Stroke Thrombectomy Alone Fails Noninferiority to Bridging tPA
In large-vessel occlusion stroke, results of a randomized trial failed to show noninferiority of direct mechanical thrombectomy using the Solitaire device to the combination of intravenous (IV) thrombolysis plus mechanical thrombectomy.
In the prospective, multicenter trial, the rate of good functional outcome was 57% for patients who underwent direct thrombectomy and 65% among patients who received IV thrombolysis before undergoing thrombectomy. This result failed to demonstrate noninferiority of direct mechanical thrombectomy compared to combination therapy, the researchers conclude.
“Good outcome was high in both treatment arms, with the point estimate in favor of the bridging cohort,” said lead investigator Urs Fischer, MD, co-chair of the stroke center at Inselspital, Bern University Hospital, in Bern, Switzerland, during his presentation. “Postinterventional reperfusion was very high in both treatment arms and higher in patients with bridging thrombolysis, compared to direct mechanical thrombectomy.”
The findings were presented at the virtual 13th World Stroke Congress (WSC) 2021.
Two Views of Thrombolysis
The value of bridging thrombolysis for patients who undergo mechanical thrombectomy is a matter of debate. One argument is that, for patients with large-vessel occlusion, IV thrombolysis may improve reperfusion before and after thrombectomy and yield better clinical outcomes. The opposing argument is that bridging thrombolysis may increase the risk for distal emboli, delay mechanical thrombectomy, and increase the rate of hemorrhage.
The researchers conducted the SWIFT DIRECT trial to investigate this question. They enrolled patients with acute ischemic stroke due to occlusion of the internal carotid artery or the M1 segment of the middle cerebral artery.
The trial was conducted at 48 sites in seven European countries and Canada. The investigators randomly assigned patients to receive IV alteplase (0.9 mg/kg) plus mechanical thrombectomy with the Solitaire device or to receive direct mechanical thrombectomy with the same device. Treatment was open label, but the assessment of endpoints was blinded.
Investigators assigned 423 patients to treatment, and 408 were included in the full analysis set. Of this group, 201 participants received direct mechanical thrombectomy, and 207 received IV thrombolysis plus thrombectomy. There were three crossovers in each treatment arm.
The primary outcome was functional independence, defined as a Modified Rankin Scale (mRS) score of 0–2, at 90 days. Secondary outcomes included mortality at 90 days, mRS shift, change in National Institutes of Health Stroke Scale (NIHSS) score at 24 hours, successful reperfusion, and symptomatic and asymptomatic intracranial hemorrhage (ICH).
Noninferiority Not Demonstrated
At baseline, patient characteristics were well balanced between the treatment groups. The median age of the patients was 72 years, and about 50% of participants were women. The median NIHSS score was 17 in both arms.
Approximately 57% of patients who underwent direct thrombectomy and 65% of those who received IV thrombolysis plus thrombectomy were functionally independent at 90 days, the primary outcome.
In addition, the researchers found no difference in mRS shift, mortality at 90 days, or change in NIHSS score at 24 hours. Postinterventional reperfusion was very high in both arms and was higher in patients who received IV tissue plasminogen activator, compared with those who received direct mechanical thrombectomy, said Fischer.
The rate of successful postinterventional reperfusion, however, was higher among patients who received thrombolysis than among those who underwent direct thrombectomy. The rate of symptomatic ICH was 1.5% in the direct thrombectomy group and 4.9% in the thrombolysis-plus-thrombectomy group.
New Endpoints Needed?
The investigators used noninferiority margins of 12%. “This question about the noninferiority margins, that’s a very tricky and difficult one in randomized clinical trials,” said Fischer. The investigators defined their margin using the 2015 HERMES data because no trials had yet compared direct mechanical thrombectomy and bridging thrombolysis at the time.
The researchers are performing a pooled analysis of all the trials that compared bridging thrombolysis with direct mechanical thrombectomy. “We are therefore looking at several margins, and I think this is the way we should look at these noninferiority margins,” said Fischer. “There’s not a clear-cut level which you can define.”
Dr Kevin Sheth
Enrollment in the trial was well balanced with respect to gender, which is not always the case in stroke studies, said Kevin Sheth, MD, professor of neurology and neurosurgery at Yale School of Medicine, in New Haven, Connecticut, who commented on the study for Medscape Medical News.
The findings indicate that the likelihood of there being a difference between groups on this question is low, said Sheth. Both groups had large-vessel occlusion, both received thrombectomy, and both achieved reperfusion. But the higher rate of successful reperfusion in the bridging cohort was not reflected in any of the clinical endpoints that the investigators examined.
Observing a difference in this context will require very large trials or different endpoints that are more responsive to the intervention, said Sheth. “This is going to be a challenge for not just this but for any neuroprotection trial in the future,” he said.
The study was supported by Medtronic. Fischer has served as a consultant for Medtronic, Stryker, and CSL Behring. Sheth has disclosed no relevant financial relationships.
13th World Stroke Congress (WSC) 2021: Abstract LB100. Presented October 28, 2021.
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