Randomised comparison of subcutaneous heparin, intravenous heparin, and aspirin in unstable angina. Studio Epoorine Sottocutanea nell'Angina Instobile (SESAIR) Refrattorie Group

Comparison of enoxaparin and unfractionated heparin in patients with non-ST-segment elevation acute coronary syndrome undergoing percutaneous coronary intervention: a systematic review and meta-analysis

Background

No randomized trial has been conducted to directly compare enoxaparin with unfractionated heparin (UFH) in patients undergoing percutaneous coronary intervention (PCI) for non-ST-segment elevation acute coronary syndrome (NSTE-ACS). In an era where early invasive strategies are recommended in high risk patients, the effect of enoxaparin and UFH needs to be re-evaluated. The authors performed a meta-analysis to determine whether enoxaparin is superior to UFH in patients with NSTE-ACS undergoing PCI.

Methods

The composite efficacy end point included all-cause mortality and myocardial infarction (MI) in the hospital or within 60 days. Major bleeding, as defined in the individual clinical trials evaluated, was the main safety endpoint within the same time period. Pooled estimates of the difference in outcome between enoxaparin and UFH were calculated using fixed or random effects models.

Results

A total of 8,861 patients from 4 trials were included. In the pooled analysis, rates of death or MI were similar in patients treated with enoxaparin and UFH [risk ratio (RR), 0.89, 95% confidence interval (CI): 0.77-1.02, P=0.09; I² =50%]. Major bleeding was also similar between enoxaparin and UFH (RR, 1.21, 95% CI: 0.94-1.56, P=0.15, I²=39%). A subgroup analysis, including randomized trials only or trials with a large sample size, and a leave-one-out sensitivity analysis, demonstrated similar results with above, respectively.

Conclusions

In patients undergoing PCI for NSTE-ACS, rates for both death/MI and major bleeding were similar between patients treated with enoxaparin and UFH.

Heparin versus placebo for non-ST elevation acute coronary syndromes

BACKGROUND

Non-ST elevation acute coronary syndromes (NSTEACS) represent a spectrum of disease including unstable angina and non-ST segment myocardial infarction (NSTEMI). Despite treatment with aspirin, beta-blockers and nitroglycerin, unstable angina/NSTEMI is still associated with significant morbidity and mortality. Although evidence suggests that low molecular weight heparin (LMWH) is more efficacious compared to unfractionated heparin (UFH), there is limited data to support the role of heparins as a drug class in the treatment of NSTEACS. This is an update of a review last published in 2008.

OBJECTIVES

To determine the effect of heparins (UFH and LMWH) compared with placebo for the treatment of patients with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

SEARCH METHODS

For this update the Cochrane Heart Group Trials Search Co-ordinator searched the Cochrane Central Register of Controlled Trials on The Cochrane Library (2013, Issue 12), MEDLINE (OVID, 1946 to January week 1 2014), EMBASE (OVID, 1947 to 2014 week 02), CINAHL (1937 to 15 January 2014) and LILACS (1982 to 15 January 2014). We applied no language restrictions.

SELECTION CRITERIA

Randomized controlled trials of parenteral UFH or LMWH versus placebo in people with non-ST elevation acute coronary syndromes (unstable angina or NSTEMI).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed quality of studies and independently extracted data.

MAIN RESULTS

There were no new included studies for this update. Eight studies (3118 participants) were included in this review. We found no evidence for difference in overall mortality between the groups treated with heparin and placebo (risk ratio (RR) = 0.84, 95% confidence interval (CI) 0.36 to 1.98). Heparins compared with placebo, reduced the occurrence of myocardial infarction in patients with unstable angina and NSTEMI (RR = 0.40, 95% CI 0.25 to 0.63, number needed to benefit (NNTB) = 33). There was a trend towards more major bleeds in the heparin studies compared to control studies (RR = 2.05, 95% CI 0.91 to 4.60). From a limited data set, there appeared to be no difference between patients treated with heparins compared to control in the occurrence of thrombocytopenia (RR = 0.20, 95% CI 0.01 to 4.24). Assessment of overall risk of bias in these studies was limited as most of the studies did not give sufficient detail to allow assessment of potential risk of bias.

AUTHORS' CONCLUSIONS

Compared with placebo, patients treated with heparins had a similar risk of mortality, revascularization, recurrent angina, and thrombocytopenia. However, those treated with heparins had a decreased risk of myocardial infarction and a higher incidence of minor bleeding. Overall, the evidence assessed in this review was classified as low quality according to the GRADE approach. The results presented in this review must therefore be interpreted with caution.

Tissue Factor Pathway Inhibitor

Objective—

To investigate in women older than 60 whether aortic stiffness or pulse pressure (PP) is associated with selected procoagulant or anticoagulant factors and to examine whether pulsatile stretch influences these factors in human vascular smooth muscle cells (VSMCs) in vitro.

Methods and Results—

Aortic pulse wave velocity (PWV) and carotid PP were studied in 123 apparently healthy postmenopausal women. PWV, PP, von Willebrand factor, and free tissue factor pathway inhibitor (TFPI), but not mean arterial pressure, increased with age. Free TFPI and PWV were positively correlated, even after adjustment for age and PP and other confounding parameters. In vitro, 5% or 10% pulsatile stretch (at 1 Hz) enhanced TFPI synthesis and secretion by VSMCs in a time-independent manner (1 to 48 hours) without changes in protein level of smooth muscle myosin heavy chain. Application of 5% static stretch had no effect.

