LIMITATION OF MFARCT SIZE



Any intervention to limit the size of an evolving infarction must be performed within the first four to six hours of infarction, before cells become ir­reversibly necrotic. The most promising tech­niques involve early reperfusion, i.e., fibrinolysis (e.g., streptokinase), coronary angioplasty, or sur­gery within the first four to six hours after infarc­tion.

Most patients with acute transmural myocar­dial infarction have complete obstruction of a cor­onary artery due to thrombosis that can be doc­umented safely with coronary arteriography within the first four hours of infarction. Admin­istration of intracoronary streptokinase to lyse clots by activating plasminogen opens the coro­nary artery in 70 to 80 per cent of these patients (somewhat lower if intravenous streptokinase is employed) (Fig. 7-3). Electrocardiographic evi­dence of infarction usually still evolves. The time course of cardiac enzyme elevation is accelerated, thought to be evidence of washout of enzymes from the heart by reperfusion. Thus, even though this technique does not prevent infarction, it may salvage a portion of the myocardium in jeopardy. There is usually a highgrade stenosis in the area of thrombosis that can be dilated acutely with cor­onary angioplasty at the time of streptokinase in­fusion or approached with angioplasty or surgery at a later date to prevent reocclusion. Long-term results and potential complications (e.g., intra-myocardial hemorrhage) are still being deter­mined. Both intracoronary and intravenous strep­tokinase have profound systemic fibrinolytic effects, and massive bleeding may occur from ar­terial puncture sites or surgical wounds.

The role of angioplasty during acute myocardial infarction either with or without streptokinase ad­ministration is also under investigation. Even though early surgical revascularization is possible after myocardial infarction, it is logistically dif­ficult to perform within the first four to six hours after the onset of chest pain and has not been dem­onstrated definitively to limit infarct size.