Hirudin in acute myocardial infarction. Thrombolysis and Thrombin Inhibition in Myocardial Infarction (TIMI) 9B trial

The toxicity assessment of neorudin in cynomolgus monkeys

In this study, the toxicity effects on circulatory system and respiratory system, and the acute toxicity test of recombinant neorudin (EPR-hirudin, EH) in cynomolgus monkeys were evaluated to provide reference information for clinical studies. Eighteen cynomolgus monkeys were randomly divided into three groups for single intravenous administration of 3, 30 mg/kg EH and normal saline, respectively. The changes of respiratory frequency, respiratory intensity, blood pressure and electrocardiogram before and after administration were recorded. In acute toxicity test, six cynomolgus monkeys were intravenously received EH at a single dose of 171, 257, 385, 578, 867 and 1300 mg/kg respectively. The vital signs, hematology, serum biochemistry, coagulation indexes and electrocardiogram indexes of the animals were determined before administration and on the 7th and 14th day after administration. As the results showed that there were no significant abnormal changes in respiratory frequency, respiratory intensity, blood pressure or electrocardiogram in cynomolgus monkeys after receiving EH at 3 mg/kg and 30 mg/kg, and there was no statistical difference between the treated groups and normal saline group. In the acute toxicity test, no significant abnormalities were observed in vital signs, hematology, serum biochemistry, coagulation indexes and electrocardiogram indexes of six cynomolgus monkeys at day 7 and 14 after EH administration. Furthermore, autopsies of all cynomolgus monkeys showed no abnormalities. The results of toxicokinetics showed that AUClast of the drug increased in proportion to the EH dose in the range of 171-578 mg/kg, and increased in over proportion to the EH dose in the range of 578-1300 mg/kg. The variation of Cmax was basically consistent with AUClast. In a sum, A single intravenous injection of 3 and 30 mg/kg of EH did not affect the circulatory system and respiratory system in cynomolgus monkeys and the maximum tolerated dose of EH in cynomolgus monkey is over 1300 mg/kg (equivalent to 619-1300 times of the proposed clinical equivalent dose).

Hirudin alleviates acute ischemic stroke by inhibiting NLRP3 inflammasome-mediated neuroinflammation: In vivo and in vitro approaches

Acute ischemic stroke is a severe condition that a vessel supplying blood to the brain is abruptly blocked mostly due to cerebral thrombosis and embolism. There is a dearth of the effective prevention and early intervention strategies. NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated neuroinflammation plays a crucial role in the pathophysiology of ischemic stroke. Hirudin is a secretion from the salivary glands of the leech Hirudo medicinalis and has a role in regulating inflammation. In this study, hirudin with a dose of 10-40 mg/kg was given to middle cerebral artery occlusion/reperfusion mice. Hirudin markedly constrained cerebral infarct area in a dose-dependent manner, and significantly improved locomotor disability at 40 mg/kg dose. Similar to MCC950, a selective NLRP3 inflammasome inhibitor, hirudin inhibited M1 polarization and promoted M2 polarization. It also strikingly suppressed the ischemia-induced overexpression of NLRP3 and its downstream components, caspase-1, apoptosis-associated speck-like protein (ASC), and interleukin-1β (IL-1β). Hirudin and MCC950 equivalently protected viability and death of BV-2 microglia cells against oxygen-glucose deprivation/reperfusion (OGD/R), an in vitro cell model of brain ischemia. Both agents had similar effects in normalizing the OGD/R-evoked aberrant microglial profiles and NLRP3 pathway dysregulation as observed in the mice. These results demonstrated anti-ischemic effects of hirudin and its association with the inhibition of microglial NLRP3 inflammasome-mediated neuroinflammation. Hirudin is a promising agent for the early intervention of acute ischemic stroke.

Application of Modern Clinical Risk Scores in the Global Assessment of Risks Related to the Diagnosis and Treatment of Acute Coronary Syndromes in Everyday Medical Practice

This article presents an overview of contemporary risk assessment systems used in patients with myocardial infarction. The full range of risk scales, both recommended by the European Society of Cardiology and others published in recent years, is presented. Scales for assessing the risk of ischemia/death as well as for assessing the risk of bleeding are presented. A separate section is devoted to systems assessing the integrated risk associated with both ischemia and bleeding. In the first part of the work, each of the risk scales is described in detail, including the clinical trials/registers on the basis of which they were created, the statistical methods used to develop them, as well as the specification of their individual parameters. The next chapter presents the practical application of a given scale in the patient risk assessment process, the timing of its application on the timeline of myocardial infarction, as well as a critical assessment of its potential advantages and limitations. The last part of the work is devoted to the presentation of potential directions for the development of risk assessment systems in the future.

