Thrombolysis

Thrombolysis is a medical therapy aimed at dissolving pathological clots that obstruct blood vessels. It works by activating plasminogen to form plasmin, an enzyme that degrades fibrin, the structural mesh of clots. This results in fibrinolysis, restoring blood flow to affected tissues. Thrombolysis can be delivered systemically through intravenous infusion or locally via catheter-directed administration to a specific vessel.

Common thrombolytic agents include recombinant tissue plasminogen activator (tPA) such as alteplase, as well as newer agents like tenecteplase and reteplase. Streptokinase, once widely used, is less common today due to antigenicity and availability of safer alternatives. Dosing and regimens depend on the clinical indication and route of administration.

Indications include acute ischemic stroke within a defined time window, typically up to 4.5 hours from onset for alteplase in eligible patients; acute ST-segment elevation myocardial infarction within a broader time window; and hemodynamically significant massive pulmonary embolism. Catheter-directed thrombolysis may be used for selective, localized clot dissolution with often lower systemic doses.

Contraindications are substantial and include active major bleeding, known intracranial hemorrhage, recent intracranial surgery or head trauma, known structural cerebrovascular abnormality, and markedly uncontrolled hypertension, among others. Relative contraindications exist as well, such as pregnancy or recent surgery, requiring careful risk–benefit assessment.

Risks include major bleeding and intracranial hemorrhage, allergic reactions with certain agents, and potential hemorrhagic transformation of an ischemic stroke. Efficacy varies with the clinical scenario; in some settings, mechanical thrombectomy may be used in combination with thrombolysis or as an alternative. Careful patient selection and monitoring are essential.