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Background: Hematoma enlargement (HE) after intracerebral hemorrhage (ICH) is a therapeutic target for improving outcomes. Hemostatic therapies to prevent HE may be more effective the earlier they are attempted. An understanding of HE in first 1 to 2 hours specifically in the prehospital setting would help guide future treatment interventions in this time frame and setting. Methods: Patients with spontaneous ICH within 4 hours of symptom onset were prospectively evaluated between May 2014 and April 2020 as a prespecified substudy within a multicenter trial of prehospital mobile stroke unit versus standard management. Baseline computed tomography scans obtained 6 mL if baseline ICH volume was < 20 mL and 33% increase if baseline volume >20 mL. The association between time from symptom onset to baseline computed tomography (hours) and HE was investigated using Wilcoxon rank-sum test when time was treated as a continuous variable and using Fisher exact test when time was categorized. Kruskal-Wallis and Wilcoxon rank-sum tests evaluated differences in baseline volumes and HE. Univariable and multivariable logistic regression analyses were conducted to identify factors associated with HE and variable selection was performed using cross-validated L1-regularized (Lasso regression). This study adhered to STROBE guidelines (Strengthening the Reporting of Observational Studies in Epidemiology) for cohort studies. Results: One hundred thirty-nine patients were included. There was no difference between baseline ICH volumes obtained 2 hours (n=45) from symptom onset (median [interquartile range], 13 mL [6–24] versus 14 mL [6–30] versus 12 mL [4–19]; P =0.65). However, within the same 3 time epochs, initial hematoma growth (volume/time from onset) was greater with earlier baseline scanning (median [interquartile range], 17 mL/hour [9–35] versus 9 mL/hour [5–23]) versus 4 mL/hour [2–7]; P 2 hours; P =0.02). HE did not occur between the scans repeated at 1 hour and 24 hours. No association between baseline variables and HE was detected in multivariable analyses. Conclusions: HE in the next hour occurs in 28% of ICH patients with baseline imaging within the first hour after symptom onset, and in 17% of those with baseline imaging between 1 and 2 hours. These patients would be a target for ultraearly hemostatic intervention.

Background: Few data exists on acute stroke treatment in patients with pre-existing disability (PD) since they are usually excluded from clinical trials. Methods: A pre-specified subgroup analysis of tPA-eligible patients with PD enrolled in a prospective multicenter trial of Mobile Stroke Units (MSUs) vs standard management by emergency medical services (EMS). All patients had baseline mRS scores. Co-primary outcomes were mean utility-weighted modified Rankin Scale score (uw-mRS) and return to baseline mRS at 90 days. Linear and logistic regression models compared outcomes in patients with vs without PD, and patients with PD treated by MSU vs EMS. Time metrics, safety, quality of life, and health-care utilization were also compared. Results: Of 1047 patients, 254 had baseline mRS >= 2 (159 MSU, 95 EMS; 31% mRS 2, 52% mRS 3, 17% mRS 4). Compared to patients without disability, patients with PD were older, had higher NIHSS, more comorbidities, less often lived at home, were treated slower, and had less thrombectomy. Patients with PD had worse 90-day uw-mRS (0.39 vs 0.80), higher mortality, more health-care utilization and worse quality of life than patients without PD. However, rates of symptomatic intracranial hemorrhage and final diagnoses of stroke mimics were similar between groups, and 52% of patients with PD returned to their baseline mRS. Patients with PD treated within the first hour had better 90-day uw-mRS than those treated later (0.48 vs 0.36, p=0.01). Comparing patients with PD treated by MSU vs EMS, time from last-known-well to tPA bolus was shorter (82 vs 111 min), and 24% vs 0% were treated in the first hour. Among patients with PD, MSU patients had non-significantly better 90-day uw-mRS (0.41 vs 0.35, p=0.09) and higher rate of returning to baseline mRS (56% vs 44%, p=0.09) than EMS patients. There was no interaction between either time to treatment (p=0.24) or MSU vs EMS group assignment (p= 0.42), 90-day uw-mRS, and PD vs no disability status. Conclusion: Although outcomes after stroke are less favorable in patients with vs without PD, in a large, controlled trial, we found no interaction between baseline disability and the benefit of MSU treatment. Our data support the earliest treatment of acute stroke patients regardless of premorbid functional status.

