A randomized comparison of intravenous heparin with oral aspirin and dipyridamole 24 hours after recombinant tissue-type plasminogen activator for acute myocardial infarction. National Heart Foundation of Australia Coronary Thrombolysis Group

ExTRACT-TIMI 25 trial: clarifying the role of enoxaparin in patients with ST-elevation myocardial infarction receiving fibrinolysis

Pharmacologic reperfusion remains the most common treatment strategy for ST-elevation myocardial infarction (STEMI) worldwide. Unfractionated heparin (UFH) is the established adjunctive antithrombotic agent used with fibrinolytic agents. Low-molecular-weight heparins (LMWHs) are a potential alternative to UFH, but have not been evaluated in large cohorts of patients. The Enoxaparin and Thrombolysis Reperfusion for Acute Myocardial Infarction Treatment (ExTRACT)-Thrombolysis in Myocardial Infarction (TIMI) 25 was a double-blind, double-dummy randomized controlled trial, of 20,479 patients, which demonstrated the superiority of enoxaparin over UFH in reducing death or nonfatal myocardial infarction (MI) at 30 days, with an increase in major bleeding. The composite of death, nonfatal MI and nonfatal intracranial hemorrhage, was reduced with enoxaparin. Elderly patients (> or = 75 years of age) received a novel enoxaparin dosing regimen and when compared with UFH, benefited from a lower relative bleeding risk than younger patients without compromising efficacy in preventing death or MI. Intracranial hemorrhage rates were similar. The net clinical benefit of enoxaparin over UFH was maintained regardless of whether patients were on clopidogrel or not, or whether percutaneous coronary intervention was performed. Enoxaparin is an appropriate choice for adjunctive therapy with fibrinolysis in patients with STEMI.

Dipyridamole with low-dose aspirin augments the infarct size-limiting effects of simvastatin

PURPOSE

Statins protect against ischemia-reperfusion injury and limit myocardial infarct size (IS). This effect is dependent on increased generation of adenosine by ecto-5' nucleotidase and downstream activation of cyclooxygenase-2 (COX2). Dipyridamole (DIP) augments the IS-limiting effects of statins by blocking the cellular reuptake of adenosine; whereas aspirin (ASA) attenuates the effect by inhibiting COX2. We studied the effect of acute administration of DIP, ASA and their combination on the IS-limiting effect of simvastatin (SIM).

METHODS

Rats received oral SIM (10 mg/kg/d) or vehicle for 3 days. Rats underwent 30 min of coronary artery occlusion and 4 h reperfusion. After 5 min of ischemia rats received i.v. DIP (5 mg/kg), ASA (20 mg/kg or 2 mg/kg) or DIP+ASA (2 mg/kg) or vehicle alone. Ischemia area at risk (AR) was assessed by blue dye and IS by TTC. Myocardial samples were analyzed for the activation of Akt, ERK 1/2, endothelial nitric oxide synthase (eNOS), and cyclic-AMP-response-element-binding-protein (CREB).

RESULTS

SIM limited IS. High- or low-dose ASA alone had no effect on IS. DIP alone or with low-dose ASA significantly reduced IS. Low-dose ASA did not attenuate the SIM effect, whereas high-dose ASA completely blocked the effect. The combination of DIP+low-dose ASA+SIM resulted in the smallest IS. Both SIM and DIP+low-dose ASA augmented Akt phosphorylation and their effect was additive. Both SIM and DIP+low-dose ASA augmented eNOS, ERK 1/2 and CREB phosphorylation.

CONCLUSIONS

During acute myocardial ischemia, DIP alone or with low-dose ASA limits IS and does not attenuate the IS-limiting effect of SIM as high-dose ASA.

The impact of fibrinolytic therapy for ST-segment-elevation acute myocardial infarction

As privileged witnesses of the initiation and widespread use of reperfusion therapy the authors review the history of fibrinolytic therapy and of tissue-plasminogen activator (t-PA) more particularly and the current indications for its use in the era of mechanical reperfusion.

Use of anticoagulants in ST-segment elevation myocardial infarction patients; a focus on low-molecular-weight heparin

INTRODUCTION

Primary percutaneous coronary intervention (PCI) is the treatment of choice for patients with ST-segment elevation myocardial infarction (STEMI), but given logistics, many patients are still managed with thrombolytics. Unfractionated heparin (UFH) is recommended for routine use in STEMI patients treated with thrombolytics. However, other anticoagulants have been evaluated for use in STEMI patients treated with thrombolysis, including the low-molecular-weight heparins (LMWHs, enoxaparin, dalteparin, and reviparin), fondaparinux and bivalirudin.

