin needs. The aim of this study was to compare ACT and heparin requirements during catheter ablation under various oral anticoagulant drugs and in controls.

METHODS

Sixty consecutive patients referred for ablation were retrospectively included: group I (n = 15, VKA), group 2 (n = 15, uninterrupted rivaroxaban), group 3 (n = 15, uninterrupted apixaban), and group 4 (n = 15, controls). Heparin requirements and ACT were compared throughout the procedure.

RESULTS

Heparin requirements during the procedure were significantly lower in patients under VKA compared to DOAC, but similar between DOAC patients and controls.Activated clotting time values were significantly higher in patients under VKA compared to DOAC and similar in DOAC patients versus controls. Furthermore, anticoagulation control as evaluated by the number/proportion of ACT> 300 as well as the time passed over 300 seconds was significantly better in patients under VKA versus DOAC, without significant differences between DOAC and controls. Finally, the number of patients/ACT with excessive ACT values was significantly higher in VKA versus DOAC patients versus controls.There was no significant difference between rivaroxaban and apixaban for ACT or heparin dosing throughout the procedure.

CONCLUSION

Vitamin K antagonists allowed less heparin requirement despite reaching higher ACT values and more efficient anticoagulation control (with more excessive values) compared to patients under DOAC therapy and to controls. There was no difference in heparin requirements or ACT between DOAC patients and controls.

An anionic polyelectrolyte induced aggregate assembly of Thioflavin-T: A prospective platform for Protamine sensing

Protamine, a polycation, is biologically and medically relevant protein. Protamine exhibits a wide array of functions in biological processes like gene transfer, tissue and organogenesis, cell reproduction, etc. Medically, Protamine is the only clinically approved antidote for Heparin and is routinely used in various surgical interventions, and hence controlling Protamine dosing in patients is very crucial. Taking into account the medical significance of Protamine, designing simple, reliable and sensitive fluorescence sensors is highly desirable. In this work, we propose one such sensitive and reliable fluorescent sensor which is based on a template of dye-polyelectrolyte assembly constituting a molecular rotor dye, Thioflavin-T and an anionic synthetic polyelectrolyte, polystyrene sulfonate. The addition of Protamine, prompts drastic modulations in spectral features of dye-polyelectrolyte assembly which enables sensitive detection of Protamine in aqueous solution. Apart from sensitive detection, our sensing platform aids in highly selective sensing of Protamine compared to other proteins. Moreover, our sensor system is constructed on label-free, inexpensive, commercially available molecules posing as an advantage over other sensor systems which involve laborious synthesis protocols. Most importantly, our sensor template is able to sense Protamine in diluted serum sample, indicating the potential practical utility of our sensor system.

Heparin sensing based on multisite-binding induced highly ordered perylene nanoaggregates

Heparin sensing based on highly ordered perylene nanoaggregates with ultra-low fluorescence and the use of host–guest complexes to improve the sensitivity.

A facile chemiluminescence sensing for ultrasensitive detection of heparin using charge effect of positively-charged AuNPs

Heparin is a glycosaminoglycan with the highest negative charge density of any known biological molecule. Herein, this highly negative charge structure of heparin and the charge effect from positively-charged AuNPs for luminol chemiluminescence (CL) reaction were combined to build a facile and sensitive CL strategy for detection of heparin. The highly negative charge structure of heparin molecules (four negatively-charged side groups per repeat unit) and the effective signal amplification of charge effect from positively-charged AuNPs make this analysis to display high sensitivity for heparin detection, and the detection limit is as low as 0.06 ng/mL. It is about two orders of magnitude lower than the previously reported colorimetric assay and far lower than the current analysis methods. The established CL strategy is to use the electrostatic interaction between heparin and signal probe (positively-charged AuNPs). Since polyanionic heparin has the highest negative charge in biological system, this CL sensing shows high selectivity for the detection of heparin, and hyaluronic acid (HA), an analogue of heparin, cannot cause interference. This CL sensing succeeded in detecting heparin in human serum samples. Besides, polycationic protamine, heparin antidote, can respond to the system's CL signals through its strong interactions with heparin, thus indirectly detecting protamine. For protamine in serum samples, the detection result was basically consistent with Coomassie brilliant blue assay.