Introduction: Stroke is a leading cause of long-term disability in the U.S., and 90% of stroke survivors have residual movement impairment. Inpatient and outpatient rehabilitation is critical for restoring functionality and quality of life among survivors. However, there are few studies evaluating the patterns and predictors of rehabilitation use among stroke survivors. Methods: This study used 947 tPA-eligibe patients from an observational, prospective, multicenter, clinical trial in the U.S., who had complete 1 year follow-up utilization data, collected quarterly as self-reported surveys. We determined the occurrence and length of stay for inpatient rehabilitation, and occurrence and number of visits for outpatient rehabilitation. Logistic and linear regressions were used to examine predictors associated with these occurrences and intensities. Results: The majority of rehabilitation use occurred during the first quarter with 19% and 33% of patients using inpatient and outpatient rehabilitation respectively, and rehabilitation use fell considerably over the rest of the year (Table 1). Higher disability at baseline (mRS≥2 and not living at home) reduced rehabilitation use, and higher disability at discharge increased rehabilitation use. Being uninsured reduced rehabilitation use. Other socio-demographic characteristics (such as age, gender and race-ethnicity), baseline comorbidities, and type and timeliness of therapies after stroke did not have an effect on rehabilitation use. Conclusion: Rehabilitation use is highest during the first 3 months after discharge. Patients with higher discharge disability are more in need of rehabilitation, hence receive it. Patients already disabled at baseline are often excluded, probably due to a combination of rehabilitation entry requirements and perceived lack of potential benefits. Access barriers, such as lack of insurance reduced rehabilitation use suggesting an unmet need among stroke survivors.

Introduction: While the goal of IV tissue plasminogen activator (TPA) is to prevent infarction, few data exist on averted stroke. Methods: Secondary analysis of a multicenter trial from 2014-2020 comparing outcomes between patients treated for stroke by mobile stroke unit (MSU) vs standard care (SC). The analytical cohort were patients with suspected stroke treated with IV TPA. The primary outcome was a time-defined averted stroke diagnosis, defined as a final diagnosis of stroke with resolution of presenting symptoms/signs by 24 hours. The secondary outcome was a tissue-defined averted stroke diagnosis, defined as a final diagnosis of stroke with resolution of presenting symptoms/signs by 24 hours and no acute infarction/hemorrhage on imaging. We used multivariable logistic regression to evaluate associations between study exposures (demographics, comorbidities, stroke characteristics) and outcomes. Results: Among 1009 patients with a median last known well-to-TPA time of 87 minutes, 276 patients (27%) had a time-defined averted stroke (31% MSU, 21% SC) and 159 patients (16%) had a tissue-defined averted stroke (18% MSU, 11% SC). Factors independently associated with time-defined averted stroke were younger age (OR, 0.98; 95% CI, 0.96-0.99), female sex (0R, 0.51; 95% CI, 0.36-0.74), hyperlipidemia (OR, 1.81, 95% CI, 1.24-2.64), normal premorbid function (0R, 2.22; 95% CI, 1.37-3.67), lower glucose (OR, 0.996; 95% CI, 0.993-0.999), lower MAP (OR, 0.991; 95% CI, 0.983-0.998), MSU care (OR, 1.77; 95% CI, 1.21-2.62), lower NIH stroke scale (OR, 0.89; 95% CI, 0.86-0.93), and no large vessel occlusion (LVO) (OR, 0.52; 95% CI, 0.32-0.83). For tissue-based averted stroke, younger age, female sex, hyperlipidemia, lower MAP, MSU treatment, lower NIH stroke scale, and no LVO were significantly associated. Conclusion: In a modern acute stroke trial, one-in-four patients treated with TPA for stroke recovered within 24 hours and one-in-six had no demonstrable brain injury on imaging. Younger age, female sex, hyperlipidemia, lower MAP, MSU care, lower stroke severity, and no LVO may increase the odds of averting stroke.

