Platelet-endothelial interactions in atherothrombotic disease: therapeutic implications

The role of the platelet and the endothelium in the pathogenesis of atherosclerosis and subsequent ischemic events has been the subject of extensive investigation. Arterial sites where endothelial function is severely impaired are often the sites of atheroma development. Lesion evolution impairs endothelial function, leading to a self-perpetuating cycle of growth. During early lesion development, overt thrombotic events are rare. However, rupture of an advanced, necrotic plaque or intimal ulceration triggers arterial thrombosis, at which point the importance of platelet function may be seen clearly. The Antiplatelet Trialists' Collaboration meta-analysis demonstrated the benefit of antiplatelet therapy to patients with atherosclerotic disease. Aspirin is the most widely studied agent and is considered the standard of antiplatelet therapy. Newer agents that intervene at different stages of the platelet activation pathway have been developed. Clopidogrel, a new adenosine diphosphate receptor antagonist, is more effective than aspirin in reducing vascular events in patients with prior myocardial infarction, stroke, or established peripheral arterial disease. The glycoprotein IIb-IIIa antagonists such as abciximab have proven effective in the setting of active arterial thrombosis and percutaneous revascularization, but their value in secondary prevention remains unknown. All patients with atherosclerosis should be treated with an antiplatelet drug. Current evidence suggests that either aspirin or clopidogrel are appropriate first-line agents. There is urgent need for an analysis of the risk/benefit ratio in various populations and clinical settings to determine the most appropriate type and intensity of therapy for a given patient.

Antithrombotic therapy and the transition to the catheterization laboratory in UA/NSTEMI

The management of unstable angina/non ST elevation myocardial infarction (UA/NSTEMI) has evolved substantially in recent years. Multiple new antithrombotic options are available; in addition, the use of interventional strategies in patients with UA/NSTEMI has become the dominant strategy, particularly in tertiary centers. On the one hand, we are doing more percutaneous interventions more rapidly in ACS patients. On the other hand, we have an ever-expanding therapeutic armamentarium to apply in these complex clinical circumstances. Much of the controversy surrounding modern-day management is not so much about the specific the choice of agent or strategy, but rather how to use these agents most effectively in a clinical environment where patients may come forward to the catheterization laboratory, sometimes rapidly, and may require percutaneous or surgical revascularization. All available antithrombotic agents act on one (or more) of the four steps of coagulation: platelet activation, platelet aggregation, thrombin generation, and thrombin activity. The antiplatelet agents, aspirin, thieno-pyridines, and glycoprotein (GP) IIb/IIIa antagonists, target the early steps of platelet activation and aggregation. The antithrombin agents, unfractionated heparin, low molecular weight (LMW) heparin, Xa inhibitors, and direct thrombin antagonists, act specifically to target thrombin generation, thrombin activity, or both. We will review the major recent trials that comprise the current state of knowledge regarding these new antithrombotic agents in ACS, and discuss some of the near-future additions to our armamentarium, including prasugrel, Cangrelor, and AZD6140. The most recent ACC/AHA and ESC unstable angina guidelines have emphasized that multiple options are available, and no one agent can be recommended over the others in all cases. There is NOT one perfect antithrombotic regimen for all patients. Antithrombotic therapy needs to be individualized, and that so-called ''standard'' therapy may need to be supplemented (or even replaced) in specific circumstances. Ultimately, determining optimal therapy means understanding the physiology, understanding the therapeutic options - not just how they work, but how they may work together, and being able to interpret a never-ending supply of new clinical trial data that have to be applied in the ''real world''.

Optimal antithrombotic treatment for percutaneous coronary intervention

Recent years have witnessed significant advances in the percutaneous treatment of patients with atherosclerotic vascular disease. Anti-platelet and anti-thrombotic agents are routinely administered to minimize the risk of peri-procedural myonecrosis, stent thrombosis and other procedural complications. This article presents a current view of optimal adjunctive antithrombotic therapy for percutaneous coronary interventions (PCI), recognizing that optimal is a necessarily subjective label. This article focuses specifically on anticoagulant agents such as unfractionated heparin (UFH), the low-molecular weight heparins (LMWH), and direct thrombin inhibitors, and antiplatelet agents, such as aspirin, thienopyridines, and glycoprotein IIb/IIIa antagonists. It starts with a general discussion of anticoagulation and percutaneous intervention, followed by a summary of the modern-day view of the coagulation process. The mechanism of action of the individual agents is then presented, followed by some of the evidence base of recent clinical trials of anticoagulant and antiplatelet agents in PCI. Finally, we present summary recommendations for procedural anticoagulation in low risk, not-low risk, and high risk PCI, and list what we feel are appropriate doses for the agents employed. Ultimately, though, it is the individual interventional cardiologists who must decide for themselves exactly what constitutes optimal antithrombotic therapy for PCI.