Specific enrichment combined with highly efficient solid-phase tagging for the sensitive detection of heparin based on boronic acid-functionalized mesoporous silica nanospheres

A combined specific enrichment and highly efficient solid-phase tagging approach is presented for heparin detection using boronic acid-functionalized mesoporous silica nanospheres as extraction sorbents and nanoscale reactors. It exhibits a faster reaction time (only 6 min), higher tagging-product purity and lower applicable sample concentration compared with liquid-phase tagging.

Comparison of activated clotting times measured using the Hemochron Jr. Signature and Medtronic ACT Plus during cardiopulmonary bypass with acute normovolemic haemodilution

Objective

This study compared the activated clotting time (ACT) measured using the Hemochron Jr. Signature (HACT) with the ACT measured using the Medtronic ACT Plus (MACT) during cardiopulmonary bypass (CPB) with acute normovolemic haemodilution (ANH) in patients undergoing cardiac surgery.

Methods

The ACT was checked at baseline with both devices after inducing anaesthesia, and 400 to 800 mL of whole blood was withdrawn to induce moderate ANH. Before initiating CPB, a 300-IU/kg bolus dose of heparin was administered to maintain the HACT at >400 s; protamine was later given to reverse the anticoagulation. The ACT was checked using both devices at baseline, during heparinisation, and after protamine administration.

Results

In total, 106 pairs of samples from 29 patients were analysed. The ACT showed a good correlation between the two devices (r = 0.956). However, Bland–Altman analysis showed that the MACT was higher, particularly at baseline and during heparinisation. Multiple regression analysis showed that the blood glucose concentration significantly influenced the differences between the two ACT devices.

Conclusions

The HACT was lower than the MACT during CPB with ANH in patients undergoing cardiac surgery. Clinicians should be cautious when using each ACT device within generally accepted reference ACT values.

Highly selective and sensitive detection of heparin based on competition-modulated assembly and disassembly of fluorescent gold nanoclusters

A simple and economical fluorescence assay for heparin using glutathione-protected gold nanoclusters via competitive binding was developed.

Factors Influencing ACT After Intravenous Bolus Administration of 100 IU/kg of Unfractionated Heparin During Cardiac Catheterization in Children

Anticoagulation using intravenous bolus administration of unfractionated heparin (UFH) aims to prevent thromboembolic complications in children undergoing cardiac catheterization (CC). Optimal UFH dosage is needed to reduce bleeding complications. We analyzed the effect of bolus UFH on activated clotting time (ACT) in children undergoing CC focusing on age-dependent, anesthesia-related, or disease-related influencing factors. This retrospective single-center study of 183 pediatric patients receiving UFH during CC analyzed ACT measured at the end of CC. After bolus administration of 100 IU UFH/kg body weight, ACT values between 105 and 488 seconds were reached. Seventy-two percent were within target level of 160 to 240 seconds. Age-dependent differences were not obtained ( P = .407). The ACT values were lower due to hemodilution (total fluid and crystalloid administration during CC, both P < .001), with premedication of acetylsalicylic acid ( P = .014) and low-molecular-weight heparin ( P = .049). Arterial thrombosis (3.85%), venous thrombosis (0.55%), and bleeding (1.65%) following CC did not correlate with ACT values but occurred more frequently in children between 1 month and 1 year of age (91%). In conclusion, with a bolus of 100 IU UFH/kg, an ACT target level of 160 to 240 seconds can be achieved during CC in children in 72%, which is influenced by hemodilution and anticoagulant and antiplatelet premedication but not by age.

