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The effect of thrombolysis in acute myocardial infarction on infarct size, left ventricular function, clinical course and patient survival was studied in a randomized trial comparing thrombolysis (269 patients) with conventional treatment (264 control patients). All 533 patients were admitted to the coronary care unit within 4 hours after the onset of symptoms related to the infarction. Baseline characteristics were similar in both groups. Informed consent was requested only of patients allocated to thrombolysis; no angiography was performed in 35. The infarct-related artery was patent in 65 patients and occluded in 169. Recanalization was achieved in 133 patients. The median time to angiographic documentation of vessel patency was 200 minutes after the onset of symptoms. The clinical course in the coronary care unit was more favorable after thrombolysis. Infarct size, estimated from myocardial enzyme release, was 30% lower after thrombolysis. In patients admitted within 1 hour after the onset of symptoms the reduction of infarct size was 51%, in those admitted between 1 and 2 hours it was 31% and in those admitted later than 2 hours it was 13%. Left ventricular function measured by radionuclide angiography before hospital discharge was better after thrombolysis (ejection fraction 48 +/- 15%) than in control patients (44 +/- 15%). Similar improvement was observed in patients with a first infarct only (thrombolysis 50 +/- 14%, control subjects 46 +/- 15%), in patients with anterior infarction (thrombolysis 44 +/- 16%, control subjects 35 +/- 14%) and in those with inferior infarction (thrombolysis 52 +/- 12%, control subjects 49 +/- 12%). Similar results were obtained by contrast angiography. Mortality was lower after thrombolysis. After 28 days 16 patients allocated to thrombolysis and 31 control patients had died. One year survival rates were 91 and 84%, respectively. On the other hand, nonfatal reinfarction occurred more frequently after thrombolysis (36 patients) than in control subjects (16 patients). Early thrombolysis by intracoronary streptokinase leads to a smaller infarct size estimated by enzyme release, preserves left ventricular function at the second week and leads to improved 1 year survival.

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The effect of early myocardial reperfusion (within 4 hours after onset of symptoms) on regional left ventricular function in patients with acute myocardial infarction has been quantitated by analysis of segmental wall motion. Of 533 patients randomized either to conventional coronary care unit therapy or to a reperfusion strategy, in 332 high quality angiograms were obtained 2 to 8 weeks after the onset of myocardial infarction. In those assigned to thrombolytic therapy, angiographic data were also available after acute reperfusion. Analysis on an "intention to treat" basis revealed significant preservation of left ventricular function after thrombolytic therapy (ejection fraction 53%) compared with conventional treatment (ejection fraction 47%). In addition, wall motion analysis showed significant improvement of regional function in the infarct zone in both inferior and anterior infarction. In addition, significant changes occurred in regional function of the remote "noninfarct zone" in the acute as well as the chronic stage. It is concluded that improved regional and global left ventricular function can be achieved with early reperfusion and that this is the likely explanation for the reduction of early and late mortality after thrombolysis observed in this study.