Stroke Etiology Does Not Alter Bridging Thrombolysis Efficacy

Refining Reperfusion Strategies in Large Vessel Occlusion

Mechanical thrombectomy is the established standard for treating acute ischemic stroke caused by large vessel occlusion, significantly improving functional independence compared to medical management alone [1, 2]. However, the clinical utility of administering intravenous thrombolysis (the use of pharmacological agents to dissolve a clot) before the procedure remains a subject of active debate, particularly for patients presenting directly to specialized centers [3, 4]. While bridging therapy may facilitate early recanalization, it also carries a potential risk of symptomatic intracranial hemorrhage (bleeding within the skull that is associated with clinical deterioration) [5, 6]. Current guidelines generally support the use of thrombolytics in eligible patients, yet there is uncertainty regarding whether the underlying mechanism of the stroke influences these outcomes [7, 8]. A new individual participant data meta-analysis (a high-level statistical synthesis that combines raw data from every person in multiple studies) now examines how specific stroke etiologies affect the risk-benefit profile of this combined approach. Pooled results from 2,313 patients across six randomized trials suggest that while thrombectomy alone is non-inferior at a -10% margin, it fails to meet a more stringent -5% non-inferiority threshold for functional independence (modified Rankin Scale 0-2) at 90 days [4].

Meta-Analysis Design and Patient Demographics

To clarify the impact of stroke origin on treatment success, researchers conducted an individual participant data meta-analysis of six randomized controlled trials. This high-level statistical approach, which involves pooling raw data from every individual enrolled across multiple studies rather than just comparing their final results, allowed for a more granular assessment of how intravenous thrombolysis (IVT) plus endovascular treatment (EVT) compares to EVT alone. The analysis focused specifically on patients with acute ischemic stroke caused by a large vessel occlusion who presented directly to centers capable of performing mechanical thrombectomy. To be eligible for inclusion, patients had to be eligible for treatment within 4.5 hours of stroke onset or the time they were last known to be well. This time window is critical for clinicians, as the efficacy of thrombolytic agents is highly time-dependent, and the risk of hemorrhagic transformation increases as the ischemic penumbra (the salvageable brain tissue surrounding the core infarct) diminishes.

The total eligible population for this meta-analysis consisted of 2,313 patients, providing a robust sample size for evaluating treatment effect heterogeneity. Within this cohort, 1,160 patients were randomized to receive bridging therapy (IVT plus EVT), while 1,153 patients were randomized to the EVT alone group. The study population reflected a typical clinical demographic for acute stroke, with a median age of 71 years (interquartile range [IQR] = 62 to 78 years). Women represented 44.3% of the total participants. By aggregating data from these six trials, the researchers sought to determine if the underlying cause of the occlusion, such as a clot originating in the heart or a blockage caused by local plaque buildup, altered the efficacy of pharmacological thrombolysis administered prior to mechanical clot retrieval.

Etiological Classification and Statistical Modeling

The researchers categorized the underlying causes of stroke to determine if the mechanism of occlusion influenced the response to bridging therapy. Among the 2,313 patients included in the analysis, stroke etiology was classified as cardioembolism in 977 patients (42%), representing the largest subgroup. Furthermore, large artery atherosclerosis was identified as the cause in 430 of the 2,313 patients (19%), while the remaining 906 patients (39%) were classified as having other or unknown/undetermined etiologies. This distribution allowed the investigators to evaluate whether thrombolytic agents are more or less effective against different clot compositions, such as the fibrin-rich clots typically associated with cardiac sources versus the platelet-rich clots often found in atherosclerotic disease. Understanding these differences is vital for the clinician, as clot composition can significantly impact the ease of mechanical retrieval and the likelihood of distal embolization during the procedure.

To evaluate whether these etiologies modified the impact of treatment, the researchers employed ordinal logistic regression models with interaction terms for stroke etiology and treatment within the intention-to-treat population. This statistical method ranks clinical outcomes, such as levels of disability on the modified Rankin Scale, to determine if the relationship between the intervention and the outcome changes based on a specific variable like the cause of the stroke. Following this, the authors conducted a subsequent mixed-effects meta-analysis, a technique that accounts for both the variation within individual studies and the variation between different studies to provide a more precise estimate of the treatment effect across the entire cohort. This approach ensures that the findings are not skewed by the specific protocols or patient populations of a single trial.

Beyond the broad etiological categories, the study included an additional analysis to assess whether the treatment effect of intravenous thrombolysis plus endovascular treatment differed by atrial fibrillation status. Atrial fibrillation, a common heart rhythm disorder and a primary driver of cardioembolic strokes, often results in distinct clot morphologies that may respond differently to pharmacological intervention. By isolating this factor, the researchers aimed to ensure that the presence of this specific arrhythmia did not create a hidden variance in how patients responded to pre-thrombectomy thrombolysis, further clarifying whether the standard of care should be tailored to the patient's cardiac history.

Consistent Outcomes Across Stroke Subtypes

The primary analysis focused on whether the underlying cause of a stroke influenced the clinical success of bridging therapy. The researchers found no evidence of treatment effect modification by stroke etiologies on the association between intravenous thrombolysis and 90-day functional outcome (P for interaction = 0.60). In clinical terms, treatment effect modification occurs when the impact of an intervention, such as thrombolysis, changes based on another variable, like the mechanism of the occlusion. This finding indicates that the functional benefit of administering thrombolysis before thrombectomy remained stable regardless of whether the patient suffered from cardioembolism, large artery atherosclerosis, or other undetermined causes. For the subgroup of patients with other or undetermined stroke etiology, the combination of intravenous thrombolysis and endovascular treatment was associated with a better 90-day functional prognosis, yielding an adjusted common odds ratio for a lower level of disability of 1.34 (95% confidence interval [CI], 1.05 to 1.69).