Modulating luminescence of Tb(3+) with biomolecules for sensing heparin and its contaminant OSCS

The detection of heparin (Hep) and its contaminant oversulfated chondroitin sulfate (OSCS) is of great importance in clinics but remains challenging. Here, we report a sensitive and selective time-resolved luminescence (TRL) biosensing system for Hep by modulating the photoluminescence of Tb(3+) with guanine-rich ssDNA and Hep-specific AG73 peptide (RKRLQVQLSIRT). With the developed system, Hep including both unfractionated Hep (UFH) and the low molecular weight Hep (LMWH) has been successfully detected with a satisfactory detection limit. Owing to the highly specific interaction between Hep and AG73 peptide, major interfering substances in Hep detection, such as Hep analogs of chondrotin sulfate (Chs) and hyaluronic acid (HA), did not interfere with Hep detection. The established TRL sensing system was then successfully used for monitoring Hep metabolism in living rats by microdialysis. Moreover, the proposed TRL sensing system was further applied to analyze OSCS contaminant in Hep with heparinases treatment by exploring the inhibition effects of OSCS on the activity of heparinases. As low as 0.002% of OSCS in Hep was identified.

A "turn on" fluorescent probe for heparin and its oversulfated chondroitin sulfate contaminant

Designing "turn on" fluorescent probes for heparin (Hep), a widely used anticoagulant in clinics, is of great importance but remains challenging. By introducing a Hep specific binding peptide AG73 to a typical aggregation induced emission (AIE) fluorogen, tetraphenylethene (TPE), a sensitive and selective "turn on" fluorescent probe named TPE-1 for Hep was developed. TPE-1 was able to detect Hep in a wide pH range of 3-10 without obvious interference from tested anions and biomolecules, especially Hep analogues known as chondroitin sulfate (Chs) and hyaluronic acid (HA). The detection limit of Hep sensing was 3.8 ng mL-1, which was far below the clinically demanded concentration of Hep. The probe was applicable to both unfractionated Hep and low molecular weight Hep, the two main heparin products clinically used. Besides, the fluorescence of Hep bound TPE-1 can be turned off via sequential treatment with heparinases. Importantly, this phenomenon allows us to develop an enzyme assisted strategy for "turn on" sensing of oversulfated chondroitin sulfate (OSCS) with a detection limit of 0.001% (w%), which is the main contaminant in Hep and may cause severe adverse reactions including death.

Anti-platelet and anti-thrombotic approaches in patients undergoing percutaneous coronary intervention

Over the past three decades, there has been a tremendous increase in the use of percutaneous coronary interventions (PCI) for the treatment of patients with atherosclerotic coronary artery disease. However, PCI causes disruption of atherosclerotic plaque and denudation of the endothelium, leading to stimulation of platelet aggregation and activation of the coagulation cascade. Therefore, anti-platelet and anti-thrombotic agents have a pivotal role as adjuncts before, during and after PCI, in order to minimize the risk of procedural ischemic complications, such as myocardial infarction, stent thrombosis, and various degrees of myonecrosis. The current article presents a comprehensive review of the evolution of current anti-platelet and anticoagulation regimens used in the setting of PCI. It starts with a summary of the current perspective of the coagulation process along with platelet activation and aggregation. The review then focuses specifically on individual anti-platelet and anti-thrombotic drugs including their mechanism of action and the scientific evidence which led to their use in PCI. Finally, we present summary recommendations from the AHA/ACC guidelines for individual anticoagulant and anti-platelet regimens given peri-PCI.

Point-of-care ecarin clotting time versus activated clotting time in correlation with bivalirudin concentration

INTRODUCTION

A thrombin inhibitor management (TIM) point-of-care test based upon the ecarin clotting time (ECT) has been developed. The ECT has been suggested to more accurately reflect the anti-coagulant effect of direct thrombin inhibitors compared with the activated clotting time (ACT). We sought to examine the correlation of the TIM-ECT test with bivalirudin concentration in patients undergoing percutaneous coronary intervention (PCI), and to compare the performance of this test with the current standard (i.e., ACT).

MATERIALS AND METHODS

In a multicenter study, blood samples were obtained at six pre-defined time-points in 170 consecutive patients undergoing PCI using bivalirudin. For each sample, the TIM-ECT (citrated and non-citrated), ACT, and bivalirudin concentration was determined.

RESULTS

Considering samples from all time-points (n=784), the correlations of TIM-ECT citrated, TIM-ECT non-citrated, and ACT with bivalirudin concentration were 0.96, 0.93, and 0.90, respectively. For samples collected at therapeutic levels of bivalirudin (n=353), the correlations of TIM-ECT citrated, TIM-ECT non-citrated, and ACT with bivalirudin concentration were lower, and showed a greater disparity between methods, with correlation coefficients of 0.75, 0.59, and 0.37, respectively. Prediction models based on the measured bivalirudin concentration were developed for TIM-ECT and ACT, and the coefficients of determination (r(2)) of actual versus predicted TIM-ECT and ACT were 0.91 and 0.81, respectively.

