New approaches to treatment of myocardial infarction

Survival of patients with acute transmural infarction is largely related to the size of the myocardial infarction. The goal of thrombolytic therapy in acute myocardial infarction is maximal salvage of myocardium by reestablishment of flow in the occluded infarct-related artery and the establishment and maintenance of a patent infarct-related artery. Results of randomized trials show a significant reduction in mortality in patients who have undergone thrombolysis. A patent infarct-related artery, even in the absence of a change in left ventricular function, is associated with reduced mortality. The Thrombolysis in Myocardial Infarction Trial and the European Cooperative Trial showed that recombiant tissue-type plasminogen activator is superior to streptokinase in reestablishing flow in a totally occluded artery. Experimental and clinical evidence suggests that thrombolysis and thrombosis occur simultaneously, and that lysis appears to increase both thrombin and platelet activity. Effective reduction of thrombosis accelerates thrombolysis. Rethrombosis after thrombolysis is due to anchored residual thrombus, which alters the hemorrheology of blood flow and produces a highly thrombogenic substrate that is largely due to residual fibrin-bound thrombin. Platelet deposition is directly related to severity of residual stenosis and shear rate. Thrombin appears to be the most potent of the 5 potential stimulators of platelet activation during arterial thrombosis. Proper anticoagulation can play an important role in reducing thrombosis. Experimental evidence strongly supports the use of heparin during and after thrombolysis. A recently reported study shows continued reduction of residal stenosis after 1 month of vigorous anticoagulation with intravenous heparin and subsequent oral anticoagulation. A recent clinical trial showed that subcutaneous heparin given during hospitalization reduced recurrent ischemia after thrombolysis, mortality and left ventricular mural thrombosis. Most current trials are using both heparin and aspirin during and after thrombolysis, with apparent reduction in rates of reocclusion. Thrombolysis with a combination of recombinant tissue-type plasminogen activator and either streptokinase or urokinase appears to reduce reocclusion. Maximal therapy to enhance continued lysis of residual mural thrombus after hospitalization includes combined anticoagulation with sodium warfarin and probably low-dose aspirin at 80 mg/day.