Tenecteplase for Stroke at 4.5 to 24 Hours with Perfusion-Imaging Selection (TIMELESS)
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In patients with ischemic stroke due to large-vessel occlusion presenting 4.5 to 24 hours after last known well, intravenous tenecteplase did not improve 90-day clinical outcomes compared to placebo, though it appeared safe without increasing symptomatic hemorrhage.
Key Findings
Study Design
Study Limitations
Clinical Significance
The TIMELESS trial demonstrated that administering tenecteplase between 4.5 and 24 hours after symptom onset to patients with large-vessel occlusions does not improve functional outcomes, particularly in modern systems where rapid endovascular thrombectomy is readily available. However, the lack of an increase in symptomatic intracranial hemorrhage suggests that late-window thrombolysis is biologically safe. Clinically, these findings indicate that routine 'bridging' tenecteplase should not be utilized for late-window patients presenting directly to thrombectomy-capable centers.
Historical Context
While intravenous thrombolysis is the standard of care for acute ischemic stroke within 4.5 hours, and endovascular thrombectomy (EVT) has proven highly efficacious up to 24 hours, the role of thrombolysis in the late window (4.5 to 24 hours) has been controversial. Prior trials (like EXTEND) showed a benefit for alteplase in the late window using perfusion imaging, but those studies largely predated routine, rapid access to EVT. Tenecteplase has increasingly replaced alteplase in the standard window due to its easier single-bolus administration and comparable or superior reperfusion rates. The TIMELESS trial sought to evaluate whether the pharmacokinetic advantages of tenecteplase could provide clinical benefit in late-window patients with salvageable tissue. Its negative primary outcome reflects a modern paradigm where mechanical reperfusion is so rapid and effective that adding a systemic lytic agent immediately prior to the procedure provides no incremental value for proximal occlusions.
Guided Discussion
High-yield insights from every perspective
How does the mechanism of action of tenecteplase differ from alteplase, and why is perfusion imaging crucial in selecting patients in the extended 4.5 to 24-hour window?
Key Response
Tenecteplase is a genetically modified variant of alteplase with higher fibrin specificity and a longer half-life, allowing single-bolus dosing. Perfusion imaging is vital in the extended window because it identifies the 'penumbra' (salvageable ischemic tissue) versus the 'core' (irreversibly infarcted tissue), demonstrating that tissue viability is dependent on collateral circulation rather than time alone.
Given the TIMELESS results, if you are admitting a patient with an MCA M1 occlusion 12 hours from last known well with a favorable perfusion mismatch who is planned for mechanical thrombectomy, should you administer IV tenecteplase prior to the procedure?
Key Response
Based on the TIMELESS trial, administering IV tenecteplase in this late-window LVO population does not improve 90-day clinical outcomes compared to placebo. Therefore, bridging with tenecteplase is not indicated; the patient should proceed directly to mechanical thrombectomy.
The TIMELESS trial showed no clinical benefit for tenecteplase in the extended window, yet the safety profile regarding symptomatic intracranial hemorrhage was similar to placebo. How might the high rate of concurrent endovascular therapy (EVT) in both arms have diluted the potential efficacy signal of tenecteplase, and does this leave room for its use in 'drip-and-ship' models?
Key Response
Over 75% of patients in TIMELESS underwent mechanical thrombectomy. The overwhelming efficacy of EVT likely creates a ceiling effect, masking any marginal benefit of early reperfusion from tenecteplase. Because tenecteplase proved safe, there remains an open question about its utility in non-EVT capable centers where transfer delays are expected, as early pharmacological reperfusion prior to transfer could still theoretically improve outcomes.
For years, the stroke community has pushed to expand the thrombolytic window, but TIMELESS halts this expansion for large vessel occlusions. How do we reconcile the safety of late-window tenecteplase with its lack of efficacy, and how does this reframe our institutional stroke protocols?
Key Response
The lack of efficacy despite safety suggests that once an LVO has persisted into the late window, the clot is likely too mature, organized, or large for pharmacological lysis alone to achieve meaningful reperfusion before EVT. Institutional protocols should focus purely on minimizing door-to-groin time for mechanical thrombectomy in late-window LVOs, rather than incorporating medical therapies that add cost and workflow complexity without proven benefit.
Scholarly Review
Critical appraisal through the lens of expert reviewers and guideline development
The TIMELESS trial utilized an ordinal shift analysis of the modified Rankin Scale as its primary efficacy endpoint. Considering the high proportion of patients receiving EVT, what statistical or design modifications could have better isolated the true treatment effect of tenecteplase?
Key Response
An ordinal shift analysis assumes proportional odds across all mRS transitions. Given the massive ceiling effect of EVT, an enrichment design targeting patients with expected EVT delays, evaluating a strictly non-EVT cohort, or powering the study to evaluate an interaction between EVT timing and tenecteplase administration might have better isolated tenecteplase's specific effect size and mitigated the dilution from thrombectomy.
As a reviewer, how does the early termination of enrollment combined with the extraordinarily high rate of mechanical thrombectomy threaten the internal validity and statistical power of the TIMELESS trial's null finding?
Key Response
Early termination inherently reduces statistical power, increasing the risk of a Type II error. When combined with massive EVT utilization, the trial effectively became a 'bridging therapy' study rather than a pure 'lytic vs. no lytic' study. Reviewers must heavily scrutinize the confidence intervals to determine if they truly exclude a clinically meaningful benefit, particularly in the underpowered non-EVT subgroup.
Current AHA/ASA guidelines strongly recommend EVT for LVOs in the 6-24 hour window with favorable imaging but restrict IV thrombolysis to the under 4.5-hour window. Does the TIMELESS trial provide sufficient evidence to formally recommend against the use of IV tenecteplase as an adjunct to EVT in the 4.5-24 hour window?
Key Response
Yes. TIMELESS provides high-quality, randomized controlled trial evidence that adding tenecteplase to standard care in the 4.5-24 hour window yields no clinical benefit for LVOs. Therefore, guidelines should maintain the 4.5-hour strict cutoff for IV thrombolysis and explicitly state that late-window bridging with tenecteplase is not recommended, solidifying direct-to-EVT pathways to avoid unnecessary interventions.
Clinical Landscape
Noteworthy Related Trials
WAKE-UP Trial
Tested
Alteplase (0.9 mg/kg)
Population
Acute ischemic stroke patients with unknown time of onset and MRI DW-FLAIR mismatch
Comparator
Placebo
Endpoint
Favorable outcome (mRS 0-1) at 90 days
EXTEND-IA TNK Trial
Tested
Tenecteplase (0.25 mg/kg)
Population
Ischemic stroke patients with large vessel occlusion scheduled for thrombectomy within 4.5 hours
Comparator
Alteplase (0.9 mg/kg)
Endpoint
Substantial reperfusion at initial angiographic assessment
EXTEND Trial
Tested
Alteplase (0.9 mg/kg)
Population
Ischemic stroke patients 4.5 to 9 hours after onset or wake-up stroke with salvageable brain tissue
Comparator
Placebo
Endpoint
Excellent functional outcome (mRS 0-1) at 90 days
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