CONCLUSIONS

In this PCI population, the TIM-ECT point-of-care test and ACT demonstrated a strong correlation with bivalirudin concentration. The TIM-ECT test had a higher correlation with bivalirudin concentration at therapeutic levels of the drug, and for individual samples appears to more consistently reflect the bivalirudin concentration compared with the ACT.

Antithrombotic therapy during percutaneous coronary intervention: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This chapter about antithrombotic therapy during percutaneous coronary intervention (PCI) is part of the seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients' values may lead to different choices (for a full understanding of the grading, see Guyatt et al, CHEST 2004;126:179S-187S). Among the key recommendations in this chapter are the following: For patients undergoing PCI, we recommend pretreatment with aspirin, 75 to 325 mg (Grade 1A). For long-term treatment after PCI, we recommend aspirin, 75 to 162 mg/d (Grade 1A). For long-term treatment after PCI in patients who receive antithrombotic agents such as clopidogrel or warfarin, we recommend lower-dose aspirin, 75 to 100 mg/d (Grade 1C+). For patients who undergo stent placement, we recommend the combination of aspirin and a thienopyridine derivative (ticlopidine or clopidogrel) over systemic anticoagulation therapy (Grade 1A). We recommend clopidogrel over ticlopidine (Grade 1A). For all patients undergoing PCI, particularly those undergoing primary PCI, or those with refractory unstable angina or other high-risk features, we recommend use of a glycoprotein (GP) IIb-IIIa antagonist (abciximab or eptifibatide) [Grade 1A]. In patients undergoing PCI for ST-segment elevation MI, we recommend abciximab over eptifibatide (Grade 1B). In patients undergoing PCI, we recommend against the use of tirofiban as an alternative to abciximab (Grade 1A). In patients after uncomplicated PCI, we recommend against routine postprocedural infusion of heparin (Grade 1A). For patients undergoing PCI who are not treated with a GP IIb-IIIa antagonist, we recommend bivalirudin over heparin during PCI (Grade 1A). In PCI patients who are at low risk for complications, we recommend bivalirudin as an alternative to heparin as an adjunct to GP IIb-IIIa antagonists (Grade 1B). In PCI patients who are at high risk for bleeding, we recommend that bivalirudin over heparin as an adjunct to GP IIb-IIIa antagonists (Grade 1B). In patients who undergo PCI with no other indication for systemic anticoagulation therapy, we recommend against routine use of vitamin K antagonists after PCI (Grade 1A).

Measurement of activated clotting time in children--comparison of the Celite i-STAT ACT with the Medtronic ACT II

BACKGROUND

To evaluate a recently introduced blood-saving method for the measurement of activated clotting time (ACT), the Celite i-STAT ACT, by comparing the values obtained with those from the widely used Medtronic ACT II device.

METHODS

In a prospective clinical study, we compared ACT values from the i-STAT device with the Medtronic ACT II device in 60 paediatric, interventional, cardiac catheterization procedures necessitating prophylactic heparinization. Blood samples were pair-analyzed using two i-STAT analyzers and one Medtronic ACT II device with double-tube-cartridges before and after heparinization. Data were compared using Bland-Altman bias analysis, Student's t-test and simple regression analysis.

RESULTS

Bias and precision between the Medtronic ACT II and the i-STAT ACT values was -5.4 +/- 26.3. The i-STAT and Medtronic ACT II values were similar before heparinization (P = 0.22), but i-STAT ACT values became significantly longer than Medtronic ACT II values after heparinization (P = 0.021). The increase of ACT after heparinization was greater (median 86.3; range 40-187 s) in the i-STAT analyzer than in the Medtronic ACT II analyzer (median 73.0; range 19-235.5 s). Increase in ACT values was inversely affected by intraoperative haemoglobin concentration in the Medtronic ACT II analyzer (P = 0.001) but not in the i-STAT analyzer.

