Intravenous streptokinase in acute myocardial infarction (I.S. A.M.): assessment of left ventricular function 1 and 7 months after infarction by radionuclide ventriculography

Abstract

I.S.A.M. was a prospective, placebo-controlled, double-blind multicentre trial of high-dose short-term intravenous streptokinase in acute myocardial infarction (AMI) within 6 h of the onset of symptoms. Determination of left ventricular ejection fraction (LVEF) by radionuclide ventriculography was performed 1 and 7 months after AMI in a subset of 192 patients at rest and, in 140 of them, also during exercise. Regional myocardial function was analysed in all 145 patients with neither a history of a previous myocardial infarction nor revascularization procedures or reinfarction within the 7-month follow-up period. One month after AMI, mean LVEF was higher in the streptokinase group in patients with anterior AMI (50 +/- 15% vs 42 +/- 16%, P = 0.013). This difference was more marked in the subgroup treated within 3 h (53 +/- 14% vs 42 +/- 15%, P = 0.004), whereas patients treated 3-6 h after the onset of symptoms did not differ from respective controls (41 +/- 16% vs 41 +/- 18%). In patients with inferior AMI, the difference in mean LVEF was small (57 +/- 11% vs 55 +/- 12%, P = 0.47). After anterior AMI benefit due to streptokinase therapy was preserved up to 7 months (52 +/- 14% vs 44 +/- 17%, P = 0.013). During exercise, the increase of mean LVEF was greater in the streptokinase group at both dates, especially 7 months after AMI (4.1 +/- 6.1% vs 1.2 +/- 6.3%, P = 0.015). In streptokinase-treated patients with anterior AMI, regional LVEF at rest was higher at both dates compared with controls, within the infarct zone as well as in remote myocardium. No treatment-control differences were demonstrable in patients with inferior AMI. During exercise, regional contractile reserve was better in the streptokinase group within the infarct zone as well as in remote myocardium, irrespective of the site of infarction. Thus, intravenous streptokinase within 3 h after the onset of AMI preserves global left ventricular function in anterior AMI over a period of at least 7 months. Intravenous streptokinase improves regional myocardial function within the infarct zone as well as in remote areas. In inferior AMI investigation solely at rest may underestimate the benefit of streptokinase therapy.