A History of Thrombolytic Therapy

Fibrinolytics for the treatment of pulmonary embolism

The use of fibrinolytic agents in acute pulmonary embolism (PE), first described over 50 years ago, hastens the resolution of RV stain, leading to earlier hemodynamic improvement. However, this benefit comes at the increased risk of bleeding. The strongest indication for fibrinolysis is in high-risk PE, or that characterized by sustained hypotension, while its use in patients with intermediate-risk PE remains controversial. Fibrinolysis is generally not recommended for routine use in intermediate-risk PE, although most guidelines advise that it may be considered in patients with signs of acute decompensation and an overall low bleeding risk. The efficacy of fibrinolysis often varies significantly between patients, which may be at least partially explained by several factors found to promote resistance to fibrinolysis. Ultimately, treatment decisions should carefully weigh the risks and benefits of the individual clinical scenario at hand, including the overall severity, the patient's bleeding risk, and the presence of factors known to promote resistance to fibrinolysis. This review aims to further explore the use of fibrinolytic agents in the treatment of PE including specific indications, outcomes, and special considerations.

Stroke Classification: Critical Role of Unusually Large von Willebrand Factor Multimers and Tissue Factor on Clinical Phenotypes Based on Novel "Two-Path Unifying Theory" of Hemostasis

Stroke is a hemostatic disease associated with thrombosis/hemorrhage caused by intracranial vascular injury with spectrum of clinical phenotypes and variable prognostic outcomes. The genesis of different phenotypes of stroke is poorly understood due to our incomplete understanding of hemostasis and thrombosis. These shortcomings have handicapped properly recognizing each specific stroke syndrome and contributed to controversy in selecting therapeutic agents. Treatment recommendation for stroke syndromes has been exclusively derived from the result of laborious and expensive clinical trials. According to newly proposed "two-path unifying theory" of in vivo hemostasis, intracranial vascular injury would yield several unique stroke syndromes triggered by 3 distinctly different thrombogenetic mechanisms depending upon level of intracranial intravascular injury and character of formed blood clots. Five major phenotypes of stroke occur via thrombogenetic paths: (1) transient ischemic attack due to focal endothelial damage limited to endothelial cells (ECs), (2) acute ischemic stroke due to localized ECs and subendothelial tissue (SET) damage extending up to the outer vascular wall, (3) thrombo-hemorrhagic stroke due to localized vascular damage involving ECs and SET and extending beyond SET to extravascular tissue, (4) acute hemorrhagic stroke due to major localized intracranial hemorrhage/hematoma into the brain tissue or space between the coverings of the brain associated with vascular anomaly or obtuse trauma, and (5) encephalopathic stroke due to disseminated endotheliopathy leading to microthrombosis within the brain. New classification of stroke phenotypes would assist in selecting rational therapeutic regimen for each stroke syndrome and designing clinical trials to improve clinical outcome.

Evidence-based diagnosis and thrombolytic treatment of cardiac arrest or periarrest due to suspected pulmonary embolism

When a previously healthy adult experiences atraumatic cardiac arrest, providers must quickly identify the etiology and implement potentially lifesaving interventions such as advanced cardiac life support. A subset of these patients develop cardiac arrest or periarrest due to pulmonary embolism (PE). For these patients, an early, presumptive diagnosis of PE is critical in this patient population because administration of thrombolytic therapy may significantly improve outcomes. This article reviews thrombolysis as a potential treatment option for patients in cardiac arrest or periarrest due to presumed PE, identifies features associated with a high incidence of PE, evaluates thrombolytic agents, and systemically reviews trials evaluating thrombolytics in cardiac arrest or periarrest. Despite potentially improved outcomes with thrombolytic therapy, this intervention is not without risks. Patients exposed to thrombolytics may experience major bleeding events, with the most devastating complication usually being intracranial hemorrhage. To optimize the risk-benefit ratio of thrombolytics for treatment of cardiac arrest due to PE, the clinician must correctly identify patients with a high likelihood of PE and must also select an appropriate thrombolytic agent and dosing protocol.

Is There Still a Role for Fibrinolysis in ST-Elevation Myocardial Infarction?

OPINION STATEMENT

Fibrinolysis had long been the reference treatment in patients with ST-Elevation Myocardial Infarction (STEMI). It was associated with a large reduction in mortality as compared with delayed or no reperfusion in patients managed early, within the first 2 hours from the onset of symptoms. Fibrinolysis also had well-known potential complications: cerebral haemorrhage, especially in patients beyond 75 years, and reinfarction. Primary percutaneous intervention (PCI) has overcome most of these limitations, but at a price: PCI-related delays that can reduce the expected benefit of primary PCI compared with fibrinolysis. That primary PCI is today the treatment of choice in patients with STEMI is no longer discussed. However, fibrinolysis should still maintain a role in the management of acute myocardial infarction (AMI) for three reasons. First, fibrinolysis is no longer a stand-alone treatment. Modern fibrinolytic strategies combine immediate fibrinolysis, loading dose of thienopyridines, and transfer to a PCI hospital for rescue or early PCI within 24 hours. These strategies capitalize on the hub-and-spoke networks that have, or should have, been built everywhere to implement primary PCI. The overall clinical results of these modern fibrinolytic strategies are now similar to those of primary PCI. Second, a substantial number of patients cannot be managed with primary PCI within the reasonable time thresholds set by the guidelines. In the case of long PCI-related delays, patients will benefit from fibrinolysis before or during transfer to a PCI hospital. Third, modern fibrinolytic strategies-immediate fibrinolysis followed by rescue or early PCI-may even offer the best results of all in a subset of patients. Patients of less than 75 years, managed within the first 2 hours and who cannot have immediate PCI, will fare better with a modern fibrinolytic strategy than with primary PCI. Guidelines advocate regional networks between hospitals with and without PCI capabilities, an efficient ambulance service and standardization of AMI management through shared protocols. These regional logistics of care are essential to take full advantage of fibrinolysis strategies. In order to check that these strategies are correctly applied, networks need ongoing registries, as well as benchmarking and quality improvement initiatives.

Erythrocyte migration and gap formation in rabbit blood clots in vitro

Thrombolytic agents must be carried by the blood circulation to thrombi to exert their functions. Structural gaps exist between blood vessels and thrombi or in the area surrounding thrombi. Therefore, information about fundamental gap formation at thrombotic areas is critically important for thrombolytic therapy. We previously reported that t-PA accelerates the activities of bovine erythrocytes and hemoglobin (Hb) towards bovine plasminogen activation. Here, we examined gap generation by observing morphological changes during thrombolytic processes in rabbit blood clots deformation of erythrocytes from blood clots and Hb transfer from erythrocytes to serum in vitro. Rabbit venous blood samples (1 ml) were stored under sterile conditions in glass tubes at 37 degrees C for 2, 24, 48 h, 1, and 2 weeks. We examined clot diameter, erythrocyte diameter and number as well as Hb volume in the serum, as well as histological changes in the clots. The diameter of blood clots did not change until 2 weeks after sampling. Erythrocyte diameter decreased within 48 h and at 2 weeks after sampling at the clot surface (p < 0.001) and interior (p < 0.001). The number of erythrocytes in the serum started to increase starting from 24 h after sampling (p < 0.01). Serum Hb volume also gradually increased from 24 h until 2 weeks after sampling (p < 0.01). The erythrocyte envelope became disrupted and cytoplasm started to flow through pores into the serum at 24 h. The results indicated that blood clots are reduced due to clot retraction, erythrocyte dissociation and cytoplasm leakage without a distinct fibrinolytic reaction. These results indicated that gaps start to form between 2 and 24 h after blood clotting.