Introduction: We studied variation in stroke rates, post-discharge health services, and outcomes across payors in Texas. Methods: Claims for 48,331 stroke patients in 2016 and hospital data covering 58,114 discharges were analyzed. Prevalence and incidence rates per region were reported as a variation from the state mean by payor type (Medicaid, Medicare and Commercial). Stroke overall, ischemic stroke, intracerebral hemorrhage (ICH), and subarachnoid hemorrhage are reported. Stroke outcomes are reported for the following measures: Discharges to rehabilitation, 30-Day Follow-Up with neurologist, death within 45 days Results: Among all payors, east Texas had the highest incidence and prevalence of ischemic stroke (Fig) but Northern Texas had the highest incidence of ICH among Medicaid and Commercial payors. Medicaid patients showed the greatest increases across ages and displayed a higher prevalence rate among those aged 40-64 than the 65+ group. Medicaid had a higher rate for each age group when compared to commercial. Within Medicaid and commercial, the 0-17 age had a very high rate of death from ischemic stroke (121/1000 and 83/1000, respectively), greater than any of the other age bands except over age 65; these high rates were not observed in ICH. Commercial and Medicaid patients had low rates of discharge to rehabilitation compared with Medicare (354/1000, 130/1000, 424/1000, respectively). Outpatient follow-up rates with a neurologist were low: Medicaid rates were very low compared to Commercial and Medicare (22/1000, 387/1000, 267/1000, respectively). Conclusion: Statewide review revealed dramatic variation in regional rates across all payors and ages. Graphic display and public reporting of statewide data on stroke through population level transparency can be leveraged to identify areas of risk, intervention strategies, and inform public health policy.

Introduction: We assessed the impact of COVID-19 pandemic on stroke admissions and care metrics within a health system of 10 stroke centers, with 4 comprehensive stroke centers (CSC) in the greater Houston region. Methods: Between January-June 2019 and January-June 2020, we compared the proportion of ischemic strokes (total & direct CSC presentations) & intracerebral hemorrhage (ICH) relative to total admissions using logistic regression, and among the direct CSC presentations, we compared door to tPA and thrombectomy times using Wilcoxon Rank Sum. Results: A total of 4808 cases were assessed (Table 1). There was an initial drop of ~30% in cases at the pandemic onset (Fig.1). Numerically fewer patients in the 2020 period were seen at primary and CSCs (Table 1). Compared to 2019, there was a significant reduction in transferred patients [N(%), 829 (36) vs. 637 (34), p=0.02], in hospital strokes [N(%), 111 (5) vs. 69 (4), p=0.04], and mild strokes (NIHSS 1-5) [N (%), 891 (43) vs. 635 (40),p=0.02], and no significant differences in the proportions of total ischemic strokes [OR (95% CI)=0.92 (0.79, 1.06), p=0.23], direct CSC presentations [OR (95% CI) =0.96 (0.86, 1.08), p=0.48] and ICH [OR (95% CI) =1.14 (0.98, 1.33), p=0.08] in 2020 (Fig. 1). Among the direct ischemic strokes at CSCs, there were similar mean (SD) (mins) door to tPA [44 (17) vs. 42 (17), p=0.14] but significantly prolonged door to thrombectomy times [94 (15) vs. 85 (20), p=0.005] in 2020. Conclusion: COVID-19 pandemic led to reduced mild stroke admissions, transfers and in hospital stroke alerts, & prolonged door to thrombectomy times. Identifying reasons to mitigate this discrepancy is crucial for next pandemic preparedness.

