Thrombolytic Therapy for Pulmonary Embolism

Although anticoagulation has been the cornerstone of treatment of acute pulmonary embolism for the past 30 years, there has been no further reduction in the mortality rate for this condition. The use of thrombolytic therapy for pulmonary embolism has been shown in randomized controlled trials to accelerate clot lysis, pulmonary reperfusion, and hemodynamic improvement. In addition, recent preliminary findings suggest that thrombolysis confers greater long-term clinical benefit than does treatment with heparin alone. No effect of thrombolytic therapy on mortality has been shown, but only small-scale trials have been performed. Fear of bleeding complications has limited the use of thrombolysis for pulmonary embolism; major bleeding is still seen in 10-15% of patients. However, recent data suggest that shorter infusion times and elimination of routine pulmonary angiograms in some patients may further reduce the incidence of bleeding. Three agents have been shown to be effective for pulmonary embolism: urokinase, streptokinase, and tissue-type plasminogen activator. Relative efficacy of the three agents is difficult to assess, given the different dosing regimens employed in previous studies. More rapid or “bolus” infusions of each agent have shown promising results, with equivalent safety profiles. Thrombolytic therapy is recommended in cases of pulmonary embolism with hemodynamic compromise, lobar or multisegmental involvement, or in the setting of smaller emboli in patients with prior cardiopulmonary disease. In contrast with its use for myocardial infarction, thrombolytic therapy may be administered as late as 14 days after onset of symptoms of pulmonary embolism. Greater familiarity with the use of these agents, coupled with the broad window of time available for their use, has resulted in increasing interest in this therapeutic option.