Understanding the role of tPA in ischemic stroke
Tissue plasminogen activator (tPA) is a potent thrombolytic drug used to dissolve blood clots that cause ischemic strokes. Restoring blood flow to the brain quickly can limit damage. Because of the risk of complications, particularly brain hemorrhage, tPA is not suitable for all stroke patients and requires rapid medical evaluation.
The crucial time windows for tPA administration
The effectiveness of tPA is strongly tied to prompt administration. The optimal window for alteplase, initially approved by the FDA, is within 3 hours of symptom onset. In select cases, this can be extended to 4.5 hours, though with additional exclusion criteria. For strokes where the onset time is unknown (like 'wake-up' strokes), the 'last known well' time is used, and advanced imaging may help identify candidates within 4.5 hours if brain tissue might be saved.
The screening process: Rule out bleeding and confirm eligibility
A rapid non-contrast CT scan is a critical first step to distinguish between an ischemic stroke and a hemorrhagic stroke. Giving tPA to a patient with a brain bleed can be dangerous. Eligibility criteria for tPA include confirmed ischemic stroke, a measurable neurological deficit, and treatment initiation within the specified timeframes.
Contraindications: When tPA cannot be used
Absolute contraindications mean tPA is not safe due to a high risk of bleeding. These include evidence of hemorrhagic stroke on a CT scan, recent surgery or trauma, a history of intracranial bleeding, uncontrolled high blood pressure (above 185/110 mmHg), and active bleeding or a bleeding disorder. Relative contraindications also require careful consideration.
A new option: Tenecteplase vs. Alteplase
While alteplase (Activase®) has been the standard for decades, tenecteplase (TNKase®) is a recently approved alternative for acute ischemic stroke.
| Feature | Alteplase (Activase®) | Tenecteplase (TNKase®) |
|---|---|---|
| Mechanism | Binds to fibrin and converts plasminogen to plasmin. | Modified alteplase with longer half-life and higher fibrin specificity. |
| Administration | Requires an IV bolus and a 60-minute infusion. | Given as a single, rapid IV bolus. |
| Time Window | Approved within 3 hours, up to 4.5 in select cases. | Approved within 3 hours. |
| Reperfusion Rate | Standard, effective with proper timing. | May lead to higher reperfusion rates, especially before thrombectomy. |
| Ease of Use | Involves a longer, controlled infusion. | Simpler and faster single bolus administration. |
Combining tPA with mechanical thrombectomy
For patients with a large vessel occlusion, tPA can be used together with mechanical thrombectomy, a procedure to physically remove the clot. Thrombectomy has a longer treatment window and is often used for larger clots. When combined, tPA is typically given first.
Weighing the risks and benefits of tPA
In appropriate patients, tPA can significantly reduce long-term disability. The primary risk is intracranial hemorrhage, occurring in about 6% of treated patients. This risk is carefully evaluated against the potential benefits of restoring blood flow. Less common side effects include other bleeding or allergic reactions.
Conclusion
Deciding when tPA can be used for stroke involves time-sensitive medical assessment. Immediate emergency transport to a stroke-equipped hospital is crucial for anyone with stroke symptoms. Rapid assessment is needed to differentiate stroke types and adhere to the narrow treatment window. While not suitable for everyone, tPA remains a vital therapy that can improve recovery and reduce long-term disability for eligible patients treated promptly after an ischemic stroke.
This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional for diagnosis and treatment. For more comprehensive information on stroke guidelines, refer to the {Link: American Heart Association/American Stroke Association https://www.stroke.org/}.
