Unresolved pulmonary embolism: the role of fibrinolysis

A minority of patients with acute pulmonary embolism (PE) show failure of resolution when assessed by serial ventilation/perfusion (V/Q) radionuclide lung imaging. The fibrinolytic systems were studied in six such patients (group I), and in 11 patients in whom PE had resolved (group II), together with 17 healthy control subjects. Assays of the fibrinolytic system included euglobulin clot lysis times (ECLT), tissue plasminogen activator (tPA), and plasminogen activator inhibitor-1 (PAI-1). Euglobulin clot lysis times were not prolonged in the unresolved PE group, but were significantly longer in patients in group II when compared to control subjects (P < 0.03). This could not be explained either on the basis of tPA levels, which were higher in group II when compared to group I (P < 0.05) and control subjects (P < 0.02), or on the basis of PAI-1 levels which did not differ significantly between the three groups. Our inability to demonstrate derangements of fibrinolysis in the patients with unresolved PE makes defective fibrinolysis an unlikely aetiological factor in the persistence of thrombosis in these patients.