Antithrombotic agents in coronary artery disease

Therapy of unstable angina with the low molecular weight heparins

Unstable angina is in most cases caused by partial or complete coronary artery occlusion due to the disruption of an atherosclerotic plaque and to thrombus formation. An immediate antithrombotic approach is essential to prevent fatal and non-fatal myocardial infarction, and the combination of aspirin and unfractionated heparin has played a pivotal role in the past years. Low molecular weight heparins have improved pharmacokinetic and pharmaco-dynamic properties over unfractionated heparin that have resulted in greater efficacy and safety in the field of venous thromboembolism. Low molecular weight heparins can be administered by once or twice daily subcutaneous injections at fixed, weight-adjusted doses without the need for monitoring. Because of their potential, many recent clinical trials have evaluated their efficacy and safety in the management of patients with unstable angina. Three low molecular weight heparins have so far been tested: nadroparin, dalteparin and enoxaparin. The results of the published trials confirm that the newer compounds are at least as safe and effective as unfractionated heparin, and offer considerable therapeutic advantages. Nevertheless, the different properties of the three compounds and perhaps the different designs of the clinical trials have led to not entirely comparable findings.

Prevention of cardioembolic stroke

Cardiac causes of ischemic stroke lead to severe neurological deficits from large intracranial artery occlusion compared to small vessel ischemic stroke. The most common cause of cardioembolic stroke is atrial fibrillation (AF), which has an increasing incidence with age. AF stroke trials demonstrate that anti-coagulation is superior to anti-platelet therapy in terms of ischemic stroke prevention. Recently, warfarin was compared with dabigatran, an oral, direct thrombin inhibitor, and was found to be at least equally effective in reducing ischemic stroke with less intracranial bleeding risk. Future research is investigating other direct thrombin inhibitors as potential alternatives to warfarin, which has a narrow therapeutic index, requires frequent blood monitoring, has multiple drug interactions, and a higher rate of intracranial bleeding. Other causes of cardioembolic stroke include myocardial infarction, left ventricular thrombus, reduced ejection fraction, valvular abnormalities, and endocarditis. Patent foramen ovale is a common finding on echocardiograms in patients with and without stroke (up to 20% of the population), and it is a controversial source of cryptogenic stroke. The best way to prevent cardioembolic stroke remains early detection and treatment of AF, and treating the underlying stroke mechanism. Cardiac magnetic resonance imaging is an emerging technology and reveals some sources of cardiac embolism missed by echocardiography, and might provide an additional diagnostic tool in investigating cardioembolic stroke.

Use of antithrombotic agents among U.S. stroke survivors, 2000-2006

BACKGROUND

Secondary stroke prevention guidelines recommend antithrombotic agents such as over-the-counter aspirin, prescription antiplatelet agents, or anticoagulant agents.

PURPOSE

The study was designed to measure whether use of outpatient antithrombotic agents is increasing among stroke survivors.

METHODS

The sample consisted of 4168 people who self-reported cerebrovascular disease and who participated in the Medical Expenditure Panel Survey, an annual representative sample of the U.S., during the years 2000-2006. Use of antithrombotic agents was calculated from face-to-face interviews about the use of aspirin and from pharmacies about the use of prescription medications. Cochran-Armitage tests were used to detect temporal trends and multivariate models to identify predictors of use of antithrombotic agents.

RESULTS

Pooling results across the 7 years, it was found that 57% were taking aspirin, 66% were using any antiplatelet agent, and 75% were using any antithrombotic agent. After excluding people who said aspirin was unsafe, 81% were using any antithrombotic agent. During the study period, use of prescription antiplatelet agents increased (p<0.001) but there was no temporal change in use of antithrombotic agents overall. In multivariate models, being aged >65 years, male gender, non-Hispanic ethnicity, having a usual source of care, and poor or fair health status were associated with use of an antithrombotic agent (p<0.05).

CONCLUSIONS

Although a high percentage of stroke survivors appear to use an antithrombotic agent, further research should investigate whether and how to improve care among the remaining 20% of stroke survivors, particularly among younger, female, and Hispanic patients.

Stroke prevention in atrial fibrillation and other major cardiac sources of embolism

The frequency of cardioembolic stroke is expected to rise as the general population ages. Much of the increase may be attributed to atrial fibrillation, the most common cause of cardioembolic stroke and one that plays a substantial role in aging adults. Other sources of cardioembolic stroke may include ventricular thrombus from myocardial infarction, heart failure, structural heart defects such as patent foramen ovale (PFO), atrial septal aneurysm, proximal aortic atheroma, valvular heart disease, and endocarditis. Diagnostic studies, such as neuroimaging, ECG, and echocardiography, are helpful in uncovering cardioembolic sources of stroke. Medical therapy is predicated on the underlying mechanism. For example, warfarin may be indicated in certain patients who have atrial fibrillation, atrial, or ventricular thrombi, and PFO with atrial septal aneurysm and cryptogenic stroke in select young patients to prevent stroke. Newer diagnostic technologies, including multidetector CT and cardiac MRI, may be useful to diagnose cardiac causes of stroke when transesophageal echocardiography is indeterminate or cryptogenic stroke is present.

