Antithrombotic agents in coronary artery disease

Low-molecular-weight heparin alone versus a combination of unfractionated heparin and low-molecular-weight heparin

OBJECTIVES

We analyzed the effect of the pharmacologic combination of 2 indirect antithrombin drugs--enoxaparin (low-molecular-weight heparin) and unfractionated heparin--versus enoxaparin alone on the recurrence of ischemia.

BACKGROUND

Blocking some key factors of the coagulation cascade supports the concept that an antithrombin effect is needed during the acute phase of ischemia.

METHODS

This was a prospective, randomized, pilot trial in patients with an acute coronary ischemic event occurring within the previous 24 hours. A total of 126 patients were allocated to receive aspirin (200 mg/day orally) plus 1 mg/kg subcutaneous enoxaparin at 8 AM and 12.500 IU of subcutaneous unfractionated heparin at 8 PM (group A) or subcutaneous enoxaparin 1 mg/kg (group B).

RESULTS

Severe recurrent ischemia provoking urgent coronary revascularization occurred in 12 patients (9.5%), 3 (5%) in group A and 9 (13%) in group B (P = .1). Refractory angina was present in 27 patients (21%), 10 (17%) in group A and 17 (25%) in group B (P = .45). The combination of severe recurrent ischemia and refractory angina occurred in 23% of group A, and 37% of group B (odds ratio 0.49; 95% confidence intervals, 0.21-1.15; P = .07). A total of 7 patients (5%) had acute nonfatal myocardial infarction develop, 3 (5%) in group A and 4 (6%) in group B. Two (1.6%) deaths were observed in the study, both in group B. The incidence of the double end point (death plus nonfatal myocardial infarction) was 5% in group A versus 9% in group B (P = .5) and the triple end point (death, nonfatal myocardial infarction, and severe recurrent ischemia) was 10.5% in group A vs 22% in group B (odds ratio 0.42, 95% confidence intervals, 0.13-1.29; P = .09).

CONCLUSIONS

The combination of 2 indirect antithrombin drugs capable of intermittently blocking the coagulation system is not associated with a significant loss of safety.

Coumadin Aspirin Reinfarction Study: Rationale and Design of the CARS Study

Acute myocardial infarction remains the leading cause of death in the United States. Following increased recognition of the role of thrombosis in the pathogenesis of myocardial infarction, both antiplatelet and anticoagulant therapy have been proven effective in preventing recurrent infarction. However, the optimal antithrombotic regimen remains undetermined. In particular, the role of combination antithrombotic therapy has not been studied. The Coumadin Aspirin Reinfarction Study (CARS) will compare the safety and efficacy of fixed-dose combination Coumadin plus aspirin versus aspirin alone among 8000 survivors of acute myocardial infarction. Patients will be followed for up to 4 years. CARS will provide important information regarding the optimal antithrombotic regimen for myocardial infarct survivors.

Antithrombotic therapy in heart failure: a randomized comparison of warfarin vs. aspirin (HELAS)

It is uncertain whether anti-thrombotic treatment reduces the incidence of thrombo-embolism in patients with heart failure, so there is a need for a large scale controlled study to assess the effects of anti-thrombotic therapy in this setting. We report the design of a randomized controlled multicenter double blind trial examining the effects of aspirin, warfarin and placebo in patients with heart failure on the risk of thrombo-embolism. We planned to recruit 6000 patients with heart failure without contraindications to anticoagulants or antiplatelet agents and to follow them for a mean time of 2 years following randomization. The study was planned to determine the rate of thrombo-embolic and haemorrhagic events and death among patients randomized to aspirin, warfarin and placebo, stratified according to the presence or absence of underlying coronary disease. Ancillary studies parallel to the main study will attempt to identify clinical and echocardiographic risk factors for thrombo-embolism and will also examine whether hemostatic or neurohormonal mechanisms contribute to an increase in the risk of thrombo-embolism in patients with heart failure. We hoped that the results of the study would improve the clinical management and cost-effectiveness of treatment for patients with heart failure. However, the recruitment of patients proved more difficult than expected and a number of centers decided not to participate. To avoid a great delay it was decided by the principal investigators and submitted to the executive committee to terminate enrolment in this study when 300 patients had been enrolled, and accept that this is a pilot study.