Conclusion—

In postmenopausal women, free TFPI increases as vascular wall function deteriorates and PP increases. These findings are supported by the increase in TFPI synthesized by VSMCs in response to cyclic stress in vitro. They suggest that VSMCs require pulsatility to interfere with the coagulation process and highlight the relevance of plasma free TFPI levels to cardiovascular diseases.

Heparin versus placebo for acute coronary syndromes

BACKGROUND

Acute coronary syndromes (ACS) represent a spectrum of disease including unstable angina (UA) and non-ST segment myocardial infarction (NSTEMI). Despite treatment with aspirin, beta-blockers and nitroglycerin, UA/NSTEMI is still associated with significant morbidity and mortality. Although emerging evidence suggests that low molecular weight heparin (LMWH) is more efficacious compared to unfractionated heparin (UFH), there is limited data to support the role of heparins as a drug class in the treatment of ACS.

OBJECTIVES

To determine the effect of heparins (UFH and LMWH) compared with placebo for the treatment of patients with ACS.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials on The Cochrane Library (issue 4, 2002), MEDLINE (1966 to May 2002), EMBASE (1980 to May 2002) and CINAHL (1982 to May 2002). Authors of included studies and pharmaceutical industry representatives were contacted to determine if unpublished studies which met the inclusion criteria were available.

SELECTION CRITERIA

Randomized controlled trials of parenteral UFH or LMWH versus placebo in people with ACS (UA or NSTEMI).

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed quality of studies. Data were extracted independently by two reviewers. Study authors were contacted to verify and clarify missing data.

MAIN RESULTS

Eight studies (3118 participants) were included in this review. We found no evidence for difference in overall mortality between the groups treated with heparin and placebo (RR = 0.84, 95% CI 0.36 to 1.98). Heparins reduced the occurrence of MI (RR = 0.40, 95% CI 0.25 to 0.63, NNT = 33). An increase in the incidence of minor bleeds (RR = 6.80, 95% CI 1.23 to 37.49, NNH = 17).

AUTHORS' CONCLUSIONS

Compared to placebo, patients treated with heparins had similar risk of mortality, revascularization, recurrent angina, major bleeding and thrombocytopenia. However, those treated with heparins had decreased risk of MI and a higher incidence of minor bleeding.

Positive end-expiratory pressure modulates perfluorochemical evaporation from the lungs

To study the effects of positive end-expiratory pressure (PEEP) level on perfluorochemical (PFC) elimination profiles (E(L)), 6 ml/kg of perflubron were instilled into healthy anesthetized rabbits. The ventilation strategy was to maintain constant minute ventilation (300 ml/kg/min) and mean airway pressure (7-8 cm H(2)O) while randomly changing the PEEP levels from 5 to 0, 1, 3, and 10 cm H(2)O, each for a period of 15 min. The PFC content in the expired gas was measured and the E(L) was calculated. There was a significant reduction in the E(L) when decreasing the PEEP levels from 5 to 0 cm H(2)O, but no differences were seen when the PEEP was increased from 5 to 10 cm H(2)O. The results indicate that PEEP levels influence PFC elimination profiles; therefore, the measurement of the E(L) and PEEP levels should be considered when optimizing supplemental PFCs during partial liquid ventilation.

The influence of direct and antithrombin-dependent thrombin inhibitors on the procoagulant and anticoagulant effects of thrombin

INTRODUCTION

Clinical trials evaluating direct thrombin inhibitors in unstable coronary artery disease (CAD) have been disappointing. The hypothesis tested in the present study was that these agents may inhibit the anticoagulant effect of thrombin to a further extent than the procoagulant effect of thrombin.

MATERIALS AND METHODS

We studied both reversible and irreversible thrombin inhibitors and compared the effects of each inhibitor on activated protein C (APC) generation vs. the effect on fibrinopeptide A (FPA) generation. A mixture of protein C, thrombin inhibitor, fibrinogen, fibrin polymerisation blocker and thrombin was incubated with thrombomodulin (TM)-expressing human saphenous vein endothelial cells (HSVECs). The inhibitors investigated were melagatran, inogatran, hirudin, hirugen, D-Phe-D-Pro-D-arginyl chloromethyl ketone (PPACK), and antithrombin (AT) alone or in combination with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH).

RESULTS

All agents, except hirugen, inhibited APC and FPA generation in a dose-dependent manner. FPA inhibition/APC inhibition ratios, based on IC50 for inogatran, melagatran, hirudin, PPACK, AT, AT-UFH and AT-LMWH were 1.73, 0.85, 0.55, 2.1, 0.5, 0.65 and 3.1 respectively.

CONCLUSIONS

All agents, except hirugen, inhibited APC and FPA generation approximately to a similar extent. Thus, it can be inferred that the poor efficacy of thrombin inhibitors in recent clinical trials in patients with unstable CAD is unlikely to be a consequence of their effects on the protein C system.

Effect of perfluorooctyl bromide on bacterial growth

BACKGROUND

Perfluorooctyl bromide (PFOB) is administered directly into the lungs of critically ill patients during partial liquid ventilation. This adjunctive therapy facilitates respiratory support in lung-injured patients and potentially interacts with pathogens in patients with pneumonia. The purpose of this study was to determine the interaction of PFOB with Pseudomonas aeruginosa.

