Depression of factor XII-dependent fibrinolytic activity in survivors of acute myocardial infarction at risk of reinfarction.

Defective fibrinolysis may constitute a risk for the development of myocardial infarction in patients with ischaemic heart disease. We studied prospectively the factor XII-dependent plasminogen proactivator system in 49 survivors of an acute myocardial infarction. Blood samples were collected 8 weeks after hospital discharge. The factor XII-dependent fibrinolytic activity in the specimens was determined on fibrin plates after complete immuno-inhibition of the urokinase-like and the t-PA related fibrinolytic systems. During the subsequent follow-up period of 2.4 years, 10 patients developed recurrent myocardial infarction, whereas the remaining 39 patients did not. The reinfarction group of patients had a significantly lower median factor XII-dependent fibrinolytic activity (24.9 blood activating units (BAU).ml-1) than the patients without a relapse (41.9 BAU.ml-1, P < 0.02). Plasma concentrations of factor XII did not deviate significantly between the groups (P > 0.05), whereas the median plasma concentrations of prekallikrein was slightly lower in the reinfarction group (90%) than in the non-reinfarction group of patients (105%, P < 0.02). These observations point to an association between a depressed factor XII-dependent fibrinolytic activity and an enhanced risk of reinfarction in patients with a previous episode of acute myocardial infarction.