Management of the Elderly Person After Myocardial Infarction

Elderly persons after myocardial infarction should have their modifiable coronary artery risk factors intensively treated. Hypertension should be treated with beta blockers and angiotensin-converting enzyme inhibitors. The blood pressure should be reduced to &lt;140/85 mmHg and to ≥130/80 mmHg in persons with diabetes or renal insufficiency. The serum low-density lipoprotein cholesterol should be reduced to &lt;100 mg/dl with statins if necessary. Aspirin or clopidogrel, beta blockers, and angiotensin-converting enzyme inhibitors should be given indefinitely unless contraindications exist to the use of these drugs. Long-acting nitrates are effective antianginal and antiischemic drugs. There are no Class I indications for the use of calcium channel blockers after myocardial infarction. Postinfarction patients should not receive Class I antiarrhythmic drugs, sotalol, or amiodarone. An automatic implantable cardioverter-defibrillator should be implanted in postinfarction patients at very high risk for sudden cardiac death. Hormonal therapy should not be used in postmenopausal women after myocardial infarction. The two indications for coronary revascularization are prolongation of life and relief of unacceptable symptoms despite optimal medical management.

Unstable angina

Properly treated unstable angina and non-Q wave myocardial infarction have low hospital mortality, but untreated, mortality is high. Symptoms and labs usually suffice for diagnosis. Abnormal physical findings are rarely helpful and often absent. Careful surveillance and management substantially reduce long-term risks.

The activated clotting time can be used to monitor the low molecular weight heparin dalteparin after intravenous administration

OBJECTIVES

This study was designed to compare the dose response of dalteparin versus unfractionated heparin (UFH) on the activated clotting time (ACT), and to determine whether the ACT can be used to monitor intravenous (IV) dalteparin during percutaneous coronary intervention (PCI).

BACKGROUND

The use of low molecular weight heparin (LMWH) during PCI has been limited by the presumed inability to monitor its anticoagulant effect using bedside assays.

METHODS

This study was performed in three phases. In vitro, ACTs were measured on volunteer (n = 10) blood samples spiked with increasing concentrations of dalteparin or UFH. To extend these observations in vivo, ACTs were then measured in patients (n = 15) who were sequentially treated with IV dalteparin and then UFH. Finally, a larger monitoring study was undertaken involving patients (n = 110) who received dalteparin 60 or 80 international U (IU)/kg alone or followed by abciximab. We measured ACT (Hemochron), activated partial thromboplastin time (aPTT), plasma anti-Xa and anti-IIa levels, tissue factor pathway inhibitor (TFPI) concentration, and plasma dalteparin concentration.

RESULTS

Dalteparin induced a significant rise in the ACT with a smaller degree of variance as compared to UFH. Five min after administration of IV dalteparin 80 IU/kg the ACT increased from 125 s (122 s, 129 s) to 184 s (176 s, 191 s) (p < 0.001). The aPTT, anti-Xa and anti-IIa activities, and TFPI concentration also demonstrated significant increases following IV dalteparin.

CONCLUSIONS

The ACT and aPTT are sensitive to IV dalteparin at clinically relevant doses. These data suggest that the ACT may be useful in monitoring the anticoagulant effect of intravenously administered dalteparin during PCI.

Does aspirin attenuate the effect of angiotensin-converting enzyme inhibitors on health outcomes of very old patients with heart failure?

OBJECTIVES

Concomitant ischemic heart disease (IHD) is common in older individuals with heart failure (HF). We estimated the effect of aspirin use on the rate of mortality, morbidity, and decline in physical functioning in nursing home residents with HF taking angiotensin-converting enzyme (ACE) inhibitors.

DESIGN

We conducted a retrospective cohort study using a nursing home database linking resident information collected via the Minimum Data Set (MDS) with drug utilization data.

SETTING

Nursing homes in four states (1992-1995).

PARTICIPANTS

Of 49,779 residents with HF admitted to these homes, 12,703 residents were taking an ACE inhibitor; 2,046 of these took aspirin.

MEASUREMENTS

Medicare enrollment files provided the date of death, and we used the Part A Medicare files to identify hospital admissions. The activity of daily living scale from repeat MDS assessments allowed us to evaluate decline in physical function. Cox proportional hazards models provided adjusted estimates of the aspirin effect, with nonusers as the reference group.

RESULTS

The overall mortality rate, hospitalization rate,and rate of decline in physical function of aspirin users were not different from those of nonusers (e.g., hospitalization rate ratio = 0.99, 95% confidence interval = 0.92-1.07). This effect did not vary by presence of concomitant IHD or by dose or type of ACE inhibitor.

CONCLUSION

In a cohort of older HF residents receiving ACE inhibitors in nursing homes, we found that treatment with aspirin did not appear to affect outcomes negatively.