Neurological complications of cardiovascular drugs

Cardiovascular drugs are used to treat arterial hypertension, hyperlipidemia, arrhythmias, heart failure, and coronary artery disease. They also include antiplatelet and anticoagulant drugs that are essential for prevention of cardiogenic embolism. Most neurologic complications of the cardiovascular drugs are minor or transient and are far outweighed by the anticipated benefits of treatment. Other neurologic complications are more serious and require early recognition and management. Overtreatment of arterial hypertension may cause lightheadedness or fatigue but often responds readily to dose adjustment or an alternative drug. Other drug complications may be more troublesome as in myalgia associated with statins or headache associated with vasodilators. The recognized bleeding risk of the antithrombotics requires careful calculation of risk/benefit ratios for individual patients. Many neurologic complications of cardiovascular drugs are well documented in clinical trials with known frequency and severity, but others are rare and recognized only in isolated case reports or small case series. This chapter draws on both sources to report the adverse effects on muscle, nerve, and brain associated with commonly used cardiovascular drugs.

Management of antithrombotic agents in patients undergoing flexible bronchoscopy

Bleeding is one of the most feared complications of flexible bronchoscopy. Although infrequent, it can be catastrophic and result in fatal outcomes. Compared to other endoscopic procedures, the risk of morbidity and mortality from the bleeding is increased, as even a small amount of blood can fill the tracheobronchial tree and lead to respiratory failure. Patients using antithrombotic agents (ATAs) have higher bleeding risk. A thorough understanding of the different ATAs is critical to manage patients during the peri-procedural period. A decision to stop an ATA before bronchoscopy should take into account a variety of factors, including indication for its use and the type of procedure. This article serves as a detailed review on the different ATAs, their pharmacokinetics and the pre- and post-bronchoscopy management of patients receiving these medications.

A novel hirudin derivative inhibiting thrombin without bleeding for subcutaneous injection

Currently, anticoagulants would be used to prevent thrombosis. Thrombin is an effector enzyme for haemostasis and thrombosis. We designed a direct thrombin inhibitor peptide (DTIP) using molecular simulation and homology modelling and demonstrated that the C-terminus of DTIP interacts with exosite I, and N-terminus with the activity site of thrombin, respectively. DTIP interfered with thrombin-mediated coagulation in human, rat and mouse plasma (n=10 per group) and blocked clotting in human whole blood in vitro. When administered subcutaneously, DTIP showed potent and dose-dependent extension of aPTT, PT, TT and CT in rats (n=10 per group). The antithrombotic dose of DTIP induced significantly less bleeding than bivalirudin determined by transecting distal tail assay in rats. Furthermore, DTIP reached peak blood concentration in 0.5-1 hour and did not cause increased bleeding after five days of dosing compared to dabigatran etexilate. The antithrombotic effect of DTIP was evaluated in mice using lethal pulmonary thromboembolism model and FeCl₃-induced mesenteric arteriole thrombus model. DTIP (1.0 mg/kg, sc) prevented deep venous thrombosis and increased the survival rate associated with pulmonary thromboembolism from 30 % to 80 %. Intravital microscopy showed that DTIP (1.0 mg/kg, sc) decelerated mesenteric arteriole thrombosis caused by FeCl₃ injury. These data establish that DTIP is a novel antithrombotic agent that could be used to prevent thrombosis without conferring an increased bleeding risk.

Trends in Enrollment, Clinical Characteristics, Treatment, and Outcomes According to Age in Non-ST-Segment-Elevation Acute Coronary Syndromes Clinical Trials

BACKGROUND

Representation by age ensures appropriate translation of clinical trial results to practice, but, historically, older patients have been underrepresented in clinical trial populations. As the general population has aged, it is unknown whether clinical trial enrollment has changed in parallel.

METHODS AND RESULTS

We studied time trends in enrollment, clinical characteristics, treatment, and outcomes by age among 76 141 patients with non-ST-segment-elevation acute coronary syndrome enrolled in 11 phase III clinical trials over 17 years (1994-2010). Overall, 19.7% of patients were ≥75 years; this proportion increased from 16% during 1994 to 1997 to 21% during 1998 to 2001 and 23.2% during 2002 to 2005, but declined to 20.2% in 2006 to 2010. The number of comorbidities increased with successive time periods irrespective of age. There were substantial increases in the use of evidence-based medication in-hospital and at discharge regardless of age. Although predicted 6-month mortality increased slightly over time, observed 6-month mortality declined significantly in all age strata (1994-1997 versus 2006-2010: <65 years: 3.0% versus 1.9%; 65-74 years: 7.5% versus 3.4%; 75-79 years: 13.0% versus 6.5%; 80-84 years: 17.6% versus 8.2%; and ≥85 years: 24.8% versus 12.6%).

CONCLUSIONS

The distribution of enrollment by age in phase III non-ST-segment-elevation acute coronary syndrome trials was unchanged over time. Irrespective of age, post-myocardial infarction mortality decreased significantly over time, concurrent with increased evidence-based care and despite increasing comorbidities.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00089895.

