• Mobile Stroke Units Show Better 90-Day Outcomes in Acute Stroke Patients vs. EMS: BEST-MSU Trial

    In acute stroke patients eligible for tissue plasminogen activator (t-PA), utility-weighted disability outcomes were better at 90 days with mobile stroke units (MSUs) than with emergency medical services (EMS), according to a new study.

    James C. Grotta, MD, of the Mobile Stroke Unit, Memorial Hermann Hospital–Texas Medical Center, Houston, and colleagues reported the results of the BEST-MSU trial in a manuscript published online and in the Sept. 9 issue of The New England Journal of Medicine.

    BEST-MSU was an observational, prospective, multicenter, alternating-week trial assessing MSU or ambulance (emergency medical services [EMS]) management outcomes within 4.5 hours of onset of acute stroke symptoms.

    Acute ischemic stroke patients were assigned to MSUs, which are ambulances with staff and a computed tomographic scanner designed to allow for quicker t-PA treatment, or standard EMS management.

    The primary outcome was the score on the utility-weighted modified Rankin scale, a measure of disability ranged from 0 to 1 (with higher score indicating better outcomes) assessed at 90 days in patients eligible to receive t-PA. It was derived from scores on the modified Rankin scale, evaluated via standardized questionnaire, ranging from 0 to 6 (0 indicating no deficit and 6 indicating death), depending on the patients’ value of level of function. The secondary outcomes included changes across the modified Rankin scale, 30% reduction in the National Institutes of Health Stroke Scale (NIHSS) score from baseline to 24 hours, percentage of eligible patients receiving treatments with t-PA and endovascular therapy (EVT), and treatment time metrics from stroke onset.

    Of 1,515 patients enrolled from August 2014 to August 2020, 617 were included in the MSU group and 430 in the EMS group, were adjudicated to be eligible to receive t-PA (the population for primary analysis). The remaining 218 patients did not receive t-PA because of intracranial bleed noted on computed tomography (CT) scan. The median time of t-PA administration from the onset of stroke was 72 minutes in the MSU group and 108 in the EMS group. At baseline, patients in both groups had similar characteristics, with median age of 67 years in the MSU group and 65 years in the EMS group. The NIHSS score was 9 and 10 in MSU and EMS groups, respectively.

    The mean score on the utility-weighted modified Rankin scale at 90 days in t-PA receiving patients was 0.72±0.35 in the MSU group and 0.66±0.36 in the EMS group (adjusted odds ratio [OR] for a score of ≥0.91: 2.43; 95% confidence interval [CI]: 1.75 to 3.36; p<0.001). At discharge, the score improved to 0.57±0.37 in the MSU group and 0.51±0.36 in the EMS group (adjusted OR for a score of ≥0.91: 1.82; 95% CI: 1.39 to 2.37; p<0.001). A modified Rankin scale score of 0 or 1 was present in 55.0% of the MSU group and 44.4% of the EMS group among t-PA-eligible patients.

    The primary analysis involved dichotomized scores on the utility-weighted modified Rankin scale (≥0.91 or<0.91) at 90 days. In the total enrolled cohort, the pooled OR was 2.43 (95% CI, 1.75 to 3.36; p<0.001), which favored MSU in the models with or without inverse-probability weighting..

    The secondary outcomes were:

    1) 30% reduction in the NIHSS score from baseline to 24 hours occurred in 75% of the MSU group and 67.8% of EMS group;

    2) Median time of t-PA administration from the onset of stroke was 72 minutes in the MSU group and 108 in the EMS group; and

    3) Median time interval from alerting of emergency services to endovascular thrombectomy (EVT) treatment was 141 minutes in the MSU group and 132 minutes in the EMS group, with 23.7% of MSU patients undergoing EVT compared to 27% of EMS patients. Approximately 2% of patients in each group had intracerebral hemorrhage post t-PA.

    The main limitations of the study included its non-randomized design, enrollment differences in both groups that might have introduced bias and a majority of patients being enrolled at one site (77.6% from Houston), which limits the generalizability of the results.

    “In this trial, MSU management of acute ischemic stroke in patients who were eligible to receive t-PA resulted in less disability at 90 days and faster and more frequent t-PA treatment than standard management by EMS,” the authors concluded.

    The BEST-MSU trial was supported by a grant from the Patient-Centered Outcomes Research Institute.


    Grotta JC, Yamal J-M, Parker SA, et al. Prospective, Multicenter, Controlled Trial of Mobile Stroke Units. N Engl J Med 2021;385:971-981.

    Image Credit: ARHIT – stock.adobe.com

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