Low-molecular-weight heparins in acute myocardial infarction: Rationale and results of a pilot study

Background: Antithrombotic adjuncts to fibrinolytic drugs for acute myocard ial infarction increase the rate and speed of infarct artery recanalization . Hypothesis: A low-molecular-weight heparin might be preferable to unfractio nated heparin for this indication, as it has been shown to be in several ot her thrombus-related vascular disorders. Methods: We performed a pilot study in 20 patients, all receiving aspirin a nd recombinant tissue plasminogen activator. Randomization was to standard dose intravenous unfractionated heparin or enoxaparin (the first dose given intravenously and followed by a subcutaneous administration). The endpoint was stability of anticoagulant effect. Results: Enoxaparin produced stable therapeutic anti-Xa levels with minimal effect on activated partial thromboplastin times. Unfractionated heparin p roduced wide swings of these parameters, often outside desired levels. Conclusions: Enoxaparin may be a better antithrombotic agent than conventio nal unfractionated heparin when used in conjunction with fibrinolytics.