Rationale for the management of coronary syndromes with low-molecular-weight heparins

The well-documented disadvantages of unfractionated heparin in the management of coronary syndromes, such as unpredictable bioavailability and maintenance of therapeutic range, has prompted several studies into the benefits of low-molecular-weight heparins (LMWHs). The favorable pharmacologic properties of LMWHs include a binding affinity for antithrombin III, anti-factor IIa activity, excellent bioavailability, minimal protein binding, predictable anticoagulant response, and clinical tolerance by patients. LMWHs are also characterized by having a specific anti-factor Xa effect and inducing only a small prolongation in general clotting tests-i.e., activated partial thromboplastin time, prothrombin time, and antithrombin activity-when used in high doses. Several studies have recently demonstrated that LMWHs are superior to placebo and are at least equal or superior to standard heparin when added to aspirin for the treatment of unstable angina and following non-Q-wave myocardial infarction. These studies, which include Thrombolysis in Myocardial Infarction (TIMI) 11A and Efficacy and Safety of Subcutaneous Enoxaparin versus intravenous unfractionated heparin in Non-Q-wave Coronary Events (ESSENCE), will be reviewed and discussed.

Thrombosis and Hemostasis in Cardiology: Review of Pathophysiology and Clinical Practice (Part I)

The adverse consequences of thrombosis are per haps nowhere more evident than in clinical cardiology. Throm bosis and hemostasis are primary issues in the management of patients with atrial fibrillation, prosthetic heart valves, severe left ventricular dysfunction, and coronary artery disease. Clini cal trials have defined a crucial role for anticoagulation with warfarin in patients with atrial fibrillation to reduce the inci dence of stroke. Anticoagulation with warfarin and aspirin in combination offers significant protection from systemic emboli in patients with mechanical prosthetic valves, without a sub stantial increased risk of hemorrhage. The risk of systemic emboli may also be reduced by anticoagulation in patients with severe left ventricular dysfunction. Disturbance of the normal balance of hemostasis is a major factor in the pathophysiology of coronary artery disease. Antiplatelet therapy, antithrombin agents, anticoagulants, and fibrinolytic agents have been used to prevent and treat acute coronary thrombosis and to prevent reocclusion following thrombolysis and interventional therapy. Guidelines are presented for antithrombotic therapy in the prac tice of clinical cardiology.

Cardioembolic stroke

Cardioembolic stroke accounts for 1 out of every 5 to 6 ischemic strokes. A potential cardiac source should be considered in all patients presenting with ischemic neurologic deficits. a clear understanding of the various types of cardiac conditions associated with cardioembolic stroke is important. This article reviews potential cardiac sources of emboli and discusses the role of anticoagulation in both primary and secondary prevention of cardioembolic stroke. The role of echocardiography in evaluating patients with possible cardioembolic stroke is also addressed, and an algorithm is proposed for the use of echocardiography in evaluating patients with ischemic neurologic deficits.

Outpatient anticoagulation issues for the primary care physician

Increasingly, primary care providers are caring for patients who require anticoagulation. In this article the indications for, complications of, and methods of dosing and monitoring warfarin in the outpatient setting are reviewed. Heparin use among ambulatory patients also is discussed.

Low molecular weight heparin versus regular heparin or aspirin in the treatment of unstable angina and silent ischemia

OBJECTIVES

This study was designed to test the hypothesis that low molecular weight heparin may lessen the severity of ischemic events in patients with unstable angina.

BACKGROUND

Unstable angina is a thrombotic process that requires intensive medical treatment. Although current treatments can reduce the number of complications, serious bleeding continues to occur. Nadroparin calcium, a low molecular weight heparin, seems to be a safe therapeutic agent that does not require laboratory monitoring.

METHODS

A total of 219 patients with unstable angina entered the study at a mean time of 6.17 h after the last episode of rest pain. Patients were randomized to receive aspirin (200 mg/day [group A]), aspirin plus regular heparin (400 IU/kg body weight per day intravenously and titered by activated partial thromboplastin time [group B]) and aspirin plus low molecular weight heparin (214 UIC/kg anti-Xa twice daily subcutaneously [group C]). The major end points determined for the in-hospital period were 1) recurrent angina, 2) myocardial infarction, 3) urgent revascularization, 4) major bleeding, and 5) death. Minor end points were 1) silent myocardial ischemia, and 2) minor bleeding. Event rates were tested by chi-square analysis.

RESULTS

Recurrent angina occurred in 37%, 44% and 21% of patients in groups A, B and C, respectively, and was significantly less frequent in group C than in either group A (odds ratio 2.26, 95% confidence interval [CI] 1 to 5.18, p = 0.03) or group B (odds ratio, 3.07, 95% CI 1.36 to 7.00, p = 0.002). Nonfatal myocardial infarction was present in seven patients in group A, four in group B and none in group C (group B vs. A, p = 0.5; group C vs. A, p = 0.01). Urgent revascularization was performed in nine patients in group A, seven in group B and one in group C (C vs. A, p = 0.01). Two episodes of major bleeding occurred in group B. Silent myocardial ischemia was present in 38%, 41% and 25% of patients in groups A, B and C, respectively, and was significantly less frequent in group C than group B (odds ratio 2.12, 95% CI 0.97 to 4.69, p = 0.04). Minor bleeding was detected in 10 patients in group B, 1 patient in group C (B vs. C, p = 0.01) and no patient in group A (A vs. B, p = 0.003).