METHODS AND RESULTS

A review of the available randomized controlled study data shows that most evidence, in terms of number of trials and number of patients treated with anticoagulants in STEMI has accumulated for LMWHs. The use of enoxaparin and reviparin improves hard clinical efficacy endpoints although there is an excess of bleeding events. Trials with dalteparin have failed to demonstrate improvement in hard clinical efficacy endpoints compared with UFH.

SUMMARY

Enoxaparin is currently the only LMWH with FDA approval for use in STEMI patients and should be considered as a preferable alternative to UFH in STEMI patients treated with fibrinolysis.

Enoxaparin versus unfractionated heparin with fibrinolysis for ST-elevation myocardial infarction

BACKGROUND

Unfractionated heparin is often used as adjunctive therapy with fibrinolysis in patients with ST-elevation myocardial infarction. We compared a low-molecular-weight heparin, enoxaparin, with unfractionated heparin for this purpose.

METHODS

We randomly assigned 20,506 patients with ST-elevation myocardial infarction who were scheduled to undergo fibrinolysis to receive enoxaparin throughout the index hospitalization or weight-based unfractionated heparin for at least 48 hours. The primary efficacy end point was death or nonfatal recurrent myocardial infarction through 30 days.

RESULTS

The primary end point occurred in 12.0 percent of patients in the unfractionated heparin group and 9.9 percent of those in the enoxaparin group (17 percent reduction in relative risk, P<0.001). Nonfatal reinfarction occurred in 4.5 percent of the patients receiving unfractionated heparin and 3.0 percent of those receiving enoxaparin (33 percent reduction in relative risk, P<0.001); 7.5 percent of patients given unfractionated heparin died, as did 6.9 percent of those given enoxaparin (P=0.11). The composite of death, nonfatal reinfarction, or urgent revascularization occurred in 14.5 percent of patients given unfractionated heparin and 11.7 percent of those given enoxaparin (P<0.001); major bleeding occurred in 1.4 percent and 2.1 percent, respectively (P<0.001). The composite of death, nonfatal reinfarction, or nonfatal intracranial hemorrhage (a measure of net clinical benefit) occurred in 12.2 percent of patients given unfractionated heparin and 10.1 percent of those given enoxaparin (P<0.001).

CONCLUSIONS

In patients receiving fibrinolysis for ST-elevation myocardial infarction, treatment with enoxaparin throughout the index hospitalization is superior to treatment with unfractionated heparin for 48 hours but is associated with an increase in major bleeding episodes. These findings should be interpreted in the context of net clinical benefit. (ClinicalTrials.gov number, NCT00077792.).

Overview of contemporary reperfusion strategies in acute ST-elevation myocardial infarction

The rupture of an atherosclerotic plaque in an epicardial coronary artery with subsequent occlusive coronary thrombosis has been established as the decisive event in the pathogenesis of an acute coronary syndrome, which encompasses the clinical entities of unstable angina, non-ST- and ST-elevation myocardial infarction. This article focuses on contemporary treatment strategies for patients with acute ST-elevation myocardial infarction and reviews the role of pharmacologic thrombolysis and mechanical reperfusion by percutaneous transluminal approaches. Statements of the latest guidelines for the treatment of ST-elevation myocardial infarction are included, as well as some recently distributed information not covered by the guideline publications. Finally, some future perspectives for the treatment of acute ST-elevation myocardial infarction are outlined.

Effects of a single oral dose of cilostazol on epicardial coronary arteries and hemodynamics in humans

Cilostazol, a novel cyclic adenosine monophosphate phosphodiesterase type III inhibitor, has been developed as an antiplatelet drug with a vasodilating action on peripheral arteries. The present study was designed to test, in humans, whether cilostazol can dilate the epicardial coronary arteries and what are its hemodynamic effects. Eight patients with chest pain syndrome were subjected to serial quantitative coronary arteriography immediately before and at 30, 60 and 150min after a single oral dose of cilostazol (200mg). Luminal cross-sectional areas (mm2) at the proximal and distal sites of major coronary arteries (6 segments at each sampling time) were significantly increased at 150 min after taking the drug. The percent increases relative to the baseline values were 25+/-7 (6.8+/-0.8-->8.3+/-1.0*) and 42+/-7% (2.1+/-0.3-->3.0+/-0.4*) in the right coronary artery, 24+/-5 (5.1+/-0.7-->6.1+/-0.8*) and 28+/-10% (1.6+/-0.31-->9+/-0.3*) in the left anterior descending artery, and 14+/-6 (5.9+/-0.9-->6.6+/-0.9*) and 24+/-10% (1.3+/-0.2-->1.5+/-0.2*) in the left circumflex artery, respectively (*p<0.05 vs baseline). This action, relative to that of nitroglycerine, was between 27% and 54%. Moreover, small but sustained decreases in systolic pulmonary pressure and stroke work index were observed. Thus, cilostazol has a mild coronary vasodilating action with minimal hemodynamic effects, thereby giving it a possible role in the treatment of coronary artery disease.

