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Antithrombotic Therapy for Coronary Artery Disease : The Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy FREE TO VIEW

Robert A. Harrington, MD; Richard C. Becker, MD, FCCP; Michael Ezekowitz, MD; Thomas W. Meade, DM, FCCP; Christopher M. O’Connor, MD; David A. Vorchheimer, MD; Gordon H. Guyatt, MD, FCCP
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Correspondence to: Robert A. Harrington, MD, Duke Clinical Research Institute, 2400 Pratt St, Durham, NC 27705; e-mail: Harri019@dcri.duke.edu

Chest. 2004;126(3_suppl):513S-548S. doi:10.1378/chest.126.3_suppl.513S
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This chapter about antithrombotic therapy for coronary artery disease (CAD) is part of the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy: Evidence Based Guidelines. Grade 1 recommendations are strong and indicate that the benefits do, or do not, outweigh risks, burden, and costs. Grade 2 suggests that individual patients’ values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S–187S). Among the key recommendations in this chapter are the following: For patients presenting with non–ST-segment elevation (NSTE) acute coronary syndrome (ACS), we recommend immediate and then daily oral aspirin (Grade 1A). For patients with an aspirin allergy, we recommend immediate treatment with clopidogrel, 300-mg bolus po, followed by 75 mg/d indefinitely (Grade 1A). In all NSTE ACS patients in whom diagnostic catheterization will be delayed or when coronary bypass surgery will not occur until > 5 days, we recommend clopidogrel as bolus therapy (300 mg), followed by 75 mg/d for 9 to 12 months in addition to aspirin (Grade 1A). In NSTE ACS patients in whom angiography will take place within 24 h, we suggest beginning clopidogrel after the coronary anatomy has been determined (Grade 2A). For patients who have received clopidogrel and are scheduled for coronary bypass surgery, we recommend discontinuing clopidogrel for 5 days prior to the scheduled surgery (Grade 2A). In moderate- to high-risk patients presenting with NSTE ACS, we recommend either eptifibatide or tirofiban for initial (early) treatment in addition to treatment with aspirin and heparin (Grade 1A). For the acute treatment of NSTE ACS, we recommend low molecular weight heparins over unfractionated heparin (UFH) [Grade 1B] and UFH over no heparin therapy use with antiplatelet therapies (Grade 1A). We recommend against the direct thrombin inhibitors as routine initial antithrombin therapy (Grade 1B). For patients after myocardial infarction, after ACS, and with stable CAD, we recommend aspirin in doses from 75 to 325 mg as initial therapy and in doses of 75 to 162 mg as indefinite therapy (Grade 1A). For patients with contraindications to aspirin, we recommend long-term clopidogrel (Grade 1A). For primary prevention in patients with at least moderate risk for a coronary event, we recommend aspirin, 75 to 162 mg/d, over either no antithrombotic therapy or vitamin K antagonist (VKA) [Grade 2A]; for patients at particularly high risk of events in whom the international normalized ratio (INR) can be monitored without difficulty, we suggest low-dose VKA (target INR, 1.5) [Grade 2A].

Figures in this Article

Antithrombotic therapies, both antiplatelet as well as anticoagulant, have become the mainstays of treatment for coronary artery diseases (CADs). Based on the important role of thrombosis in the pathogenesis and complications of the atherosclerotic process, antithrombotic therapy has become essential treatment for both acute and chronic CAD. This section will cover the broad topic of CAD with the exception of reperfusion therapies for ST-segment elevation acute myocardial infarction (AMI) and antithrombotic therapy for patients undergoing percutaneous coronary intervention (PCI).

Interpretation of the results of the trials of antithrombotic therapies in CAD requires familiarity with the changing nomenclature for categorizing patients with acute coronary disease. Following the observation by DeWood et al1 in the late 1970s that intracoronary thrombosis was a key mechanism in the pathophysiology of AMI, the focus in acute cardiovascular research throughout the 1980s and into the early 1990s centered on reperfusion therapy. Data from the large trials demonstrated the importance of rapid and accurate diagnosis coupled with rapid administration of fibrinolytic therapy. Such an approach reduced premature deaths and therefore became incorporated into the quality assessment of the care given to these patients.