CONCLUSION

Activated clotting times obtained from the Celite i-STAT ACT and the Medtronic ACT II demonstrated poor agreement. The technical principles are quite different and the two methods showed diverse susceptibility to intraoperative haemoglobin concentration. Users have to be aware of technique-specific ACT target ranges and their confounders, which need to be provided by the manufacturers.

Effect of abciximab versus tirofiban on activated clotting time during percutaneous intervention and its relation to clinical outcomes--observations from the TARGET trial

Previous evidence suggests that the monoclonal antibody abciximab may have a more potent anticoagulant effect than small-molecule glycoprotein (GP) IIb/IIIa inhibitors. We prospectively reviewed collected heparin dose, activated clotting time (ACT), and corresponding clinical outcome data from The Do Tirofiban and ReoPro Give Similar Efficacy Outcome Trial (TARGET), a direct comparison of tirofiban versus abciximab in patients who underwent percutaneous intervention. Of the 4,809 patients enrolled in the trial, 3,739 patients (78%) had an ACT measured after the administration of GP IIb/IIIa and heparin (peak procedural ACT); this formed the population for the present study. Mean total heparin dose was 75 +/- 32 and 76 +/- 31 U/kg in the tirofiban and abciximab groups, respectively. The resultant mean peak ACTs were 296 +/- 91 and 299 +/- 89 seconds (p = 0.09). In a subset of patients with both baseline ACT (before any heparin or GP IIb/IIIa therapy) and peak procedural ACT measurements, the difference in ACT between these time points was 80 +/- 97 vs 82 +/- 101 seconds (p = 0.44) for the tirofiban and abciximab groups, respectively. After adjusting for patients' weight, weight-adjusted heparin dose, and method of ACT measurement in a multiple linear regression analysis, the type of GP IIb/IIIa inhibitor was not predictive of the peak ACT (p = 0.24). When stratified by ACT quartile, no statistically significant difference in bleeding or ischemic end points between the tirofiban and abciximab cohorts was observed. In this large contemporary percutaneous coronary intervention trial, there was no observed difference in the anticoagulant effect of tirofiban and abciximab, as measured by the ACT, or in the incidence of bleeding or ischemic complications in each ACT quartile.

Heparin dose during percutaneous coronary intervention: how low dare we go?

Despite dramatic advances in percutaneous coronary intervention, including coronary stents and potent antiplatelet agents, unfractionated heparin remains the standard procedural anticoagulant. Tradition and habit may have considerable influence over dose selection. A review of the role and dosage of heparin during PCI appears to be overdue

Unfractionated versus fractionated heparin for percutaneous coronary intervention

Since the advent of percutaneous coronary intervention (PCI), intravenous unfractionated heparin has been the primary antithrombotic therapy to prevent periprocedural ischemic complications. As compared with unfractionated heparin, low molecular weight heparins (LMWHs) have a greater bioavailability and a more predictable therapeutic response. In several recent studies of patients undergoing PCI, LMWHs have been shown to be as safe and effective as unfractionated heparin; given their better pharmacokinetic profile and the lack of need for coagulation monitoring, they have the potential to replace unfractionated heparin during coronary interventions. This article reviews the current status of anticoagulation therapy with unfractionated heparin and LMWHs in the cardiac catheterization laboratory.

Activated clotting time as a screening test prior to catheter-based cardiovascular procedures

The activated clotting time (ACT) was investigated as a rapid, inexpensive, point-of-service screening test for coagulation abnormalities prior to catheter-based procedures. A total of 963 patients were screened by obtaining a history, standard coagulation profile, and activated coagulation time. The prevalence of normal patients (normal ACT and coagulation profile) was 94% (sensitivity = 91%; specificity = 27%). A normal ACT had a positive predictive value of 95%. The ACT was an acceptable screening test due to its ability to predict positively a low rate of bleeding complication and normal coagulation studies. Patients with ACT > 150 sec should be further evaluated with a screening coagulation panel. Additionally, given its low specificity, coagulation studies should be obtained in high-risk patients since an abnormal ACT does not effectively correlate with abnormal coagulation studies.