Acute Myocardial Infarction and the Role of Aspirin, Heparin, and Warfarin

Acute myocardial infarction is initiated by plaque disruption of a fatty plaque with a thin fibrous cap which has been infiltrated by macrophages. The macrophages are attracted and stimulated by oxidized lipids to secrete metalloproteinases which dissolve collagen and arterial wall matrix and to synthesize tissue factor which accumulates in the fatty gruel, and initiates the thrombotic process when exposed to flowing blood after plaque disruption. This initiates thrombin generation which is greatly amplified by the coagulation cascade.Minute amounts of thrombin initiate platelet aggregation, deposition and secretion with growth of platelet-rich thrombus and an accompanying network of fibrin which is at the base of platelet deposition, and increased over regions of deep injury where there appears to be enhanced thrombin generation. Thrombin is necessary for upregulation of platelet membrane receptors, growth of thrombus, maintenance of platelet cohesion, conversion of fibrinogen to fibrin, cross-linking of fibrin and, in part, for activation of the fibrinolytic system.Thrombosis is directly related to local rheology (shear force, turbulence), thrombogenicity of the exposed arterial wall substrates, and modified by systemic factors. Acute vasoconstriction is directly related to platelet deposition, enhanced by endothelial dysfunction or absence, and increased by hypercholesterolemia which induces production of the potent vasoconstrictor endothelin.Direct thrombin inhibition with a high affinity inhibitor, such as hirudin, totally blocks growth of thrombus, inhibits fibrin formation at lower doses and platelet deposition at somewhat higher doses, and enhances dissolution of residual thrombus. Dissolution of residual thrombus reduces luminal obstruction, and may reduce the need for revascularization procedures since plaque disruption most often occurs in arteries with minor obstruction (<50% stenosis).Current recommendations include intravenous heparin 5000 U bolus + 1,000 U/hr to maintain the aPTT at 60-85 sec, and aspirin (160-325 mg loading followed by 80 mg/day). Maximal inhibition of thrombus at the culprit lesion includes maintenance of heparin infusion plus daily aspirin and conversion of heparin to warfarin to maintain the INR at 2.0-3.0 for 3-6 months along with aspirin 80 mg/day as suggested by the ATACS trial. The value of fixed-dose warfarin plus low-dose aspirin in the acute and chronic phase after myocardial infarction is currently being evaluated in the Coumadin Aspirin Reinfarction Study.

Improving the Efficacy and Stability of Coronary Reperfusion Following Thrombolysis: Exploring the Thrombin Hypothesis

A major assumption in the treatment of patients with acute myocardial infarction (MI) implies that the speed of coronary arterial reperfusion correlates directly with the overall extent of myocardial salvage, and that the extent of mycardial salvage, in turn, determines the absolute reduction in patient mortality. While a growing experience has made it clear that myocardial salvage-independent (time-independent) mechanisms of benefit also exist, few would argue with the hypothesis that the greatest benefit derived from coronary thrombolysis occurs with early (time-dependent) treatment. Thus, improvements in the efficacy of reperfusion and the stability of reperfusion are likely to have considerable impact on patient outcome.

Death and nonfatal reinfarction within the first 24 hours after presentation with an acute coronary syndrome: experience from GUSTO-IIb. Global Utilization of Strategies for Total Occlusion

BACKGROUND

A large proportion of deaths among patients with myocardial infarction occurs within the first 24 hours after presentation. It is not clear whether this phenomenon is also true of patients without ST-segment elevation who may or may not have infarction at the time of presentation. Thrombin activity may also be greatest during the first 24 hours after plaque rupture. Accordingly, this study was designed to examine the pattern of early ischemic events among patients with acute coronary syndromes and to determine whether the direct thrombin inhibitor desirudin (r-hirudin) would be most effective during this period.