During this period of intense investigation of AMI, investigators became increasingly aware of a much larger group of patients presenting to hospitals for evaluation of acute chest pain who did not have the dramatic findings of ST-segment elevation on the initial ECG. Overview analyses2 from the Fibrinolytic Trialists’ Collaboration showed that among patients with suspected AMI, virtually all ECG subgroups benefited from treatment with fibrinolysis with the notable exception of patients presenting initially with ST-segment depression.

The Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) IIb trial3 was one of the first large-scale attempts to study the spectrum of patients presenting with acute chest pain, stratifying the randomization on the basis of their initial ECG findings (ST-segment elevation or not). GUSTO IIb results showed that patients without ST-segment elevation represent a different population from those with ST-segment elevation. They were older, more likely to be female, and have more comorbidity than the group with ST-segment elevation. For descriptive purposes, these patients were being categorized not on the basis of their admitting diagnosis, but rather on the diagnosis that became clear 12 to 24 h later, namely unstable angina (UA) or myocardial infarction (MI), typically non–Q-wave infarction.

Investigators were performing fewer studies in the UA and non–Q-wave MI patients, due in part to the heterogeneity of the presenting symptoms and signs and in part to a lack of knowledge of the seriousness of the condition. Unlike patients presenting with ST-segment elevation, these patients had much more diverse and much less dramatic initial clinical presentations. Consequently, their initial medical evaluation was less urgent and less focused, and they were typically admitted to the hospital for observation (ie, to rule out MI) rather than treated aggressively. Recognition of the size and clinical importance of this neglected group of patients shifted the focus of acute cardiovascular clinical research from fibrinolytic therapy in ST-segment elevation infarction patients to those with non–ST-segment elevation (NSTE).

The diagnoses of UA and non–Q-wave infarction are made retrospectively, after a period of observation and a review of serial ECGs and cardiac enzymes. The results of these trials showed that these patients have a moderate-to-high risk of early adverse outcomes, and therefore may benefit from more rapid assessment, triage, and treatment.4

A change in the terminology describing these patients reflects this evolution in thinking. Patients presenting with symptoms consistent with acute ischemic chest pain can be quickly differentiated by their ECG as having an acute coronary syndrome (ACS) with or without persistent ST-segment elevation. Those with ST-segment elevation can be rapidly evaluated for treatment with reperfusion therapy, and those without ST-segment elevation can be further risk stratified (including with troponin testing) and treated with appropriate antiplatelet and antithrombin therapies.

The recently revised American College of Cardiology (ACC)/American Heart Association (AHA) guidelines for the management of patients with UA and NSTE MI reflect this changing nomenclature.5 The initial focus of the guidelines is to consider the patients with acute ischemic symptoms as having an ACS, and then to further differentiate them into ACS with or without ST-segment elevation. The immediate treatment decisions then flow from this differentiation and categorization.

This chapter is organized around the various disease states, with a focus on the antithrombotic recommendations for each patient group: (1) those presenting with NSTE ACSs; (2) ACS patients post-MI; (3) patients with chronic, stable CAD; (4) patients with congestive heart failure (CHF); and (5) patients without a clinical diagnosis of CAD. Table 1 describes the question definition and eligibility criteria for the studies considered in each section of the recommendations that follow.

1.1 Antiplatelet therapies
1.1.1 Aspirin

The chapter by Patrono et al in this Supplement describes aspirin and other antiplatelet agents. Aspirin causes irreversible inhibition of platelet cyclooxygenase, thereby preventing the formation of thromboxane A2, a platelet aggregant and potent vasoconstrictor.6 Aspirin has no effect on platelet aggregation induced by other agonists, and is therefore a weak platelet inhibitor. The adverse effects of aspirin are primarily related to bleeding, particularly GI, which is less common at the low dosage of 75 to 162 mg/d needed to inhibit platelet aggregation than at higher doses.

An estimated 5.2 to 40% of aspirin-treated patients have some level of GI intolerance.6An analysis7 from the Duke Databank for Cardiovascular Diseases reported that among a sample of 2,694 patients with CAD, > 13% did not report aspirin use at the 1-year follow-up; more detailed surveying revealed that 1.9% had symptoms or signs consistent with a true allergic reaction.