Introduction: The benefit of intravenous tPA in acute ischemic stroke patients with large vessel occlusions (LVOs) is limited but time dependent. We evaluated pre-hospital treatment with tPA on the Mobile Stroke Unit (MSU) to explore the recanalization rate in patients with LVOs and its effect on clinical improvement upon ED arrival. Methods: Prospectively derived data were analyzed from patients on the Houston MSU who were treated with tPA and had LVOs identified by hyperdense artery on MSU CT or arterial occlusion on MSU CTA. The primary outcome was early recanalization, categorized as resolution of LVO on repeat vascular imaging in the ED or on emergent angiography versus no recanalization. Secondary outcome was change in baseline NIHSS at 24 hours. Differences in NIHSS were evaluated using Wilcoxon rank sum test with continuity correction. Results: Seventy-one patients received tPA and had proximal LVOs both in the anterior and posterior circulation. Eleven had recanalization on CTA upon ED arrival (15.5%), while 7 had recanalization on emergent angiography (9.9%). The total early recanalization rate with tPA was 25.4%. Forty-seven patients with persistent LVOs on ED arrival (66.2%) underwent endovascular thrombectomy (EVT). Time from symptom onset (last known normal) to tPA bolus did not differ significantly between the early recanalization vs non-early recanalization groups (64.5 minutes [IQR 43.0-78.5] vs 64.0 minutes [52.5-92.0]; p = 0.41). Early recanalization resulted in greater improvement in baseline to ED arrival NIHSS (median NIHSS change 4.0 [0-11.8] vs 0 [0-3.5]; p = 0.01). There were no differences in ED arrival to 24 hour NIHSS between the early recanalization versus non-early recanalization groups irrespective of EVT. Conclusions: Recanalization by ED arrival occurs in 25% of LVO patients with tPA treatment on a MSU and was associated with early clinical improvement. Subsequent EVT did not “make up” for the clinical benefit of early recanalization.

Introduction: Most clinical research stopped during COVID due to possible impact on data quality and personnel safety. We aimed to assess the impact of COVID on study conduct at sites that continued to enroll patients during the pandemic. Methods: BEST-MSU is an ongoing study of Mobile Stroke Units (MSU) vs standard management of tPA eligible acute stroke patients in the pre-hospital setting. MSU personnel include a vascular neurologist via telemedicine, and a nurse, CT tech, and medics on board using appropriate PPE. During COVID, consent, 90 d mRS and EQ5D could be obtained by phone instead of in person, otherwise management was the same. We compared patient demographics, study metrics, and infection of study personnel during intra- vs pre-COVID eras. Results: Four of 6 BEST-MSU sites continued to enroll during COVID. There was no difference in intra- (n= 41) vs pre- (n= 763) COVID enrolled tPA eligible patients’ age, sex, race (45% vs 41% Black), ethnicity (23% vs 19% Hispanic), or NIHSS (12 vs 12). MSU alert frequency did not change, but percent of screened patients enrolled and treated with tPA declined to 12% from 23% (p Conclusion: Clinical research in the pre-hospital setting can be carried out accurately and safely during a pandemic. Study enrollment and tPA treatment rates declined, but otherwise there was no difference in patient demographics, deterioration of study processes, or serious infection of study staff.

