Clinical Use of Intravenous GP IIbIIIa Antagonists in Patients with NonST Elevation ACS

Data from the PRISM, PRISM-PLUS, and PURSUIT studies favor the use of tirofiban or eptifibatide in patients with non-ST-elevation ACS, particularly among high-risk patients with positive troponins, or in patients undergoing adjunctive PCI.

However, unlike the decision to administer GP IIb/IIIa antagonists to patients undergoing elective PCI, the administration of this form of antiplatelet therapy to patients presenting with ACS is less straightforward. Indeed, the diagnosis of unstable angina remains largely clinical. Furthermore, the diagnosis of non-ST-elevation myocardial infarction is frequently made retrospectively, based upon the examination of enzymatic markers of myocardial necrosis. Therefore, GP IIb/IIIa antagonist therapy is commonly initiated in an "empiric" way in this group of patients, in spite of the observation that the benefit of this therapy seems to be somewhat confined to high-risk unstable angina patients particularly to those with elevated troponin levels and to those who proceed to PCI. A meta-analysis of the six trials shown in Table 5 and Fig. 7 indicates hat GP IIb/IIIa antagonist therapy is associated with a 9% relative (or 1% absolute) reduction in the odds of death or myocardial infarction at 30 d (119). Subgroup analyses of this study suggest that patients with elevated troponins or who undergo PCI, are those who derive most benefit from GP IIb/IIIa blockade.

Putting these data in context with the TACTICS trial, patients presenting within the first few h (<3 h) after the onset of the non-ST-elevation ACS, in whom troponin elevation would not be detected yet, should probably receive intravenous GP IIb/IIIa antagonists (tirofiban or eptifibatide) and undergo early coronary catheterization and revascularization if deemed appropriate. If, however, a patient is found to not have an elevated troponin level 12 h or more after the onset of symptoms, a noninvasive approach would seem adequate. If GP IIb/IIIa antagonists were to be administered to a patient with these characteristics, benefit from this form of therapy would not be expected to be significant.

One concern of the "up-front" or empiric administration of GP IIb/IIIa therapy is that patients with ACS may require coronary artery bypass grafting (CABG) surgery. A sub-

Table 7

High Risk Features in Patients with Non-ST-Elevation ACS

Table 7

High Risk Features in Patients with Non-ST-Elevation ACS

Feature

High Risk

At least 1 of the following must be present:

History

Accelerating tempo of ischemic symptoms In preceding 48 h

Character of pain

Prolonged, ongoing (>20 min) rest pain.

Clinical findings

Pulmonary edema, most likely due to ischemia.

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