Various drugs inhibiting thromboxane A2 synthase or blocking the thromboxane A2 receptor, or both, have been investigated in clinical trials. Although they do not decrease prostacyclin production, they have shown no advantage over aspirin.

Evidence from clinical trials. Oral antiplatelet therapy, mainly aspirin, has been the cornerstone of short-term treatment for > 10 years.6 Despite its biochemical limitations, aspirin profoundly reduces adverse clinical events among a broad group of patients treated for acute and chronic vascular diseases.812

In the systematic review by the Antithrombotic Trialists’ Collaboration,8 there were 5,031 patients with UA in 12 trials comparing aspirin to either placebo or no treatment. Treatment with aspirin was associated with an odds reduction in vascular events of 46%.

Most of the excess bleeding related to aspirin is GI. In the Clopidogrel vs Aspirin in Patients at Risk of Ischemic Events (CAPRIE) study13 comparing clopidogrel vs aspirin among patients with chronic vascular disease, the risk of GI bleeding that led to aspirin discontinuation was 0.93%.

While the risk of side effects, particularly GI bleeding, appears to increase with increasing dose, the relationship between efficacy and aspirin dose is less certain. Analyses8 from the Antithrombotic Trialists’ Collaboration suggested that the benefits of aspirin were consistent on a relative basis across a wide range of doses (< 160 mg/d to approximately 1,500 mg/d), while other analyses by Kong et al14 suggested that the effect of aspirin is weaker at higher doses. Although a head-to-head comparison is necessary to completely resolve the issue, given that the bulk of the available evidence suggests equivalent or even superior effectiveness at lower doses, clinicians can be confident in administering relatively low aspirin doses.

1.1.1. For all patients presenting with NSTE ACS, without a clear allergy to aspirin, we recommend immediate aspirin, 75 to 325 mg po, and then daily, 75 to 162 mg po (Grade 1A).

1.1.2 Thienopyridines

Ticlopidine and clopidogrel are adenosine diphosphate (ADP) receptor antagonists that inhibit ADP-induced platelet aggregation and prolong bleeding time (see chapter by Patrono et al).15 Combining platelet antagonists that have different mechanisms of actions is attractive. Aspirin inhibits the thromboxane A2-mediated activation and clopidogrel inhibits ADP-mediated activation.

Evidence from clinical trials. The safety profile of ticlopidine is unfavorable, with frequent GI side effects, rash, neutropenia (rarely fatal), thrombocytopenia, and liver function abnormalities (rare). Clopidogrel has a much more favorable safety profile and is well tolerated, as demonstrated in the CAPRIE study13 of > 19,000 patients. The benefit derived from antiplatelet therapy in patients with coronary heart disease, UA, AMI, and previous MI is well established; however, the question of added benefit from multitargeted antiplatelet regimens, particularly among high-risk patients with NSTE ACS, until recently remained unanswered.

In the Clopidogrel in Unstable Angina to Prevent Recurrent Events (CURE) trial,16 12,562 patients with NSTE ACS were randomly assigned to receive clopidogrel (300 mg immediately followed by 75 mg qd) or placebo in addition to aspirin, 75 to 325 mg/d, for 3 to 12 months. The first primary outcome—a composite of death from cardiovascular causes, nonfatal MI, or stroke—occurred in 9.3% and 11.4% of patients receiving clopidogrel and placebo, respectively (relative risk [RR], 0.80; 95% confidence interval [CI], 0.72 to 0.90; p < 0.001). Considered individually, CURE16 showed significant reductions in nonfatal MI (5.2% vs 6.7%; RR, 0.77; 95% CI, 0.67 to 0.89) and trends toward reduction in death (5.1% vs 5.5%; RR, 0.93; 95% CI, 0.79 to 1.08), and stroke (1.2% vs 1.4%; RR, 0.86; 95% CI, 0.63 to 1.18) with clopidogrel. The rate of the second primary outcome—death from cardiovascular causes, nonfatal MI, stroke, or refractory ischemia—was also lower in the clopidogrel group (16.5% vs 18.8%; RR, 0.86; 95% CI, 0.79 to 0.94; p = 0.001). Significantly fewer patients in the clopidogrel group had severe ischemia (2.8% vs 3.8%; RR, 0.74; 95% CI, 0.61 to 0.90; p = 0.003) or recurrent angina (20.9% vs 22.9%; RR, 0.91; 95% CI, 0.85 to 0.98; p = 0.01). The benefits of clopidogrel were consistent across a broad range of patient subsets, including those with MI, ST-segment deviation, elevated cardiac biomarkers, diabetes mellitus, age > 65 years, and high-risk features. Although the absolute use of concomitant glycoprotein (GP) IIb/IIIa inhibitors was low in CURE,16 the treatment effect of clopidogrel was consistent among those receiving and not receiving the IV platelet inhibitors.

