Unfractionated heparin STEMI

Three influential studies explore thrombolysis followed by obligatory coronary intervention compared with thrombolysis alone. These results diminished enthusiasm for a combined approach. A primary objective of one component of the TIMI II trial (TTMI Ha) was to determine whether early invasive management after acute STEMI would improve outcome (12). Patients eligible for enrollment in TTMI n were those with symptoms of less than 4 hours in duration and electrocardiographic manifestations of acute STEMI. All patients were treated with intravenous recombinant t-PA. In addition to t-PA, patients were treated with contemporary conjunctive and adjunctive therapy that included aspirin, unfractionated heparin, and intravenous hdocaine for a minimum of 24 hours. Within 1 hour after onset of infusion of t-PA, patients were given a bolus of 5000 units of unfractionated heparin in addition to a continuous infusion of 10(X) units per dose to induce a 1.5- to 2-fold... 

The European Cooperative Study had already randomized 367 patients with acute STEMI (13). t-PA had been administered to eligible patients within 5 hours after onset of symptoms. Conjunctive therapy had included aspirin (250 mg) and unfractionated heparin (5000 units bolus plus 1000 units per hour infusion). Treatment with warfarin was allowed at the discretion of the treating physician. In those randomized to subsequent early intervention, angiography had been performed as promptly as possible (within 165 minutes), and PCI had been performed when anatomy was appropriate. 

In the prefibrinolytic era, antithrombins were principally administered to patients with STEMI to reduce the risks of pulmonary embolism, stroke, and reinfarction. The theoretical benefits of conjunctive use of unfractionated heparin (UFH) with a fibrinolytic include the possibility of augmentation of the initial lytic effect, reduction of the risk of reocclusion of an initially successfully reperfused infarct artery (with attendant risk of reinfarction), and reduction of the risk of early mural thrombus formation (28). Despite the logic of these arguments, clinical trials of conjunctive use of UFH with fibrinolytic therapy produced confusing results that continue to impact on clinical practice. Synthesis of a large body of information on studies with UFH leads to several conclusions ... 

Figure 7.4 Design of ExTRACT-TIMI 25 trial. Patients with STEMI are treated with one of the four standard fibrinolytics and are randomized to receive either unfractionated heparin (UFH) or enoxaparin. Elderly patients do not receive the bolus of enoxaparin and are given only 15% of the subcutaneous dose of the younger patients.

---