Cost effectiveness of aspirin, clopidogrel, or both for secondary prevention of coronary heart disease

BACKGROUND

Both aspirin and clopidogrel reduce the rate of cardiovascular events in patients with coronary heart disease. We estimated the cost effectiveness of the increased use of aspirin, clopidogrel, or both for secondary prevention in patients with coronary heart disease.

METHODS

We used the Coronary Heart Disease Policy Model, a computer simulation of the U.S. population, to estimate the incremental cost effectiveness (in dollars per quality-adjusted years of life gained) of four strategies in patients over 35 years of age with coronary disease from 2003 to 2027: aspirin for all eligible patients (i.e., those who were not allergic to or intolerant of aspirin), aspirin for all eligible patients plus clopidogrel for patients who were ineligible for aspirin, clopidogrel for all patients, and the combination of aspirin for all eligible patients plus clopidogrel for all patients.

RESULTS

The extension of aspirin therapy from the current levels of use to all eligible patients for 25 years would have an estimated cost-effectiveness ratio of about $11,000 per quality-adjusted year of life gained. The addition of clopidogrel for the 5 percent of patients who are ineligible for aspirin would cost about $31,000 per quality-adjusted year of life gained. Clopidogrel alone in all patients or in routine combination with aspirin had an incremental cost of more than $130,000 per quality-adjusted year of life gained and remained financially unattractive across a wide range of assumptions. However, clopidogrel alone or in combination with aspirin would cost less than $50,000 per quality-adjusted year of life gained if its price were reduced by 70 to 82 percent, to $1.00 and $0.60 per day, respectively.

CONCLUSIONS

Increased prescription of aspirin for secondary prevention of coronary heart disease is attractive from a cost-effectiveness perspective. Because clopidogrel is more costly, its incremental cost effectiveness is currently unattractive, unless its use is restricted to patients who are ineligible for aspirin.

Department of Veterans Affairs Cooperative Studies Program Clinical Trial comparing combined warfarin and aspirin with aspirin alone in survivors of acute myocardial infarction: primary results of the CHAMP study

BACKGROUND

Both aspirin and warfarin when used alone are effective in the secondary prevention of vascular events and death after acute myocardial infarction. We tested the hypothesis that aspirin and warfarin therapy, when combined, would be more effective than aspirin monotherapy. Methods and Results- We conducted a randomized open-label study to compare the efficacy of warfarin (target international normalized ratio 1.5 to 2.5 IU) plus aspirin (81 mg daily) with the efficacy of aspirin monotherapy (162 mg daily) in reducing the total mortality in 5059 patients enrolled within 14 days of infarction and followed for a median of 2.7 years. Secondary end points included recurrent myocardial infarction, stroke, and major hemorrhage. Four hundred thirty-eight (17.3%) of 2537 patients assigned to the aspirin group and 444 (17.6%) of 2522 patients assigned to the combination group died (log-rank P=0.76). Recurrent myocardial infarction occurred in 333 patients (13.1%) taking aspirin and in 336 patients (13.3%) taking combination therapy (log-rank P=0.78). Stroke occurred in 89 patients (3.5%) taking aspirin and in 79 patients (3.1%) taking combination therapy (log-rank P=0.52). Major bleeding occurred more frequently in the combination therapy group than in the aspirin group (1.28 versus 0.72 events per 100 person years of follow-up, respectively; P<0.001). There were 14 individuals with intracranial bleeds in both the aspirin and combination therapy groups.

CONCLUSIONS

In post-myocardial infarction patients, warfarin therapy (at a mean international normalized ratio of 1.8) combined with low-dose aspirin did not provide a clinical benefit beyond that achievable with aspirin monotherapy.

Direct thrombin inhibitors in acute coronary syndromes: principal results of a meta-analysis based on individual patients' data

BACKGROUND

To obtain more reliable and precise estimates of the effect of direct thrombin inhibitors in the management of acute coronary syndromes, including patients undergoing percutaneous coronary intervention, we undertook a meta-analysis based on individual patients' data from randomised trials comparing a direct thrombin inhibitor (hirudin, bivalirudin, argatroban, efegatran, or inogatran) with heparin.

METHODS

We included trials that involved at least 200 patients. The primary efficacy outcome was death or myocardial infarction, and the primary safety outcome was major bleeding. Data from individual trials were combined by use of a modified Mantel-Haenszel method.

FINDINGS

In 11 randomised trials, 35,970 patients were assigned up to 7 days' treatment with a direct thrombin inhibitor or heparin and followed up for at least 30 days. Compared with heparin, direct thrombin inhibitors were associated with a lower risk of death or myocardial infarction at the end of treatment (4.3% vs 5.1%; odds ratio 0.85 [95% CI 0.77-0.94]; p=0.001) and at 30 days (7.4% vs 8.2%; 0.91 [0.84-0.99]; p=0.02). This was due primarily to a reduction in myocardial infarctions (2.8% vs 3.5%; 0.80 [0.71-0.90]; p<0.001) with no apparent effect on deaths (1.9% vs 2.0%; 0.97 [0.83-1.13]; p=0.69). Subgroup analyses suggested a benefit of direct thrombin inhibitors on death or myocardial infarction in trials of both acute coronary syndromes and percutaneous coronary interventions. A reduction in death or myocardial infarction was seen with hirudin and bivalirudin but not with univalent agents. Compared with heparin, there was an increased risk of major bleeding with hirudin, but a reduction with bivalirudin. There was no excess in intracranial haemorrhage with direct thrombin inhibitors.

