Unfractionated and low-molecular-weight heparin as adjuncts to thrombolysis in aspirin-treated patients with ST-elevation acute myocardial infarction: a meta-analysis of the randomized trials

Adjunctive benefits from low-molecular-weight heparins as compared to unfractionated heparin among patients with ST-segment elevation myocardial infarction treated with thrombolysis. A meta-analysis of the randomized trials

BACKGROUND

Improvement in adjunctive antithrombotic therapy is a key point in pharmacologic reperfusion for ST-segment elevation myocardial infarction (STEMI). The aim of the current study was to perform an updated meta-analysis of all randomized trials comparing low-molecular-weight heparins (LMWHs) versus unfractionated heparin (UFH) in patients with STEMI treated with thrombolysis.

METHODS

We obtained results from all randomized trials comparing LMWHs versus UFH among patients with STEMI treated with thrombolysis. The literature was scanned by formal searches of electronic databases (MEDLINE and CENTRAL) from January 1990 to June 2007. The following keywords were used: randomized trial, myocardial infarction, reperfusion, thrombolysis, duteplase, reteplase, tenecteplase, alteplase, UFH, LMWHs, dalteparin, nadroparin, enoxaparin, reviparin, parnaparin. Clinical end points assessed were mortality and reinfarction at 30-day follow-up, whereas major bleeding complications were assessed as safety end point. The relationship between mortality benefits from LMWHs and patient's risk profile was evaluated by using a weighted least-square regression in which results from each trial were weighted by the square root of the number of patients in each trial. No language restriction was applied.

RESULTS

We identified a total of 8 randomized trials, including 13,940 patients randomized to LMWHs and 13,818 to UFH. Low-molecular-weight heparins were associated with a trend in reduction in mortality (6.6% vs 7.2%, odds ratio [OR] 0.92, 95% CI 0.84-1.01, P = .08, P heterogeneity [P het] = 0.7) and significant reduction in reinfarction (3.2% vs 4.8%, OR 0.65, 95% CI 0.58-0.64, P < .0001, P het = 0.39), but a higher risk of major bleeding complications (2.4% vs 1.8%, OR 1.37, 95% CI 1.16-1.61, P < .001, P het = 0.32).

CONCLUSIONS

Among patients with STEMI treated with thrombolysis, LMWHs, as compared to UFH, are associated with a trend in mortality benefits and a significant reduction in reinfarction (reMI) at 30-day follow-up, but with higher risk of major bleeding complications. In view of the additional practical advantages, such as reduced interindividual variability in therapeutic response and no need for frequent activated partial thromboplastin time (aPTT) monitoring and dose adjustment, LMWHs should be considered, instead of UFH, among patients with STEMI treated with thrombolysis.

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.

Combined antiplatelet and anticoagulant therapy: clinical benefits and risks

The combination of anticoagulant and antiplatelet therapy is more effective than antiplatelet therapy alone for the initial and long-term management of acute coronary syndromes but increases the risk of bleeding. Antiplatelet therapy is often combined with oral anticoagulants in patients with an indication for warfarin therapy (e.g. atrial fibrillation) who also have an indication for antiplatelet therapy (e.g. coronary artery disease) but the appropriateness of such an approach is unresolved. Anticoagulation appears to be as effective as antiplatelet therapy for long-term management of acute coronary syndrome and stroke, and possibly peripheral artery disease, but causes more bleeding. Therefore, in such patients who develop atrial fibrillation, switching from antiplatelet therapy to anticoagulants might be all that is required. The combination of anticoagulant and antiplatelet therapy has only been proven to provide additional benefit over anticoagulants alone in patients with prosthetic heart valves. The combination of aspirin and clopidogrel is not as effective as oral anticoagulants in patients with atrial fibrillation, whereas the combination of aspirin and clopidogrel is more effective than oral anticoagulants in patients with coronary stents. Whether the benefits of triple therapy outweigh the risks in patients with atrial fibrillation and coronary stents requires evaluation in randomized trials.

Efficacy and Safety of Enoxaparin Versus Unfractionated Heparin in Patients With ST-Segment Elevation Myocardial Infarction Also Treated With Clopidogrel

OBJECTIVES

The purpose of this study was to determine the efficacy and safety of enoxaparin (ENOX) versus unfractionated heparin (UFH) in patients with ST-segment elevation myocardial infarction (STEMI) receiving fibrinolytic therapy with and without clopidogrel.

BACKGROUND

The efficacy and safety of ENOX and clopidogrel given together in STEMI remains to be defined.

