First EDition: Mobile Stroke Units Becoming More Common, more

MITCHEL L. ZOLER

FRONTLINE MEDICAL NEWS

Mobile stroke units—specially equipped ambulances that bring a diagnostic computed tomography (CT) scanner and therapeutic thrombolysis directly to patients in the field—have begun to proliferate across the United States, although they remain investigational, with no clear proof of their incremental clinical value or cost-effectiveness.

The first US mobile stroke unit (MSU) launched in Houston, Texas in early 2014 (following the world’s first in Berlin, Germany, which began running in early 2011), and by early 2017, at least eight other US MSUs were in operation, most of them put into service during the prior 15 months. United States MSU locations now include Cleveland, Ohio; Denver, Colorado; Memphis, Tennessee; New York, New York; Toledo, Ohio; Trenton, New Jersey; and Northwestern Medicine and Rush University Medical Center in the western Chicago, Illinois region. A tenth MSU is slated to start operation at the University of California, Los Angeles later this year.

Early data collected at some of these sites show that initiating care of an acute ischemic stroke patient in an MSU shaves precious minutes off the time it takes to initiate thrombolytic therapy with tissue plasminogen activator (tPA), and findings from preliminary analyses suggest better functional outcomes for patients treated this way. However, leaders in the nascent field readily admit that the data needed to clearly prove the benefit patients receive from operating MSUs are still a few years off. This uncertainty about the added benefit to patients from MSUs couples with one clear fact: MSUs are expensive to start up, with a price tag of roughly $1 million to get an MSU on the road for the first time; they are also expensive to operate, with one estimate for the annual cost of keeping an MSU on the street at about $500,000 per year for staffing, supplies, and other expenses.

“Every US MSU I know of started with philanthropic gifts, but you need a business model” to keep the program running long-term, James C. Grotta, MD, said during a session focused on MSUs at the International Stroke Conference sponsored by the American Heart Association. “You can’t sustain an MSU with philanthropy,” said Dr Grotta, professor of neurology at the University of Texas Health Science Center in Houston, director and founder of the Houston MSU, and acknowledged “godfather” of all US MSUs.

“We believe that MSUs are very worthwhile and that the clinical and economic benefits of earlier stroke treatment [made possible with MSUs] could offset the costs, but we need to show this,” admitted May Nour, MD, a vascular and interventional neurologist at the University of California, Los Angeles (UCLA), and director of the soon-to-launch Los Angeles MSU.

The concept behind MSUs is simple: Each one carries a CT scanner on board so that once the vehicle’s staff identifies a patient with clinical signs of a significant-acute ischemic stroke in the field and confirms that the timing of the stroke onset suggests eligibility for tPA treatment, a CT scan can immediately be run on-site to finalize tPA eligibility. The MSU staff can then begin infusing the drug in the ambulance as it speeds the patient to an appropriate hospital.

In addition, many MSUs now carry a scanner that can perform a CT angiogram (CTA) to locate the occluding clot. If a large vessel occlusion is found, the crew can bring the patient directly to a comprehensive stroke center for a thrombectomy. If thrombectomy is not appropriate, the MSU crew may take the patient to a primary stroke center where thrombectomy is not available.

Another advantage to MSUs, in addition to quicker initiation of thrombolysis, is “getting patients to where they need to go faster and more directly,” said Dr Nour.

“Instead of bringing patients first to a hospital that’s unable to do thrombectomy and where treatment gets slowed down, with an MSU you can give tPA on the street and go straight to a thrombectomy center,” agreed Jeffrey L. Saver, MD, professor of neurology and director of the stroke unit at UCLA. “The MSU offers the tantalizing possibility that you can give tPA with no time hit because you can give it on the way directly to a comprehensive stroke center,” Dr Saver said during a session at the meeting.

Early Data on Effectiveness

Dr Nour reported some of the best evidence for the incremental clinical benefit of MSUs based on the reduced time for starting a tPA infusion. She used data the Berlin group published in September 2016 that compared the treatment courses and outcomes of patients managed with an MSU to similar patients managed by conventional ambulance transport for whom CT scan assessment and the start of tPA treatment did not begin until the patient reached a hospital. The German analysis showed that, in the observational Pre-hospital Acute Neurological Therapy and Optimization of Medical Care in Stroke Patients–Study (PHANTOM-S), among 353 patients treated by conventional transport, the median time from stroke onset to thrombolysis was 112 minutes, compared with a median of 73 minutes among 305 patients managed with an MSU, a statistically significant difference.¹ However, the study found no significant difference for its primary endpoint: the percentage of patients with a modified Rankin Scale score of 1 or lower when measured 90 days after their respective strokes. This outcome occurred in 47% of the control patients managed conventionally and in 53% of those managed by an MSU, a difference that fell short of statistical significance