INTERPRETATION

Direct thrombin inhibitors are superior to heparin for the prevention of death or myocardial infarction in patients with acute coronary syndromes. This information should prompt further clinical development of direct thrombin inhibitors for the management of arterial thrombosis.

Left Ventricular Thrombus

Left ventricular thrombus (LVT) is a frequent complication in patients with acute anterior myocardial infarction (MI) and in those with dilated cardiomyopathy (DCM). The clinical importance of LVT lies in its potential to embolize. The current treatment of patients with acute MI centers on reperfusion, and although controversial, the incidence of LVT complicating acute anterior MI is probably reduced when compared with historical controls. Nevertheless, stroke continues to be a clinically important complication of acute MI and is most common in patients with anterior MI, in part secondary to embolization of LVT. Therapeutic anticoagulation during acute MI reduces the incidence of LVT, and long-term anticoagulation has been associated with a reduction in recurrent infarction and ischemic stroke, but carries hemorrhagic risk. Primary treatment strategies for patients with acute MI center on reperfusion therapy followed by antiplatelet agents and pharmacologic blockade of abnormal neurohumoral mechanisms. Strategies to prevent stroke following infarction include risk stratification for development of LVT and embolism. For patients with anterior MI, particularly those with apical akinesis or dyskinesis, therapeutic anticoagulation reduces the number of LVT and cardioembolic strokes. However, the absolute number of ischemic strokes prevented with this strategy may only be marginal, given the anticoagulation risk, particularly if antiplatelet agents are used concurrently. An attractive alternative strategy is echocardiographic evaluation following anterior infarction with therapeutic anticoagulation reserved for those with demonstrable thrombus. The efficacy of this strategy, however, never has been proven in a clinical study. Primary prevention of cardioembolic stroke through therapeutic anticoagulation is controversial in patients with DCM; the greatest benefit would be expected for those with severe left ventricular dysfunction. If LVT is detected during the course of MI or DCM, therapeutic anticoagulation is usually indicated with the expectation that the majority of thrombi will resolve without clinical evidence of systemic embolism. Additional therapeutic intervention is rarely needed.

Perioperative cardiac complications

Although infrequent, perioperative cardiac complications are a source of major morbidity and mortality. As the population ages, the prevalence of cardiovascular disease is increasing. For physicians who refer patients for surgery as well as for clinicians directly involved in perioperative medical care, an understanding of perioperative cardiac complications, reduction of such complications, and treatment of complications is essential. This article summarizes the approach to perioperative hypertension, hypotension, myocardial ischemia, myocardial infarction, and congestive heart failure.

Advances create opportunities: implementing the major tenets of the new unstable angina guidelines in the emergency department

Of all the clinical syndromes with which emergency physicians must deal, chest pain of coronary cause has benefited from the most striking recent advances both in diagnostic approach (cognitive and technologic) and in therapeutic options. Chest pain evaluation and management have become important foci of research in emergency medicine, and entire units are dedicated to its clinical prosecution in emergency departments and elsewhere in the hospital. New diagnostic tools are proposed and studied on a regular basis. Antiplatelet, antithrombin, and fibrinolytic agents unknown in clinical practice as recently as 5 years ago have secured places in the emergency physician's armamentarium for treating acute coronary syndrome. Many of these diagnostic and therapeutic tools have been developed in the coronary care unit and in the cardiac catheterization laboratory. Although intuitively they may also be useful outside of those settings, they have unreliably been brought to the ED for implementation and resultant appropriate prompt and early care of the coronary patient who does not meet fibrinolytic criteria. As emergency physicians seek to bring accurate chest pain risk stratification into their practice and begin to use new therapeutic agents to minimize myocardial damage before turning the patient's care over to other specialists, it is essential that they are familiar with the data supporting these approaches. In this commentary, we seek to place the American College of Cardiology/American Heart Association unstable angina guidelines into the clinical context of the ED.

New recommendations from the 1999 American College of Cardiology/American Heart Association acute myocardial infarction guidelines

OBJECTIVE

To review literature relating to significant changes in drug therapy recommendations in the 1999 American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for treating patients with acute myocardial infarction (AMI).

DATA SOURCES

1999 ACC/AHA AMI guidelines, English-language clinical trials, reviews, and editorials researching the role of drug therapy and primary angioplasty for AMI that were referenced in the guidelines were included. Additional data published in 2000 or unpublished were also included if relevant to interpretation of the guidelines.

STUDY SELECTION

The articles selected influence AMI treatment recommendations.