Introduction: Endovascular thrombectomy (ET) is an effective but time sensitive treatment of acute ischemic stroke. Time from Emergency Department (ED) arrival to start of ET (door-to-puncture time, DTPT) is a modifiable metric. One of the most time consuming steps in prolonging DTPT is identification of large vessel occlusion (LVO) by CT angiography (CTA). BEST-MSU is a prospective multicenter comparative effectiveness study of tPA-eligible patients managed on a mobile stroke unit (MSU) vs Emergency Medical Services (Standard Management, SM). After discovering that DTPT was greater than 60 minutes in both groups at three BEST-MSU centers in 2018, we began to routinely obtain CTA on the MSU and directly alert the ET team at receiving hospitals if a LVO was identified. We hypothesized this would shorten DTPT by over 30 minutes. Methods: In this single center experience, we compared the median (interquartile range, IQR) DTPT and MSU on-scene time for MSU patients having on-board CTA and then ET from 9/2018 to 7/2019 to corresponding MSU ET patients (excluding any that had on-board CTA) from 8/2014 to 8/2018. All CTAs were completed after tPA bolus and during tPA infusion on a Ceretom 8 slice scanner with OptiStat hand injector. All imaging occurred on-scene with the MSU stationary. Consent was obtained for all patients and strict radiation safety guidelines followed. Results: 13 consecutive patients having CTA on-board the MSU and then ET were compared to 84 patients in the pre-on-board CTA group. Baseline characteristics including median NIHSS score (20 in both groups) and frequency of tPA (85% on-board CTA vs 89% pre-on-board CTA) were comparable. Median DTPT was 60 minutes shorter with on-board CTA and direct notification of the interventional team from the MSU; 34 minutes (IQR 30-57) vs 94.5 minutes (IQR 69.75-117.25) (p < 0.001). Despite the additional time to obtain the CTA on the MSU, on-scene time was only slightly prolonged and did not offset the reduction in DTPT (on-board CTA 30 minutes (IQR 28-33) vs pre-on-board CTA 27 minutes (IQR 23-31) (p = 0.01). Conclusion: Pre-hospital identification and notification of LVO by a MSU allows a one hour reduction of DTPT, and can be utilized to establish a direct to angiosuite protocol.

Introduction: The American Heart Association (AHA) recently raised the bar on timely treatment of acute ischemic stroke (AIS) with intravenous (IV) alteplase, by recommending door-to-needle times of 30 minutes or less for 50% or more of the AIS patients. Our study looks at the effectiveness of this new standard, by examining the effect of varying door-to-needle times on efficiency and quality of care, and clinical outcomes. Methods: Our study examined 762 AIS patients treated with IV alteplase in a large academic health system from 2015-2018, and compared their outcomes after treatment within 30, 45 and 60 minutes of arrival. The outcomes compared were: 1) Efficiency of care outcome - Length of stay (LOS); 2) Quality of care outcomes - Inpatient mortality and Disability at discharge; 3) Clinical outcomes - Discharge and 90-day modified Rankin Scale (mRS), and Post-alteplase (24 hr) NIH Stroke Scale (NIHSS). Adjusted logistic and linear regression analyses were used, after controlling for baseline patient socio-demographic and clinical characteristics. Results: Based on the adjusted regression analyses (Table 1), being treated within 30 minutes of arrival reduced the average LOS by 1.3 days (p-value: 0.02), but did not affect the quality of care outcomes. Similarly, being treated within 45 minutes of arrival reduced LOS by 0.9 days (p-value: 0.04). Being treated within 60 minutes of arrival did not affect LOS, but reduced the odds of inpatient mortality by 68% (p-value: 0.00), and disability at discharge by 29% (p-value: 0.08). Being treated within 30 minutes of arrival was associated with better mRS and NIHSS scores as compared with being treated within 45 or 60 minutes. Conclusion: Quicker IV alteplase treatment significantly improved efficiency of care and clinical outcomes. Quality of care outcomes did not improve beyond the 60 minute door-to-needle threshold. This study provides evidence supporting AHA’s new recommendation of 30 minutes or less door-to-needle time.