Relationship between the heparin management test and the HemoTec activated clotting time in patients undergoing percutaneous coronary intervention

Point-of-care whole blood coagulation tests are critical in the management of patients who undergo percutaneous coronary intervention. The Hemochron and HemoTec devices have been traditionally used to measure the activated clotting time (ACT) in the cardiac catheterization laboratory. The heparin management test (HMT) was recently introduced into clinical practice as an alternative method to current ACT measurements that uses a different sample volume, contact activators and detection system to measure whole blood coagulation. We compared the HMT to the HemoTec ACT in 68 prospectively enrolled patients (127 blood samples) undergoing percutaneous coronary intervention. Measurements were performed 10 minutes after the initial heparin bolus and thereafter at the discretion of the attending physician. The mean HMT was 41 seconds higher (approximately 15%) than the HemoTec ACT (HMT 304+/-59 vs. ACT 263+/-52, P< 0.0001), but there was a significant correlation between the methods (r=0.77, P<0.0001). However, there was increasing disagreement between the two methods as the level of anticoagulation increased. The relationship between HMT and ACT was similar in patients in whom glycoprotein IIb/IIIa inhibitors were used. The HMT, therefore, appears to be more sensitive to heparin anticoagulation that the HemoTec ACT and correlates well with it in the range required for percutaneous coronary intervention.

Comparison of anticoagulant effects and safety of argatroban and heparin in healthy subjects

STUDY OBJECTIVE

To evaluate and compare the relationship between dosage and coagulation parameters, as well as safety profiles, of ascending bolus and infusion dosages of argatroban versus heparin in three phase I studies.

DESIGN

Two randomized, double-blind studies compared argatroban and heparin, and one open-label, dose-escalation study further evaluated argatroban.

SETTING

University teaching hospital clinical research unit.

PATIENTS

Healthy men (aged 22-62 yrs).

INTERVENTION

In the first study, 36 subjects received an argatroban 30-, 60-, 120-, or 240-microg/kg bolus, or a heparin 30-, 60-, 120-, or 240-U/kg bolus for three subjects, then amended to 15, 30, 60, or 120 U/kg. In the second study, 37 subjects received argatroban 1.25, 2.5, 5, or 10 microg/kg/minute with or without a 250-microg/kg bolus, or heparin 0.15, 0.20, 0.25, or 0.30 U/kg/minute with or without a 125-U/kg bolus. In the third study (open-label), nine subjects received an argatroban 250-microg/kg bolus plus an infusion of 15, 20, 30, and 40 microg/kg/minute.

MEASUREMENTS AND MAIN RESULTS

When administered as a bolus dose in the first study, argatroban and heparin both produced dose-related increases in activated clotting time (ACT) and activated partial thromboplastin time (aPTT) within 10 minutes of administration. Dissipation of anticoagulant effect was approximately 4-fold faster for argatroban than for heparin. When administered by infusion with or without a bolus in the second study, argatroban, but not heparin, produced predictable dose-related increases in ACT and aPTT that were generally consistent across both effect measures and modes of administration. Effect steady state was attained by five or more subjects per dosing group receiving argatroban (5-9) but typically two or fewer subjects per group receiving heparin (0-7). Furthermore, upon cessation of infusion, anticoagulant effects dissipated faster for argatroban (effect half-life 18-41 min) than for heparin (effect half-life 23-134 min). When argatroban was infused without a bolus, peak and effect steady-state values for ACT and aPTT generally were attained within 1-3 hours. Data from the second and third studies show that for argatroban dosages up to 40 microg/kg/minute, plasma drug concentrations attained at 4 hours of infusion increased linearly with dose, and weight-adjusted plasma clearance was dose independent. In all studies, argatroban and heparin were well tolerated.

CONCLUSION

Anticoagulation was more predictable with argatroban than with heparin as measured by ACT and aPTT, with comparable safety profiles.