There was a 34% RR reduction (RRR) [95% CI, 0.51 to 0.86] in the occurrence of cardiovascular death, MI, stroke, or severe ischemia at 24 h among patients receiving clopidogrel (p < 0.01). A significant benefit was reported at 7 days (RR, 0.77; 95% CI, 0.67 to 0.89), and an appreciable trend at 30 days (RR, 0.86; 95% CI, 0.73 to 1.01).

Major bleeding (defined as disabling hemorrhage, intraocular hemorrhage leading to visual loss, or bleeding requiring transfusion of at least 2 U of blood) was significantly more common in clopidogrel-treated patients (3.7% vs 2.7%; RR, 1.38; 95% CI, 1.13 to 1.67; p = 0.001). Life-threatening bleeding (fatal hemorrhage or causing a reduction in hemoglobin of 5 g/dL or to substantial hypotension requiring inotropic support, or surgical intervention; symptomatic intracranial hemorrhage or transfusing of ≥ 4 U of blood) was also more common, although the difference did not reach conventional levels of statistical significance (2.2% vs 1.8%; RR, 1.21; 95% CI, 0.95 to 1.56). There was not an excess rate of fatal bleeding, bleeding that required surgical intervention, or hemorrhagic stroke. The number of patients requiring transfusion of ≥ 2 U of blood was higher in the clopidogrel group (2.8% vs 2.2%, p = 0.02).

The rate of major bleeding with clopidogrel was higher early (within 30 days of randomization (2.0% vs 1.5%; RR, 1.31; 95% CI, 1.01 to 1.70) and also late (> 30 days after randomization: 1.7% vs 1.1%; RR, 1.48; 95% CI, 1.10 to 1.99). Bleeding associated with coronary artery bypass grafting (CABG) was particularly high among patients receiving clopidogrel within 5 days of surgery (9.6% vs 6.3%; RR, 1.53; p = 0.06). Overall, the risk of minor bleeding was significantly higher in clopidogrel-treated patients (5.1% vs 2.4%; p = 0.001). For all NSTE ACS patients with an aspirin allergy, we recommend immediate treatment with clopidogrel, 300-mg bolus po, followed by 75 mg/d indefinitely (Grade 1A). In all NSTE ACS patients in whom diagnostic catheterization will be delayed or when coronary bypass surgery will not occur until > 5 days following coronary angiography, we recommend clopidogrel be administered immediately as bolus therapy (300 mg), followed by 75 mg/d for 9 to 12 months in addition to aspirin (Grade 1A).

Underlying values and preferences: This recommendation places a relatively high value on avoiding MI and a relatively low value on avoiding major bleeding. In NSTE ACS patients in whom angiography will take place rapidly (≤ 24 h), we suggest beginning clopidogrel after the coronary anatomy has been determined (Grade 2A).

Underlying values and preferences: This recommendation places a relatively high value on avoiding serious bleeding balanced against a low absolute benefit of clopidogrel in the first 24 h of treatment. For patients who have received clopidogrel and are scheduled for coronary bypass surgery, we recommend discontinuing clopidogrel for 5 days prior to the scheduled surgery (Grade 2A).