DATA SYNTHESIS

Many clinicians and health systems use the ACC/AHA AMI guidelines to develop treatment plans for AMI patients. This review highlights important changes in AMI drug therapy recommendations by reviewing the results of recent clinical trials. Insights into evolving drug therapy strategies that may impact future guideline development are also described.

CONCLUSIONS

Several changes in drug therapy recommendations were included in the 1999 AMI ACC/AHA guidelines. There is emphasis on administering fibrin-specific thrombolytics secondary to enhanced efficacy. Selection between fibrin-specific agents is unclear at this time. Low response rates to thrombolytics have been noted in the elderly, women, patients with heart failure, and those showing left bundle-branch block on the electrocardiogram. These patient groups should be targeted for improved utilization programs. The use of glycoprotein (GP) IIb/IIIa receptor inhibitors in non-ST-segment elevation MI was emphasized. Small trials combining reduced doses of thrombolytics with GP IIb/IIIa receptor inhibitors have shown promise by increasing reperfusion rates without increasing bleeding risk, but firm conclusions cannot be made until the results of larger trials are known. Primary percutaneous coronary intervention (PCI) trials suggest lower mortality rates for primary PCI when compared with thrombolysis alone. However, primary PCI, including coronary angioplasty, is only available at approximately 13% of US hospitals, making thrombolysis the preferred strategy for most patients. Clopidogrel has supplanted ticlopidine as the recommended antiplatelet agent for patients with aspirin allergy or intolerance following reports of a better safety profile. The recommended dose of unfractionated heparin is lower than previously recommended, necessitating a separate nomogram for patients with acute coronary syndromes. Routine use of warfarin, either alone or in combination with aspirin, is not supported by clinical trials; however, warfarin remains a choice for antithrombotic therapy in patients intolerant to aspirin. Beta-adrenergic receptor blockers continue to be recommended, and emphasis is placed on improving rates of early administration (during hospitalization), even in patients with moderate left ventricular dysfunction. New recommendations for drug treatment of post-AMI patients with low high-density lipoprotein cholesterol and/or elevated triglycerides are included, with either niacin or gemfibrozil recommended as an option. Supplementary antioxidants are not recommended for either primary or secondary prevention of AMI, with new data demonstrating lack of efficacy vitamin E in primary prevention. Estrogen replacement therapy or hormonal replacement therapy should not be initiated solely for prevention of cardiovascular disease, but can be continued in cardiovascular patients already taking long-term therapy for other reasons. Bupropion has been added as a new treatment option for smoking cessation. As drug therapy continues to evolve in treating AMI, more frequent updates of therapy guidelines will be necessary.

GENERAL PHARMACOLOGIC TREATMENT OF ACUTE MYOCARDIAL INFARCTION

The general pharmacotherapeutic issues surrounding AMI are complex and expanding, especially with regard to treatment aimed at the [table: see text] culprit, coronary atherosclerotic thrombus. Basic, well-established therapy includes the routine administration of oxygen, nitroglycerin, aspirin, and at times morphine, with selected cases invoking caution with respect to these agents (e.g., nitroglycerin and the risk of hypotension in right ventricular infarction; contraindication to nitrolycerin in patients on sildenafil). Cardioprotective agents, especially beta-adrenergic antagonists, should be considered early in light of their demonstrated benefit; others, such as ACE inhibitors, need not be administered in the ED. Heparin, both UFH and the newer LMWHs, have well-established roles in acute coronary syndromes. The GP IIb/IIIa inhibitors are the most recent addition to the pharmacologic armamentarium; their role is evolving rapidly as research on this frontier continues. Table 2 reviews recommended dosing of selected agents in acute coronary syndromes.

Unstable angina pectoris and non-Q-wave myocardial infarction

Unstable angina pectoris and non-Q-wave myocardial infarction are clinical syndromes that share many pathophysiologic and clinical features. In the spectrum of coronary artery disease, these syndromes lie between chronic stable angina and Q-wave myocardial infarction. Although both conditions are associated with significant morbidity and mortality, patients presenting with these syndromes can be further risk stratified into higher and lower risk based on a number of readily available clinical features and biochemical parameters. Such risk stratification can allow for more tailored treatment and better resource allocation. Although routine early coronary angiography and revascularization has not been shown to be superior to conservative management, certain high-risk patients may benefit from a more aggressive strategy. Medical therapy with the use of antiplatelet, anticoagulant, and antiischemic agents remains the cornerstone of emergent treatment for patients presenting with these syndromes. The recent demonstration of a reduction in both morbidity and mortality with the glycoprotein IIb/IIIa antagonists has further expanded the armamentarium of available agents. Following initial stabilization, risk stratification with stress testing can help identify patients with a large residual ischemic burden who may benefit from coronary angiography with revascularization if feasible.

Low-molecular weight heparins in coronary artery disease

Recently published trials strongly support the use of low-molecular weight heparins in the treatment of unstable coronary syndromes. These agents provide an alternative to heparin that is at least as effective and safe, and does not require intravenous infusions or meticulous monitoring. Although comparative trials are not yet available, the available evidence allows for selection of specific agents in acute management of unstable angina. This review summarizes the current clinical data supporting the use of these agents.

