Laboratory Evaluation of Fibrinolysis in Patients with a History of Myocardial Infarction

The aims of this study were to determine whether elevated plasminogen activator inhibitor type 1 (PAI-1) activity after myocardial infarction reflects baseline PAI-1 or represents an acute-phase response secondary to the infarction, and to determine how tissue plasminogen activator (t-PA) activity and total t-PA antigen levels in healthy control subjects differ from those in patients after myocardial infarction. Compared with healthy control subjects, patients studied 1-3 months after infarction had elevated levels of PAI-1 activity and fibrinogen but normal levels of C-reactive protein and von Willebrand factor antigen, whereas patients with a noncardiac acute-phase response showed elevation of all four proteins. Elevated PAI-1 activity in the absence of elevations in other acute-phase proteins suggests an intrinsic increase in PAI-1 secretion in the post-myocardial infarction group. In addition, when compared with healthy control subjects, post-myocardial infarction patients had higher levels of total t-PA antigen (bound and free t-PA) but lower t-PA activity and a lower percentage of active t-PA. Overall, survivors of myocardial infarction have reduced t-PA activity and increased PAI-1 activity that is not due to a prolonged acute-phase response.