METHODS

The antimicrobial activity of PFOB against P. aeruginosa was determined using modified time-kill methods. PFOB concentrations of 25, 50, 75, 90 and 99% were studied. Electron microscopy was used to evaluate morphologic changes following PFOB exposure to the organism.

RESULTS

Viable counts at baseline were approximately 1 log(10) lower when P. Aeruginosa was exposed to PFOB compared to controls. Significant bacterial killing occurred over the first 2 h for the 90% (p = 0.023) and 99% (p = 0.045) PFOB concentrations versus control. Electron microscopy demonstrated that PFOB disturbs the bacterial cell wall, and produces vacuolizations within the cell.

CONCLUSIONS

PFOB kills P. aeruginosa in a concentration-dependent manner through disruption of the cell architecture.

Inhibition of endothelial cell-mediated generation of activated protein C by direct and antithrombin-dependent thrombin inhibitors

The present study investigated the effect of the thrombin inhibitors antithrombin (AT) (with and without unfractionated heparin or low molecular weight heparin), hirudin, inogatran and melagatran on thrombin-thrombomodulin-mediated generation of activated protein C (APC), in solution and on endothelial cells. Sequential incubation with thrombin, thrombin inhibitors and protein C was followed by measurement of APC by an amidolytic assay. The approximate concentrations resulting in 50% inhibition of endothelial cell-mediated APC generation for AT, AT-unfractionated heparin, AT-low molecular weight heparin, hirudin, melagatran and inogatran were 200, 4, 9, 1, 8 and 60 nmol/l, respectively. The normal plasma level of AT is 2800 nmol/l and relevant therapeutic concentrations from clinical trials are 200 nmol/l for hirudin, 500 nmol/l for melagatran and 1000 nmol/l for inogatran. The present study indicates that clinically relevant concentrations of the tested thrombin inhibitors interfere with endothelial-mediated APC generation, which may offer an explanation for the lack of a dose-response effect in clinical trials with thrombin inhibitors.

Utility of a weight-based heparin nomogram for patients with acute coronary syndromes

BACKGROUND

Unfractionated heparin has been pivotal in the management of acute coronary syndromes (ACS), and continues to be used widely despite the emerging role of low molecular weight heparins (LMWH). The apparent superiority of LMWH over unfractionated heparin may, at least partially, reside in its more predictable achievement of therapeutic effect, with high rates of non-therapeutic activated partial thromboplastin time (APTT) results being observed in the intravenous heparin treatment groups.

AIM

To evaluate the impact of introduction of a weight-based heparin nomogram developed for use in patients with ACS on frequency of 'therapeutic' APTT results.

METHODS

The effectiveness of an existing non-weight-based heparin nomogram in achieving a therapeutic APTT was compared sequentially with that of a weight-based heparin nomogram in 89 and 84 consecutive patients admitted with a diagnosis of ACS.

RESULTS

Patients in whom heparin dosage adjustment was weight based rapidly achieved therapeutic APTT. The median time to achieve an APTT within the target range was 8.75 h in the weight-based group versus >24 h in the non-weight-based group. Utilization of a weight-based nomogram was associated with markedly increased proportions of readings within the therapeutic APTT range at 6 h and at 24 h (51%vs. 26% and 72%vs. 36%, respectively).

CONCLUSIONS

The current study confirms the marked superiority of the weight-based heparin regimen for treatment of patients with ACS. The nomogram dramatically facilitated the attainment of therapeutic APTT, and may represent the optimal method for titration of heparin dosage to individual heparin requirements in patients with ACS.

Tissue factor and tissue factor pathway inhibitor levels in unstable angina patients during short-term low-molecular-weight heparin administration

High tissue factor (TF), tissue factor pathway inhibitor (TFPI) levels and a hypercoagulability state have been documented in unstable angina patients. We evaluated whether short-term enoxaparin administration (100 IU/kg b.i.d. for 3 d) reduces the high TF levels and the hypercoagulability state, and whether it influences the fibrinolytic system in 20 unstable angina patients. On d 3, we observed a significant reduction in TF levels both 1 h and 4 h after the morning injection (-25.6% and -21.7%; P < 0.001 respectively) in comparison with the base-line levels. Both 1 and 4 h after the morning injection on the d 3, TFPI levels significantly (P < 0.001) increased (+96.4%, +96.9% respectively) with respect to the base-line values. After enoxaparin administration, at all observation times, thrombin-antithrombin complexes and prothrombin fragment F1 + 2 levels were significantly (P < 0.001) lower with respect to base-line levels. We observed a slight but significant increase in tissue plasminogen activator antigen levels in preinjection samples, as well as 1 h and 4 h after enoxaparin administration, in comparison with the base-line values. This study provides evidence that low-molecular-weight heparin (LMWH) administration, in addition to a reduction of hypercoagulability and a mild fibrinolytic activation, is associated with decreased TF levels, so indicating a novel mechanism of interference of LMWH with the haemostatic system.

Liquid ventilation: from experimental use to clinical application

Despite advances in perinatal care of preterm infants, complications of prematurity are still common. If new conventional ventilatory interventions fail, ECMO is the only alternative method, but is a complex, invasive and costly technique and difficult to apply to small infants. Perfluorocarbon liquid ventilation is a promising technique. It has been demonstrated to be effective in experimental models, in mature and immature animals. However, its role in the management of human neonates, infants, older children and adults with acute respiratory failure is still not established. Both liquid ventilation strategies, total and partial, are able not only to maintain gas exchange, but also to reduce inflammatory changes. While total liquid ventilation remains as an experimental technique, partial liquid ventilation could be readily applied, but its implementation in clinical practice awaits results from ongoing and future clinical trials that may define its effectiveness.