Selective serotonin reuptake inhibitors yield additional antiplatelet protection in patients with congestive heart failure treated with antecedent aspirin

Clinical depression has been identified as an independent risk factor for increased mortality in patients with coronary artery disease. Enhanced platelet activity has been suggested as the mechanism responsible for this adverse association. Selective serotonin reuptake inhibitors (SSRIs) are known to inhibit platelets in patients undergoing coronary stenting. We sought to determine whether concomitant therapy with SSRIs would yield additional anti-platelet benefit in patients with congestive heart failure (CHF) already treated with antecedent aspirin. A total of 88 patients with left ventricular ejection fraction (LVEF) <40% or CHF symptoms in the setting of preserved systolic function and NYHA Class II-IV were analyzed. Of these, 23 patients (26%) were chronic SSRI users (SSRI+), and 65 patients were free from SSRI therapy (SSRI-). All patients received aspirin (325 mg) for at least 1 month prior to platelet studies. Platelets were assessed by aggregometry, flow cytometry and a rapid analyzer. The SSRI+ group exhibited a substantial decrease in platelet activity when compared with SSRI- patients, as manifested by a significant reduction in ADP- (P=0.001), and collagen-induced (P=0.02) aggregation, and the expression of PECAM-1 (P=0.03), GPIb (P=0.03), GP IIb/IIIa antigen (P=0.02) and GP IIb/IIIa activity with PAC-1 antibody (P=0.04) and P-selectin (P=0.02). Therapy with SSRIs also resulted in the reduced formation of platelet-leukocyte microparticles (P=0.01). Epinephrine-induced aggregation in plasma, collagen-induced whole blood aggregation, closure time and expression of vitronectin receptor, CD63, CD107a, CD107b and CD151 did not differ between groups. In patients with CHF already on aspirin, SSRI therapy was associated with further inhibition of platelet function. This observation may help to explain some of the clinical benefits associated with SSRI therapy. Further clinical trials may help to elucidate the potential outcome benefits of SSRIs in other potential thrombotic circumstances.

"Hot" unstable angina--is it worse than subacute unstable angina? Results from the GUARANTEE Registry

BACKGROUND AND METHODS

Because time to presentation to the hospital affects time to treatment and is known to be important in acute myocardial infarction, we evaluated this variable in patients with unstable angina/non-ST segment elevation myocardial infarction (UA/NSTEMI). Among 2909 consecutive patients with UA/NSTEMI admitted to 35 hospitals in 6 geographic regions of the United States, we compared patients with acute (onset of pain <12 hours before admission) and subacute (onset >12 hours) unstable angina.

RESULTS

Patients with "hot" (acute) unstable angina presented more often to the emergency department and were subsequently admitted more often to an intensive care unit. Hospital administration of medications did not differ between the two groups, with the exception of heparin, which was paradoxically used more often in subacute patients (p<0.001). All cardiac invasive procedures were undertaken less often in the acute patients (catheterization, 41.4% vs. 58.7%, p=0.001; percutaneous coronary intervention, 11.3% vs. 21.1%, p=0.001; coronary artery bypass grafting, 5.6% vs. 12.0%, p=0.001). A greater percentage of acute patients were found to have no significant coronary artery disease at cardiac catheterization (20.1% vs. 15.0%, p=0.006). Mortality did not differ between the two groups; however, the composite endpoint of death and MI favored the acute patients (1.3% vs. 2.2%, p=0.032).

CONCLUSIONS

Contrary to our initial hypothesis, "hot" UA patients tended to be at lower risk than patients with subacute presentation, highlighting the fact that patients with UA/NSTEMI remain at high risk even after the initial 12-hour period.

Therapeutic potential of GP IIb/IIIa receptor antagonists in acute myocardial infarction

The management of acute myocardial infarction (AMI) has changed dramatically over the last two decades, with the addition of fibrinolytic agents and primary coronary intervention (PCI). The more recent development of the glycoprotein (GP) IIb/IIIa antagonists, a new class of potent antiplatelet drugs, has the potential to considerably enhance the treatment of AMI patients. A number of recent studies have highlighted the potential incremental benefits with adjunctive IIb/IIIa-targeted therapy. In this review, we will discuss the pathophysiology of myocardial infarction (MI), the physiology and role of platelets in thrombosis and describe the currently available drugs. We will briefly summarise the results of recent clinical trials, discuss some key forthcoming trials and attempt to describe how GP IIb/IIIa antagonists may directly impact the immediate and near future day-to-day care of patients with AMI.

The current practice of intra-aortic balloon counterpulsation: results from the Benchmark Registry

OBJECTIVES

This study presents clinical data from the first large registry of aortic counterpulsation, a computerized database that incorporates prospectively gathered data on indications for intra-aortic balloon counterpulsation (IABP) use, patient demographics, concomitant medication and in-hospital outcomes and complications.

BACKGROUND

The intra-aortic balloon pump (IABP) is widely used to provide circulatory support for patients experiencing hemodynamic instability due to myocardial infarction, cardiogenic shock, or in very high risk patients undergoing angioplasty or coronary artery bypass grafting.

METHODS

Between June 1996 and August 2000, 203 hospitals worldwide (90% U.S., 10% non-U.S.) collected 16,909 patient case records (68.8% men, 31.2% women; mean age 65.9 +/- 11.7 years).