Administration of low molecular weight and unfractionated heparin during percutaneous coronary intervention

This systematic review with meta-analysis sought to determine the efficacy and safety of unfractionated heparin (UFH) and low molecular weight heparin (LMWH) on clinical outcomes following percutaneous coronary intervention. Medline, Embase, Elsevier, and web of knowledge as well as Google scholar literature were used for selecting appropriate studies with randomized controlled design. After screening 445 studies, a total of 23 trials (including a total of 43,912 patients) were identified that reported outcomes. Pooled analysis revealed that LMWH compared to UFH could significantly increase thrombolysis in myocardial infarction grade 3 flow (p<0.001), which was associated with similar target vessel revascularization (p=0.6), similar incidence of stroke (p=0.7), and significantly lower incidence of re-myocardial infarction (p<0.001), major bleeding (p=0.02) and mortality (p<0.001). Overall, LMWH was shown to be a useful type of heparin for patients with MI undergoing PCI, due to its higher efficacy and lower rate of complication compared to UFH. It is also associated with increased myocardial perfusion, decreased major hemorrhage, and mortality.

Sex-Stratified Trends in Enrollment, Patient Characteristics, Treatment, and Outcomes Among Non-ST-Segment Elevation Acute Coronary Syndrome Patients: Insights From Clinical Trials Over 17 Years

BACKGROUND

Adequate representation by sex in trials allows generalizability of results. We examined representation of women in clinical trials during a 17-year period in which inclusion criteria were broadened and federal mandates for representativeness were launched.

METHODS AND RESULTS

Using mixed models, we studied sex-stratified temporal trends in enrollment, clinical characteristics, treatment, and outcomes among 76 148 non-ST-segment elevation acute coronary syndrome patients using patient-level data merged from 11 phase III trials conducted from 1994 to 2010. Overall, 33.3% of patients were women, which changed minimally over time. Women were consistently 4 to 5 years older than men (median age 68 [interquartile range 61-75] versus 64 [interquartile range 56-72] years) and more frequently had diabetes mellitus, hypertension, and heart failure; men more frequently had prior myocardial infarction and revascularization. GRACE risk scores increased over time for both sexes with the inclusion of older patients with more comorbidities. Use of percutaneous coronary intervention, in-hospital and discharge angiotensin-converting enzyme inhibitor/angiotensin II receptor blockers, β-blockers, and lipid-lowering drugs also increased among both sexes. Kaplan-Meier estimates of 6-month mortality declined from 7.0% [95% confidence interval 6.5%-7.6%] to 4.5% [95% confidence interval 4.0%-5.0%] among women and 6.3% [95% confidence interval 6.0%-6.7%] to 3.1% [95% confidence interval 2.9%-3.4%] among men during the 17-year period.

CONCLUSIONS

The relative proportion of women in non-ST-segment elevation acute coronary syndrome trials changed minimally over time. Nevertheless, in parallel with men, use of evidence-based care and outcomes improved significantly over time among women.

The effect of dalteparin versus unfractionated heparin on the levels of troponin I and creatine kinase isoenzyme MB in elective percutaneous coronary intervention: a multicenter study

Background

The aim of this study was to investigate the safety and efficacy of dalteparin during an elective percutaneous coronary intervention (PCI) procedure in a large cohort.

Materials and methods

In this prospective, randomized, open-label design study, 733 patients undergoing elective PCI were divided into an unfractionated heparin group (group 1, 323 patients) or a dalteparin group (group 2, 410 patients). Blood samples were collected before and 18–24 h after the PCI procedure to determine the serum levels of cardiac troponin I (cTnI) and creatine kinase isoenzyme MB. Major adverse cardiac events (MACEs) and bleeding events during hospitalization were also recorded. Patients with an increased level of serum cTnI before PCI were excluded from the study.

Results

After PCI, the cTnI values were greater than three times the upper limit of normal in 43 cases (13.3%) in group 1 and 52 cases (12.7%) in group 2, without a statistically significant difference between the two groups (P=0.801). An increased creatine kinase isoenzyme MB level of greater than two times the upper limit of normal was found in 10 cases (3.1%) in group 1 and 12 cases (2.9%) in group 2, without a statistically significant difference between the two groups (P=0.894). Postoperative bleeding was observed in nine patients (2.8%) in group 1 and six patients (1.5%) in group 2. Postoperative MACEs were observed in two patients (0.6%) in group 1 and two patients (0.5%) in group 2. There were no significant differences between the two groups with respect to bleeding events or MACEs.

Conclusion

Our study showed that dalteparin might be as effective and safe as unfractionated heparin for anticoagulation during elective PCI.