Antithrombotic therapy in acute coronary syndromes

Current therapy of acute coronary syndromes (i.e., unstable angina and non-Q-wave myocardial infarction, Q-wave myocardial infarction) consists of thrombolytic, anti-platelet, and anti-coagulant therapy. In most cases of acute coronary syndromes, the pathogenesis is a mural thrombus formation on a ruptured or eroded atherosclerotic plaque. Both platelets and thrombin play an essential role in the pathophysiology of acute coronary syndromes. Aspirin and heparin are essential treatments for patients with acute coronary syndromes. Novel thrombin and platelet inhibitors have been developed and demonstrated useful effects for improving both acute and long-term clinical outcomes in acute coronary syndromes. Tissue plasminogen activator is the compound for effective thrombolytic therapy. New developments like reteplase and TNK-tPA can be administered as bolus injection and result in rapid reperfusion. Combination of thrombolytic therapy and glycoprotein IIb/IIIa inhibitors seem to accelerate and improve reperfusion. Clopidogrel as anti-aggregatory compound demonstrated profound effects following stent implantation as well as in patients with aspirin intolerance. Administration of glycoprotein IIb/IIIa inhibitors like abciximab, eptifibatide, tirofiban results in reduction of cardiovascular events in patients with unstable angina and following coronary intervention. Low-molecular-weight heparins like enoxiparin and dalteparin seem to be more effective than heparin, and their use is evolving in patients with unstable angina. Anti-thrombin therapy with hirudin results in slight reduction of cardiovascular events in combination with tolerable safety profile. It has yet to be determined which combination of agents and procedural strategies most significantly reduces mortality and serious events in patients with acute coronary syndromes.

Clinical trials of unfractionated heparin and low-molecular-weight heparin in addition to aspirin for the treatment of unstable angina pectoris: do the results apply to all patients?

We sought to determine how the results of available randomized controlled trials of intravenous unfractionated heparin (UH) and low-molecular weight heparin (LMWH) apply to unselected patients with unstable angina pectoris (UAP). Although UH is widely used in addition to aspirin for treatment of UAP, the evidence is weak for a net benefit over aspirin alone. LMWH preparations may confer a net benefit over UH for the treatment of UAP in clinical trials. It is not clear, however, how trial results are generalized to unselected patients with UAP. Using criteria from the Agency for Health Care Policy and Research Unstable Angina Clinical Practice Guideline, we identified 277 consecutive patients with primary UAP. Exclusion criteria were applied from 6 trials of UH in addition to aspirin and 5 trials of LMWH in addition to aspirin for the treatment of UAP. Clinical outcomes were compared among ineligible and eligible patients for trial enrollment. Patients meeting exclusion criteria were older and had more extensive coexisting medical illness than eligible patients for trial enrollment. Thirty-eight percent to 42% of our study population met > or = 1 exclusion criteria for each of the 6 trials of UH, and 14% to 46% met > or = 1 exclusion criteria for each of the 5 LMWH trials. The 1-year all-cause death rate was higher in UH ineligible patients compared with UH eligible patients (16% vs 4%, p = 0.003) and in LMWH ineligible patients compared with LMWH eligible patients (16% vs 7%, p = 0.005). Thus, clinical trials of UH and LMWH may have limited generalizability to unselected patients with UAP, many of whom have characteristics that would exclude them from trial enrollment and put them at risk for adverse outcomes.

High-frequency oscillatory ventilation, partial liquid ventilation, or conventional mechanical ventilation in newborn piglets with saline lavage-induced acute lung injury. A comparison of gas-exchange efficacy and lung histomorphology

It has been reported that, in diseased lungs, either partial liquid ventilation (PLV) or high-frequency oscillatory ventilation (HFOV) can improve oxygenation better and with less lung injury than conventional mechanical ventilation (CMV). This study was intended as a preclinical comparison between the effects of HFOV, PLV and CMV on gas exchange, lung mechanics and histology. Fifteen anesthetized newborn piglets, with respiratory insufficiency due to repeated saline lung lavage, were allocated to either a PLV, HFOV or CMV (n = 5 each) strategy, and treated for 4 h. Within 30 min of commencing therapy, PLV, HFOV, and CMV improved arterial PO2 (Pa,O2), alveoloarterial oxygen gradient (P(A-a),O2), oxygenation index (OI), venous admixture (va), and arterial PCO2 (Pa,CO2). After 4 h, oxygenation parameters (Pa,O2, P(A-a),O2, OI and venous admixture) were significantly better in the HFOV group than in the PLV group; the CMV group showed a higher Pa,O2 and lower OI than the PLV group. Gas exchange at the end of the experiment was not different from baseline in the HFOV and CMV groups. Lung histology and morphometry were performed after perfusion-fixation at endotracheal deflation pressure corresponding to mean airway pressure at the end of the experiment. Lung injury score and mean linear intercept were not different between the three treatment groups. We conclude that in this model, gas exchange improved significantly in all three ventilation strategies. Indices of oxygenation improved less during PLV. The saline lavage-induced acute lung injury model used as in this study, is less stable than previously thought. The final lung injury is not influenced by the ventilation strategy. We speculate that the impaired gas exchange during PLV is an expression of diffusion limitation and ventilation-perfusion mismatch in a recovering lung.

