Thrombolytic treatment in acute myocardial infarction.

All thrombolytic agents convert plasminogen to plasmin, either directly, as in the case of urokinase, saruplase, and alteplase, or indirectly, as in the case of streptokinase. In the majority of recent clinical trials with streptokinase, a high-dose (0.7-1.5 million units), brief-duration (30-90 minutes) drug regimen has been used. After a mean interval of 4.2 hours from onset of chest pain to intravenous infusion of streptokinase, repeat angiography performed 60-90 minutes after the start of thrombolytic treatment gave a reperfusion rate of 43%; the corresponding figures for anistreplase, saruplase, and alteplase are 56%, 67%, and 69%. The patency rates obtained in similar studies with the same end point are 56% for streptokinase, 77% for anistreplase, 62% for urokinase, 71% for saruplase, and 75% for alteplase. The in-hospital mortality in randomized trials (six large studies in a total of 31,713 randomized patients) with intravenous high-dose streptokinase decreased from 12.0% in the control group to 9.47% in the streptokinase group. In a mortality study involving 1,258 patients randomized to intravenous anistreplase or placebo, the 30-day mortality was reduced by 47%, from 12.2% to 6.4%. In a large trial in which 5,011 patients were randomized to alteplase or placebo, the 30-day mortality was 7.2% compared with 9.8% in controls, a reduction of 27% by alteplase. In another trial, 721 patients were randomized to placebo or alteplase; all patients received acetylsalicylic acid and intravenous heparin. The 14-day mortality was only 2.8% in the alteplase group, 51% less than that in the control group. It is most important that the favorable impact on hospital survival be maintained at 1 year for any thrombolytic drug. Large-scale trials directly comparing mortality after alteplase, streptokinase, or anistreplase are being performed or are in the planning phase. The risk of bleeding exists with any thrombolytic agent; intracranial bleeding is the most serious risk. In a large trial in 5,011 patients with acute myocardial infarction, stroke occurred in 1.1% of alteplase-treated patients compared with 1.0% in placebo-treated controls. Haunting problems are residual stenosis of the coronary artery and reocclusion. Urgent angioplasty does not seem to be the right answer; more effective antithrombotic strategies have yet to be developed.