METHODS AND RESULTS

Among the 11,142 patients enrolled in GUSTO-II, death or (re)infarction occurred within 24 hours in 210 patients (1.7%), representing 19% of the 1135 deaths that had occurred by 30 days. Death or (re)infarction occurred within 24 hours in 113 patients (2. 7%) with ST-segment elevation and in 97 patients without ST-segment elevation (1.2%, P <.001), representing 26% and 14% of the 30-day event rates, respectively, for the 2 enrollment strata. Among patients with ST-segment elevation, most of these events were deaths, whereas among patients without ST-segment elevation, most events were (re)infarctions. Death or (re)infarction by 24 hours occurred in 80 (1.3%) patients treated with desirudin and 130 (2.1%) patients treated with heparin (P =.01). This finding predominantly consisted of prevention of death among patients with ST-segment elevation and of (re)infarction among patients without ST-segment elevation.

CONCLUSIONS

These findings have important implications for early triage of patients with acute coronary syndromes and for the development of new therapies directed at stabilizing the unstable atherosclerotic plaque.

Antiplatelet and anticoagulant use after myocardial infarction

Coronary thrombosis leading to myocardial infarction is a complex process involving the interaction of the arterial wall, the coagulation cascade, and platelets. Increased understanding of the molecular biology of thrombosis has prompted an evolution in antithrombotic therapy, from the early use of warfarin following myocardial infarction to agents targeting specific receptors or modulators in the thrombotic process. The complexity of thrombosis allows for numerous sites of pharmacologic intervention; the multiple pathways leading to platelet aggregation and thrombin formation provide the opportunity for combined therapies. This review presents the current clinical data on antiplatelet, anticoagulant, and specific antithrombin therapies following myocardial infarction.

Reocclusion: the flip side of coronary thrombolysis

Since the introduction of thrombolytic therapy for acute myocardial infarction, the incidence of coronary artery reocclusion has been intensively studied. Also, the prediction and diagnosis of reocclusion by angiographic and clinical variables, as well its invasive and pharmacologic prevention, have gained much attention. By angiographic definition, reocclusion requires three angiographic observations: one with an occluded artery, one with a reperfused artery and a third for the assessment of subsequent occlusion (true reocclusion). Since the introduction of early intravenous reperfusion therapy, most studies use only two angiograms: one with a patent and one with a nonpatent infarct-related artery. A search for all published reocclusion studies revealed 61 studies (6,061 patients) with at least two angiograms. The median time interval between the first angiogram after thrombolysis and the second was 16 days (range 0.1 to 365). Reocclusion was observed in 666 (11%) of 6,061 cases. Interestingly, the 28 true reocclusion studies showed an incidence of reocclusion of 16 +/- 10% (mean +/- SD), and the 33 studies with only two angiograms 10 +/- 8% (p=0.04), suggesting that proven initial occlusion of the infarct-related artery is a risk factor for reocclusion after successful thrombolysis. The other predictors for reocclusion are probably severity of residual stenosis of the infarct-related artery after thrombolysis and perhaps the flow state after lysis. Reocclusion is most frequently seen in the early weeks after thrombolysis. The clinical course in patients with reocclusion is more complicated than in those without this complication. Left ventricular contractile recovery after thrombolysis is hampered by reocclusion. Routine invasive strategies have not been proven effective against reocclusion. In the prevention of reocclusion, both antiplatelet and antithrombin strategies have been tested, including hirudin and hirulog, but the safety of these agents in thrombolysis is still questionable. Thus, reocclusion after thrombolysis is an early phenomenon and is more frequent after proven initial occlusion of the infarct-related artery. Reocclusion can be predicted by angiography after thrombolysis. Because reocclusion is detrimental, strategies to prevent it should be developed and carried out after thrombolytic therapy for acute myocardial infarction as soon as they are deemed safe.

Heparin as an adjuvant to thrombolytic therapy in acute myocardial infarction

For the treatment of acute myocardial infarction, heparin has been a topic of continuing debate for the past four decades. After review of the available data, the American College of Cardiology/American Heart Association Guidelines for the Early Management of Patients with Acute Myocardial Infarction, published in 1990, recommended intravenous heparin administration together or immediately after thrombolytic therapy to maintain the activated partial thromboplastin time approximately 1.5 to 2.0 times the control value for 24 to 72 hours. Over the past five years, with the proven benefits or thrombolytic therapy and antiplatelet therapy, investigators have been in search of the ideal thrombolytic agent as well as the best adjunctive antithrombotic strategy. We review a number of angiographic patency trials as well as the major thrombolytic mortality reduction trials in which adjunctive heparin therapy was directly assessed. These trials established the need for intravenous heparin administration with tissue plasminogen activator, but, on the other hand, do not substantiate the need for either subcutaneous or intravenous heparin use with streptokinase. New data from a large scale trial emphasizes the importance of maintaining the aPTT in the 55-70 second range to prevent bleeding complications and optimize clinical outcomes.

