In the early phase of development of tissue plasminogen activator for stroke in the United States, there were 9 placebo-controlled trials. Functional recovery was more frequent in the tissue plasminogen activator group than in the placebo group when treatment was started within the first 3 hours, but there was no survival benefit. The positive effects of tissue plasminogen activator on all outcome measures were not affected by age, severity of stroke, use of aspirin before onset of stroke, or baseline classification of stroke type. The National Institutes of Neurological Disorders and Stroke trial showed statistically significant results in combined 4 end points: National Institute of Health Stroke Scale, Modified Rankin Scale, Barthel Index, and Glasgow Outcome Scale; and mortality was lower in the tissue plasminogen activator-treated group (04). There was a higher incidence of intracerebral hemorrhage in patients treated with tissue plasminogen activator, but there was improvement in clinical outcome at 3 months in patients treated with a dose of 0.9 mg/kg within 3 hours of onset of stroke.
The European perspective is based on the results of the intent-to-treat analysis of the European Cooperative Acute Stroke Study trial in which tissue plasminogen activator was used within a 6-hour time window and no statistically significant benefit for tissue plasminogen activator-treated patients was seen in the primary end points: Modified Rankin Scale and the Barthel Index (14). However, in the target population analysis 1 primary end point (Modified Rankin Scale) and all secondary end points, except for mortality, were statistically significantly better for the tissue plasminogen activator-treated patients. This led to the reluctance of European neurologists to support broader use of tissue plasminogen activator, but for a subset of patients without early signs of infarction on CT scan. In a reassessment of tissue plasminogen activator in acute ischemic stroke (European Cooperative Acute Stroke Study II), the European investigators did not confirm a statistical benefit for thrombolysis within 6 hours of stroke onset, although it was felt that there was a clinically relevant improvement in selected patients (16). Secondary analysis of European Cooperative Acute Stroke Study data by time stratification, however, support the efficacy of early thrombolytic therapy in acute hemispheric stroke (40).
A prospective, multicenter, single-arm, open-label trial was conducted in Japanese patients using different doses of tissue plasminogen activator (51). Results showed that tissue plasminogen activator, when administered at 0.6 mg/kg to Japanese patients, provides clinical efficacy and safety comparable to that reported in patients in North America and the European Union for a 0.9 mg/kg dose.
Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST) has shown that intravenous tissue plasminogen activator is safe and effective in routine clinical use when used within 3 hours of stroke onset, even by centers with little previous experience of thrombolytic therapy for acute stroke (45). In a randomized, double-blind study, intravenous tissue plasminogen activator administered between 3 and 4.5 hours after the onset of symptoms significantly improved clinical outcomes in patients with acute ischemic stroke as compared to placebo, but it was more frequently associated with symptomatic intracranial hemorrhage (15).
Results of the RECANALISE study--a prospective cohort study in patients with stroke and confirmed arterial occlusion--showed that a combined intravenous-endovascular approach is associated with higher recanalization rates than is intravenous tissue plasminogen activator in patients with stroke and confirmed arterial occlusion (29).
Results of the European Cooperative Acute Stroke Study III (ECASS III) support the use of tissue plasminogen activator up to 4.5 hours after the onset of stroke symptoms across a broad range of subgroups of patients who meet the requirements of the European product label but miss the approved treatment window of 0 to 3 hours (06).
An updated pooled analysis of ECASS, ATLANTIS, NINDS, and EPITHET trials show that patients with ischemic stroke benefit from intravenous tissue plasminogen activator when treated up to 4.5 hours from onset (24).
An exploratory analysis of patients enrolled in the Japan Alteplase Clinical Trial II (J-ACT II) with unilateral occlusion of the middle cerebral artery showed that a residual vessel length less than 5 mm on magnetic resonance angiography can identify poor responders to tissue plasminogen activator (18).
A randomized open-label trial showed that early administration of intravenous aspirin in patients with acute ischemic stroke treated with tissue plasminogen activator does not improve outcome at 3 months and increases the risk of intracerebral hemorrhage (52). These results do not support a change of the current guidelines for starting antiplatelet therapy 24 hours after administration of tissue plasminogen activator.
