Thrombolysis is the breakdown (lysis) of blood clots formed in blood vessels, using medication. It is used in ST elevation myocardial infarction, stroke, and very large pulmonary embolisms.
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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:
Apart from streptokinase, all thrombolytic drugs are administered together with heparin (unfractionated or low molecular weight heparin), usually for 24 to 48 hours.
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. As such, the prehospital practitioner will often consult with the receiving cardiologist as to treatment decisions—many cardiologists have personal preferences to available treatment options.
Contraindications
There are absolute and relative contraindications to thrombolysis.
Absolute
Previous intracranial bleeding at any time, stroke in less than 6 months, closed head or facial trauma within 3 months, suspected aortic dissection, ischemic stroke within 3 months (except in ischemic stroke within 3 hours time), active bleeding diathesis, uncontrolled high blood pressure (>180 systolic or >100 diastolic), known structural cerebral vascular lesion, arterio-venous malformations, thrombocytopenia, known coagulation disorders, aneurysm, brain tumors, pericardial effusion, septic embolus.
Relative
Current anticoagulant use, invasive or surgical procedure in the last 2 weeks, prolonged cardiopulmonary resuscitation (CPR) defined as more than 10 minutes, known bleeding diathesis, pregnancy, hemorrhagic or diabetic retinopathies, active peptic ulcer, controlled severe hypertension.
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. These drugs are either derived from Streptococcus species, or, more recently, using recombinant biotechnology whereby tPA is manufactured by bacteria, resulting in a recombinant tissue plasminogen activator or rtPA.
Some thrombolytics are:
Research
In people who receive thrombolytic therapy delivered through a catheter, 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.