CONCLUSIONS

In this study, treatment with aspirin plus a high dose of low molecular weight heparin during the acute phase of unstable angina was significantly better than treatment with aspirin alone or aspirin plus regular heparin.

Acute myocardial infarction. Then and now

Dramatic changes in the management of acute myocardial infarction (AMI) have occurred in the past decade. While previous management strategies were primarily supportive, current strategies focus on achieving and maintaining patency of the infarct-related artery restoring blood flow to jeopardized myocytes, preserving left ventricular function, and preventing recurrences and complications in addition to promoting healing. Restoration of blood flow can be achieved pharmacologically with thrombolytic agents or mechanically with percutaneous transluminal coronary angioplasty (PTCA). Early use of antiplatelet agents and anticoagulants helps maintain patency of the infarct-related arteries and prevents thromboembolic complications. Administration of beta-blockers and angiotensin enzyme inhibitors are more specific means of conserving myocardium and preserving ventricular function. Additionally, several strategies for preventing arrhythmias such as prophylactic lidocaine use and routine long-term suppression of premature ventricular contractions with antiarrhythmic drugs are no longer routinely advocated. Basically, in the era prior to the eighth decade of this century, the primary direction of the therapeutic strategy for AMI was to reduce the oxygen demands in the infarcted myocardium; whereas in the subsequent years, the emphasis shifts to improvement in oxygen delivery, via thrombolysis, PTCA, and coronary artery bypass graft surgery. These interventional changes, when added to greater sophistication in the use of drugs to reduce oxygen demands, resulted in significant lowering of myocardial mortality.

Prevention of thrombosis and rethrombosis and enhancement of the thrombolytic actions of recombinant tissue-type plasminogen activator in the canine heart by DMP728, a glycoprotein IIb/IIIa antagonist

1. We studied DMP728, a non-peptide glycoprotein (GP) IIb/IIIa receptor antagonist, for prevention of coronary artery thrombosis or rethrombosis in a chronic canine model subjected to arterial injury. 2. In protocol I, DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered and a 150 microA anodal current was applied to the intimal surface of the left circumflex coronary artery (LCX). Dogs were monitored for 6 h and again on each of 5 subsequent days. 3. Ex vivo platelet aggregation was inhibited but returned to baseline 1 day after drug administration. Thrombus weight was reduced (saline, 20.7 +/- 5.0 mg; DMP728 1.7 +/- 0.4 mg; P < 0.05), as was infarct size [saline, 27.5 +/- 4.3; DMP728, 1.6 +/- 0.7 (per cent left ventricle); P < 0.05]. All control animals died by day 3, while all but one of the treated dogs survived the entire protocol (P < 0.05). 4. In protocol II, an LCX thrombus was induced and thrombolytic therapy was initiated 30 min later. DMP728 (1.0 mg kg-1, i.v., n = 8) or saline (n = 8) was administered 5 min after recombinant tissue-type plasminogen activator infusion had begun. The incidence of reocclusion was reduced by DMP728 (saline, 4/8; DMP728, 1/8). One day after thrombolysis, 7/8 DMP728-treated animals were alive compared with 1/8 in the control group (P = 0.01). 5. DMP728 inhibited ex vivo platelet aggregation, prevented primary and secondary occlusive thrombus formation, reduced thrombus weight and infarct size and increased survival in a chronic canine model of coronary artery thrombus formation. DMP728 is an effective anti-platelet intervention when used as the singular adjunctive agent in association with thrombolytic therapy.

Stroke prophylaxis: hypertension management and antithrombotic therapy

OBJECTIVE

To review trials involving risk factor management and pharmacologic therapy for the prevention of stroke.

DATA SOURCES

English-language literature published between 1966 and 1992 was analyzed; pertinent literature is reviewed.

STUDY SELECTION

Studies that evaluated the impact of risk factor management on prevention of vascular events were selected. In addition, trials assessing the safety and efficacy of pharmacologic intervention in primary and secondary stroke prevention were evaluated.

DATA EXTRACTION

Trials were evaluated for their ability to demonstrate a decrease in stroke occurrence.

DATA SYNTHESIS

Various trials were analyzed in several categories. Studies evaluating risk factor management of hypertension and cardiogenic cerebral emboli were reviewed and recommendations made based on a consensus of these trials. The use of antiplatelet agents in stroke prevention was addressed by a review of pertinent trials and meta-analyses.

CONCLUSIONS

The control of risk factors and the use of antiplatelet agents significantly reduces the risk of vascular events. Benefit from different therapies may be specific to certain patient populations and recommendations are made for these patients.