1.1.3 Dipyridamole

The effects of dipyridamole appear to be related to an increase in platelet cyclic adenosine monophosphate. Its antithrombotic effects are more evident on prosthetic surfaces. In contrast to aspirin, it does not increase the risk of GI bleeding even when combined with warfarin. Currently, there is no evidence to support use of dipyridamole either instead of, or in addition to, aspirin and the thienopyridines in the acute treatment of patients presenting with NSTE ACS.

1.1.4 GP IIb/IIIa inhibitors

GP IIb/IIIa receptor inhibitors have been tested as arterial antithrombotics, and three have gained market approval for clinical use: abciximab, a monoclonal antibody fragment; eptifibatide, a peptide inhibitor; and tirofiban, a peptidomimetic inhibitor. Abciximab and eptifibatide are indicated as adjunctive antithrombotics in patients undergoing PCI, while eptifibatide and tirofiban are approved among patients presenting with NSTE ACSs.

The chapter by Popma et al in this Supplement covers the use of the GP IIb/IIIa inhibitors during PCI, and the chapter by Ohman et al contains information regarding their role in NSTE MI. This chapter will review use of these drugs in patients with NSTE ACS.

Clinical trials. A systematic overview by Boersma and colleagues20 included all 31,402 patients presenting with NSTE ACS enrolled in trials of GP IIb/IIIa inhibitors randomizing ≥ 1,000 patients. Overall, there was a significant 1.2% absolute decrease in the 30-day incidence of death or MI (5.7% vs 6.9%). The data were consistent across multiple subgroups with the exception of women, in whom the estimate of the treatment effect favored placebo (interaction p < 0.0001 for the difference in effect between men and women; Fig 1 ). In the overview by Boersma and colleagues,,17men and women who are troponin positive have a similar beneficial treatment effect, while men and women who are troponin negative do not appear to gain a benefit from the platelet inhibitors. Men were twice as likely in this analysis to be troponin positive as women. This suggests that the observed gender difference is less likely to be a treatment issue and more likely to be an issue with diagnosis. This hypothesis warrants further consideration and evaluation but is consistent with the general observation that these therapies are most beneficial among the groups at highest risk, such as those with diabetes1819 or dynamic ST-segment changes.20Boersma, in an overview analysis of three trials (Chimeric 7E3 Antiplatelet Therapy in Unstable Angina Refractory to Standard Treatment, Platelet Receptor Inhibition in Ischemic Syndrome Management in Patients Limited by Unstable Signs and Symptoms [PRISM-PLUS], and Platelet Glycoprotein IIb/IIa in Unstable Angina: Receptor Suppression Using Integrilin Therapy [PURSUIT])2122 also demonstrated a convincing effect of the GP IIb/IIIa inhibitors before, after, and independent of coronary procedures.

Abciximab. The GUSTO IV ACS trial2223 enrolled 7,825 patients presenting with ischemic symptoms and either biomarker or ECG evidence of MI/ischemia. Patients were randomized to one of three treatment groups, in addition to receiving heparin or aspirin: placebo, abciximab bolus plus 24-h infusion, or abciximab bolus plus 48-h infusion.23 Patients were treated conservatively without early cardiac catheterization. The primary end point was the 30-day composite of death and MI. At 30 days, there were no significant differences among the treatment groups with regard to the primary efficacy composite, but abciximab was associated with a fivefold increased risk in major bleeding (1.0% vs 0.2%) and an increased risk of thrombocytopenia.

Eptifibatide. The large, international PURSUIT study24 enrolled 10,948 patients presenting with a NSTE ACS and randomized to one of three drug regimens on a background of aspirin and unfractionated heparin (UFH): eptifibatide, 180 μg/kg bolus, followed by an infusion of either 2.0μg/kg/min or 1.3 μg/kg/min or placebo bolus plus infusion. The primary end point of the PURSUIT study24was the composite of death or MI at 30 days. Since neither dose of eptifibatide had yet been studied in randomized clinical trials, the study was designed to drop the lower dose if the high dose appeared to have an acceptable bleeding profile after approximately 1,000 patients had been enrolled per treatment group. In the primary analysis of high dose vs placebo, eptifibatide reduced the 30-day composite from 15.7 to 14.2% (p = 0.042). The benefit was maintained at 6 months. Bleeding was increased overall among the treated patients, with GUSTO moderate or severe bleeding occurring at a rate of 12.8% among eptifibatide patients compared with 9.9% among placebo patients. This bleeding difference was confined to patients not undergoing CABG. There was a significant increase in thrombocytopenia among the patients treated with the platelet inhibitor.25 There was no increase in the risk of intracranial hemorrhage among those treated with eptifibatide.

