Thrombolysis, also called fibrinolytic therapy, is the breakdown (lysis) of blood clots formed in blood vessels, using medication. It is used in ST elevation myocardial infarction, stroke, and in cases of severe venous thromboembolism (massive pulmonary embolism or extensive deep vein thrombosis). The main complication is bleeding (which can be dangerous), and in some situations thrombolysis may therefore be unsuitable. Thrombolysis can also play an important part in reperfusion therapy that deals specifically with blocked arteries.

Medical uses

Diseases where thrombolysis is used: Thrombolysis is usually intravenous. It may also be used directly into the affected blood vessel during an angiogram (intra-arterial thrombolysis), e.g. when patients present with stroke beyond three hours or in severe deep vein thrombosis (catheter-directed thrombolysis). Thrombolysis is performed by many types of medical specialists, including interventional radiologists, vascular surgeons, cardiologists, interventional neuroradiologists, and neurosurgeons. In some countries such as the United States of America, emergency medical technicians may administer thrombolytics for heart attacks in prehospital settings, by on-line medical direction. In countries with more extensive and independent qualifications, prehospital thrombolysis (fibrinolysis) may be initiated by the emergency care practitioner (ECP). Other countries which employ ECP's include, South Africa, the United Kingdom, and New Zealand. Prehospital thrombolysis is always the result of a risk-benefit calculation of the heart attack, thrombolysis risks, and primary percutaneous coronary intervention (pPCI) availability.

Contraindications

Thrombolysis is not without risks. Therefore, clinicians must select patients who are to be best suited for the procedure, and those who have the least risk of having a fatal complication. An absolute contraindication is in itself enough to avoid thrombolysis, while a relative contraindication needs to be considered in relation to the overall clinical situation.

Myocardial infarction

Absolute contraindications: Relative contraindications:

Stroke

Absolute contraindications: Relative contraindications:

Side-effects

Hemorrhagic stroke is a rare but serious complication of thrombolytic therapy. If a patient has had thrombolysis before, an allergy against the thrombolytic drug may have developed (especially after streptokinase). If the symptoms are mild, the infusion is stopped and the patient is commenced on an antihistamine before infusion is recommenced. Anaphylaxis generally requires immediate cessation of thrombolysis.

Agents

Thrombolysis therapy uses thrombolytic drugs that dissolve blood clots. Most of these drugs target fibrin (one of the main constituent of blood clots) and are therefore called fibrinolytics. All currently approved thrombolytic drugs are biologics, either derived from Streptococcus species, or, more recently, using recombinant biotechnology whereby tPA is manufactured using cell culture, resulting in a recombinant tissue plasminogen activator or rtPA. Some fibrinolytics are:

Catheter-directed thrombolysis

A 2023 meta-analysis of 44 studies compared treatments for pulmonary embolism including thrombolytic therapy delivered through a catheter. Catheter-directed thrombolysis (CDT) methods included fragmentation and ultrasound use. CDT was associated with better outcomes than anticoagulation alone or systemic thrombolysis, but the studies were mostly small and observational. In people who receive CDT, there is a risk of hemorrhage as a side effect. Scientists have studied whether measuring fibrinogen in blood can be used as a biomarker to predict hemorrhage. As of 2017 it was not known if this works or not.

Research

Researchers showed a 10-fold variation in the proportion of patients who received thrombolysis after stroke in England and Wales, ranging from 1 in 50 (2%) to 1 in 4 (24%). The team also showed that most of the variation was explained by hospital processes (such as how quickly people can have a brain scan) and in doctors’ decision-making (who they think should or should not receive thrombolysis) rather than knowledge of the time of stroke. Prospective, randomized clinical trials to evaluate the utility of catheter-directed thrombolysis in pulmonary embolism include HI-PEITHO (Higher-Risk Pulmonary Embolism Thrombolysis).