RESULTS

The most frequent indications for use of IABP were as follows: to provide hemodynamic support during or after cardiac catheterization (20.6%), cardiogenic shock (18.8%), weaning from cardiopulmonary bypass (16.1%), preoperative use in high risk patients (13.0%) and refractory unstable angina (12.3%). Major IABP complications (major limb ischemia, severe bleeding, balloon leak, death directly due to IABP insertion or failure) occurred in 2.6% of cases; in-hospital mortality was 21.2% (11.6% with the balloon in place). Female gender, high age and peripheral vascular disease were independent predictors of a serious complication.

CONCLUSIONS

This registry provides a useful tool for monitoring the evolving practice of IABP. In the modern-day practice of IABP, complication rates are generally low, although in-hospital mortality remains high. There is an increased risk of major complications in women, older patients and patients with peripheral vascular disease.

Long-term mortality benefit with abciximab in patients undergoing percutaneous coronary intervention

OBJECTIVES

The goal of this study was to test: 1) if platelet glycoprotein IIb/IIIa (GP IIb/IIIa) blockade with abciximab bolus plus 12-h infusion reduces mortality after percutaneous coronary intervention (PCI); 2) if prevention of early myocardial infarction (MI) after PCI is a mechanism for reducing mortality; and 3) for risk factors for mortality after PCI.

BACKGROUND

Studies of PCI suggest that MI after intervention is predictive of mortality. Abciximab, a platelet GP IIb/IIIa receptor inhibitor, has consistently reduced the incidence of MI among PCI patients in several trials. The presumed mechanism is prevention of platelet thrombus associated with vessel wall injury and downstream embolization into the microcirculation.

METHODS

In eight trials, 5,154 patients were randomized to a regimen comprising conventional therapy plus a bolus of abciximab within 1 h before PCI followed by a 12-h infusion; 4,136 controls were randomized to conventional therapy alone. Patient follow-up from six months to three years was available. Survival differences are examined using proportional hazards regression and survival curves.

RESULTS

A hazard ratio of 0.71 (95% confidence interval 0.57 to 0.89; p = 0.003) suggests a mortality benefit with abciximab. The absolute reduction in mortality was estimated to be 0.5% through 30 days, 0.7% through six months, 0.9% through one year and 1.8% through three years. Early MI explained 18% of the observed mortality benefit at one year. Multivariate regression suggests that patients with advanced cardiovascular disease may derive the greatest mortality benefit from abciximab.

CONCLUSIONS

The evidence from 9,290 randomized PCI patients shows a mortality benefit provided by abciximab bolus plus 12-h infusion.

Enoxaparin and abciximab adjunctive pharmacotherapy during percutaneous coronary intervention

Randomized controlled trials of patients with non-ST segment elevation acute coronary syndromes have established the superiority of enoxaparin (versus unfractionated heparin) for reducing adverse ischemic outcomes. Furthermore, adjunctive abciximab therapy during percutaneous coronary intervention (PCI) is associated with improved clinical outcomes. Since algorithms for integrating these pharmacotherapies have not been determined, patients undergoing elective PCI were enrolled into 2 distinct and separate studies conducted by the National Investigators Collaborating on Enoxaparin (NICE) study groups (NICE 1 and NICE 4 studies). Patients in NICE 1 were administered enoxaparin 1.0 mg/kg intravenously (without abciximab) and those enrolled in NICE 4 were administered a reduced dose (0.75 mg/kg) of enoxaparin in combination with standard-dose abciximab intravenously during PCI. Bleeding events and ischemic outcomes assessed in-hospital and at 30-days post-PCI were infrequent with either pharmacologic regimen. In the dose regimens studied, enoxaparin with or without abciximab appears to provide safe and effective anticoagulation during PCI. The combination of reduced-dose enoxaparin and abciximab was associated with a low incidence of adverse outcomes (bleeding or ischemic events). Additional studies may be required to establish the relative safety and efficacy of this new adjunctive pharmacologic strategy when compared with the combination of low-dose, weight-adjusted unfractionated heparin and abciximab.

Unstable angina and non-ST-segment elevation myocardial infarction: perspectives on combination therapy

We reviewed recent clinical data on the management of unstable angina and non-ST segment elevation myocardial infarction. We concentrated on the use of new therapies, particularly in combination with both older agents and other new methods, in order to present health care providers with an overview of available treatment options. The clinical trials reviewed herein provide strong evidence and proof of principle that combination therapies targeting 1) platelet function (aspirin, thienopyridines, and GP IIb/IIIa antagonists), 2) the coagulation cascade (unfractionated heparin and low-molecular-weight heparin), and 3) the physical characteristics of the active lesion (percutaneous intervention) reduce the risk of death or ischemic complications after thrombotic progression of coronary atherosclerosis.