Lamifiban. Lamifiban, while not approved for clinical use, has been studied in two moderate-to-large-scale randomized clinical trials: Platelet IIb/IIIa Antagonism for the Reduction of Acute Coronary Syndrome Events in a Global Organization Network (PARAGON) A and PARAGON B.26 PARAGON A enrolled 2,282 patients in a modified 3 × 2 factorial design to either high- or low-dose lamifiban or placebo, and UFH or placebo.26No patients were enrolled into a group with double placebo. The primary end point of the trial was the 30-day composite of death or MI. The primary results showed no significant differences among the treatment groups with an increased risk of bleeding among lamifiban patients. Post hoc analyses demonstrated that a mid-range concentration of lamifiban was associated with substantial reductions in the 30-day and 6-month composite end points.27

Based on these post hoc analyses, PARAGON B27was designed to test the adjusted dosing strategy of lamifiban; consequently, 5,225 patients were randomized to receive lamifiban (adjusted for weight and estimated creatinine clearance [CrCl]) or placebo on a background of aspirin and either UFH or low molecular weight heparin (LMWH).28 The primary end point was the 30-day composite of death, MI, or severe recurrent ischemia. There was no significant benefit of lamifiban over placebo (11.8% vs 12.8%, p = 0.329) while lamifiban was associated with a greater incidence of intermediate bleeding (14.0% vs 11.5%, p = 0.002). Based on the nonsignificant findings of these two trials, product registration was not sought.

Tirofiban. Two moderate-size trials have been completed and reported with tirofiban in an NSTE ACS population: Platelet Receptor Inhibition in Ischemic Syndrome Management (PRISM)29and PRISM-PLUS.30 The PRISM trial29 randomized 3,231 patients presenting with an ACS to either tirofiban (loading dose of 0.6 μg/min for 30 min followed by 0.15 μg/kg/min for 47.5 h) or heparin. The drugs were to be administered for 48 h, and cardiac catheterization was to be deferred until the study drug was discontinued. The 48-h primary composite of death, MI, or refractory ischemia was reduced with tirofiban from 5.6 to 3.8% with heparin (p = 0.01). The absolute benefit of tirofiban was maintained through 30 days although the relative benefit was lessened, as expected when additional events accrued in both treatment arms after discontinuation of the therapy. Both groups had a 0.4% incidence of major bleeding.

In the PRISM-PLUS trial,291,915 patients were randomized to treatment with tirofiban alone, tirofiban with heparin, or heparin alone. The primary end point was the composite of death, MI, or refractory ischemia at 7 days. During an interim review by the Data Safety and Monitoring Board, the tirofiban-alone arm was dropped due to excess mortality at 7 days. The trial continued with the remaining two treatment arms. Tirofiban plus heparin was associated with a significant reduction in the primary composite compared with heparin alone (12.9% vs 17.9%, p = 0.004). This benefit was maintained at 30 days and 6 months. Thrombolysis in Myocardial Infarction (TIMI) trial major bleeding was not significantly increased among the non-CABG patients (1.4% vs 0.8%, p = 0.23).30

Broad drug class issues to consider with GP IIb/IIIa inhibitors. Three trials,2829,31 PRISM, CAPTURE (Chimeric 7E3 Antiplatelet Therapy in Unstable Angina Refractory to Standard Treatment), and PARAGON B, have reported a preferential treatment effect of the GP IIb/IIIa inhibitor among patients with elevated troponin levels. Newby et al31a have shown that there is a strong treatment interaction with this subgroup, suggesting that the quantitative difference in effect seen in this group is greater than in the troponin-negative population. The ACC-AHA Taskforce Guidelines are consistent with this in putting forth GP IIb/IIIa inhibitors as a class IA recommendation for moderate- to high-risk patients.5