Background and Purpose— Mobile stroke units (MSUs) can speed treatment with intravenous tPA (tissue-type plasminogen activator). We previously showed substantial agreement between a telemedicine-based vascular neurologist (TM-VN) and an onboard vascular neurologist (OB-VN) for the evaluation of patients with stroke for tPA eligibility on an MSU. However, the time efficiency of the telemedicine-based evaluation remained uncertain. In this study, we examined the speed of decision and treatment from MSU arrival for the TM-VN compared with an OB-VN. Methods— In 50 consecutive situations, the TM-VN served as the primary decision maker. Times from MSU arrival to tPA decision and tPA bolus were compared with the same metrics for when the OB-VN served as the primary decision maker. Results— Time to tPA decision for the TM-VN was 21 minutes (interquartile range, 16.25–26) versus 18 minutes (interquartile range, 14–22) for the OB-VN ( P =0.01). Initiation of tPA bolus was 24 minutes (interquartile range, 19.75–30) for the TM-VN versus 24 minutes (interquartile range, 19–27.75) for the OB-VN ( P =0.5). Conclusions— Assessment by a TM-VN is comparable with an OB-VN in making decisions about tPA administration on an MSU and does not lead to treatment delays. Clinical Trial Registration— URL: https://www.clinicaltrials.gov . Unique identifier: NCT02190500.

Background and Purpose- The impact of a mobile stroke unit (MSU) on access to intraarterial thrombectomy (IAT) is a prespecified BEST-MSU substudy (Benefits of Stroke Treatment Delivered Using a Mobile Stroke Unit Compared to Standard Management by Emergency Medical Services). On the MSU, IAT decision-making steps, such as computed tomography, neurological exam, and tPA (tissue-type plasminogen activator) treatment are completed before emergency department arrival. We hypothesized that such pre-ED assessment of potential IAT patients on an MSU improves the time from ED arrival to skin puncture time (door-to-puncture-time, DTPT). Methods- BEST-MSU is a prospective comparative effectiveness study of MSU versus standard management by emergency medical services (EMS). We compared ED DTPT among the following groups of MSU and EMS patients: all IAT patients, IAT patients post-tPA, and IAT patients post-tPA meeting thrombolytic adjudication criteria over the first 4 years of the study. Results- From August 2014 to July 2018, a total of 161 patients underwent IAT. Ninety-four patients presented to the ED via the MSU and 67 by EMS. One hundred forty patients received tPA before IAT, 85 in the MSU arm, and 55 in the EMS arm. One hundred twenty-six patients received tPA within thrombolytic adjudication criteria: 76 MSU and 50 EMS. DTPT in minutes was shorter for MSU patients (all IAT MSU versus EMS 89 versus 99, P=0.01; IAT post-tPA MSU versus EMS 93 versus 100, P=0.03; and IAT post-tPA within adjudicated criteria MSU versus EMS 93 versus 99.5, P=0.03). From 2014 to 2018, DTPT decreased at a faster rate for EMS compared with MSU-managed patients, improving by about an hour. Conclusions- Pre-ED IAT evaluation on an MSU results in faster DTPT compared with arrival by EMS. Since 2014, dramatic improvement in ED IAT metrics has attenuated this difference. However, DTPT in all groups indicates substantial room for improvement.

Introduction: Early ischemic changes (EIC) on non-contrast computed tomography (NCCT) can appear within 6 hours of last known normal (LKN), and can be quantified using the Alberta Stroke Program Early CT Score (ASPECTS). However, there is lack of data describing when EIC first appear. We leveraged our Mobile Stroke Unit (MSU) to determine the incidence of EIC on NCCT within 1 hour of LKN. Methods: Prospectively derived data were analyzed from patients on our MSU who were independently adjudicated as tissue plasminogen activator (tPA) eligible, had NCCT within 1 hour of LKN, and had definite strokes based on subsequent testing. EIC, defined as ASPECTS ≤ 7, was measured and correlated to time from LKN, stroke severity (National Institutes of Health Stroke Scale, NIHSS), and presence of large vessel occlusion (LVO) on neuroimaging. All scans were obtained on an 8 slice Ceretom (Neurologica Corp) and graded by a Vascular Neurology fellow, with random scans compared with a Vascular Neurology attending (κ=0.69). Results: 80 tPA eligible patients with NCCT within 1 hour of LKN were identified. 57 had definite strokes and/or strokes reversed by tPA. Of these, 54 (95%) had NCCT with sufficient diagnostic quality. Mean ASPECTS was 9.2 (median 10, interquartile range (IQR) 9-10) with a mean of 45.3 minutes (median 46, IQR 39-52) from LKN. Average NIHSS was 14.9. EIC (e.g. ASPECTS 6, 6, 7, 7) was identified in 4 patients (7%). There was no association between ASPECTS and time from LKN to CT (p=0.63), stroke severity (p=0.12) or presence of LVO (p= 0.09); the LVO analysis was limited by the small number of EIC patients (n=4). Conclusions: Based on our experience, EIC may be present but ASPECTS is not < 6 within the first hour after LKN. Close scrutiny of NCCT for EIC within this timeframe may not be necessary for determining eligibility for tPA or endovascular thrombectomy.