Combining low-molecular-weight heparin and glycoprotein IIb/IIIa antagonists for the treatment of acute coronary syndromes: the NICE 3 story. National Investigators Collaborating on Enoxaparin

In recent years, a number of new therapies have become available that have significantly improved the care of patients with acute coronary syndromes (ACS). A number of studies have documented the significant superiority of the low-molecular-weight heparin (LMWH), enoxaparin, over unfractionated heparin (UFH) in the treatment of ACS. However, there are insufficient data regarding the safety of using LMWH in combination with glycoprotein (GP) IIb/IIIa antagonists. The NICE 3 study is an open-labeled, non-randomized, observational study examining the feasibility, safety, and preliminary efficacy of the LMWH, enoxaparin, in combination with each of the three commercially available GP IIb/IIIa antagonists in ACS patients. Approximately 600 patients at 45 clinical centers in North America will be divided between the three arms of the trial, representing each of the three GP IIb/IIIa antagonists. Once therapy is initiated, patients will receive no UFH (unless they require a coronary artery bypass graft) and will continue treatment even if invasive cath lab procedures are necessary. NICE 3 builds on the previous experiences of NICE 1 and NICE 4 with LMWH in the cath lab (with or without GP IIb/IIIa antagonists) to more aggressively extend the use of LMWHs into the medical management of ACS patients.

Endoluminal reconstruction of the arterial wall with endothelial cell/glue matrix reduces restenosis in an atherosclerotic rabbit

OBJECTIVES

The objectives of this study were 1) to improve the attachment of reimplanted endothelial cells (EC) using a fibrin glue, and 2) to assess the impact of endothelial reseeding on restenosis eight weeks after balloon angioplasty.

BACKGROUND

A possible mechanism contributing to restenosis after balloon angioplasty is the loss of the EC lining. Previous attempts to reseed EC had little effect due to rapid loss of the seeded cells.

METHODS

Twelve atherosclerotic rabbits were subjected to angioplasty of iliac arteries and reseeding procedure. One iliac artery was subjected to EC/glue reconstruction and a contralateral site to EC seeding without glue. The animals were sacrificed after 4 h. In another series 12 rabbits were treated in the same fashion and were restudied at eight weeks. Additionally, in 10 animals one iliac was subjected to glue treatment, and another served as control.

RESULTS

Histological examination demonstrated the ability of this method to reattach the EC/glue matrix circumferentially to 68.0 +/- 6.7% of the arterial wall in comparison with 13.5 +/- 3.9% reattachment after EC seeding. Morphometry at eight weeks showed that the lumen area was significantly greater in the EC/glue group (1.23 +/- 0.35 mm2) than in the EC seeding alone (0.65 +/- 0.02 mm2) and 0.72 +/- 0.41 mm2 in the glue group. This was principally accounted for by the statistically significant differences in the intimal area (0.76 +/- 0.18 mm vs. 1.25 +/-0.26 mm2 and 1.01 +/- 0.53 mm2, respectively).

CONCLUSIONS

The attachment of EC after angioplasty can be greatly improved with fibrin glue matrix. The near 70% endothelial coverage achieved by this method resulted in a significant reduction of restenosis in atherosclerotic rabbit.

New insights in cardiac structural changes in patients with Fabry's disease

BACKGROUND

Fabry's disease is an X-linked recessive genetic deficiency of the enzyme alpha-galactosidase leading to the pathologic intracellular deposition of neutral glycosphingolipids. Although cardiac involvement is frequent, there is controversy regarding the character of the associated left ventricular (LV) changes and the severity of valvular involvement.

METHODS

Clinical evaluation (disease severity scaling, laboratory tests, and echocardiography) was performed in 13 hemizygous men (mean age 39 +/- 10 years) and 17 heterozygous women (mean age 35 +/- 19 years).

RESULTS

LV hypertrophy (LVH) was frequent in subjects older than 30 years, more often in men (61%) than in women (18%, P <.001). The degree of LVH was independently associated with age and the logarithm of alpha-galactosidase activity (r(2) = 0.70, P <.001). The predominant LV geometric patterns were concentric LVH and remodeling, both present in 11 subjects (36%). Three patients had an asymmetric septal hypertrophy mimicking hypertrophic cardiomyopathy. In most subjects with LVH, the systolic function was normal and severe diastolic dysfunction (restrictive pattern) was not noted. Minor structural abnormalities of the mitral valve were found in 17 subjects (57%). The aortic valve was affected in 14 patients (47%). Valvular abnormalities were frequently accompanied by regurgitation of minor to mild degree. The presence of LVH or valvular changes was associated with increased disease severity.

CONCLUSIONS

Echocardiographically detectable cardiac involvement is frequent with Fabry's disease, particularly in older subjects, and more pronounced in affected hemizygous men than in heterozygous women. LVH is frequently observed but usually not associated with significant systolic or restrictive diastolic dysfunction. Concentric LVH and remodeling appear to be the major manifestations of LV structural alteration. The frequently noted valvular abnormalities were not associated with a significant degree of regurgitation. Valvular and especially LV structural changes may serve as a useful marker of disease severity.

