Randomized factorial trial of high-dose intravenous streptokinase, of oral aspirin and of intravenous heparin in acute myocardial infarction. ISIS (International Studies of Infarct Survival) pilot study.
619 patients with suspected acute myocardial infarction (MI) were randomized to receive either a high-dose short-term intravenous infusion of streptokinase (1.5 MU over one hour) or placebo. Using a '2 X 2 X 2 factorial' design, patients were also randomized to receive either oral aspirin (325 mg on alternate days for 28 days) or placebo, and separately randomized to receive either intravenous heparin (1000 IU h-1 for 48 hours) or no heparin. Streptokinase (SK) was associated with a nonsignificant (NS) increase in non-fatal reinfarction (3.9% SK vs 2.9% placebo) and decrease in mortality (7.5% vs 9.7% in hospital plus 6.1% vs 8.7% after discharge). After SK, there were significantly fewer strokes (0.5% vs 2.4%; 2P less than 0.05), but significantly more minor adverse events (e.g. hypotension and bradycardia, allergies, bruises or minor bleeds, nausea). Aspirin was associated with fewer non-fatal reinfarctions (3.2% aspirin vs 3.9% placebo; NS), deaths (in hospital: 6.1% vs 10.5%; 2P less than 0.05, and after discharge: 7.0% vs 6.9%; NS), and strokes (0.3% vs 2.0%; NS). Heparin was associated with a decrease in reinfarction (2.2% heparin vs 4.9% no heparin; NS), though not in mortality (in hospital: 8.0% vs 8.5%; NS, and after discharge: 7.0% vs 6.9%; NS), and with a trend towards more strokes (1.6% vs 0.7%; NS) and more bruising and bleeding (14% vs 12%; NS). To assess more reliably the effects of aspirin and of this SK regimen on mortality, about 400 hospitals worldwide are now collaborating in a large (about 20,000 patients planned) randomized trial (ISIS-2), for which the present study was a pilot.