Thrombolytic therapy of non-cardiac disorders

Tissue-type plasminogen activator: a historical perspective and personal account

Over the past two decades tissue-type plasminogen activator (t-PA), the main physiological plasminogen activator, has been developed as a fibrin-specific thrombolytic agent for the treatment of various thromboembolic diseases. Milestones in this development include: first purification of human t-PA from uterine tissue, elucidation of the interactions regulating physiological fibrinolysis, thus providing a molecular basis for the concept of fibrin-specific plasminogen activation, first animal models of thrombosis and pilot studies in patients supporting the therapeutic potential of t-PA, cloning and expression of recombinant t-PA providing sufficient amounts for large scale clinical use, and demonstration of its therapeutic benefit in large multicenter clinical trials, mainly in patients with acute myocardial infarction (AMI), but also in patients with massive pulmonary embolism, ischemic stroke, deep vein thrombosis and peripheral arterial occlusion. Genetically modified variants of t-PA have been developed for bolus administration in patients with AMI.

[Fibrinolytic therapy of deep vein thrombosis]

BACKGROUND

The most important complications of deep vein thrombosis are pulmonary embolism and postthrombotic syndrome. While the medicine of lethal pulmonary embolism is reduced to less than 2% by conventional anticoagulation, fibrinolytic therapy aims at a reduction of the greater than 50% incidence of postthrombotic syndrome. The optimal therapeutic regimen concerning risks and effect has not been established yet.

RESULTS

A review of 26 studies involving ultrahigh-dose streptokinase (UHSK), urokinase (UK), and tissue-type plasminogen activator (rt-PA) shows the highest success rate for UHSK (45% complete and 40% parital patency), whereas there are lower rates for UK (25% and 40%) and low-dose locoregionally applied rt-PA (22% and 44%). The studies were not directly comparative, however. Published data concerning complications range from 1.7% mortality for UHSK to 0.9% for UK and 0.0% for rt-PA. Success criteria, however, are varying and not well defined. The influence of fibrinolytic therapy on the incidence of postthrombotic syndrome has not been established prospectively, but a reduction by 40 to 50% can be assumed. Calf vein thromboses are not indication for lytic therapy. In patients with iliacal vein thromboses there is an increased risk of pulmonary embolism using UHSK.

CONCLUSIONS

UHSK can be regarded the standard concerning success rate in deep vein thromboses. DATA involving locoregional therapy with rt-PA are inconsistent and worse, but bleeding complications might be less frequent. Large prospective studies evaluating the impact on incidence and severity of the postthrombotic syndromes, which involve a controlled application of compression therapy are needed.