Platelet glycoprotein IIb/IIIa receptor antagonists: current concepts and future directions

Platelets play a key role in the development of thrombosis. Glycoprotein (GP) IIb/IIIa antagonists are a new class of potent drugs that profoundly inhibit platelet function by blocking the key receptor involved in platelet aggregation. Several antiplatelet agents with varying characteristics have emerged in the past few years and have been evaluated in a variety of potential clinical settings. Clinical trials have established the effectiveness of these drugs in conditions where thrombosis plays a major contributing role such as unstable angina pectoris, myocardial infarction, and high-risk coronary intervention. Despite their potent antiplatelet effects, GP IIb/IIIa antagonists appear to be remarkably well tolerated, provided that the concomitant use of other anticoagulants such as heparin is managed carefully. Ongoing and future studies will further refine the role of GP IIb/IIIa antagonists, explore new applications, and further test their safety and cost effectiveness in the short and long term.

Racial differences in the management of unstable angina: results from the multicenter GUARANTEE registry

BACKGROUND

Prior studies, usually conducted with the use of insurance databases, have shown differences in the use of cardiac procedures between black patients and white patients hospitalized with various types of coronary artery disease. However, few data are available in prospectively collected cohorts of patients with unstable angina or on the use of appropriate medications or interventions.

METHODS AND RESULTS

We evaluated 2948 consecutive patients with unstable angina admitted to 35 hospitals across the United States in 1996, comparing nonwhite and white patients. Seventy-seven percent of patients were white, 14% were black, 4% were Hispanic, 1% were Asian, and 3% were other or unknown race. Differences were seen in coronary risk profile, with a higher incidence of hypertension and diabetes mellitus in nonwhites. Cardiac catheterization was performed less often in nonwhites compared with whites (36% vs 53%, P =.001). Even in patients meeting the criteria for appropriate catheterization in the Agency for Health Care Policy Research unstable angina guidelines, fewer nonwhites underwent catheterization (44% vs 61%, P =.001), but among these, fewer nonwhites had significant coronary stenosis (72% vs 90%, P =.001). However, among patients catheterized who had indications for revascularization, angioplasty and coronary artery bypass grafting were performed equally often in nonwhites and whites.

CONCLUSIONS

Current guidelines would recommend more aggressive use of cardiac catheterization for nonwhite patients. However, our findings suggest that racial differences may need to be included in the diagnostic and interventional algorithms.

Differences between men and women in the management of unstable angina pectoris (The GUARANTEE Registry). The GUARANTEE Investigators

Few data are available in prospectively collected cohorts of patients with unstable angina pectoris or on the use of appropriate medications or interventions. Accordingly, we evaluated 2,948 consecutive patients with unstable angina admitted to 35 hospitals in the United States in 1996, and comparing men and women (39% of the patients were women). Differences were seen in coronary risk profiles with a higher incidence of systemic hypertension, diabetes mellitus, and a family history of coronary disease in women. Women were less likely to receive Agency for Health Care Policy Research (AHCPR) recommended pharmacologic treatment than men. Cardiac catheterization, coronary angioplasty, and bypass was performed less often in women compared with men (44% vs. 53%, p = 0.002; 12% vs. 18%, p = 0.02; 7% vs. 10%, p = 0.001, respectively). At catheterization, women were more likely to have no significant coronary artery disease (25% vs. 14%, p = 0.001). Although fewer women than men fulfilled the AHCPR criteria for cardiac catheterization (54% vs. 64%, p = 0.001), a similar rate of men and women with positive criteria underwent catheterization and angioplasty. However, fewer women with positive criteria underwent bypass surgery (36% vs. 46%, p = 0.03). More men "ruled-in" for a myocardial infarction at admission (13% vs. 8%, p = 0.001), but there was no difference in recurrent angina, in-hospital myocardial infarction, or death. Despite different epidemiologic profiles and less evidence of coronary artery disease by noninvasive and invasive tests, women and men had similar outcomes.

Trials of glycoprotein IIb-IIIa inhibitors in non-ST-segment elevation acute coronary syndromes: applicability to the practice of medicine in the United States

Platelet-mediated thrombosis has been recognized as the primary pathophysiologic mechanism of acute coronary syndromes (ACS) and acute complications of percutaneous coronary intervention (PCI). Despite the clinical efficacy of the two most widely used antithrombotic agents, aspirin and heparin, each of them has significant therapeutic limitations. As a result, thrombosis and clinical events may occur despite the use of aspirin and heparin. The discovery that the platelet glycoprotein (GP) IIb-IIIa represents the final common pathway to platelet aggregation and the growing recognition of the key role of platelets in the progression of thrombosis prompted the development of several GP IIb-IIIa inhibitors as a potentially more effective form of antithrombotic therapy. Numerous trials of various GP IIb-IIIa inhibitors as adjuncts to PCI have strongly supported this hypothesis. The subject of this supplement is the review of more recent evaluations of GP IIb-IIIa inhibitors in the context of various treatment strategies for the management of patients with unstable angina or non-ST-segment elevation myocardial infarction, collectively known as non-ST-segment elevation ACS. Appropriate translation of these trials into clinical practice requires not only the knowledge of the trials' results but also the understanding of the design of individual studies, most notably the entry criteria and patient management strategies.