Assessment of low-molecular-weight heparin trials in cardiology

This review assesses the trial data for low-molecular-weight heparin (LMWH) use in cardiology. LMWHs have been shown to be more convenient to use compared with unfractionated heparin. The use of LMWHs in prevention and treatment of deep vein thrombosis is now established. Use of LMWHs in cardiology is gathering momentum. The most compelling published data are in unstable angina and non-Q-wave myocardial infarction (MI). LMWHs are at least as effective as unfractionated heparin in terms of the composite endpoint of death and MI. Conclusive benefits of LMWH use to prevent restenosis after stent insertion or percutaneous transluminal coronary angioplasty have not been established. The data in MI and atrial fibrillation are still preliminary, but encouraging.

Unfractionated heparin and low-molecular-weight heparin in acute coronary syndrome without ST elevation: a meta-analysis

BACKGROUND

In acute coronary syndrome without ST elevation, the role of unfractionated and low-molecular-weight heparin in aspirin-treated patients remains unclear, and there is conflicting evidence regarding the efficacy and safety of low-molecular-weight heparin (LMWH) relative to unfractionated heparin. We did a systematic overview of the randomised trials to assess the effect of unfractionated heparin and LMWH on death, myocardial infarction, and major bleeding.

METHODS

Randomised trials comparing unfractionated heparin or LMWH with placebo or untreated control, or comparing unfractionated heparin with LMWH, for the short-term and long-term management of patients with acute coronary syndrome without ST elevation, were identified by electronic and manual searches and through contact with experts and industry representatives. Odds ratios for death, myocardial infarction, and major bleeding were calculated for each trial, and results for the individual trials were combined by a modification of the Mantel-Haenszel method.

FINDINGS

12 trials, involving a total of 17157 patients, were included. The summary odds ratio (OR) for myocardial infarction or death during short-term (up to 7 days) unfractionated heparin or LMWH compared with placebo or untreated control was 0.53 (95% CI 0.38-0.73; p=0.0001) or 29 events prevented per 1000 patients treated; during short-term LMWH compared with unfractionated heparin was 0.88 (0.69-1.12; p=0.34); and during long-term LMWH (up to 3 months) compared with placebo or untreated control was 0.98 (0.81-1.17; p=0.80). Long-term LMWH was associated with a significantly increased risk of major bleeding (OR 2.26, [95% CI 1.63-3.14], p<0.0001), which is equivalent to 12 major bleeds per 1000 patients treated.

INTERPRETATION

In aspirin-treated patients with acute coronary syndrome without ST elevation, short-term unfractionated heparin or LMWH halves the risk of myocardial infarction or death. There is no convincing difference in efficacy or safety between LMWH and unfractionated heparin. Long-term LMWH has not been proven to confer benefit additional to aspirin and there is no evidence to support its use after the first 7 days.

The ineffectiveness of a non-weight based heparin regimen in achieving therapeutic activated partial thromboplastin time (aPTT) in acute coronary syndrome

Although low molecular weight heparin (LMWH) is increasingly being used in the treatment of acute coronary syndrome (ACS), unfractionated intravenous (IV) heparin infusion is still widely used in Australian hospitals for the treatment of ACS. This paper evaluates the effectiveness of a non-weight based heparin regimen in achieving a therapeutic activated partial thromboplastin time (aPTT) within 24 hours of IV heparin commencement. A sequential retrospective chart review of 99 medical records of ACS patients in a district hospital in south western Sydney, Australia, was performed. These patients were prescribed IV heparin and did not receive thrombolytic or warfarin therapy. Only 35 per cent reached a therapeutic aPTT level within 24 hours of commencement of IV heparin therapy. Comparison of therapeutic aPTT and non-therapeutic aPTT groups revealed that body weight was the only factor that was significantly different in the two groups. Patients who reached the therapeutic aPTT threshold within 24 hours weighed significantly less (mean body weight: 70.3 kg versus 80.3 kg) than those who did not reach the therapeutic threshold within 24 hours of heparin commencement (t = 3.80, d.f. = 86, p < 0.001). Given that a significant proportion of patients who require IV heparin therapy exceed the 70 kg body weight, the findings from this study suggest that a non-weight based heparin regimen is ineffective in the rapid achievement of therapeutic aPTT.

Role of low-molecular-weight heparins in the management of patients with unstable angina pectoris and non-Q-wave acute myocardial infarction