Safety profiles remained similarly uniform across the different etiological groups. The study reported that no treatment effect modification by stroke etiology was found for safety outcomes, suggesting that the risk of complications, such as intracranial hemorrhage, does not increase disproportionately in one etiological subgroup over another when bridging therapy is used. Furthermore, the investigators examined the specific influence of atrial fibrillation, a common source of cardiac emboli. Their analysis confirmed that no treatment effect heterogeneity by atrial fibrillation was found for all outcomes. Treatment effect heterogeneity refers to the variation in how different individuals or subgroups respond to the same medical intervention. The lack of such heterogeneity suggests that the presence or absence of this arrhythmia should not dictate the decision to use pre-thrombectomy thrombolysis.

Ultimately, the study concluded that stroke etiologies do not modify the overall efficacy or safety of intravenous thrombolysis before endovascular treatment in patients presenting directly to centers capable of performing mechanical thrombectomy. For the practicing clinician, these results suggest that the etiological workup, while critical for long-term secondary prevention, does not need to be a deciding factor in the acute administration of thrombolytic agents prior to clot retrieval. The data support a consistent approach to bridging therapy across the major ischemic stroke subtypes, ensuring that treatment decisions in the hyperacute window can proceed without the need for prior knowledge of the specific embolic or atherosclerotic source.

Potential Benefit in Undetermined Etiologies

While the primary analysis demonstrated a uniform treatment effect across the major stroke categories, a specific subgroup analysis identified a distinct advantage for a particular patient population. For patients with other or undetermined stroke etiology, intravenous thrombolysis plus endovascular treatment was associated with better 90-day functional prognosis. This finding was supported by an adjusted common odds ratio (aCOR) for a lower level of disability of 1.34 (95% confidence interval [CI] = 1.05 to 1.69). The adjusted common odds ratio is a statistical measure used to estimate the likelihood of achieving a better outcome on a multi-level scale, such as the modified Rankin Scale, after accounting for baseline variables. In this context, it suggests that patients with less common or unknown stroke mechanisms may derive a more pronounced benefit from receiving thrombolytic agents before mechanical clot retrieval.

Despite the statistical significance of this finding within the other or undetermined subgroup, the researchers maintain a cautious clinical interpretation. The authors noted that this isolated benefit observed in the other or undetermined subgroup requires confirmation through further prospective study. Because this result emerged from a subgroup analysis rather than the primary study population, it does not yet warrant a shift in the broader clinical consensus or a change in standard protocols for patients with known cardioembolic or atherosclerotic sources. For the practicing clinician, these data reinforce the utility of bridging therapy in the acute setting, particularly when the underlying cause of the large vessel occlusion is not immediately apparent during the initial presentation. This provides reassurance that the standard of care remains effective even when the diagnostic picture is incomplete at the time of arrival.

References

1. Berkhemer OA, Fransen P, Beumer D, et al. A Randomized Trial of Intraarterial Treatment for Acute Ischemic Stroke. New England Journal of Medicine. 2014. doi:10.1056/nejmoa1411587

2. Balami JS, Sutherland BA, Edmunds LD, et al. A systematic review and meta-analysis of randomized controlled trials of endovascular thrombectomy compared with best medical treatment for acute ischemic stroke.. International journal of stroke : official journal of the International Stroke Society. 2015. doi:10.1111/ijs.12618

3. Wang X, Ye Z, Busse JW, et al. Endovascular thrombectomy with or without intravenous alteplase for acute ischemic stroke due to large vessel occlusion: a systematic review and meta-analysis of randomized trials.. Stroke and vascular neurology. 2022. doi:10.1136/svn-2022-001547

4. Horvath LC, Bergmann F, Hosmann A, et al. Endovascular thrombectomy with or without intravenous thrombolysis in large-vessel ischemic stroke: A non-inferiority meta-analysis of 6 randomised controlled trials.. Vascular pharmacology. 2023. doi:10.1016/j.vph.2023.107177

5. Lin C, Saver JL, Ovbiagele B, Huang W, Lee M. Endovascular thrombectomy without versus with intravenous thrombolysis in acute ischemic stroke: a non-inferiority meta-analysis of randomized clinical trials.. Journal of neurointerventional surgery. 2022. doi:10.1136/neurintsurg-2021-017667

6. Zhang J, Yuan C, Deng X, et al. Efficacy and safety of endovascular treatment with or without intravenous alteplase in acute anterior circulation large vessel occlusion stroke: a meta-analysis of randomized controlled trials.. Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology. 2022. doi:10.1007/s10072-022-06017-8

7. Majoie CB, Cavalcante F, Gralla J, et al. Value of intravenous thrombolysis in endovascular treatment for large-vessel anterior circulation stroke: individual participant data meta-analysis of six randomised trials. The Lancet. 2023. doi:10.1016/s0140-6736(23)01142-x

8. Tan C, Wang H, Ji J, Tan M, Tan L, Yu J. Endovascular Treatment Versus Intravenous Thrombolysis for Acute Ischemic Stroke: a Quantitative Review and Meta-Analysis of 21 Randomized Trials.. Molecular neurobiology. 2017. doi:10.1007/s12035-016-9738-0