Risks and Benefits of Thrombolytic, Antiplatelet, and Anticoagulant Therapies for ST Segment Elevation Myocardial Infarction: Systematic Review

Objectives. Assess the impact of associating thrombolytics, anticoagulants, antiplatelets, and primary angioplasty (PA) on death, reinfarction (AMI), and major bleeding (MB) in STEMI therapy. Methods. Medline search was performed to identify randomized trials comparing these classes in STEMI treatment, at least 500 patients, providing death, AMI, and MB rates. Similar arms were grouped. Correlation between number of drugs and PA and the outcomes was evaluated, as well as correlation between the year of the study and the outcomes. Results. Fifty-nine papers remained after exclusions. 404.556 patients were divided into 35 groups of arms. There was correlation between the number of drugs and rates of death (r = -0.466, P = 0.005) and MB (r = 0.403, P = 0.016), confirmed by multivariate regression. This model also showed that PA is associated with lower mortality and increased MB. Year and period of publication correlated with the outcomes: death (r = -0.380, P < 0.001), MB (r = 0.212, P = 0.014), and AMI (r = -0.231, P = 0.009). Conclusion. The increasing complexity of STEMI treatment has resulted in significant reduction in mortality along with increased rates of MB. Overall, however, the benefits of treatment outweigh the associated risks of MB.

Newer anticoagulants in critically ill patients

Critically ill patients are at increased risk for development of thrombosis. In addition, thrombosis is often unrecognized in this population. Furthermore, these patients are particularly susceptible to bleeding complications from anticoagulants. Herein the authors review the pharmacology, data from clinical trials, management of bleeding complications, and perioperative use of these agents in the intensive care unit population. Well-designed clinical trials are needed to improve our understanding of the safety and efficacy of these newer agents in critically ill patients.

A randomized, open-label pilot study comparing desirudin and argatroban in patients with suspected heparin-induced thrombocytopenia with or without thrombosis: PREVENT-HIT Study

Because of an extreme risk for thromboemboli, patients with suspected heparin-induced thrombocytopenia (HIT) require immediate initiation of an alternative anticoagulant. The only therapies approved by the Food and Drug Administration require intravenous infusion of expensive direct thrombin inhibitors. This prospective, randomized, open-label, exploratory study compared the clinical and economic utility of subcutaneous desirudin vs argatroban, the most frequently used agent for suspected or immunologically confirmed HIT, with or without thrombosis. Sixteen patients were randomized to treatment with fixed-dose desirudin (15 or 30 mg) every 12 hours or activated partial thromboplastin time-adjusted argatroban by intravenous infusion. Arm A included 8 patients naive to direct thrombin inhibitor therapy, whereas Arm B included 8 patients on argatroban for at least 24 hours before randomization. The primary efficacy measure was the composite of new or worsening thrombosis (objectively documented), amputation, or death. Other end points included major and minor bleeding while on drug therapy, time to platelet count recovery, and pharmacoeconomics. No amputations or deaths occurred. One patient randomized to argatroban had worsening of an existing thrombosis. Major bleeding occurred in 2 patients on argatroban and in none during desirudin treatment. There was 1 minor bleed in each treatment group. The average medication cost per course of treatment was $1688 for desirudin and $8250 for argatroban. Desirudin warrants further study as a potentially cost-effective alternative to argatroban in patients with suspected HIT.

Management of bleeding complications in the anticoagulated patient

As new anticoagulants become available, and the number of anticoagulated patients continues to rise, it is necessary to know how to deal with associated bleeding complications. In this review, reversal strategies for traditional anticoagulants (warfarin and heparin) as well as newer anticoagulants are described. Prothrombin complex concentrates (PPCs) can be used to reverse vitamin K antagonists (VKA), and plasma may be used where they are not available. Recombinant activated factor VII (rFVIIa) may be useful to reverse pentasaccharide anticoagulants. 1-Desamino-8-D-arginine vasopressin (DDAVP), cryoprecipitate, PCCs, and dialysis may help to reverse direct thrombin inhibitors, while rFVIIa seems to be ineffective. The effect of direct factor Xa inhibitors may be reversed by PCCs, FVIIa, or factor Xa concentrates.

Parenteral anticoagulants: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

This article describes the pharmacology of approved parenteral anticoagulants. These include the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid, as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin, factor Xa, and other clotting enzymes. Heparin also binds to cells and plasma proteins other than antithrombin causing unpredictable pharmacokinetic and pharmacodynamic properties and triggering nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and plasma proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and are associated with a lower risk of nonhemorrhagic side effects. LMWHs can be administered once daily or bid by subcutaneous injection, without coagulation monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin. Therefore, fondaparinux-associated HIT or osteoporosis is unlikely to occur. Fondaparinux exhibits complete bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without coagulation monitoring. Three additional parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in patients with HIT.