Thrombolysis with recombinant unglycosylated single-chain urokinase-type plasminogen activator (saruplase) in acute myocardial infarction: influence of heparin on early patency rate (LIMITS study). Liquemin in Myocardial Infarction During Thrombolysis With Saruplase

OBJECTIVES

The Liquemin in Myocardial Infarction During Thrombolysis With Saruplase (LIMITS) study was instituted to evaluate and characterize the effect of a prethrombolytic heparin bolus (5,000 IU) on the efficacy and safety of saruplase in patients with acute myocardial infarction.

BACKGROUND

Heparin has been used after thrombolytic therapy for acute myocardial infarction to prevent reocclusion of the infarct-related artery.

METHODS

The study was designed as a randomized, parallel-group, double-blind, multicenter trial. Patients were treated within 6 h of onset of symptoms with either a bolus of 5,000 IU of heparin (Liquemin) (n = 56, HSH group) or placebo (n = 62, PSH group) before thrombolytic treatment with saruplase given as a 20-mg bolus followed by an infusion of 60 mg over 60 min. Thirty minutes after completion of thrombolysis, an intravenous heparin infusion was administered for 5 days. Before coronary angiography was performed at 6 to 12 h after start of lysis, an additional bolus of 5,000 IU heparin was given to all patients. End points studied were patency of the infarct-related artery, changes in the hemostatic system and bleeding complications.

RESULTS

In the HSH group (heparin-saruplase-heparin), 78.6% of patients had an open infarct-related vessel (Thrombolysis in Myocardial Infarction [TIMI] flow grade 2 or 3) compared with 56.5% in the PSH group (placebo-saruplase-heparin) (intention-to-treat analysis, p = 0.01). No significant difference was observed between the two groups with regard to changes in fibrinogen and fibrin/fibrinogen degradation products. A total of eight bleeding complications (14.3%) were observed in the HSH group and five (8.1%) in the PSH group; no cerebrovascular event occurred, and no allergic reaction was reported. A total of 12 patients died during the hospital stay, 3 in the HSH group (5.4%) and 9 in the PSH group (14.5%).

CONCLUSIONS

In acute myocardial infarction, the administration of a heparin bolus before thrombolytic therapy with saruplase is associated with a significantly higher patency at angiography 6 to 12 h after the start of thrombolysis without any appreciable increase in risk of bleeding.

A pooled analysis of coronary arterial patency and left ventricular function after intravenous thrombolysis for acute myocardial infarction

Individual studies of patency rates and left ventricular (LV) function after thrombolysis have generally been limited by small numbers of observations, wide confidence intervals, and limited numbers of time points. To obtain a more reliable estimate of patterns of patency and LV ejection fraction, a systemic overview of angiographic studies was performed after intravenous thrombolytic therapy. A total of 14,124 angiographic observations from 58 studies evaluating patency after no thrombolytic agent, streptokinase, standard dose tissue-type plasminogen activator (t-PA), accelerated dose t-PA, or anistreplase (anisoylated plasminogen streptokinase activator complex [APSAC]) were included. At 60 and 90 minutes, streptokinase had the lowest patency rates of 48% and 51%, respectively, standard dose t-PA and APSAC had similar intermediate rates of approximately 60% and 70%, and accelerated t-PA had the highest patency rates of 74% and 84%. By 2 to 3 hours and longer, the patency rates were similar for the various regimens. Reocclusion rates in studies including 1,172 patients randomized to t-PA versus a nonfibrin-specific agent were higher after t-PA (13.4% vs 8.0%, p = 0.002). Ten studies enrolling 4,088 patients treated with thrombolytic therapy versus control demonstrated a modest improvement in mean LV ejection fraction in the thrombolytic group at each of the times after thrombolytic therapy: hour 4, day 1, day 4, day 7 to 10, and day 10 to 28 after thrombolysis. By 4 days, mean ejection fraction was 53% versus 47% (thrombolytic vs control therapy, p < 0.01); by 10 to 28 days it was 54.1% and 51.5%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute myocardial infarction. Reperfusion strategies

Acute myocardial infarction is the result of an acute interruption of myocardial blood flow resulting in ischemic myocardial necrosis. The pathogenesis of this phenomenon nearly always involves acute thrombosis superimposed on a disrupted atherosclerotic plaque. Thrombolytic agents have been conclusively shown to reduce mortality in many patient subgroups with myocardial infarction, including the elderly, patients with inferior myocardial infarction, and patients with systolic hypertension. Nearly all patients with acute myocardial infarction of less than 6 h in duration with S-T segment elevation should receive thrombolysis unless significant contraindications exist and outweigh the potential benefits. Aspirin should be given to almost all patients regardless of whether they receive thrombolysis. Angioplasty and coronary artery bypass surgery are useful as primary or secondary modes of reperfusion in selected patients with infarction.