The development of effective approaches to the management of the unstable coronary syndromes has resulted from an improved understanding of interactions between the vascular wall, platelets, and coagulation factors, and of their response to pharmacologic and mechanical interventions. Furthermore, the occurrence of frequent adverse events after discharge in patients with unstable coronary artery disease (CAD) treated with these therapies alone would argue that, for many of these patients, such stabilization is not the end of the therapeutic pathway; rather, these therapies are for many a preparation for ultimate revascularization, to preserve myocardium and minimize periprocedural complications. The low-molecular-weight heparins with their unique pharmacology offer a new option in the therapy of patients with unstable CAD. There is now extensive experience in the use of several of the low-molecular-weight heparins, particularly dalteparin and enoxaparin, in the management of patients with unstable angina. Several trials have investigated the questions raised by these observations, taking advantage of the unique pharmacologic properties of the low-molecular-weight heparins for both acute inpatient use and prolonged outpatient administration. Although differences in study design preclude direct comparison between the available low-molecular-weight heparins, in these trials low-molecular-weight heparins have been shown to be effective alternatives to conventional heparin for the management of patients with unstable angina and non-Q-wave infarction. These include several small-scale trials and the larger FRagmin during InStability in Coronary artery disease (FRISC), Fragmin in Unstable Coronary Artery Disease (FRIC), Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events (ESSENCE), FRISC II, and Thrombolysis in Myocardial Infarction (TIMI)-11B trials. Thus, the low-molecular-weight heparins appear to be a superior alternative to traditionally administered intravenous unfractionated heparin. They are more predictable in action, do not require frequent activated partial thromboplastin time (aPTT) measurements and dosage adjustments, are easier to administer, and are potentially more efficacious. With their proven efficacy, predictability of action, and convenience of administration and dosing, there are very good reasons for selecting them as first-line therapies for patients presenting with unstable angina and non-Q-wave myocardial infarction.

Low molecular weight heparins and coronary artery disease

Coronary artery disease encompasses a wide spectrum of conditions including silent ischemia, exertional angina, unstable angina, and myocardial infarction. Acute coronary syndromes (unstable angina and myocardial infarction) are caused by the rupture of an atherosclerotic plaque, platelet activation, and fibrin deposition resulting in thrombosis. Aspirin and unfractionated heparin (UFH) have traditionally been the treatment of choice in patients with acute coronary syndromes; however, low molecular weight heparins (LMWHs) offer potential advantages over UFH. Available evidence indicates that LMWH is superior to UFH in reducing ischemic events or death in the acute phase of unstable angina or non-Q-wave myocardial infarction. Long-term therapy with lower doses of LMWH may not offer any advantage to aspirin in the prevention of coronary events or death. Major bleeding complications are similar for LMWH and UFH although minor bleeding complications are more common with LMWH, primarily due to injection-site hematomas. Finally, use of LMWH appears to be cost- effective compared with UFH. The available evidence supports improved clinical outcomes, favorable safety profile, and cost savings associated with LMWH use in the management of unstable angina and non-Q-wave myocardial infarction and should be favored over UFH.

Thrombin inhibitors suppress the thrombin-thrombomodulin-mediated generation of activated protein C

In the treatment of unstable coronary artery disease, direct thrombin inhibitors have shown no or only limited benefit as compared with heparin, despite theoretical advantages. One explanation may be that the direct thrombin inhibitors to a greater extent than heparin have an inhibiting effect on the generation and activity of activated protein C. In the present study, this hypothesis was tested in an in vitro, "purified" system, where human protein C underwent activation to activated protein C by the thrombin-thrombomodulin complex. Direct thrombin inhibitors, inogatran and hirudin, unfractionated heparin+antithrombin, or dalteparin+antithrombin, were added to the system before activation to evaluate their inhibitory effect on the generation of activated protein C. At inhibitor concentrations well below the achieved plasma levels in major clinical trials, the thrombin-thrombomodulin-mediated activation of protein C was inhibited by all the studied inhibitors in a dose-dependent manner, but, contrary to our hypothesis, to a greater extent by unfractionated heparin+antithrombin and dalteparin+antithrombin than by the direct thrombin inhibitors, hirudin and inogatran. Despite difficulties to draw conclusions for the in vivo situation, the in vitro inhibition, by all studied inhibitors, of the generation of activated protein C, found in this study may be a possible explanation for ongoing cardiovascular events despite adequate treatment with thrombin inhibitors, in patients with unstable coronary artery disease. This inhibition of the generation of activated protein C may also contribute to the rebound in cardiovascular events after withdrawal of effective antithrombotic treatment.

Anticoagulant therapy in unstable angina

The goal of anticoagulant therapy in unstable angina is to prevent progression of a subocclusive coronary thrombus to complete occlusion of the coronary artery, thereby preventing myocardial infarction and death. Although these have been many advances in therapy with anticoagulants, considerable morbidity and mortality remains. Also, although combination therapy with potent novel anticoagulants and antiplatelet agents may be an alternative strategy, this needs to be balanced against the risks of hemorrhagic complications. More precise and biologically relevant methods of monitoring anticoagulant effect, along with appropriately modified doses given in combination offers promise.

Enhanced monocyte tissue factor response after experimental balloon angioplasty in hypercholesterolemic rabbit: inhibition with dietary L-arginine

BACKGROUND

There is evidence that tissue factor (TF) is a major contributor to the thrombogenicity of a ruptured atherosclerotic plaque. Nitric oxide (NO) has antiatherogenic and antithrombotic properties. We investigated whether L-arginine (L-arg), the endogenous precursor of NO, might affect the ability of monocytes to produce TF.