The Creating an Optimal Warfarin Nomogram (CROWN) Study

A significant proportion of warfarin dose variability is explained by variation in the genotypes of the cytochrome P450 CYP2C9 and the vitamin K epoxide reductase complex, VKORC1, enzymes that influence warfarin metabolism and sensitivity, respectively. We sought to develop an optimal pharmacogenetic warfarin dosing algorithm that incorporated clinical and genetic information. We enroled patients initiating warfarin therapy. Genotyping was performed of the VKORC1, -1639G>A, the CYP2C9*2, 430C>T, and the CYP2C9*3, 1075C>A genotypes. The initial warfarin dosing algorithm (Algorithm A) was based upon established clinical practice and published warfarin pharmacogenetic information. Subsequent dosing algorithms (Algorithms B and Algorithm C) were derived from pharmacokinetic / pharmacodynamic (PK/PD) modelling of warfarin dose, international normalised ratio (INR), clinical and genetic factors from patients treated by the preceding algorithm(s). The primary outcome was the time in the therapeutic range, considered an INR of 1.8 to 3.2. A total of 344 subjects are included in the study analyses. The mean percentage time within the therapeutic range for each subject increased progressively from Algorithm A to Algorithm C from 58.9 (22.0), to 59.7 (23.0), to 65.8 (16.9) percent (p = 0.04). Improvement also occurred in most secondary endpoints, which included the per-patient percentage of INRs outside of the therapeutic range (p = 0.004), the time to the first therapeutic INR (p = 0.07), and the time to achieve stable therapeutic anticoagulation (p < 0.001). In conclusion, warfarin pharmacogenetic dosing can be optimised in real time utilising observed PK/PD information in an adaptive fashion.

Rationale and design of the PREVENT-HIT study: a randomized, open-label pilot study to compare desirudin and argatroban in patients with suspected heparin-induced thrombocytopenia with or without thrombosis

BACKGROUND

Desirudin, a bivalent direct thrombin inhibitor (DTI), is approved by the US Food and Drug Administration for the prevention of deep vein thrombosis, which may lead to pulmonary embolism, in patients undergoing elective hip replacement surgery. It became available in the United States in March 2010.

OBJECTIVE

The goal of the present article was to provide an overview of the rationale and design of the PREVENT-HIT study, a randomized, prospective, open-label, active drug-controlled, exploratory trial comparing the clinical and economic utility of desirudin versus argatroban in patients with suspected heparin-induced thrombocytopenia (HIT), with or without thrombosis.

SUMMARY

The PREVENT-HIT study was designed to enroll approximately 120 patients from 20 to 25 US centers. All eligible patients were required to be aged >or=18 years. Patients with suspected HIT with or without thrombosis were divided into 2 treatment arms and randomized to receive treatment with desirudin or argatroban in a 1:1 ratio using a block randomization method. Arm A comprised patients who were naive to DTI therapy; arm B included patients whose condition was previously stabilized with intravenous argatroban. Desirudin was administered as a fixed-dose injection (15 or 30 mg SC q12h in patients without or with thrombosis, respectively). Argatroban was administered by continuous intravenous infusion in accordance with approved prescribing information or institutional prescribing guidelines at each study site. The primary efficacy outcome measure included the occurrence of any of the following up to 30 days after study drug discontinuation: new-onset or worsening thrombosis requiring discontinuation of study drug; amputation; or all-cause mortality. Other outcomes that were assessed included platelet recovery, bleeding, and pharmacoeconomic parameters. In addition, adverse events and other safety parameters were evaluated. Study enrollment began in November 2008 and ended in December 2009 due to slow enrollment (N = 16). The study results will be published separately.

CONCLUSION

The results from the PREVENT-HIT study should enhance understanding of the comparative clinical and economic utility of desirudin and argatroban in patients with HIT with or without thrombosis. ClinicalTrials.gov identifier: NCT00787332.

The use and limitations of unfractionated heparin

Despite the development of newer anticoagulants, unfractionated heparin remains an indispensible agent in the treatment of thrombotic disorders. Heparin exerts its major effect via antithrombin, converting antithrombin to a more efficient inhibitor of circulating thrombin (factor IIa), factor Xa, factor IXa, factor XIIa, and kallikrein. However, due to the multiple anticoagulant mechanisms of heparin, differential molecular weight-based clearance, issues of heparin resistance, and patient-specific characteristics (age, weight, gender, and tobacco), attaining therapeutic anticoagulation is complicated. As a result, a minority of patients in major clinical trials achieve an activated partial thromboplastin time within the target window in an appropriate time-frame despite the use of weight-based titration nomograms. The resultant under- or over-therapeutic anticoagulation is associated with increased risks of ischemic and bleeding complications, suggesting the importance of maintaining heparin anticoagulation within a relatively narrow therapeutic range. In this review we discuss the mechanisms of heparin action, clinical ramifications of incorrect dosing in major trials, and attempts to improve the achievement of therapeutic anticoagulation.

The antithrombotic effect of a novel hirudin derivative after reconstruction of carotid artery in rabbits

INTRODUCTION

Hirudin is a direct thrombin inhibitor that has potential mechanistic advantages over indirect inhibitors. Peptides containing the RGD motif competitively inhibit binding of fibrinogen to glycoprotein IIb/IIIa on platelets, thus inhibiting platelet aggregation. A novel hirudin derivative, recombinant RGD-hirudin (r-RGD-hirudin), was engineered by fusing the tripeptide RGD sequence to the native hirudin. We tested the antithrombotic effect of r-RGD-hirudin using a carotid artery reconstruction model in rabbits.