METHODS

We compared the rates of major adverse cardiovascular events (MACE) as well as the rates of bleeding in medically managed patients randomized to ENOX versus UFH in the ExTRACT-TIMI 25 (Enoxaparin and Thrombolysis Reperfusion for Acute Myocardial Infarction Treatment-Thrombolysis In Myocardial Infarction 25) trial, stratified by concomitant clopidogrel use.

RESULTS

Enoxaparin significantly reduced the rate of the composite of death, recurrent myocardial infarction, myocardial ischemia, or stroke, compared with UFH, both in patients (n = 2,173) treated with clopidogrel (10.8% vs. 13.9%, adjusted odds ratio [OR(adj)] 0.70, p = 0.013) and in patients (n = 12,918) not treated with clopidogrel (13.3% vs. 15.3%, OR(adj) 0.85, p = 0.003) with no evidence of heterogeneity (p(interaction) = 0.21). The excess risk of TIMI major bleeding with ENOX versus UFH was numerically but not statistically significantly higher in patients treated with clopidogrel (2.7% vs. 1.0%) versus those who were not (2.1% vs. 1.2%) (p(interaction) = 0.61). Net clinical benefit (MACE and major bleeding) favored treatment with ENOX over UFH, either with concomitant clopidogrel (absolute risk reduction 2.4%, 95% confidence interval [CI] -0.5% to 5.3%) or without (absolute risk reduction 1.7%, 95% CI 0.5% to 3.0%) (p(interaction) = 0.61).

CONCLUSIONS

In patients with STEMI receiving fibrinolytic therapy, the net benefit of ENOX is similar in patients who are and are not treated with clopidogrel. The totality of trial data suggest that the combination of a fibrinolytic, aspirin, clopidogrel, and ENOX offers an attractive pharmacologic reperfusion strategy in STEMI.

The impact of bleeding in patients with acute coronary syndromes: how to optimize the benefits of treatment and minimize the risk

Recurrent ischemic events after an acute coronary syndrome (ACS) remain common. Antithrombotic therapy with coronary revascularization reduces the frequency of such life-threatening events. However, with the greater use of antithrombotic medications and early revascularization, bleeding has become an increasingly important problem. Not only does bleeding result in an immediate threat, but it is also associated with increased coronary artery disease mortality and reinfarction, both in the short and long term. Older patients and women, as well as patients with anemia, renal dysfunction, high-risk ACS, diabetes, hypertension and those undergoing invasive procedures, are at especially high risk for bleeding. Major bleeding is associated with a 60% increased risk of in-hospital death, and a fivefold increase in one-year mortality and reinfarction. However, the causal link between bleeding and increased coronary artery disease events is unproven. Although there is no proof that reducing bleeding events improves outcomes, the current paradigm for the management of ACS is a strategy to minimize recurrent ischemic events but also to minimize the risk of bleeding. Such a strategy includes matching the ACS risk to the most appropriate treatment, assessing the bleeding risk, using vascular access techniques to minimize bleeding, selecting the antithrombotic agent that is best for the patient, minimizing the duration of exposure to antithrombotic agents, using the correct dose of medications, recognizing the early signs of bleeding and using gastroprotective agents to minimize upper gastrointestinal bleeding.

The impact of renal dysfunction on outcomes in the ExTRACT-TIMI 25 trial

OBJECTIVES

The ExTRACT-TIMI 25 (Enoxaparin and Thrombolysis Reperfusion for Acute Myocardial Infarction Treatment-Thrombolysis In Myocardial Infarction 25) trial provided the opportunity to evaluate the impact of renal dysfunction on outcomes in patients with ST-segment elevation myocardial infarction (STEMI) and compare enoxaparin (ENOX) and unfractionated heparin (UFH).

BACKGROUND

It is unclear how renal dysfunction influences the balance between benefit and risk of antithrombotic therapy.

METHODS

In the ExTRACT-TIMI 25 trial, 20,479 patients were randomized to UFH or ENOX. A reduced ENOX dose was administered to patients age > or =75 years and those with an estimated creatinine clearance (CrCl) <30 ml/min.

RESULTS

A powerful relationship was observed between the severity of renal dysfunction (per 10 ml/min decrement in CrCl) and death, stroke, intracranial hemorrhage, and major and minor bleeding (p < 0.001 for each). There was a progressive increase in the treatment benefit with ENOX on death or nonfatal myocardial infarction (p < 0.01) with better renal function. Net clinical benefit (death, nonfatal MI, or nonfatal major bleeding) was significantly superior with ENOX (p < 0.001) for patients with a CrCl >60 ml/min (79.1% of the study population). Major bleeding and intracranial hemorrhage did not differ for patients with preserved renal function (CrCl >90 ml/min), but in those with renal dysfunction there was a progressively greater increase in the risk of major and minor bleeding with ENOX.

