Page 550 - Cardiac Nursing

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526 PA R T I V / Pathophysiology and Management of Heart Disease
4. For UA/NSTEMI patients in whom an initial conservative needed for an acute drop in platelets and/or with bleeding associated
strategy is selected, clopidogrel should be added to ASA and an- with thrombocytopenia. Monitor for potential bleeding at arterial
ticoagulant therapy as soon as possible after admission and ad- and venous puncture sites and gastrointestinal, genitourinary, and
ministered for at least 1 month (Class I, level of evidence: A) retroperitoneal sites. Postural BPs should be measured prior to am-
and ideally up to 1 year. (Class I, level of evidence: B) bulation to rule out potential extracellular fluid volume deficit sec-
5. For UA/NSTEMI patients in whom an initial conservative ondary to bleeding. If an allergic reaction occurs, stop the drug im-
strategy is selected, if recurrent symptoms/ischemia, heart fail- mediately and initiate resuscitative measures if indicated.
ure, or serious arrhythmias subsequently appear, then diagnos-
tic angiography should be performed. (Class I, level of evi- Anticoagulant Agents
dence: A) Either an IV GP IIb/IIIa inhibitor or clopidogrel
should be added to ASA and anticoagulant therapy before di- For patients with STEMI and UA/NSTEMI, anticoagulant ther-
agnostic angiography. (Class I, level of evidence: C) apy should be initiated at the time of presentation to prevent
thrombus-related events. 2,4
Actions/Indications. There are three IV antiplatelet agents,
abciximab, eptifibatide, and tirofiban, which are classified as GP UFH and Low-Molecular-Weight Heparin
IIb/IIIa receptor antagonists. The smaller molecules, tirofiban and
eptifibatide, are less expensive to manufacture than abciximab, a Actions/Indications. UFH accelerates the action of circulat-
monoclonal antibody. 85 Abciximab has a short half-life but a ing antithrombin, which inactivates factor IIa (thrombin), factor
strong affinity for the GP IIb/IIIa receptor. Platelet aggregation IXa, and factor Xa. UFH prevents thrombus propagation but does
gradually returns to normal in 48 hours after discontinuation of not cause lysis of existing thrombi. UFH binds to a number of
abciximab, although the drug remains in the circulation for 10 to plasma proteins, blood cells, and endothelial cells leading to poor
15 days in a platelet-bound state, resulting in sustained an- bioavailability and marked variability in anticoagulant response.
4
tiplatelet activity. Abciximab is indicated for patients with ACS The anticoagulant effect of heparin requires monitoring with
who undergo PCI and for patients treated with conventional aPTT. A weight-adjusted dosing regimen is needed to provide
medical therapy with planned PCI within 24 hours. Abciximab more predictable anticoagulation. 4
has been studied primarily in PCI trials with clinical reduction in Enoxaparin has been studied more frequently than other low-
rates of MI and need for urgent revascularization. 4 molecular-weight heparin (LMWH) preparations. It has antithrom-
Eptifibatide and tirofiban are synthetic receptor antagonists botic properties with inhibition of factor Xa and antithrombin (fac-
that bind to the GP IIb/IIIa receptor. Receptor occupancy with tor IIa) occurring 3 to 5 hours after SC injection. Enoxaparin has a
these two agents is reversible. Platelet aggregation returns to nor- longer half-life than does UFH, resulting in a more predictable and
mal 4 to 8 hours following cessation of the infusion. Eptifibatide sustained anticoagulant effect. Enoxaparin is weight-based, adminis-
and tirofiban are indicated for patients with ACS who are man- tered once or twice a day subcutaneously, and does not require lab-
aged medically and with PCI. 4 oratory monitoring. Enoxaparin does not prolong routine coagula-
tion tests (i.e., prothrombin time, aPTT, or activated clotting time)
Contraindications/Adverse Reactions. GP IIb/IIIa in- in a predictable manner, thus monitoring is not suitable to evaluate
hibitors should not be used in patients with a known hypersensi- level of anticoagulation. Consequently, UFH is frequently preferred
4
tivity; history of bleeding tendency or evidence of active bleeding during PCI to allow close monitoring of anticoagulation and re-
within previous 30 days; severe hypertension (systolic BP 180 versibility if the patient is going to undergo CABG.
mm Hg or diastolic BP 110 mm Hg); major surgery within Patients with ACS/NSTEMI who are treated with conservative
previous 4 to 6 weeks; history of stroke within 30 days or hemor- medical management can be treated with either UFH or LMWH.
rhagic stroke; international normalized ratio greater than 1.2; Several trials have found a benefit with enoxaparin over UFH with
prior administration of a GP IIb/IIIa inhibitor within the previ- conservative management in ACS, demonstrating reductions in
ous 24 to 48 hours; acute pericarditis; presumed or documented death and nonfatal MI. 88,89 The ACC/AHA recommends an
3
vasculitis; platelet count less than 100,000/mm ; and creatinine anticoagulant preference of fondaparinux, enoxaparin, and UFH
4
level greater than 4.0 mg/dL (eptifibatide). 85 for patients with a noninvasive strategy. Patients with ACS/
Administration of abciximab may result in antibody formation NSTEMI who are treated with an early aggressive approach were
that could potentially cause allergic or hypersensitivity reactions evaluated in the SYNERGY (Superior Yield of the New strategy
including anaphylaxis. The most common adverse reactions of GP of Enoxaparin, Revascularization and GlYcoprotein IIb/IIIa in-
IIb/IIIa antagonists include minor bleeding from access sites and hibitors) trial. 90 Enoxaparin was found to be safe and an effective
rarely major bleeding including ICH. There is a potential increase alternative to UFH but without significant advantage. There was
in bleeding risk with combination use of anticoagulants or fibri- a modest increase in major bleeding with enoxaparin compared
3
nolytics. Severe thrombocytopenia (platelets 50,000/mm ) has with UFH. The advantage of LMWH is the ease of SC adminis-
been reported in 0.5% patients receiving GP IIb/IIIa antagonists. tration and the absence of monitoring. Compared with UFH,
Although thrombocytopenia is reversible, it is associated with in- LMWH stimulates platelets less and is less frequently associated
creased risk of bleeding. 86,87 with heparin-induced thrombocytopenia. However, compared
with UFH, the anticoagulant effect of LMWH is less effectively
Nursing Implications. Monitor the complete blood cell reversed with protamine. When LMWH is administered during
count and differential and platelet count prior to treatment, 2 to 4 PCI, the activated clotting time cannot be monitored so that the
hours following the bolus dose, and at 24 hours or prior to discharge. degree of anticoagulation cannot be monitored. 2
If a patient experiences an acute decrease in platelets, the drug should
be discontinued and additional platelet counts should be monitored Contraindications/Adverse Reactions. Heparin is con-
until the platelet count returns to normal. Platelet infusions may be traindicated in patients with a history or current diagnosis of