MATERIALS AND METHODS

A fusion gene encoding r-RGD-hirudin was constructed and expressed at high levels in Pichia pastoris. Following traumatic injury and anastomosis, 42 New Zealand White rabbits were randomized to receive normal saline, abciximab, wild-type hirudin, or r-RGD-hirudin. Fibrinogen concentration, aPTT, TT, PT, and PAGm were measured prior to and following the operation. Carotid angiography and pathological examination of the anastomotic site were performed to compare patency rates among the groups.

RESULTS

The r-RGD-hirudin significantly prolonged aPTT, TT, PT and inhibited PAGm following carotid anastomosis in rabbits. The median dose of r-RGD-hirudin (0.5 mg/kg) had a therapeutic effect equal to that of wild-type hirudin (1.0 mg/kg) and higher than that of abciximab (0.2 mg/kg) with regard to patency rates.

CONCLUSIONS

Compared to wild-type hirudin or antiplatelet agent, the novel anticoagulant, r-RGD-hirudin was capable of inhibiting both thrombin activity and platelet aggregation, and was demonstrated to be effective in the prevention of thrombosis.

The thrombin hypothesis in ACS: a disappointing disconnect between bench data and bedside clinical trials

Studies have demonstrated the efficacy and safety of unfractionated heparin and low-molecular-weight heparin in the management of patients with acute coronary syndrome. However, a common limitation of unfractionated heparin and low-molecular-weight heparin is that neither can neutralize clot-bound thrombin. To overcome this limitation of the broad heparin-based anticoagulants, novel anticoagulants targeted for both the free and clot-bound forms of thrombin (direct thrombin inhibitors), or other individual components of the coagulation cascade (eg, direct and indirect factor Xa inhibitors), were developed. These targeted anticoagulation agents showed promising results in preclinical testing and have been evaluated in large-scale clinical acute coronary syndrome trials. This review discusses the disconnect between the excellent preclinical findings obtained with these novel, targeted agents and the efficacy and safety data observed in patients with acute coronary syndrome, compared with the broader-range heparin-based anticoagulants.

In vivo models for the evaluation of antithrombotics and thrombolytics

The development and application of animal models of thrombosis have played a crucial role in the discovery and validation of novel drug targets and the selection of new agents for clinical evaluation, and have informed dosing and safety information for clinical trials. These models also provide valuable information about the mechanisms of action/interaction of new antithrombotic agents. Small and large animal models of thrombosis and their role in the discovery and development of novel agents are described. Methods and major issues regarding the use of animal models of thrombosis, such as positive controls, appropriate pharmacodynamic markers of activity, safety evaluation, species specificity, and pharmacokinetics, are highlighted. Finally, the use of genetic models of thrombosis/hemostasis and how these models have aided in the development of therapies that are presently being evaluated clinically are presented.

Anticoagulants in coronary artery disease

Anticoagulant therapy for acute coronary syndromes is becoming more complex as newer agents are added to unfractionated heparin and warfarin. The anticoagulants used in current clinical practice are low molecular weight heparins, direct thrombin inhibitors, and heparinoids. Properties of and recent clinical trial data regarding these newer anticoagulants are reviewed in reference to current American College of Cardiology/American Heart Association guidelines.

Pathophysiologic bases for adjunctive therapies in the treatment and secondary prevention of acute myocardial infarction

Postmyocardial infarction (MI) survival has been steadily improving. This improvement has been due, in part, to the actions of the adjunctive medical therapies for the treatment of MI. Aspirin, beta blockers, angiotensin-converting enzyme (ACE) inhibitors, and lipid-lowering agents have been shown to improve survival in the treatment and secondary prevention of MI. Nitrates have beneficial effects as well. These medications complement the reperfusion strategies through different mechanisms. Other adjunctive medical therapies, namely magnesium, antiarrhythmic agents, and calcium-channel blockers, have not been shown to improve mortality with routine post-MI use despite their theoretical benefits.

Future directions in thrombolysis

An extensive body of research conducted in the past 25 years has helped foster understanding of the mechanisms and pathogenesis of the acute coronary syndromes and occlusive disease. Thus, it is well established that thrombosis is caused by vascular injury and that immediate lysis of the arterial thrombus and subsequent prevention of thrombotic reocclusion are critical to the treatment of these disorders. Remarkable progress in the understanding of the biological and molecular mechanisms involved in vascular-wall-platelet interactions, platelet-platelet interactions, and coagulation has led to the identification of multiple targets for drug discovery and the development of numerous antithrombotic drugs. The purpose of this article is to review emerging antithrombotic therapies, introduce potential future molecular targets for drug discovery efforts, and discuss novel strategies for managing patients with coronary disease.

Emergency department thrombolysis critical pathway reduces door-to-drug times in acute myocardial infarction

BACKGROUND

Rapid time to treatment with thrombolytic therapy is an important determinant of survival in acute myocardial infarction (AMI).