Prevention and treatment of thromboembolic and ischemic complications associated with endovascular procedures: Part I--Pathophysiological and pharmacological features

Thromboembolic and ischemic complications frequently occur during and after endovascular procedures, because of associated arterial injury and the thrombogenic characteristics of arterial catheters, contrast agents, and implanted devices such as coils and stents. Platelet adhesion, activation, and aggregation occurring at the site of arterial injury are mediated by local factors, including thromboxane A2 (inhibited by aspirin) and adenosine diphosphate (inhibited by ticlopidine and clopidogrel). Concomitantly, thrombin is formed by serial activation of clotting factors via contact with subendothelial tissue factor. Thrombin cleaves fibrinogen into fibrin. Thrombin activation is indirectly blocked by heparin and its analogs. However, after thrombin is clot-bound (with fibrin), it is relatively protected from heparin and is effectively blocked only by direct thrombin inhibitors (hirudin and its analogs). The final common pathway in clot formation is the binding of fibrinogen to platelets via platelet glycoprotein IIb/IIIa receptors, which is inhibited by antibodies to platelet IIb/IIIa receptors. New treatment modalities, such as the use of direct thrombin inhibitors and antibodies to platelet glycoprotein IIb/IIIa, seem to be more effective for prophylaxis and treatment than conventional anticoagulation and antiplatelet therapies.

The heparin management test: a new device for monitoring anticoagulation during coronary intervention

Whole blood coagulation analysers are widely used during percutaneous coronary interventions. The precise degree of anticoagulation in patients is important in this setting. The aim of this investigation was to compare the results obtained with ACT (Hemochron) and HMT, the Heparin Management Test (TAS) in patients undergoing percutaneous coronary interventions. Patients (n = 100) were enrolled prospectively. Each patient received 10,000 units of heparin. At the end of the procedure, the mean ACT was 284+/-31 seconds and the mean HMT was 292+/-33 seconds. The correlation between the two methods was highly significant (r = 0.64, p<0.001). The HMT correlates well with ACT values in patients undergoing percutaneous coronary interventions. Its use in the management of these patients should be considered.

Comparison of activated clotting times to heparin management test for adequacy of heparin anticoagulation in percutaneous transluminal coronary angioplasty

The aim of this study was to compare the activated clotting time (ACT) obtained with the Hemochron device and the Heparin Management Test (HMT) on a new automated whole-blood coagulometer, the Thrombolytic Assessment System, in patients undergoing angioplasty. Fifty patients undergoing balloon angioplasty were prospectively enrolled. The mean ACT after a 10,000 unit bolus of heparin was 283 +/- 39 sec at the end of the procedure. The mean HMT after 10,000 units of heparin was 286 +/- 31 sec at the end of the procedure in the same patients. The correlation between the two methods was significant (r = 0.6; P < 0.01). The HMT appears to correlate well with standard values obtained with the Hemochron ACT monitor in patients undergoing percutaneous transluminal coronary angioplasty.

Heparin dosing in patients undergoing coronary intervention

Unfractionated heparin remains an essential component of the antithrombotic regimen in patients undergoing coronary intervention, although the timing, dosing, and duration of heparin therapy have evolved over the past several years. Complications associated with heparin use include bleeding events, which occur in 3.9-16.4% of patients receiving conventional heparin. Less commonly, clinically significant thrombocytopenia develops, related to the duration of heparin administration. In patients undergoing coronary intervention who do not receive platelet glycoprotein (GP) IIb/IIIa inhibitors, sufficient heparin should be given to achieve an activated clotting time (ACT) of 250-300 seconds with the HemoTec device and 300-350 seconds with the Hemochron device. There is a general trend to use lower, weight-adjusted heparin dosing (70-100 units/kg) to avoid excessive levels of anticoagulation, with additional heparin boluses to achieve a therapeutic ACT level. When GP IIb/IIIa inhibitors are used, weight-adjusted heparin dosing can be decreased to 70 units/kg to achieve a target ACT of 200 seconds with either the HemoTec or Hemochron device. After uncomplicated coronary intervention, there appears to be little value associated with continued heparin therapy, and the risk of bleeding complications clearly increases with longer durations and higher levels of anticoagulation after coronary intervention.

Platelet glycoprotein IIb/IIIa receptor blockade and low-dose heparin during percutaneous coronary revascularization

BACKGROUND

Blockade of the platelet glycoprotein IIb/IIIa receptor with abciximab (a monoclonal-antibody Fab fragment directed against the receptor) has been shown to diminish ischemic complications among patients undergoing high-risk coronary angioplasty or directional atherectomy but increases bleeding complications. The widespread applicability of this treatment is unknown, particularly in view of the observed risk of hemorrhage.

