Emergency coronary artery bypass grafting (CABG) after failed coronary artery intervention--caution regarding the combined use of aspirin, ticlopidine and abciximab

Avoidance of Bleeding During Surgery in Patients Receiving Anticoagulant and/or Antiplatelet Therapy

Perioperative management of chronically anticoagulated patients and/or patients treated with antiplatelet therapy is a complex medical problem. This review considers the pharmacokinetic and pharmacodynamic properties of commonly used antiplatelet and anticoagulant drugs with special emphasis on loss of effects after discontinuation and possible counteracting (or antidote) strategies. These drugs are aspirin (acetylsalicylic acid), ticlopidine/clopidogrel, abciximab, tirofiban and eptifibatide, heparin (unfractionated and low-molecular-weight), warfarin and direct thrombin inhibitors. Since the pharmacological mechanisms of some of these drugs are based on irreversible or slowly reversible effects, their pharmacokinetic profiles are not necessarily predictive for their pharmacodynamic profiles. A close and direct relationship between plasma concentrations and effects is seen only for the glycoprotein (GP) IIb/IIIa inhibitors tirofiban and eptifibatide with a fast off-rate for dissociation from the GPIIb/IIIa receptor, and for direct thrombin inhibitors (hirudin and argatroban). For other compounds, drug concentrations in plasma and pharmacodynamic effects are not closely correlated because of, for example, irreversible binding to their target (aspirin, clopidogrel and abciximab), inhibition of the generation of a subset of clotting factors with differing regeneration and degradation rates (coumarins) or sustained binding to the vascular wall (heparins). Surgery in patients on anticoagulant and/or antiplatelet therapy may be categorised as: (i) elective versus urgent; and (ii) cardiopulmonary bypass (CPB) versus non-CPB. Monotherapy with clopidogrel or aspirin need not be discontinued in elective non-CPB surgery, and temporary discontinuation of warfarin should be accompanied by preoperative intravenous heparin only in selected high-risk patients. Vitamin K as an antidote for warfarin should only be used subcutaneously and solely in urgent/emergency surgery. In elective surgery requiring CPB (coronary artery bypass grafting), it is recommended to discontinue aspirin 7 days preoperatively in patients with a low risk profile. Patients requiring urgent CPB surgery (e.g. after failure of a percutaneous coronary angioplasty with or without coronary stent deployment) are usually pretreated with several antiplatelet agents (e.g. aspirin and clopidogrel, together with a GPIIb/IIIa inhibitor) together with unfractionated or low-molecular-weight heparin. With judicious planning, urgent/emergency cardiac surgery can be safely performed on these patients. Delaying surgery (e.g. for 12 hours in patients treated with abciximab) should be considered if possible. Standard heparin doses should be given to achieve optimal anticoagulation for CPB. Prophylactic use of aprotinin (intra- and/or postoperatively), aminocaproic acid or tranexamic acid should be considered. Early (in the operating theatre prior to chest closure) and judicious use of replacement blood products (platelets) should be commenced when clinically indicated.

Current status of cardiac surgery in the abciximab-treated patient

BACKGROUND

Early surgical experience with abciximab and other glycoprotein (GP) IIb/IIIa receptor antagonists suggested a tendency toward excessive bleeding in patients treated with these agents. With increased use of GP IIb/IIIa inhibitors, cardiac surgeons have become aware of their hazards, as well as potential benefits, during and after cardiac surgery. Although published experience with the GP IIb/IIIa inhibitor abciximab is limited in scope, it suggests management guidelines for urgent coronary artery bypass grafting in abciximab-treated patients. As more urgent and elective surgical data are presented, a clearer picture of true bleeding risk will evolve.

METHODS

Two large retrospective studies examining reexploration for postoperative bleeding have identified risk factors, including advanced age, preoperative renal dysfunction, and operation/reoperation other than coronary artery bypass grafting. Other risk factors for transfusion requirement and increased morbidity and mortality are emergent operation, postoperative coagulopathy, and prolonged bypass time.

RESULTS

To minimize real and perceived bleeding effects, some authors have suggested delaying operation until platelet function has normalized, employing platelet transfusion in patients in whom delay is not possible, and exacting heparin management during cardiopulmonary bypass. Later reports have not noted increased bleeding when incorporating these modifications plus early platelet transfusion, if required. Further experience with abciximab removal and reversal may also ultimately reduce or eliminate excess transfusion requirements.

CONCLUSIONS

Surgeons should work closely with perfusionists and anesthesiologists on issues of heparinization in the abciximab-treated patient. The apparent paradox of preserved platelet numbers and depressed platelet function with abciximab use has led to speculation about a role for this agent and other shorter-acting GP IIb/IIIa inhibitors for "platelet anesthesia" during cardiopulmonary bypass. With careful surgical care, GP IIb/IIIa receptor antagonists can maintain and improve beneficial outcomes.