HYPOTHESIS

We hypothesized that establishment of an AMI thrombolysis critical pathway in the Emergency Department could successfully reduce the "door-to-drug" time, the time between patient arrival and start of thrombolysis.

METHODS AND RESULTS

Before establishment of the AMI critical pathway, median door-to-drug time was 73 min, which was reduced to 37 min after critical pathway implementation (p < 0.05). The percentage of patients treated within 30 min rose from 0% prior to establishment of the pathway to 43% (p = 0.03). Similarly, the percentage treated in within 45 min rose from 0 to 67% (p = 0.0005). Door-to-drug times were longer for women than for men (median 105 min for women vs. 70 min for men before pathway implementation). The pathway reduced door-to-drug time for both genders, but the median door-to-drug times were higher for women than for men (Mann-Whitney p = 0.013). The difference between men and women was 35 min before establishment of the pathway to 10 min by the end of the study period.

CONCLUSIONS

Our critical pathway was successful in reducing door-to-drug times. We observed a "gender gap" in door-to-drug times, with longer mean times for women, which was reduced by the AMI critical pathway. Thus, our data provide support for the use of critical pathways to reduce door-to-drug times, as recommended by the National Heart Attack Alert Program.

Excess heparin dosing among fibrinolytic-treated patients with ST-segment elevation myocardial infarction

BACKGROUND

Although the use of heparin with fibrinolytics is associated with more rapid ST-segment resolution and increased infarct-related artery patency among patients with ST-segment elevation myocardial infarction (STEMI), its associated increase in bleeding risk is well documented and might be augmented by excess heparin dosing.

METHODS

We sought to characterize the incidence and associated bleeding risk of excess heparin dosing among patients with STEMI treated with fibrinolysis who were enrolled in the Can Rapid Risk Stratification of Unstable Angina Patients Suppress Adverse Outcomes with Early Implementation of the American College of Cardiology/American Heart Association Guidelines initiative. Excess dosing was defined as a bolus more than 60 U/kg or an infusion more than 12 U/kg/h per American College of Cardiology/American Heart Association guidelines and was further stratified into major and mild excess (major defined as a bolus>70 U/kg or infusion >15 U/kg/h).

RESULTS

Among 964 fibrinolytic-treated patients with STEMI, 758 (79%) received adjunctive unfractionated heparin therapy. Of these, 368 patients (49%) received excess dosing of unfractionated heparin and 137 patients (18%) received major excess heparin dosing. Factors significantly associated with excess dosing included low body weight and female sex. Patients who received major excess dosing had higher unadjusted rates of major bleeding (19.2% vs 12.4%, P=.004) and transfusion (13.5% vs 4.7%, P=.0002) than patients without excess dosing. After adjustment, a trend persisted for the association with higher transfusion risk (odds ratio 1.39 [0.61-3.14]).

CONCLUSION

Approximately half of fibrinolytic-treated patients with STEMI in contemporary practice received an excess dose of unfractionated heparin. Careful attention to dosing is needed to limit the compounded bleeding risk when heparin is added to fibrinolytic therapy.

Long-term outcome of primary angioplasty compared with fibrinolysis across age groups: a Danish Multicenter Randomized Study on Fibrinolytic Therapy Versus Acute Coronary Angioplasty in Acute Myocardial Infarction (DANAMI-2) substudy

BACKGROUND

Primary angioplasty in patients with acute ST-elevation myocardial infarction has been shown to be superior to fibrinolysis. Whether elderly patients have the same long-term benefit from angioplasty, compared with fibrinolysis, as younger patients is unknown.

METHODS

The effect of angioplasty versus fibrinolysis was investigated in 1,572 patients from the DANAMI-2 study across age groups. End points were total mortality and a composite end point of death, reinfarction, or disabling stroke. Follow-up was 3 years.

RESULTS

Increasing age was associated with mortality (adjusted hazard ratio [HR] 2.45 per 10 year increment, 95% confidence interval [CI] 1.78-3.37, P < .0001) and a higher composite event rate (adjusted HR 1.51, CI 1.26-1.82, P < .0001). The long-term superiority of angioplasty over fibrinolysis on the combined outcome was independent of age: patients aged <56 years (HR 0.73, CI 0.41-1.31); 56 to 65 years (HR 0.83, CI 0.52-1.33); 66 to 75 years (HR 0.71, CI 0.48-1.04); and >75 years (HR 0.83, CI 0.59-1.17) (P = .006 for overall treatment effect and P = .5 for interaction between age and treatment). There was no long-term effect of angioplasty versus fibrinolysis on mortality and no interaction with age (P = .5 and P for interaction = .6).

CONCLUSIONS

The long-term effect of primary angioplasty compared with fibrinolysis in patients with ST-elevation myocardial infarction is not affected by age.