Introduction: The impact of a Mobile stroke unit (MSU) on access to Endovascular Thrombectomy (ET) is a pre-specified BEST-MSU sub-study. On the MSU, ET decision-making steps such as CT, neurologic exam, and tPA treatment are completed prior to Emergency Room (ER) arrival. We hypothesized that such pre-ER assessment of potential ET patients on a MSU improves metrics. Methods: BEST-MSU is a prospective comparative effectiveness study of MSU vs Standard Management by Emergency Medical Services (SM). We compared ER door-to-puncture-time (mins, DTPT) among the following groups of MSU and SM patients: all ET patients (ETP), ET patients post-tPA (ETT), and ET patients post-tPA meeting thrombolytic adjudication criteria (ETTA) over the first four years of the study. Results: There were 161 ETP (67 SM, 94 MSU), 140 ETT (55 SM, 85 MSU), and 126 ETTA (50 SM, 76 MSU) patients. DTPT was shorter for MSU patients (ETP 89 vs 99, p=0.01; ETT 93 vs 100, p=0.03; ETTA 93 vs 99.5, p=0.03). From 2015 to 2018, DTPT decreased at a faster rate for SM compared with MSU-managed patients, improving by about an hour (Figure). Conclusion: Pre-ER ET evaluation on a MSU results in faster DTPT. Since 2015, dramatic improvement in ER ET metrics has attenuated this difference. However, DTPT of 90-100 mins in all groups indicates substantial room for improvement.

Background and Purpose— Faster treatment with intravenous tissue-type plasminogen activator (tPA) is likely to improve outcomes. Optimizing prehospital triage by mobile stroke units (MSUs) may speed treatment times. The Benefits of Stroke Treatment Delivered Using a Mobile Stroke Unit (BEST-MSU) study was launched in May 2014 using the first MSU in the United States to compare stroke management using an MSU versus standard management (SM). Herein, we describe the results of the prespecified, nonrandomized run-in phase designed to obtain preliminary data on study logistics. Methods— The run-in phase consisted of 8 MSU weeks when all-patient care occurred on the MSU and 2 SM weeks when the MSU nurse met personnel on scene or at the emergency department to ensure comparability with MSU patients. Telemedicine was independently performed in 9 MSU cases. Results— Of 130 alerts, 24 MSU and 2 SM patients were enrolled. Twelve of 24 MSU patients received tPA on board; 4 were treated within 60 minutes of last seen normal, and 4 went on to endovascular treatment. There were no hemorrhagic complications. Four had primary intracerebral hemorrhage. Agreement on tPA eligibility between the onsite and telemedicine physician was 90%. Conclusions— The run-in phase provided a tPA treatment rate of 1.5 patients per week, assured us that treatment within 60 minutes of onset is possible, and enabled enrollment of patients on SM weeks. We also recognized the opportunity to assess the effect of the MSU on endovascular treatment and intracerebral hemorrhage. Challenges include the need to control biased patient selection on MSU versus SM weeks and establish inter-rater agreement for tPA treatment using telemedicine.