CONCLUSIONS

Enoxaparin was superior to UFH for the majority of subjects. With more severe renal dysfunction, the net clinical benefit between ENOX and UFH did not differ, despite the rise in adverse events in both treatment groups. Future studies should take renal dysfunction into account when assessing antithrombotic regimens.

Fondaparinux in the management of patients with ST-elevation acute myocardial infarction

The death rate of patients with ST-segment elevation myocardial infarction (STEMI) remains substantial. Fondaparinux is a synthetic selective Factor Xa inhibitor with a high efficacy and good safety, in terms of bleeding risk, in the prevention and treatment of venous thromboembolism, and in the treatment of non-ST elevation acute coronary syndromes (OASIS-5). The OASIS-6 trial was a randomized, double-blind trial comparing fondaparinux 2.5 mg once daily with standard therapy, either placebo or unfractionated heparin according to the indication, in 12092 patients with STEMI. At day 30, fondaparinux significantly reduced the occurrence of the primary efficacy outcome (death or recurrent myocardial infarction) by 14% (p=0.008). Consistent reductions in both death and recurrent MI were observed at 6-month follow-up. The benefits were significant in patients who received no reperfusion therapy or a thrombolytic agent, but not in patients undergoing primary percutaneous coronary interventions. There was a trend (p=0.13) towards fewer severe bleeds in the fondaparinux group (1.0% vs 1.3% in the control group). In conclusion, fondaparinux significantly reduced mortality without increasing severe bleeding in patients with STEMI. Overall, the data from the OASIS studies showed that fondaparinux 2.5 mg may represent a new anticoagulant standard in patients with acute coronary syndromes.

Early management of ST elevation myocardial infarction: a review of practice

The last two decades of the 20th century witnessed continuous evolution in the understanding of the pathophysiology of ST elevation myocardial infarction. In parallel, the management of these patients developed steadily throughout this time and into the early years of the 21st century. From humble beginnings involving oxygen therapy, bed rest and analgesia, the relative merits of different strategies to open 'infarct-related arteries' (IRAs) are now being debated: pharmacological reperfusion, mechanical reperfusion or a combination of both these modalities. The current understanding of the process of thrombotic occlusion of the coronary artery has led to the appreciation of the importance of not simply opening the IRA, but also maintaining its patency once opened. Considerable attention is now being afforded to the significant minority of patients who do not achieve early, complete myocardial reperfusion, despite restoration of adequate flow down the epicardial IRA. Those patients who fail to achieve myocardial reperfusion, either due to late presentation or failure of reperfusion therapy, and are left with permanent myocardial scarring can now be considered. This article critically appraises the recent and emerging evidence and clinical implications of the contemporary management of ST elevation myocardial infarction.

Rescue Angioplasty or Repeat Fibrinolysis After Failed Fibrinolytic Therapy for ST-Segment Myocardial Infarction

OBJECTIVES

We sought to best estimate the benefits and risks associated with rescue percutaneous coronary intervention (PCI) and repeat fibrinolytic therapy as compared with conservative management in patients with failed fibrinolytic therapy for ST-segment myocardial infarction (STEMI).

BACKGROUND

Fibrinolytic therapy is the most common treatment for STEMI; however, the best therapy in patients who fail to achieve reperfusion after fibrinolytic therapy remains uncertain.

METHODS

We performed a meta-analysis of randomized trials using a fixed-effects model. We included 8 trials enrolling 1,177 patients with follow-up duration ranging from hospital discharge to 6 months.

RESULTS

Rescue PCI was associated with no significant reduction in all-cause mortality (relative risk [RR] 0.69; 95% confidence interval [CI] 0.46 to 1.05), but was associated with significant risk reductions in heart failure (RR 0.73; 95% CI 0.54 to 1.00) and reinfarction (RR 0.58; 95% CI 0.35 to 0.97) when compared with conservative treatment. Rescue PCI was associated with an increased risk of stroke (RR 4.98; 95% CI 1.10 to 22.5) and minor bleeding (RR 4.58; 95% CI 2.46 to 8.55). Repeat fibrinolytic therapy was not associated with significant improvements in all-cause mortality (RR 0.68; 95% CI 0.41 to 1.14) or reinfarction (RR 1.79; 95% CI 0.92 to 3.48), but was associated with an increased risk for minor bleeding (RR 1.84; 95% CI 1.06 to 3.18).

CONCLUSIONS

Rescue PCI is associated with improved clinical outcomes for STEMI patients after failed fibrinolytic therapy, but these benefits must be interpreted in the context of potential risks. On the other hand, repeat fibrinolytic therapy is not associated with significant clinical improvement and may be associated with increased harm.

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.).