Clinical use of new antithrombotic therapies for medical management of acute coronary syndromes

Prevention and management of acute coronary syndromes (ACS) are focal points of interest among health care providers. Acute coronary syndromes is an all-encompassing term that refers to unstable angina, non-Q wave myocardial infarction, and Q wave myocardial infarction. These syndromes are usually the result of atherosclerotic plaque rupture leading to thrombus formation in a coronary artery. Heparin and aspirin are traditional antithrombotic treatments. They typically are administered with antiischemic therapies and often with fibrinolytic agents for patients with ST segment elevation associated with acute myocardial infarction. Although aspirin and heparin are important, they have significant limitations that have prompted development of newer antithrombotic approaches. Adenosine diphosphate inhibitors have been evaluated as either alternatives or adjunctive treatment to aspirin. Glycoprotein IIb-IIIa receptor inhibitors, low-molecular-weight heparins, and direct thrombin inhibitors have been studied as concurrent therapy with, or as alternatives to, heparin.

Prevention of venous thromboembolism

Recognition of the patient at risk and delivery of appropriate prophylaxis are imperative to reduce the incidence of VTE (including fatal PE) in hospitalized patients. This article provides estimates of risk and a summary of effective prophylaxis methods such that physicians can tailor an individual patient's prophylaxis regimen to maximize DVT risk reduction in the safest and most cost-effective manner.

Dosing and monitoring of low-molecular-weight heparins in special populations

As a result of numerous clinical trials and meta-analyses supporting the superior efficacy and relative safety of low-molecular-weight heparins (LMWHs) compared with unfractionated heparin (UFH), LMWHs are emerging as the antithrombotic agents of choice for the prevention and treatment of deep vein thrombosis and pulmonary embolism. In addition, data indicate that enoxaparin given with low-dosage aspirin is more effective than UFH in treating acute coronary syndromes. Anti-Xa activity can be used as a biologic marker of LMWH activity. Because of the more predictable anticoagulant response to subcutaneous administration of LMWHs compared with UFH, routine monitoring of anti-Xa activity in clinically stable adults with uncomplicated disease is not recommended. Because the optimal dosage of LMWHs has not been established for patients with renal insufficiency or extremes of body weight, during pregnancy, or for children, anti-Xa activity monitoring may be warranted in these subsets.

Arterial indications for the low molecular weight heparins

Antithrombotic treatment is of proven importance in patients with acute coronary syndromes. There is now accumulating evidence from several clinical trials in patients with unstable angina pectoris that the low molecular weight heparins (LMWHs) are at least as effective as unfractionated heparin. The LMWHs are easier to use, with the potential to facilitate long-term outpatient treatment. The results of the trials have actually failed to show any clear advantage, however, of the LMWHs over the standard antiplatelet treatment, despite the evidence of a sustained hypercoagulability. Potentially, the use of higher doses of LMWHs could improve the outcomes, but this is as yet unproven and could be associated with unacceptably increased risk of bleeding. During the acute phase of a stroke, aspirin is the first choice of antithrombotic drug because it reduces the risk of recurrent stroke. LMWH cannot be recommended as an antithrombotic agent for the acute treatment of stroke. Prophylactic use of low dose LMWH for the prevention of venous thromboembolism should be considered in every patient with a stroke.

Advances in the pharmacology of acute coronary syndrome. Platelet inhibition

The development of potent inhibitors of platelet aggregation has led to significant decreases in morbidity and mortality rates among patients undergoing percutaneous coronary intervention. Clinical trials have demonstrated that agents that block glycoprotein IIb/IIIa receptor-mediated platelet aggregation have an outcome benefit when used acutely in patients with chest pain and ST depression or elevated cardiac enzymes, leading to the integration of these agents into emergency medicine clinical practice. This article provides an overview of the pathophysiology of acute coronary syndrome and the pharmacology of platelet inhibition and reviews the evidence from the clinical trials pertaining to the use of these agents in the emergency department.

Determination of who may derive most benefit from aspirin in primary prevention: subgroup results from a randomised controlled trial

OBJECTIVE

To determine which groups of patients may derive particular benefit or experience harm from the use of low dose aspirin for the primary prevention of coronary heart disease.

DESIGN

Randomised controlled trial.

SETTING

108 group practices in the Medical Research Council's general practice research framework who were taking part in the thrombosis prevention trial.

PARTICIPANTS

5499 men aged between 45 and 69 years at entry who were at increased risk of coronary heart disease.

MAIN OUTCOME MEASURES

Myocardial infarction, coronary death, and stroke.