METHODS AND RESULTS

We studied TF expression in 18 rabbits with atherosclerosis induced by bilateral iliac damage and 10 weeks of a 2% cholesterol diet. Six weeks after the initiation of the diet, an angioplasty was performed. After angioplasty, the surviving rabbits (n=15) were randomized to receive L-arg (2.25%) supplementation in drinking water (L-arg group, n=8) or no treatment (untreated group, n=7). TF expression was evaluated in mononuclear cells from arterial blood in the presence and absence of endotoxin stimulation. Monocyte TF expression, as assessed with an amidolytic assay, did not differ significantly before or after the induction of atherosclerotic lesions (87+/-15 versus 70+/-12 mU of TF/1000 monocytes, P=NS). Endotoxin-stimulated TF activity increased significantly 4 weeks after angioplasty (138+/-22 versus 70+/-12 mU of TF/1000 monocytes, P=0.02). This increase was blunted by L-arg (43+/-16 mU of TF/1000 monocytes, P=0.01).

CONCLUSIONS

This study demonstrates that angioplasty-induced plaque rupture is associated with a marked increase in monocyte TF response that is blunted by the oral administration of L-arg. This suggests that the documented antithrombotic properties of NO may be related in part to an inhibitory effect on monocyte TF response.

Is a standard regime for anticoagulation with heparin in unstable angina adequate?

AIM

To establish the proportion of patients with unstable angina in whom adequate anticoagulation is achieved using a standard regime of intravenous heparin.

METHOD

A prospective series of 108 Emergency Department attendees over a six-month period with a clinical diagnosis of unstable angina for whom anticoagulation with heparin was prescribed were included in the study. The standard regime was a 5000 unit bolus followed by an intravenous infusion of 1000 units per hour (1200 units if the patient's weight was greater than 80 kg), with subsequent adjustments being made by reference to a nomogram. The activated partial thromboplastin time (APTT) was measured at six and 12 hours after treatment began. Two commonly used criteria for adequate heparinisation were compared: 1. APTT greater than 1.5 times control and 2. APTT in the range of 60-85 seconds.

RESULTS

There were valid data for 90 patients at six hours and 79 at 12 hours. Compared to the criterion for adequate anticoagulation of APTT greater than 1.5 times the control, 25% of patients were subtherapeutic at six hours and 12% at 12 hours. Compared to the criterion APTT greater than 60 seconds, 53% of patients were subtherapeutic at 6 hours and 47% at 12 hours. At 6 hours, 26% of patients were over-anticoagulated as defined as APTT greater than 85 seconds. This had reduced to 13% by 12 hours.

CONCLUSIONS

In the context of recent research suggesting that an APTT of greater than 1.5 times the control is sufficient to reduce complications in unstable angina, our results demonstrate that a standard regime of heparinisation will achieve this goal in the majority of patients within 6 hours of starting heparin therapy. However, if an APTT of 60-85 seconds is the goal, this standard regime is inadequate.

Anti-ischemic and anti-anginal effects of thoracic epidural anesthesia versus those of conventional medical therapy in the treatment of severe refractory unstable angina pectoris

BACKGROUND

Cardiac sympathetic blockade by thoracic epidural anesthesia (TEA) dilates stenotic coronary arteries and has been used to control pain in patients with unstable angina. The aim of the present study was to evaluate the potential anti-ischemic effects of cardiac sympathetic blockade by TEA in severe, refractory, unstable angina.

METHODS AND RESULTS

Forty patients with unstable angina refractory to standard anti-anginal therapy were randomized to receive either continuous epidural infusion of bupivacaine (TEA, Th1 to Th5) or to standard anti-anginal therapy including beta-blockers, calcium antagonists, aspirin, heparin, and nitroglycerin infusion (control group). The primary end points were number of anginal attacks and severity of myocardial ischemia assessed by 48-hour ambulatory Holter monitoring. The incidence of myocardial ischemia was lower in the TEA group (22% versus 61%; P<.05). The number of ischemic episodes per patient was 1.0+/-0.6 in the TEA group and 3.6+/-0.9 in the control group (P<.05). The episode duration per patient was 4.1+/-2.5 minutes and 19.7+/-6.2 minutes in the TEA and the control groups, respectively (P<.05). The mean area-under-the-ST-time-curve was 6.8+/-4.3 and 32.2+/-14.3 (mm-min) in the TEA and the control groups, respectively (P<.05). Fifteen anginal attacks were recorded in the control group and one attack in the TEA group (0.83+/-0.21 versus 0.06+/-0.06/patient, respectively, P<.01).

CONCLUSIONS

The anti-ischemic and anti-anginal effects of continuous TEA are superior to those of conventional therapy in the treatment of refractory unstable angina.

Low-molecular-weight heparin (Fragmin) during instability in coronary artery disease (FRISC). FRISC Study Group

This study evaluated whether the low-molecular-weight (LMW) heparin dalteparin sodium (Fragmin) had protective effects against cardiac events in aspirin-treated patients with unstable coronary artery syndromes. Patients (n = 1,506) with unstable angina or non-Q-wave myocardial infarction were randomized to double-blind, placebo-controlled treatment with LMW heparin. The treatment was given as subcutaneous injections: 120 U/kg body weight/12 hours during the first 5-7 days and 7,500 U once daily during the following 35-45 days. The primary endpoint, death or myocardial infarction after 6 days, showed a 3% (4.7%-1.7%) absolute and a 65% relative reduction in the LMW heparin group. There was a 6.8% (15.5%-8.7%) absolute and a 47% relative reduction of urgent revascularization or need for heparin or nitroglycerin infusions in combination with the primary endpoint. After 40 days there was an absolute reduction of death or myocardial infarction of 2.8% (10.7%-7.9%) and its combination with incapacitating angina was reduced by 5.9% (30.7%-24.8%). The survival analysis indicated a reactivation of the instability soon after lowering the dose at 5-7 days. With long-term follow-up, 3-4 months after termination of LMW heparin, the differences between groups were no longer statistically significant. However, the cumulative reduction in death, myocardial infarction, and revascularization because of incapacitating angina of 5.1% (25.3%-20.4%) was maintained. No cerebral and few major bleeds occurred. Compliance was adequate. Thus, subcutaneous LMW heparin protects against cardiac events in the acute phase of unstable coronary artery disease. The subcutaneous regimen also allows prolongation of treatment in the outpatient setting, which might maintain the initial benefits over a longer period.