IIb/IIIa receptor blockade in acute myocardial infarction

To appreciate the clinical potential of antiplatelet therapy in the treatment of patients with acute myocardial infarction (MI), it is important to understand the mechanism and pathophysiology of acute MI and to understand the role that platelets play in the process of acute thrombus formation. Recognition of the limitations of current therapy has sparked intense interest in the development of more potent platelet inhibitors such as antagonists of the platelet glycoprotein (GP) IIb/IIIa receptor. Because this receptor represents the final common pathway of platelet aggregation, it emerges as a very attractive therapeutic target for phamacologic interventions. The purpose of this review is to summarize the results of recent large-scale clinical trials that use GP IIb/IIIa antagonist therapy in patients with acute MI both as an adjunct to percutaneous coronary interventions and as an adjunct to exogenously administered fibrinolytic therapy. As an adjunct to percutaneous coronary interventions, GP IIb/IIIa antagonists have shown significant benefit in the prevention of composite end points of death, MI, and emergency revascularization. As an adjunct to fibrinolytic agents, GP IIb/IIIa antagonists enhance the speed and degree of reperfusion achievable pharmacologically. Although the potential risk of bleeding remains a concern (particularly with higher doses of streptokinase), recent phase II trials such as TIMI 14 and SPEED suggest considerable potential for these potent antiplatelet agents in the medical treatment of patients with acute MI.

Influence of different stent materials on endothelialization in vitro

The objective of our study was to investigate the influence of different stent materials on endothelialization in vitro. Using the non-destructive Alamar Blue assay and scanning electron microscopy, we compared long-term growth and morphology of vascular cells on disks of three prospective stent materials, i.e., 316 L stainless steel, 18 K, and 24 K gold. Our results demonstrate superior human EC proliferative capacity on gold surfaces compared to that on 316 L stainless steel. Thus, both the hyperplasia and thrombotic complications which often follow stenting might be minimized by employing gold stents, which have a greater capacity than steel in supporting a functional neo-endothelium.

Pharmacodynamic efficacy, clinical safety, and outcomes after prolonged platelet Glycoprotein IIb/IIIa receptor blockade with oral xemilofiban: results of a multicenter, placebo-controlled, randomized trial

BACKGROUND

Parenteral administration of platelet glycoprotein IIb/IIIa (GP IIb/IIIa) receptor blockers can reduce ischemic complications of coronary angioplasty. Orally active GP IIb/IIIa blockers may allow more sustained receptor antagonism with the potential for long-term secondary prevention. The pharmacodynamic efficacy, clinical safety, and outcomes after prolonged receptor blockade with an orally active GP IIb/IIIa antagonist are not known. The Oral Glycoprotein IIb/IIIa Receptor Blockade to Inhibit Thrombosis (ORBIT) Trial is a multicenter, placebo-controlled, randomized trial of xemilofiban, an oral platelet GP IIb/IIIa blocking agent, administered to patients after percutaneous coronary intervention.

METHODS AND RESULTS

After successful elective percutaneous coronary intervention, 549 patients were randomized to receive either placebo or xemilofiban in a dose of 15 or 20 mg. Stented patients randomized to placebo also received ticlopidine 250 mg orally BID for 4 weeks. Patients who received abciximab during the coronary intervention and who were randomized to receive xemilofiban were administered a reduced dosage (10 mg TID for 2 weeks) followed by the randomized maintenance dose of 15 or 20 mg BID for 2 more weeks. All patients received 325 mg aspirin PO QD. Ex vivo platelet aggregation in response to 20 micromol/L ADP and 4 microg/mL collagen was measured over time after the initial dose of study drug and at days 14 and 28 of long-term therapy in 230 patients. All patients were followed clinically for 90 days. Xemilofiban inhibited platelet aggregation to both ADP and collagen with peak levels of inhibition that were similar at 14 and 28 days of long-term oral therapy. Plasma levels of xemilofiban correlated with the degree of platelet inhibition. Peak platelet inhibition on day 1 correlated with the subsequent occurrence of insignificant or mild bleeding events. Although this study was not powered to evaluate differences in clinical outcomes, a trend (P=0.04) was observed for reduction of cardiovascular events at 3 months in patients not treated with abciximab who received the highest dose (20 mg) of xemilofiban studied.

CONCLUSIONS

Xemilofiban inhibited platelet aggregation and was well tolerated during 28 days of long-term oral therapy. The observed trend in reduction of cardiovascular events in follow-up awaits confirmation in the larger-scale phase III study (EXCITE trial) currently in progress.

Complications associated with combined use of abciximab and an intracoronary thrombolytic agent (urokinase or tissue-type plasminogen activator)

A potent platelet inhibitor combined with an intracoronary thrombolytic agent is aggressive therapy that may be used for high-risk, complex, refractory thrombotic coronary lesions. A retrospective review of the records of 56 patients who received abciximab plus an intracoronary thrombolytic agent during a coronary interventional procedure did not reveal a prohibitive incidence of major bleeding with this combination therapy.

Influence of insurance type on the use of procedures, medications and hospital outcome in patients with unstable angina: results from the GUARANTEE Registry. Global Unstable Angina Registry and Treatment Evaluation

OBJECTIVES

The purpose of this study was to investigate whether or not there is an association between managed care insurance and the delivery and outcome of care in patients presenting with unstable angina.