RESULTS

Aspirin reduced coronary events by 20%. This benefit, mainly for non-fatal events, was significantly greater the lower the systolic blood pressure at entry (interaction P=0.0015), the relative risk at pressures 130 mm Hg being 0.55 compared with 0.94 at pressures >145 mm Hg. Aspirin also reduced strokes at low but not high pressures, the relative risks being 0.41 and 1.42 (P=0.006) respectively. The relative risk of all major cardiovascular events-that is, the sum of coronary heart disease and stroke-was 0.59 at pressures <130 mm Hg compared with 1.08 at pressures >145 mm Hg (P=0.0001).

CONCLUSION

Even with the limitations of subgroup analyses the evidence suggests that the benefit of low dose aspirin in primary prevention may occur mainly in those with lower systolic blood pressures, although it is not clear even in these men that the benefit outweighs the potential hazards. Men with higher pressures may be exposed to the risks of bleeding while deriving no benefit through reductions in coronary heart disease and stroke.

A European view on the North American fifth consensus on antithrombotic therapy

An American-Canadian group of experts have, in the November 1998 issue of CHEST, published for the fifth time their recommendations for antithrombotic therapy. This remarkable consensus document was the result of an extensive review of the literature by an interdisciplinary group. Considering the impact of this document on medical practice, also outside North America, a group of European experts reviewed in detail the fifth report, particularly the sections on clinical indications of antithrombotic treatment. The aim was not to indicate the many areas of agreement and to quote literature that has become available since publication of the last consensus documents, but rather to refer to the gray zones of uncertainty and limited number of divergent opinions.

Rapid oral challenge-desensitization for patients with aspirin-related urticaria-angioedema

BACKGROUND

Acetylsalicylic acid (ASA), commonly known as aspirin, is indicated in the treatment of coronary artery disease (CAD). Many patients are denied treatment with ASA because of a history of ASA or nonsteroidal anti-inflammatory drug (NSAID)-induced urticaria or angioedema.

OBJECTIVE

We sought to develop a safe and practical protocol to allow the administration of ASA to patients with a history of ASA- or NSAID-induced urticaria-angioedema.

METHODS

Eleven subjects with a history of ASA- or NSAID-induced urticaria-angioedema were challenged-desensitized by oral protocols based on rapidly escalating doses of ASA. Most had CAD, one had a history of pulmonary embolism, and one had refractory chronic sinusitis and asthma. Starting doses ranged from 0.1 to 10 mg and were administered at intervals of 10 to 30 minutes. Dosing was individualized for each patient but followed this general sequence (in milligrams): 0.1, 0.3, 1, 3, 10, 20, 40, 81, 162, 325.

RESULTS

Nine patients tolerated the procedure without adverse effects and continued taking ASA for periods ranging from 1 to 24 months, without development of urticaria or angioedema. A patient who had a history of chronic idiopathic urticaria in addition to aspirin-induced urticaria had chest tightness during the protocol. Another patient who had continuing urticaria and angioedema associated with antithyroid antibodies developed angioedema several hours after completing the protocol.

CONCLUSION

In patients with historical ASA- or NSAID-induced urticaria-angioedema reactions but who did not have urticaria and angioedema independent of ASA/NSAID, rapid oral challenge-desensitization to ASA was performed safely and permitted patients with CAD and other diseases to receive treatment with ASA.

Newer antithrombotic strategies in the initial management of non-ST-segment elevation acute coronary syndromes

OBJECTIVE

To review the place in therapy of currently available antithrombotic agents in the non-ST-segment elevation acute coronary syndromes, that is, unstable angina and non-Q-wave myocardial infarction (MI). Recommendations are made based on currently available data.

DATA SOURCE

English-language clinical studies, position statements, and review articles pertaining to the management of unstable angina and non-Q-wave MI with currently available products.

STUDY SELECTION

Selection of prospective clinical studies was limited to those focusing on the management of the non-ST-segment elevation acute coronary syndromes, unstable angina, and non-Q-wave MI.

DATA SYNTHESIS

It has yet to be determined which combination of agents (dalteparin, enoxaparin, lepirudin, clopidogrel, ticlopidine, abciximab, eptifibatide, tirofiban) and procedural strategies most significantly reduces mortality and serious events in these patients. The relevant pathophysiology, diagnostic criteria, and risk-stratifying procedures are reviewed in context with information from clinical studies regarding currently available agents for the management of non-ST-segment elevation acute coronary syndromes.

CONCLUSIONS

A large number of new therapeutic classes and agents are available for the treatment of unstable angina and non-Q-wave MI. Although the diagnoses of unstable angina or non-Q-wave MI identify risk, treatment decisions are often based on the presence or absence of ST-segment elevations. Limited prospective evidence delineates the proper utilization of resources to best manage these patients. Efforts should be aimed at identifying particular patients who will best benefit from recently available therapies.

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.

Cerebral microembolism in acute myocardial infarction

BACKGROUND AND PURPOSE

This study was undertaken to determine the frequency of cerebral microemboli (high-intensity transient signals; HITS) detected by transcranial Doppler (TCD) in patients with acute myocardial infarction (AMI) and to relate them to the various putative risk factors and clinical embolic events.