Thrombolytic therapy in acute myocardial infarction--selected recent developments

Thrombolytic therapy is the established treatment of choice for most eligible patients with acute myocardial infarction. Early initiation of treatment and early, complete and maintained patency of the infarct-related coronary artery are desirable, because these variables correlate with a reduction in mortality. As a consequence, considerable efforts have been undertaken to develop new pharmacological agents that serve these purposes. Among these, new plasminogen activators such as reteplase (r-PA), saruplase (scuPA), and staphylokinase are in clinical development, and DSPA (bat t-PA) and antibody-targeted plasminogen activators (ScuPA-59D8) have undergone extensive animal testing. Anticoagulants such as recombinant hirudin, hirulog, argatrobane, and Factor Xa inhibitors, as well as antiplatelet agents on the basis of monoclonal antibody 7E3 offer promise as adjunctive therapy to thrombolysis or to invasive intracoronary procedures.

A randomized trial of intravenous heparin in conjunction with anistreplase (anisoylated plasminogen streptokinase activator complex) in acute myocardial infarction: the Duke University Clinical Cardiology Study (DUCCS) 1

OBJECTIVES

We designed a randomized trial to evaluate the effects of heparin administration in conjunction with anistreplase (anisoylated plasminogen streptokinase activator complex [APSAC]) on arterial patency and clinical end points.

BACKGROUND

The role of conjunctive intravenous heparin therapy with APSAC has not been tested despite the recommendations that intravenous heparin should be used.

METHODS

Four hours after APSAC administration, 250 patients with acute myocardial infarction were randomly assigned to receive 325 mg of either aspirin alone or aspirin and a continuous infusion of heparin (15 IU/kg body weight per h). Clinical ischemic events and bleeding complications were monitored. On hospital day 5, coronary arteriography and left ventriculography were performed.

RESULTS

The primary end point of the trial (the combined outcome of death, reinfarction, recurrent ischemia and occlusion of the infarct-related artery) occurred in 42% of the heparin-treated group versus 43% of the group treated without heparin (p = 0.94). A patent infarct-related artery was present in 80% of the patients treated with heparin and in 73% of those treated without heparin (p = 0.26). Left ventricular function, as measured by ejection fraction, was well preserved in both groups (52% vs. 50.5%, respectively, p = 0.29). The overall bleeding rate was higher in patients with (32%) than without (17.2%) heparin (p = 0.006).

CONCLUSIONS

Weight-adjusted intravenous heparin therapy after APSAC in acute myocardial infarction does not reduce the combined incidence of death, reinfarction, recurrent ischemia and occlusion of the infarct-related artery. Furthermore, withholding intravenous heparin therapy is associated with a 46% reduction in bleeding complications. Our findings do not support the addition of intravenous heparin after APSAC therapy, as currently recommended, and suggest that a strategy of withholding heparin is simpler and safer and does not place the patient at increased risk for ischemic complications after myocardial infarction.

Embolic potential, prevention and management of mural thrombus complicating anterior myocardial infarction: a meta-analysis

OBJECTIVES

The management of mural thrombus complicating acute anterior myocardial infarction remains controversial in part because of the small size of studies on this topic. We performed a meta-analysis of published studies to address three questions: 1) What is the embolic risk of mural thrombi after myocardial infarction? 2) What is the impact of systemic anticoagulation in reducing the embolic risk of mural thrombi? 3) What is the impact of systemic anticoagulation, thrombolytic therapy and antiplatelet therapy in preventing mural thrombus formation?

METHODS

Studies were identified by a computerized and manual search and were included if they were published in manuscript form in the English-language literature. Pooling of data was performed by calculating the Mantel-Haenszel odds ratio and an event rate difference by the method of DerSimonian and Laird.