BACKGROUND

The proportion of U.S. patients with managed care health insurance is increasing. This may be associated with recent improvements in the control of health care costs. It is unknown whether or not there is a difference in process of care in angina patients presenting with managed care versus fee-for-service health insurance.

METHODS

We compared baseline characteristics, process and outcome of care in 636 patients with managed care insurance (MC) and 1,404 patients with fee-for-service (FFS) insurance who presented with unstable angina to 35 hospitals participating in the global Unstable Angina Registry and Treatment Evaluation (GUARANTEE) Registry.

RESULTS

Although, there was little difference in baseline characteristics and hospital treatments between cohorts, MC patients were more likely to be discharged on guideline-recommended medications (aspirin and beta-adrenergic blocking agents). In addition, FFS patients were more likely to undergo cardiac catheterization (odds ratio = 1.25 95% confidence interval = 1.1 to 1.5), but not revascularization during the hospitalization. There was no difference in hospital mortality (0.9% versus 1.2% in MC versus FFS; p = 0.60).

CONCLUSIONS

In patients admitted with suspected unstable angina, MC patients are less likely to undergo coronary angiography, but are more likely to be discharged on indicated medications.

Platelet glycoprotein IIb/IIIa receptor blockade with abciximab reduces ischemic complications in patients undergoing directional coronary atherectomy. EPILOG Investigators. Evaluation of PTCA to Improve Long-term Outcome by c7E3 GP IIb/IIIa Receptor Blockade

We determined the efficacy of abciximab, a platelet glycoprotein IIb/IIIa receptor antagonist, combined with low-dose weight-adjusted heparin in reducing ischemic complications in patients undergoing directional coronary atherectomy (DCA). The Evaluation of IIb/IIIa platelet receptor antagonist 7E3 in Preventing Ischemic Complications (EPIC) trial demonstrated a reduction in the incidence of non-Q-wave myocardial infarction in DCA patients who were treated with abciximab bolus and infusion plus heparin. This benefit, however, was associated with increased bleeding complications. Of the 2,792 patients who had coronary intervention in the Evaluation of PTCA to Improve Long-term Outcome by c7E3 GP IIb/IIIa receptor blockade (EPILOG) trial, 144 (5%) underwent DCA. Patients were randomly assigned to 3 treatment groups: placebo with standard-dose, weight-adjusted heparin; abciximab with low-dose weight-adjusted heparin; or abciximab with standard-dose weight-adjusted heparin. Study end points included 30-day and 6-month composite incidence of death, myocardial infarction, or revascularization. Compared with those undergoing percutaneous transluminal coronary angioplasty (PTCA), DCA patients had a higher rate of myocardial infarction (11.1 % vs 4.9%, p = 0.001) and predominantly non-Q-wave myocardial infarction (9.7% vs 4.4%, p = 0.004). Abciximab was associated with a 57% lower combined rate of death, myocardial infarction, or urgent revascularization within 30 days following DCA (20% placebo vs 8.7% abciximab with low-dose heparin) without excess risk of bleeding complications. A combined analysis of data from the EPIC and EPILOG trials demonstrates a reduction in the rate of death or myocardial infarction (19.9% vs 8.4%, p = 0.008) at 30 days that was sustained for up to 6 months in the abciximab-treated patients. These findings support the premise that non-Q-wave myocardial infarction in DCA patients are platelet mediated.

Fundamentals of coagulation and glycoprotein IIb/IIIa receptor inhibition

An understanding of the coagulation process and the role of platelets is essential to recognizing the shortcomings of older anticoagulant therapies and appreciating the clinical potential of newer forms of antiplatelet and anticoagulant therapy for acute coronary syndromes. The anticoagulant actions of heparin are severely limited by dependence on antithrombin III, neutralization by platelet factor 4, and the resistance of clot-bound thrombin and platelet membrane-bound factor Xa to the heparin-antithrombin III complex. Unlike heparin, the direct thrombin inhibitors (such as hirudin) are active against both circulating and clot-bound thrombin. However, in recent clinical trials they have not resulted in major improvements in patient outcome. Another new class of drugs, the glycoprotein IIb/IIIa receptor antagonists, blocks the final common pathway of platelet aggregation and is capable of preventing platelet accumulation at sites of injury. The net effect is a dramatic reduction in the amount of platelet membrane available to support the process of coagulation. Clinical trials with the glycoprotein IIb/IIIa inhibitors have suggested that this class of agents may be particularly effective in reducing the thrombotic complications associated with coronary interventional procedures and may be useful in the treatment of acute coronary syndromes.