Impact of red blood cell transfusion on clinical outcomes in patients with acute myocardial infarction

Divergent views remain regarding the safety of treating anemia with red blood cell (RBC) transfusion in patients with acute coronary syndrome (ACS). We used a prospective database to study effect of RBC transfusion in patients with acute myocardial infarction (MI; n = 2,358). Cox regression models were used to determine the association between RBC transfusion and 6-month outcomes, incorporating transfusion as a time-dependent variable. The models adjusted for baseline variables, propensity for transfusion, and nadir hemoglobin previous to the transfusion. One hundred ninety-two patients (8.1%) received RBC transfusion. Six-month mortality rates were higher in patients receiving transfusion (28.1% vs 11.7%, p <0.0001). The adjusted hazard ratio (HR) for mortality was 1.9 in transfused patients (95% confidence interval [CI] 1.3 to 2.9). Interaction between RBC transfusion and nadir hemoglobin with respect to mortality (p = 0.004) was significant. Stratified analyses showed a protective effect of transfusion in patients with nadir hemoglobin < or=8 g/dL (adjusted HR 0.13, 95% CI 0.03 to 0.65, p = 0.013). By contrast, transfusion was associated with increased mortality in patients with nadir hemoglobin >8 g/dL (adjusted HR 2.2, 95% CI 1.5 to 3.3; p <0.0001). Similar results were obtained for the composite end point of death/MI/heart failure (p for interaction = 0.04). In conclusion, RBC transfusion in patients with acute MI and hemoglobin < or =8 g/dL may be appropriate. The increased mortality observed in transfused patients with nadir hemoglobin above 8 g/dL underscores the clinical difficulty of balancing risks and benefits of RBC transfusion in the setting of ACS.

New anticoagulant strategies in ST elevation myocardial infarction: trials and clinical implications

New data have re-established the importance of anticoagulation of patients with ST segment elevation myocardial infarction (STEMI), both as an adjuvant to reperfusion therapy or in patients ineligible for reperfusion. Recent randomized trials have found newer agents to be superior to conventional unfractionated heparin. This article summarizes current understanding of the underlying pathophysiology of STEMI and provides a comprehensive review of emerging trial data for low molecular weight heparins, anti-factor Xa agents and direct thrombin inhibitors in this setting.

Antithrombotic strategies in non-ST elevation acute coronary syndromes: focus on bivalirudin

Acute coronary syndromes (ACS) are a common presentation of coronary artery disease, accounting for more than one million hospital admissions in the US annually. Owing to high rates of mortality and reinfarction, ACS represent a major public health concern. The following review discusses the pathogenesis of ACS and optimal approaches for the management of patients with ACS, with special focus on new antithrombotic strategies, including the direct thrombin inhibitor bivalirudin. Bivalirudin has several notable mechanistic advantages compared with unfractionated heparin, including activity against clot-bound thrombin, inhibition of thrombin-induced platelet activation, short plasma half-life in patients with normal or mildly impaired renal function (25 minutes), and linear pharmacokinetics less affected by plasma proteins and renal insufficiency. These properties provide a more predictable inhibition of coagulant activity than unfractionated heparin, with less degree of inter-patient variability in anticoagulation response. The findings from the several clinical trials assessing safety and efficacy of bivalirudin are analyzed in detail, including the recent randomized controlled Acute Catheterization and Urgent Intervention Triage Strategy (ACUITY) trial. Based on the results of the ACUITY trial, a newer streamlined strategy for the invasive treatment of moderate- and high-risk patients with ACS is discussed.

Myocardial infarction: contemporary management strategies

Myocardial infarction (MI) is a common clinical diagnosis, associated with significant morbidity and mortality, not only in the short term, but also years following the index event. A more complete understanding of the pathophysiology of MI has ushered the era of multipronged treatment approach, with a combination of goal-directed revascularization, a broad adjunctive pharmacological therapy and aggressive secondary prevention measures. The goals of this article are to review the basic pathophysiological processes, which lead up to a clinical diagnosis of MI, to highlight the essential elements of clinical presentation and to summarize the evidence for comprehensive therapy. Emphasis has been placed on the choice of primary reperfusion therapy for ST-elevation MI, on risk-stratification of patients with non-ST elevation MI, and on rationale behind the selection of anti-ischaemic and antithrombotic therapy. Finally, evidence-based approach to secondary prevention is outlined.

Pharmacological antithrombotic adjuncts to percutaneous coronary intervention

Stent thrombosis is the major cause of early adverse events during percutaneous coronary intervention. Its incidence has fallen considerably in recent years, principally due to the introduction of effective antithrombotic therapies. The selection of an appropriate antithrombotic regimen is critical in achieving a balance between reducing ischaemic events and minimising bleeding complications in patients undergoing percutaneous coronary intervention. In this article, evidence for the role of antiplatelet and anticoagulant therapies is discussed, including the thienopyridines, glycoprotein IIb/IIIa receptor antagonists, direct thrombin inhibitors and pentasaccharides.