A comparison of low-molecular-weight heparin with unfractionated heparin for unstable coronary artery disease. Efficacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coronary Events Study Group

BACKGROUND

Antithrombotic therapy with heparin plus aspirin reduces the rate of ischemic events in patients with unstable coronary artery disease. Low-molecular-weight heparin has a more predictable anticoagulant effect than standard unfractionated heparin, is easier to administer, and does not require monitoring.

METHODS

In a double-blind, placebo-controlled study, we randomly assigned 3171 patients with angina at rest or non-Q-wave myocardial infarction to receive either 1 mg of enoxaparin (low-molecular-weight heparin) per kilogram of body weight, administered subcutaneously twice daily, or continuous intravenous unfractionated heparin. Therapy was continued for a minimum of 48 hours to a maximum of 8 days, and we collected data on important coronary end points over a period of 30 days.

RESULTS

At 14 days the risk of death, myocardial infarction, or recurrent angina was significantly lower in the patients assigned to enoxaparin than in those assigned to unfractionated heparin (16.6 percent vs. 19.8 percent, P=0.019). At 30 days, the risk of this composite end point remained significantly lower in the enoxaparin group (19.8 percent vs. 23.3 percent, P=0.016). The need for revascularization procedures at 30 days was also significantly less frequent in the patients assigned to enoxaparin (27.1 percent vs. 32.2 percent, P=0.001). The 30-day incidence of major bleeding complications was 6.5 percent in the enoxaparin group and 7.0 percent in the unfractionated-heparin group, but the incidence of bleeding overall was significantly higher in the enoxaparin group (18.4 percent vs. 14.2 percent, P=0.001), primarily because of ecchymoses at injection sites.

CONCLUSIONS

Antithrombotic therapy with enoxaparin plus aspirin was more effective than unfractionated heparin plus aspirin in reducing the incidence of ischemic events in patients with unstable angina or non-Q-wave myocardial infarction in the early phase. This benefit of enoxaparin was achieved with an increase in minor but not in major bleeding.

Effects of low-dose heparin infusion on arterial endothelin-1 release in humans

BACKGROUND

The aim of this study was to evaluate the effect of low-dose heparin infusion on arterialized endothelin-1 (ET-1) release in the presence of fasting or high insulin levels in healthy humans.

METHODS AND RESULTS

Eleven normal subjects underwent two tests in random order lasting 240 minutes. A primed (250 IU), continuous heparin (600 IU/h) infusion was performed in test 1; saline was infused in test 2 as control. At 120 minutes, a euglycemic hyperinsulinemic clamp (25 mU.kg-1.h-1) was started that lasted 2 hours in both tests. Two hours after heparin infusion (test 1), ET-1 levels decreased by 32% (3.52 +/- 0.60 to 3.02 +/- 0.73 pg/mL), while nitric oxide (NO) and forearm blood flow increased by 29% and 14%, respectively. During saline infusion, ET-1, nitric oxide, and forearm blood flow remained unchanged. There was a significant interaction between the effect of decreasing ET-1 levels and the heparin treatment (F, 4.06; df, 3.30; P < .01). The decrease in ET-1 levels was significantly correlated with the increase in forearm blood flow in test 1 (r = .74; P < .01) but not in test 2. During the heparin/insulin period, ET-1 increased by 25%, returning to fasting values; nitric oxide levels increased by 12%; and forearm blood flow remained unchanged.

CONCLUSIONS

The present study showed that it is possible to decrease ET-1 levels by use of low-dose heparin infusion in humans. This effect seems mediated by a simultaneous increase in nitric oxide levels and is completely reversed by a mild increase in insulin concentrations.

Coronary heart disease, unstable angina, PTCA: new indications for low molecular weight heparins?

Unstable angina in patients with coronary heart disease carries a high risk of myocardial infarction (MI) and death. Partial thrombotic occlusions of coronary arteries are a major causal factor in the development of unstable angina and consecutive thrombotic occlusions may lead to MI. Treatment with unfractionated heparin (UFH) has been shown to significantly reduce the frequency of anginal attacks, but not to affect the frequency of MI, PTCA and death within one month. Prolonged treatment with low molecular weight heparins (LMWHs) may improve the outcome in patients with unstable angina. New clinical studies in this area seem promising. In the prevention of early reocclusions after PTCA LMWHs may be more effective than UFH. Late restenosis after PTCA within 6 months occurs in 25-35% of patients. To date, no effective prophylaxis exists. In a recent trial, short-term treatment with a LMWH had no preventive effect on late restenoses. Ongoing trials with long-term treatment may lead to better results. In the near future long-term treatment, up to six months, with a LMWH alone or in combination with a platelet function inhibitor, possibly with reduced doses of both drugs, may reduce the frequency of restenosis.