Fundamentals of coagulation and glycoprotein IIb/IIIa receptor inhibition

An understanding of the coagulation process and the role of platelets is essential to recognizing the shortcomings of older anticoagulant therapies and appreciating the clinical potential of newer forms of antiplatelet and anticoagulant therapy for acute coronary syndromes. The anticoagulant actions of heparin are severely limited by dependence on antithrombin III, neutralization by platelet factor 4, and the resistance of clot-bound thrombin and platelet membrane-bound factor Xa to the heparin-antithrombin III complex. Unlike heparin, the direct thrombin inhibitors (such as hirudin) are active against both circulating and clot-bound thrombin. However, in recent clinical trials they have not resulted in major improvements in patient outcome. Another new class of drugs, the glycoprotein IIb/IIIa receptor antagonists, blocks the final common pathway of platelet aggregation and is capable of preventing platelet accumulation at sites of injury. The net effect is a dramatic reduction in the amount of platelet membrane available to support the process of coagulation. Clinical trials with the glycoprotein IIb/IIIa inhibitors have suggested that this class of agents may be particularly effective in reducing the thrombotic complications associated with coronary interventional procedures and may be useful in the treatment of acute coronary syndromes.

Safe use of platelet GP IIb/IIIa inhibitors

The platelet membrane glycoprotein IIb/IIIa receptor inhibitor abciximab is used for the treatment of patients undergoing high-risk percutaneous coronary interventions and is used in approximately one third of coronary interventions in the United States and a growing number of procedures in Europe. Recent clinical trials have shown that this potent antiplatelet agent significantly reduces the incidence of death and nonfatal myocardial infarction and the need for revascularization. With expanding experience since the commercial release of abciximab in February 1995, several strategies to enhance the safety of abciximab have emerged. In particular, new data confirm that the risk of bleeding--identified as a concern in the original EPIC trial--can be substantially reduced through the use of low-dose adjunctive heparin, early sheath removal, and fastidious postprocedure vascular access site care. Other recommendations for enhancing the safety of potent antiplatelet agents in a variety of clinical situations are provided. The following article reflects insights regarding the safety of glycoprotein IIb/IIIa inhibitors expressed by a group of international experts convened in Davos, Switzerland, February 16, 1997. This report attempts to review clinical progress to date, formulate recommendations, and map out potentially fruitful lines of inquiry for future investigation.

Safe use of platelet GP IIb/IIIa inhibitors

The platelet membrane glycoprotein IIb/IIIa receptor inhibitor abciximab is used for the treatment of patients undergoing high-risk percutaneous coronary interventions and is used in approximately one third of coronary interventions in the United States and a growing number of procedures in Europe. Recent clinical trials have shown that this potent antiplatelet agent significantly reduces the incidence of death and nonfatal myocardial infarction and the need for revascularization. With expanding experience since the commercial release of abciximab in February 1995, several strategies to enhance the safety of abciximab have emerged. In particular, new data confirm that the risk of bleeding-identified as a concern in the original EPIC trial-can be substantially reduced through the use of low-dose adjunctive heparin, early sheath removal, and fastidious postprocedure vascular access site care. Other recommendations for enhancing the safety of potent antiplatelet agents in a variety of clinical situations are provided. The following article reflects insights regarding the safety of glycoprotein IIb/IIIa inhibitors expressed by a group of international experts convened in Davos, Switzerland, February 16, 1997 This report attempts to review clinical progress to date, formulate recommendations, and map out potentially fruitful lines of inquiry for future investigation.

Primary care

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Sustained platelet glycoprotein IIb/IIIa blockade with oral xemilofiban in 170 patients after coronary stent deployment

BACKGROUND

Inhibition of platelet aggregation with parenteral glycoprotein (GP) IIb/IIIa receptor blockers can reduce the ischemic complications of angioplasty. Sustained efficacy and safety of protracted GP IIb/IIIa blockade with an orally administered agent have not previously been determined. This study is the first randomized, dose-ranging, single-blind, placebo-controlled trial of xemilofiban, an oral platelet GP IIb/IIIa receptor antagonist, administered to patients after intracoronary stent deployment. The pharmacodynamic efficacy of xemilofiban-induced platelet inhibition and clinical safety of this agent was evaluated during chronic therapy.

METHODS AND RESULTS

After elective intracoronary stent deployment, patients were randomized to receive placebo (250 mg ticlopidine P.O. BID) or xemilofiban in doses of 5, 10, 15, or 20 mg P.O. BID. All patients received 325 mg aspirin P.O. QD. Inhibition of ex vivo platelet aggregation in response to 20 micromol/L ADP and 4 microg/mL collagen was measured over time after the initial dose of study drug and at 1 and 2 weeks of chronic therapy. Study drug was discontinued after 2 weeks, and all patients were followed clinically for > or = 30 days. Oral xemilofiban resulted in a dose-dependent inhibition of platelet aggregation in response to both agonists that was sustained through 2 weeks of chronic therapy. Doses of xemilofiban required to achieve > or = 50% inhibition of platelet aggregation were > or = 10 mg, and the duration of inhibition was 8 to 10 hours. No significant hemorrhagic episodes or blood transfusions were observed in this trial.

CONCLUSIONS

Oral xemilofiban in doses of > or = 10 mg produced > or = 50% inhibition of platelet aggregation in response to ADP and collagen for 8 to 10 hours after dosing. Platelet inhibition was sustained through 2 weeks of chronic therapy. The optimal duration of oral GP IIb/IIIa blockade to effectively suppress recurrent ischemic events after coronary intervention remains to be determined.