METHODS

We investigated 112 consecutive patients within 72 hours of admission to an acute coronary care unit using TCD to monitor for cerebral microemboli. Twelve patients were excluded because of failure of ultrasound insonation. All patients had 2-dimensional echocardiograms within the study period.

RESULTS

HITS were detected in 17% of patients, with significantly higher frequency in patients with reduced (<65%) left ventricular (LV) ejection fraction (P=0. 019), akinetic LV segments (P=0.002), and LV thrombus (P=0.015). A marginally significant (P=0.059) increase of HITS was found in patients with anterior AMI. Stroke was significantly more frequent in patients with cerebral microemboli (P=0.01).

CONCLUSIONS

HITS were detected in 17% of patients in spite of adequate antithrombotic therapy and were increased in patients with reduced LV function, akinetic myocardial segments, and LV thrombus. They were present in all 3 patients with stroke and may represent a predictor of clinical embolic events.

[Practice guidelines of the Spanish Society of Cardiology. Recommendations for the use of antithrombotic treatment in cardiology]

The indications for the use of antithrombotic therapy are evolving as new drugs become available or new indications or dosages are recommended for drugs already in use. This document reviews and updates the former one published in 1994. To that end, an exhaustive revision of the literature published in the last 15 years has been undertaken. Following the evidence based medicine dictates, and aiming to select all the relevant publications for each pathology, all studies were selected through MEDLINE, using the specified key words for each subject, and were filtered using the following steps: a) only randomized, controlled studies, meta-analysis, guidelines and review articles were chosen; b) then, the Best-Evidence and Cochrane Collaboration databases were consulted; c) finally, the evidence based medicine validation, relevance and applicability criteria were assessed for each publication. The use of antiaggregants and anticoagulants are given for the following conditions: a) prevention of deep vein thrombosis and pulmonary embolism; b) prevention of systemic emboli in patients with lone atrial fibrillation, atrial fibrillation associated or not with rheumatic heart disease, in patients with biological or mechanical cardiac valvular prostheses and in dilated cardiomyopathy; c) antithrombotic therapy in coronary heart disease and in coronary intervention; d) the interactions with oral anticoagulants and how to control these therapies are also discussed.

Anticoagulants in acute coronary syndromes

Antithrombotic and antiplatelet agents, particularly unfractionated heparin and aspirin, are longstanding therapeutic mainstays for acute coronary syndromes such as unstable angina and non-Q-wave myocardial infarction (MI). Early studies demonstrated that aspirin reduces the risk of mortality or nonfatal MI by 50-70% in patients presenting with unstable angina or non-Q-wave MI. Added to aspirin, heparin regimens further diminish the incidence of these myocardial ischemic events in the acute setting. Three major clinical studies demonstrated that such enhanced risk reductions can be achieved without significant increases in bleeding complications. The low-molecular-weight (LMW) heparin, dalteparin, proved superior to placebo but not unfractionated heparin in diminishing the incidence of (1) death or MI; (2) death, MI, or recurrence of angina; or (3) frequency of revascularization procedures. On the other hand, another LMW heparin, enoxaparin, did reduce these events at 14 and 30 days, as well as 1 year after treatment. The principal biophysical limitation of heparins, however, is that they cannot inactivate clot-bound thrombin, which probably contributes to morbidity and mortality in acute coronary syndromes. The natural leech-derived polypeptide hirudin and its derivatives (e.g., lepirudin) inactivate both fibrin-bound and free thrombin. Lepirudin has been approved in certain countries for the treatment of heparin-induced thrombocytopenia and is now being evaluated in the clinical management of acute myocardial ischemic syndromes. The well-documented pathophysiologic foundation for acute coronary syndromes is partial or intermittent thrombotic occlusion of a coronary artery as the result of atherosclerosis. Although a stable atherosclerotic plaque may not be clinically problematic, plaque rupture, which occurs under a variety of stimuli, touches off a cascade of enzymatic and cellular responses that frequently culminate in thrombotic occlusion. In the coronary circulation, such an occlusion may cause transmural MI, unstable angina, or non-Q-wave MI. Because the pathogenetic mechanisms of atherosclerosis with thrombotic complications have been elucidated, this knowledge can be translated into a rational clinical approach using antithrombotic therapies.

Haemostatic function, arterial disease and the prevention of arterial thrombosis

Recent years have seen the expansion of information linking raised plasma levels of individual clotting factors and evidence of disturbances of fibrinolytic activity with the risk of thrombotic manifestations of arterial disease, both in community-based, apparently healthy populations and in patients with known atherosclerosis. Some of these prothrombotic changes in the haemostatic system may result partly from underlying chronic inflammation or acute infection and may, in turn, contribute substantially to the thrombotic risk which accompanies these underlying processes. The importance of the coagulation system in the pathogenesis of arterial thrombosis is further illustrated by the benefit in the Thrombosis Prevention Trial of low-intensity, dose-adjusted warfarin in the primary prevention of ischaemic heart disease. Clinical trials of bezafibrate, which is being used for its fibrinogen-lowering as well as lipid-modifying properties, are in progress.