In an open-label, international, multicenter, randomized trial, patients with ischemic stroke were randomly allocated within 6 hours of onset to either intravenous tissue plasminogen activator plus standard care or standard care alone (20). Results showed that intravenous tissue plasminogen activator did not affect survival in acute ischemic stroke but did lead to statistically significant and clinically relevant improvements in functional outcome that were sustained for at least 18 months. A randomized clinical trial showed similar safety outcomes and no significant difference in functional independence with endovascular therapy after intravenous tissue plasminogen activator, as compared with intravenous tissue plasminogen activator alone (08).
A randomized trial has shown that tenecteplase is associated with significantly better reperfusion and clinical outcomes than alteplase in patients with stroke who were selected on the basis of CT perfusion imaging (33). In a phase 2 randomized trial, administration of tenecteplase prior to thrombectomy was associated with a higher incidence of reperfusion and better functional outcome than alteplase in patients with ischemic stroke treated within 4.5 hours after symptom onset (10). In a phase 3 trial that enrolled mainly patients with mild stroke who were not expected to have thrombectomy, the superiority of tenecteplase was not shown at a dose of 0.4 mg per kilogram, as compared with conventional doses of alteplase (25). Ongoing trials involving patients with stroke who are not expected to proceed to thrombectomy include TASTE (Tenecteplase vs. Alteplase for Stroke Thrombolysis Evaluation; Australian New Zealand Clinical Trials Registry number, ACTRN12613000243718) and ATTEST2 (Alteplase-Tenecteplase Trial Evaluation for Stroke Thrombolysis; ClinicalTrials.gov number, NCT02814409).
Concluding remarks on clinical trials. A review of various trials of thrombolytic therapy shows that intravenous thrombolytic therapy for ischemic stroke using tissue plasminogen activator and a "therapeutic window" treatment time of 3 hours is still the best available approach to improve the clinical outcome safely as there is still some concern about hemorrhagic complications beyond the 3-hour window. However, a European study has shown that there was no increase in hemorrhagic complications when the window was extended to 4.5 hours, and in 1 trial even to 6 hours.
More than 2 decades since the publication of the landmark National Institute of Neurological Disorders and Stroke trials, the efficacy as well as safety of intravenous tissue plasminogen activator has been consistently verified in international real-world clinical practice (13). Although tissue plasminogen activator has considerably improved stroke outcomes, skeptics still challenge the reliability of the evidence, and it is not a universal therapy as only to 5% to 10% of patients with acute stroke receive it (37). A meta-analysis of clinical trials in patients receiving intravenous tissue plasminogen activator shows that thrombectomy with a stent retriever versus tissue plasminogen activator alone is associated with significant improvement of functional independence 90 days after for acute ischemic stroke (43). The study “Perfusion Imaging Selection of Ischemic Stroke Patients for Endovascular Therapy (POSITIVE) Stroke Trial” started to investigate thrombectomy versus best medical treatment (in patients ineligible for thrombolysis) for stroke within 6 to 12 hours of onset but was stopped because of the clearly better results with thrombectomy in this as well as other similar trials (NCT01852201). Trial recruitment is currently suspended. Published results of the POSITIVE trial support the already established practice of delayed thrombectomy for appropriately selected patients presenting within 0 to 12 hours selected by perfusion imaging from any vendor (30).
Results of the Extending the Time for Thrombolysis in Emergency Neurological Deficits (EXTEND) trial, in which patients with specific imaging features were randomly assigned to receive standard doses of intravenous alteplase or placebo between 4.5 and 9 hours after the onset of stroke, revealed the likelihood of a good outcome (a score of 0 or 1 on the modified Rankin scale at 90 days) was 44% higher in the alteplase group than in the placebo group, although the study was terminated after only two thirds of the intended population were enrolled (27). The success of this trial is attributable to an image-guided approach to patient selection that had already brought success to mechanical thrombectomy performed many hours after the onset of stroke symptoms. Patients were eligible for the EXTEND trial if they had a mismatch between the core volume of infarction and the volume of potentially salvageable brain tissue in the ischemic penumbra. This trial represents a major successful step in using an image-guided approach to extend the seemingly immutable time limit for pharmacologic thrombolysis in patients with acute stroke (28).
As of March 2021, 162 clinical trials mentioning tissue plasminogen activator are listed on the U.S. Government web site for clinical trials:https://clinicaltrials.gov/ct2/results?cond=Acute+Stroke%2C+Ischemic&term=tissue+plasminogen+activator&cntry=&state=&city=&dist=&Search=Search.
These included completed and discontinued trials including combination of other treatments with tissue plasminogen activator.