METHODS

In a prospective, double-blind trial, we randomly assigned patients undergoing urgent or elective percutaneous coronary revascularization at 69 centers to receive abciximab with standard-dose, weight-adjusted heparin (initial bolus of 100 U per kilogram of body weight); abciximab with low-dose, weight-adjusted heparin (initial bolus of 70 U per kilogram); or placebo with standard-dose, weight-adjusted heparin. The primary efficacy end point was death from any cause, myocardial infarction, or urgent revascularization within 30 days of randomization.

RESULTS

The trial was terminated at the first interim analysis, with 2792 of the planned 4800 patients enrolled. At 30 days, the composite event rate was 11.7 percent in the group assigned to placebo with standard-dose heparin; 5.2 percent in the group assigned to abciximab with low-dose heparin (hazard ratio, 0.43; 95 percent confidence interval, 0.30 to 0.60; P<0.001); and 5.4 percent in the group assigned to abciximab with standard-dose heparin (hazard ratio, 0.45; 95 percent confidence interval, 0.32 to 0.63; P<0.001). There were no significant differences among the groups in the risk of major bleeding, although minor bleeding was more frequent among patients receiving abciximab with standard-dose heparin.

CONCLUSIONS

Inhibition of the platelet glycoprotein IIb/IIIa receptor with abciximab, together with low-dose, weight-adjusted heparin, markedly reduces the risk of acute ischemic complications in patients undergoing percutaneous coronary revascularization, without increasing the risk of hemorrhage.

Management of intracoronary thrombosis complicating percutaneous transluminal coronary angioplasty

With technological advances in equipment and increased experience of operators, the success rates of percutaneous transluminal coronary angioplasty (PTCA) now exceed 90%. However, acute periprocural occlusion continues to complicate approximately 6% of all procedures, and many of these occlusions are due to intracoronary (IC) thrombus. Patients at highest risk for this complication include those with acute ischemic syndromes or with angiographically apparent thrombus. These individuals may be candidates for the use of prolonged heparin infusions prior to dilatation, intracoronary thrombolytic therapy, or monoclonal antibody directed against the platelet glycoprotein IIb/IIIa receptor. All patients undergoing PTCA should receive adequate antiplatelet therapy, including aspirin, and heparin with dosing monitored by activated clotting times (ACT). In addition, some recommend the use of ionic contrast material. When IC thrombus accumulates following intervention, initial therapy should include IC nitroglycerin followed by a combination of redilatation and IC urokinase infusion. Prolonged balloon inflations may be useful, particularly with the use of autoperfusion catheters. Platelet glycoprotein IIb/IIIa receptor antagonists may prove to be beneficial in this situation as well. If the patient's clinical status deteriorates in spite of these measures, emergency coronary artery bypass graft surgery may be required.

Percutaneous transluminal coronary angioplasty: comparison of arterial vs. venous activated clotting time

When arterial blood samples for activated clotting time (ACT) are difficult to obtain from the arterial sheath during coronary intervention, venous ACT serves as a substitute. Data are lacking on whether arterial and venous ACT are identical and whether one can serve as an effective substitute for the other. Forty-eight patients undergoing percutaneous transluminal coronary angioplasty (PTCA) were prospectively evaluated to answer this question. Simultaneous arterial and venous ACT samples were drawn from femoral artery and vein vascular sheaths before and during each procedure, and ACT values were determined with a Hemochron automated electronic timer. Porcine heparin dosing was guided by arterial ACT in the first 25 patients and by venous ACT in the last 23 patients. The target ACT value used for continued heparin dosing was 400 sec. At baseline and throughout the study up to 60 min, venous ACT was slightly and significantly greater than arterial ACT. Despite this statistical difference in ACT values, there was no difference in complication rate between the two groups, and the amount of heparin used during either guiding regimen was the same. Therefore, although venous ACT values are slightly higher than arterial, the more convenient venous ACT can be safely used to guide heparin dosing during PTCA when using a target ACT value of 400 sec.