Part of the reason for the recommendations that this class of drugs should be used in moderate- to high-risk patients is their value in an invasive strategy.5,32None of the six large randomized trials specifically addressed the issue of whether the GP IIb/IIIa inhibitors add incremental value to medical therapy without PCI or CABG by randomizing an appropriate group of patients. Inappropriate analysis of postrandomization subgroups (ie, PCI subgroups that accrue after randomization and thus are subject to bias) suggested that the GP IIb/IIIa inhibitors preferentially benefit patients undergoing percutaneous procedures more than those not undergoing such procedures.33 Two important issues help to understand this controversy. First, at the time of presentation, it is challenging to predict which specific patients will undergo PCI or CABG based on clinical characteristics alone. It is knowledge of the coronary anatomy gained from a diagnostic cardiac catheterization that dictates revascularization strategy. Second, although the evidence suggests that an early invasive strategy (early cardiac catheterization followed by anatomy-driven revascularization) is superior to a conservative management strategy, the optimal timing of the early catheterization strategy is unknown. In US-based practices, where the median time to catheterization is approximately 24 h, there is a substantial period prior to the procedure that corresponds with the period of highest risk.

The use of multiple antithrombotic agents is complicated for this group of patients. It is clear from the trial data that GP IIb/IIIa inhibitors add clinical value on background therapy of aspirin and heparin. But, the major trials of the GP IIb/IIIa inhibitors were performed prior to the completion of the CURE trial, which itself was predominantly conducted in countries where there was a low usage of the IV platelet inhibitors. Thus, while the effect of clopidogrel, administered in addition to aspirin and heparin, was consistent among the groups receiving and not receiving concomitant GP IIb/IIIa inhibitors, the incremental value of adding GP IIb/IIIa inhibitors to aspirin, heparin, and clopidogrel remains all uncertain. In moderate- to high-risk patients presenting with NSTE ACS, we recommend either eptifibatide or tirofiban for initial (early) treatment in addition to treatment with aspirin and heparin (Grade 1A). In these moderate- to high-risk patients who are also receiving clopidogrel, we recommend eptifibatide or tirofiban as additional initial treatment (Grade 2A). For patients presenting with NSTE ACS, we recommend againstabciximab as initial treatment except when coronary anatomy is known and PCI is planned within 24 h (Grade 1A).

Pharmacologic therapies designed to attenuate thrombin generation and activity are clinically attractive because of the critical role of thrombosis in ACSs.

1.2.1. UFH

UFH is a heterogeneous mixture of polysaccharide molecules (average molecular weight, 15,000 to 18,000 d) [see chapter by Hirsh et al in this Supplement]. In addition to a high degree of size/length heterogeneity, there is also a substantial amount of compositional heterogenicity. Typically, one third of the molecules found within a standard pharmaceutical heparin preparation contain the pentasaccharide sequence required for antithrombin binding and anticoagulant activity.

A pooled analysis of the Antithrombotic Therapy in Acute Coronary Syndromes study,3435 Research on Instability in Coronary Artery Disease,36 and Théroux et al11 studies yields an RR of 0.44 (95% CI, 0.21 to 0.93) for death/MI with combination aspirin and UFH therapy compared with aspirin alone.3538

The first trial, conducted by Théroux and colleagues,11 compared aspirin (325 mg bid), UFH (5,000-U bolus, 1,000 U/h IV), their combination, and placebo in 479 patients. It is the only study that compared UFH (alone) and aspirin (alone) as well as combination therapy. Refractory angina occurred in 8.5%, 16.5%, and 10.7% of patients, respectively (0.47 RR for UFH compared with aspirin; 95% CI, 0.21 to 1.05; p = 0.06). MI occurred in 0.9%, 3.3%, and 1.6% of patients, respectively (RR, 0.25; 95% CI, 0.03 to 2.27; p = 0.18) while any event was observed in 9.3%, 16.5%, and 11.5% of patients, respectively (RR, 0.52; 95% CI, 0.24 to 1.14; p = 0.10). Serious bleeding, defined as a fall in hemoglobin of ≥ 2 g or the need for a transfusion, occurred in 1.7%, 1.7%, and 3.3% of patients, respectively. A majority of events were associated with cardiac catheterization.