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Thrombin antagonists and antiplatelet agents
1Division of Cardiology, University of Massachusetts Medical School, Worcester 01655.
Insights
Thrombolytic therapy for myocardial infarction faces challenges like clot resistance and reocclusion due to procoagulant activity. Newer, targeted agents show promise in overcoming these limitations.
Area of Science:
- Cardiovascular Medicine
- Hematology
- Pharmacology
Background:
- Thrombolytic therapy is crucial for myocardial infarction but limited by resistant thrombi and reocclusion.
- These issues stem from localized procoagulant activity at plaque rupture sites, involving thrombin and platelet activation.
- Current treatments use heparin and aspirin but have limitations.
Purpose of the Study:
- To review the limitations of current thrombolytic therapy for myocardial infarction.
- To explore the role of procoagulant activity in thrombolytic resistance and reocclusion.
- To discuss the potential of novel antithrombotic agents.
Main Methods:
- Review of existing clinical evidence and experimental models.
- Analysis of the mechanisms underlying thrombolytic resistance and reocclusion.
- Evaluation of current and emerging therapeutic strategies.
Main Results:
- 20-25% of coronary thrombi resist lysis; 10-15% of patients experience reocclusion.
- Heightened procoagulant activity, particularly thrombin and platelet activation, contributes significantly.
- Heparin and aspirin improve outcomes but are not fully effective.
Conclusions:
- More potent and selective agents targeting thrombin and platelets are needed.
- Experimental models suggest specific thrombin antagonists and antiplatelet agents are superior to current therapies.
- Further research is required to establish the safety and efficacy of these novel agents for widespread clinical use.
Abstract:
The clinical benefits of thrombolytic therapy for the treatment of myocardial infarction are recognized widely. However, 2 major limiting factors have become evident: (1) 20-25% of coronary arterial thrombi are resistant to lysis; and (2) coronary reocclusion occurs in 10-15% of patients. There is increasing evidence that both phenomena are caused by heightened procoagulant activity localized primarily at the site of atheromatous plaque rupture. Thrombin, the pivotal enzyme in all coagulation processes, is activated, stimulating fibrin formation and platelet aggregation. Platelet activation, by thrombin- and nonthrombin-mediated mechanisms, occurs as well, further increasing thrombotic tendency. Thus, a potent and well-localized procoagulant state may be continuously amplified, increasing both during and frequently after thrombolytic therapy. Current treatment strategies are designed to enhance fibrinolytic and anticoagulant activity, while neutralizing the expression of procoagulant factors. Thrombin antagonism and platelet inhibition, primarily with heparin and aspirin, respectively, form the mainstay of conjunctive therapy. Their benefits have been recognized, decreasing thromboembolic events and patient mortality. However, intrinsic limitations suggest that more potent and selective agents will be required to overcome effectively the problems of thrombolytic resistance and coronary reocclusion. In experimental models, specific thrombin antagonists and antiplatelet agents have shown superiority over heparin and aspirin. Further investigation to define the overall safety and efficacy profile of these newer agents will be required, however, prior to their widescale implementation in clinical practice.