Tenecteplase for Stroke at 4.5 to 24 Hours with Perfusion-Imaging Selection (TIMELESS)
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The TIMELESS trial demonstrated that administration of tenecteplase between 4.5 and 24 hours after stroke onset in patients with large-vessel occlusions and salvageable tissue did not improve functional outcomes at 90 days compared with placebo, despite demonstrating a favorable safety profile.
Key Findings
Study Design
Study Limitations
Clinical Significance
The study suggests that while tenecteplase is safe to administer within an extended 4.5 to 24-hour window in patients selected with advanced imaging, it does not provide additional functional benefit for patients undergoing standard-of-care mechanical thrombectomy, arguing against routine use of thrombolytics in this specific late-window population.
Historical Context
Following the success of DAWN and DEFUSE 3 in expanding the thrombectomy window to 24 hours based on perfusion mismatch, the stroke community sought to determine if pharmacological thrombolysis (specifically tenecteplase, preferred for its pharmacokinetics over alteplase) could provide further benefit as an adjunct therapy in this late window, a hypothesis that TIMELESS investigated but failed to confirm.
Guided Discussion
High-yield insights from every perspective
Why is perfusion imaging (CTP/MRI) preferred over non-contrast CT for selecting patients in the 4.5 to 24-hour 'late window' for stroke therapy?
Key Response
The traditional 4.5-hour window is based on a 'time clock,' assuming tissue death follows a standard timeline. However, the 'tissue clock' varies per patient; perfusion imaging identifies the ischemic penumbra (salvageable tissue) vs. the infarct core. In the late window, clinicians only treat those with a 'mismatch' (small core, large penumbra), as seen in TIMELESS, to ensure there is actually tissue left to save.
In a patient presenting 12 hours after stroke onset with an internal carotid artery occlusion and favorable perfusion imaging, should tenecteplase be administered prior to endovascular thrombectomy (EVT) based on the TIMELESS results?
Key Response
No. The TIMELESS trial showed that tenecteplase (0.25 mg/kg) was not superior to placebo in improving 90-day functional outcomes (mRS 0-2) in this late window. Since 77% of patients in both arms received EVT, the primary standard of care for these patients remains immediate thrombectomy according to DAWN and DEFUSE-3 criteria, without the addition of late-window thrombolysis.
How do the results of TIMELESS compare to the EXTEND trial regarding late-window thrombolysis, and what might explain the discrepancy in efficacy findings?
Key Response
EXTEND showed benefit for alteplase in the 4.5-9 hour window using perfusion selection, whereas TIMELESS (4.5-24h) was neutral for tenecteplase. Discrepancies may be due to: 1) The 'treatment dilution' effect, as TIMELESS had a very high rate of EVT which likely masked the benefit of thrombolysis; 2) The extended 24-hour window in TIMELESS vs the 9-hour window in EXTEND; and 3) TIMELESS specifically targeted large vessel occlusions (LVOs) which are often resistant to thrombolysis alone.
Does the safety profile of tenecteplase observed in TIMELESS justify its use in 'drip-and-ship' scenarios where a patient is at a primary stroke center and faces a multi-hour delay before EVT can be performed?
Key Response
While TIMELESS was neutral for efficacy, it proved that tenecteplase did not increase the risk of symptomatic intracranial hemorrhage (sICH) or death in the late window. In practice-changing terms, if EVT is significantly delayed, the safety data might tempt clinicians to use it, but because efficacy was not established, it cannot currently be recommended as a standard of care. It highlights the need for further trials specifically targeting the 'drip-and-ship' population where EVT is not immediately available.
Scholarly Review
Critical appraisal through the lens of expert reviewers and guideline development
Critique the statistical power and endpoint selection in TIMELESS: How did the high rate of rescue endovascular therapy (EVT) in both arms act as a confounding variable in detecting the treatment effect of tenecteplase?
Key Response
The trial was powered to detect a 10% difference in the primary endpoint (mRS 0-2). However, because 77.3% of the tenecteplase group and 77.3% of the placebo group underwent EVT—a highly effective treatment—the potential marginal benefit of tenecteplase was likely 'washed out.' This is a classic problem in modern stroke trials where the 'standard of care' (EVT) is so powerful that adjunctive therapies require much larger sample sizes or more specific patient selection to reach statistical significance.
As a reviewer, how would you evaluate the external validity of the TIMELESS results given that the median time from last known well to randomization was approximately 12.5 hours?
Key Response
A critical reviewer would note that while the window extended to 24 hours, the majority of patients were enrolled in the 'early' part of the late window. This leaves the 18-24 hour window under-represented. Furthermore, because the trial only included patients with LVOs (ICA or MCA-M1/M2), the results cannot be generalized to patients with distal occlusions or those with salvageable tissue who are not candidates for EVT.
Based on the TIMELESS evidence, should the AHA/ASA guidelines be updated to include tenecteplase for the 4.5-24 hour window? Compare this to current recommendations for EVT.
Key Response
Currently, AHA/ASA guidelines give a Class I recommendation for EVT in the 6-24 hour window (DAWN/DEFUSE-3). Based on TIMELESS, there is insufficient evidence to support a recommendation for tenecteplase in this window. The committee would likely issue a 'Class No Benefit' or a 'Class IIb' recommendation at best, emphasizing that thrombolysis should not delay EVT and is not a substitute for it in the 4.5-24 hour period for LVO patients.
Clinical Landscape
Noteworthy Related Trials
DAWN Trial
Tested
Mechanical thrombectomy
Population
Patients with acute ischemic stroke 6 to 24 hours after last known well
Comparator
Standard medical care
Endpoint
Degree of disability (utility-weighted modified Rankin Scale score)
DEFUSE 3 Trial
Tested
Mechanical thrombectomy
Population
Patients with ischemic stroke 6 to 16 hours after last known well with target mismatch profile
Comparator
Standard medical care
Endpoint
Modified Rankin Scale score of 0-2 at 90 days
EXTEND Trial
Tested
Alteplase
Population
Ischemic stroke patients 4.5 to 9 hours after onset or wake-up stroke
Comparator
Placebo
Endpoint
Modified Rankin Scale score of 0-1 at 90 days
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