Antithrombotic therapy in acute myocardial infarction: Prevention of venous, left ventricular and coronary artery thromboembolism

The antithrombotic approach to patients with acute myocardial infarction in the prevention of venous, left ventricular and coronary artery thromboembolic events should be based on an understanding of pathogenesis and risk. Coronary thrombotic events involve conditions of high shear rate present in areas of vessel stenosis or disrupted atherosclerotic plaque, which lead to activation of both platelets and the coagulation system, and are best prevented by platelet inhibitors alone or in combination with an anticoagulant. However, thromboembolism that originates in the venous system or cardiac chambers is related to situations of blood stasis and low shear rate, which predominantly result in clotting activation and fibrin-thrombus formation and are best approached with anticoagulant therapy. For prevention of venous thrombosis and pulmonary embolism, early mobilization is essential and should be supplemented by low-dose heparin in patients at high risk, including the elderly and those with large infarcts, heart failure or previous thromboembolic events. For prevention of left ventricular mural thrombosis and systemic embolism, high-dose heparinization is indicated in patients with large infarcts, particularly in the anterior location and in those with heart failure. Subsequently, warfarin therapy should be considered for patients at high embolic risk, including those with echocardiographic evidence of mobile and protruding thrombi, severe left ventricular dysfunction or prior emboli. In patients with acute infarction, aspirin is recommended for preventing coronary reocclusion and reinfarction. Although anticoagulants may also be of benefit for this purpose, their use is still controversial. In situations of high risk of reocclusion, such as after administration of a thrombolytic agent, a combination of aspirin and heparin seems most appropriate, pending the results from randomized trials that will address this issue. Finally, for secondary prevention of myocardial infarction and cardiac mortality, chronic aspirin therapy is indicated. Long-term anticoagulation may also be beneficial but is associated with significant cost, discomfort and adverse effects.