RESULTS

The odds ratio for increased risk of emboli in the presence of echocardiographically demonstrated mural thrombus (11 studies, 856 patients) was 5.45 (95% confidence interval [CI] 3.02 to 9.83), and the event rate difference was 0.09 (95% CI 0.03 to 0.14). The odds ratio of anticoagulation versus no anticoagulation in preventing embolization (seven studies, 270 patients) was 0.14 (95% CI 0.04 to 0.52) with an event rate difference of -0.33 (95% CI -0.50 to -0.16). The odds ratio of anticoagulation versus control in preventing mural thrombus formation (four studies, 307 patients) was 0.32 (95% CI 0.20 to 0.52), and the event rate difference was -0.19 (95% CI -0.09 to -0.28). The odds ratio for thrombolytic therapy in preventing mural thrombus (six studies, 390 patients) was 0.48 (95% CI 0.29 to 0.79) with an event rate difference of -0.16 (95% CI 0.10 to -0.42), whereas for antiplatelet agents (two studies, 112 patients) the odds ratio was 1.43 (95% CI 0.04 to 56.8) with an event rate difference of 0.16 (95% CI -0.20 to 0.52).

CONCLUSIONS

This analysis supports the hypotheses that 1) mural thrombus after myocardial infarction poses a significantly increased risk of embolization, 2) the risk of embolization is reduced by systemic anticoagulation, and 3) anticoagulation can prevent mural thrombus formation. Thrombolytic therapy may prevent mural thrombus formation, but evidence for a similar benefit of antiplatelet therapy is lacking.

Influence of heparin and systemic lysis on coronary blood flow after reperfusion induced by the novel recombinant plasminogen activator BM 06.022 in a canine model of coronary thrombosis

OBJECTIVES

We sought to evaluate whether anticoagulation by an intravenous heparin infusion prevents deterioration of coronary blood flow restored by the novel recombinant plasminogen activator BM 06.022, and to compare the effects of profound fibrinogenolysis with those of an intravenous bolus injection of heparin.

BACKGROUND

Recent clinical studies indicate that heparin appears to be effective in reducing reocclusion when combined with recombinant tissue-type plasminogen activator (rt-PA), but that heparin is associated with an increased bleeding incidence. Therefore, the need for heparin has to be critically evaluated in the development of BM 06.022.

METHODS

BM 06.022 is an unglycosylated variant of human tissue-type plasminogen activator. Thrombus formation in anesthetized open chest dogs was induced by electrical injury. Left circumflex coronary artery blood flow was monitored for 4 h using an electromagnetic flow probe. Twenty dogs were randomized to receive intravenous heparin (100 IU/kg bolus plus 100 IU/kg per h) in group B or saline solution in group A before an intravenous bolus injection of 200 kU/kg (= 0.34 mg/kg) BM 06.022 1 h after thrombus formation. Another 14 dogs were randomized to receive a single intravenous bolus injection of 200 IU/kg heparin plus 200 kU/kg BM 06.022 in group D or saline solution plus 1,000 kU/kg BM 06.022 in group C.

RESULTS

In the absence of a systemic lytic state, heparin infusion prolonged (p < 0.05) the cumulative patency time (sum of time intervals during which the coronary artery was patent) to 204.3 +/- 7.4 min (group B) compared with 34.6 +/- 10.8 min with saline solution (group A), and increased (p < 0.05) the area under the curve for coronary blood flow versus time (AUCFlow) to 34.0 +/- 3.4 ml.h.min-1 compared with 7.7 +/- 4.6 ml.h.min-1. Profound fibrinogenolysis after administration of 1,000 kU/kg BM 06.022 (group C) and a single intravenous heparin injection (group D) did not differ in their effects on the cumulative patency time (182 +/- 30.3 vs. 177.5 +/- 25.4 min) and AUCFlow (36.0 +/- 10.3 vs. 30.5 +/- 4.8 ml.h.min-1), but these values were improved (p < 0.05) compared with those obtained after administration of saline solution plus 200 kU/kg BM 06.022 (group A).

CONCLUSIONS

In the absence of a systemic lytic state, intravenous heparin is required as an adjunct to BM 06.022 to maintain coronary blood flow in dogs.

Heparin-induced prolongation of partial thromboplastin time after thrombolysis: relation to coronary artery patency. HART Investigators

Having previously shown in the Heparin Aspirin Reperfusion Trial that the empiric use of early intravenous heparin after recombinant tissue-type plasminogen activator (rt-PA) is an important component in the overall treatment strategy, we examine in this report the specific relation between the degree of prolongation of activated partial thromboplastin time and coronary artery patency. To evaluate the hypothesis that arterial patency after administration of rt-PA for acute myocardial infarction is sustained by effective anticoagulation, activated partial thromboplastin time of heparin recipients was determined 8 and 12 h after the start of thrombolysis. Mean activated partial thromboplastin time was higher among patients with an open infarct-related artery than in those with a closed artery (81 +/- 4 vs. 54 +/- 9 s, p less than 0.02). Only 45% of patients with values less than 45 s at both 8 and 12 h had Thrombolysis in Myocardial Infarction (TIMI) flow grade 2 or 3 in the infarct-related artery at 18 h. In contrast, 88% of patients with activated partial thromboplastin time greater than 45 s and 95% of those with values greater than 60 s had an open infarct-related artery at 18 h (p = 0.003 and 0.0006, respectively). Among patients with an initially patent infarct-related artery who underwent repeat angiography at 7 days, activated partial thromboplastin time was similar in those with a persistently patent artery and those with late reocclusion. Excessive anticoagulation did not appear to increase hemorrhagic risk except that access site-related hemorrhage was more common in patients with activated partial thromboplastin time greater than 100 s at 8 h.(ABSTRACT TRUNCATED AT 250 WORDS)

The Role of Heparin in the Thrombolytic Treatment of Acute Myocardial Infarction

Objective:

To review the literature to determine the most appropriate role of heparin when using thrombolytic therapy.

Data Sources:

English-language journal articles published between 1985 and 1991.

Study Selection:

Ten trials comparing the effects of thrombolytic therapy with and without heparin. Desired outcomes that the authors were interested in were coronary vessel patency, reocclusion, recurrent ischemia, reinfarction, mortality, and bleeding complications.

Data Extraction:

Studies were assessed based on methodology.

Data Synthesis:

The concurrent use of heparin with tissue plasminogen activator (tPA) enhances coronary vessel patency without significantly increasing the risk of bleeding complications. The concurrent use of heparin with streptokinase enhances survival; however, the risk of bleeding associated with heparin use is unclear at present. Data are not currently available for anistreplase. Studies are underway to further address the role of heparin with thrombolytic therapy.

Conclusions:

Based on data currently available, it appears that beginning intravenous heparin during the first hour of the tPA infusion and continuing heparin for 24 hours appears most appropriate and has a minimal risk of bleeding. Delaying heparin for 9–12 hours after the streptokinase infusion appears to produce clinical benefits; however, it is not clear whether these benefits outweigh the potential risks of bleeding.

Role of heparin in coronary thrombolysis

Although the benefits of coronary thrombolysis are well established, the optimal therapeutic strategy for ensuring rapid and sustained coronary artery patency remains controversial. The available data suggest that the success of coronary thrombolysis depends not only on the induction of clot lysis, but also on the extent to which procoagulant activity that promotes recurrent thrombosis is inhibited. Procoagulant activity increases almost immediately in patients treated with fibrinolytic agents, and persistent increases in thrombin activity have been associated with recurrent coronary thrombosis. Heparin administered intravenously appears to markedly attenuate the thrombin activity associated with thrombolysis and, in patients treated with tissue plasminogen activator (t-PA), prevents early recurrent coronary thrombosis. The results of clinical trials of coronary thrombolysis indicate that conjunctive treatment of patients with heparin improves survival compared with treatment with fibrinolytic agents alone. Although recent clinical trials in which patients were treated with streptokinase suggested that 12,500 units of heparin administered subcutaneously twice daily decreases mortality, this dosage regimen does not induce therapeutic levels of anticoagulation within the first 24 h in most patients. The failure to achieve early therapeutic anticoagulation may account for the lack of mortality benefit in trials in which patients given t-PA were treated with conjunctive subcutaneous heparin therapy. Thus, the available experimental and clinical data suggest that intravenous heparin should be given to patients treated with fibrinolytic agents for acute myocardial infarction.

Advances in thrombolytic therapy

Alteplase and saruplase are more fibrin-specific thrombolytic drugs than anistreplase. These and the thrombolytic drugs of the first generation (streptokinase and urokinase) have shortcomings and limitations. The prolonged intravenous maintenance infusions have been replaced by a bolus injection, accelerated infusions, or the combined intravenous administration of thrombolytic agents. Numerous truncated alteplase or saruplase molecules have been constructed by deletion and domain substitution or hybrids made of the two molecules without gaining in thrombolytic potency. Recombinant staphylokinase and plasminogen activator from bat saliva have some interesting properties and are being investigated. Thrombus-targeted thrombolytic drugs were constructed using monoclonal antibodies against fibrin fragments or against epitopes of activated platelets. Fibrin-specific thrombolytic drugs require the concomitant use of a potent antithrombotic drug to prevent reocclusion. Whether hirudin or synthetic thrombin inhibitors are superior to heparin and whether novel antiplatelet agents, including monoclonal antibodies to platelet receptors and disintegrins, are more effective than aspirin is under clinical investigation. The place of stable analogues of prostacyclin during thrombolytic treatment is still unsettled.