tPA Given in Mobile Stroke Unit Linked to Better Outcomes

March 10, 2017

HOUSTON — A new analysis of data from the first study of giving thrombolytic therapy in a mobile stroke unit has suggested that this approach is associated with improved outcomes.

"Our preliminary estimate indicates that out of every 1000 patients treated with prehospital thrombolysis rather than conventional thrombolysis in the emergency department, 182 will have a less disabled final outcome, including 58 more who would be free from disability," said May Nour, MD, from the University of California, Los Angeles.

"If confirmed in larger controlled clinical trials, these findings suggest that giving thrombolysis in a mobile stroke unit would have a substantial clinical benefit."

Their findings were presented here at the International Stroke Conference (ISC) 2017.

The new analysis used data from the PHANTOM-S observational registry study, conducted in Berlin from 2011 to 2014. The main analysis of the study was published last year ( Lancet Neurology. 2016;15:1035-1043), and showed a trend toward improved primary outcome — no disability (modified Rankin Scale [mRS] score, 0 - 1) at 3 months — which did not reach significance.

The multivariable logistic regression analysis, adjusted for demographics, comorbidities, and stroke severity, did approach significance (P = .052).

Researchers from the University of California, Los Angeles, who are setting up their own mobile stroke unit program, analyzed the data from Berlin, looking at different outcomes: all possible dichotomizations of the mRS of global disability and net benefit per 1000 treated patients.

Dr Nour explained that the PHANTOM-S study was underpowered for statistical significance: "We wanted to look more closely at the data to see if we could find a benefit," she said. "There is no US data available yet, so we used the Berlin data, as this is where the most experience has been had so far."

"We wanted to look at the data from the Berlin experience in a different way, to try to assess benefits of prehospital administration of tPA (tissue plasminogen activator)," Dr Nour said. "So we conducted an analysis with 'number needed to treat' and 'benefit per 1000 patients treated' as endpoints, and we did indeed show meaningful improvements."

The PHANTOM S study included 427 patients who received treatment in the mobile stroke unit, who were compared with 505 patients who received conventional care with in-hospital thrombolysis.

The current analysis used group data, which were available for 305 patients treated with intravenous tPA in the mobile unit and 353 patients treated conventionally in the emergency department. Results showed that of the six cut-points on the mRS, five showed more favorable outcomes with mobile stroke unit care.

The benefit per 1000 patients ranged from −21 to 93, depending on the outcome, with the greatest benefit seen at mRS 0 to 3, and 58 more patients reaching the primary outcome of freedom from disability (mRS 0 - 1).

For the benefit of improving by one or more level across all six transitions of the mRS, the benefit per 1000 patients treated was 182, and the number needed to treat was 5.5.

Table. mRS Scores at 3 Months After Treatment in Mobile Stroke Unit

mRS Scores Benefit per 1000 Patients Treated Number Needed to Treat
0 vs 1 - 6 −21 −47.6
0 - 1 vs 2 - 6 58 17.2
0 - 2 vs 3 - 6 7 142.9
0 - 3 vs 4 - 6 93 10.8
0 - 4 vs 5 - 6 60 16.7
0 - 5 vs 6 49 20.4
Improvement of one or more levels across the whole of the mRS 182 5.5

Commenting on the study for Medscape Medical News, James Grotta MD, from the University of Texas Medical School at Houston, who leads the most established mobile stroke unit program in the United States, said: "This analysis is accurate and is another way of looking at the benefit of using mobile stroke units, but it is based on an underpowered study that wasn't randomized. So this is not a study that you're going to hang your hat on to know for sure that mobile stroke units are effective."

He added: "We know mobile stroke units can save time, and everyone knows that reducing time to treatment with tPA will improve outcomes, but we need to show that mobile stroke units are effective in the new modern world, where hospital treatment times are coming down because of the new endovascular studies."

Dr Grotta also pointed out that the mobile stroke units have large up-front costs. "We therefore have to establish the costs of the units and if the amount of benefit is worth those costs. We need larger, better-designed studies for this. "

The Berlin group is now doing another study to look at these issues, and Dr Grotta is leading a similar US study called Benefits of Stroke Treatment in Mobile Stroke Units (BEST MSU).

The Houston mobile stroke unit program started in 2014, and Dr Grotta estimates they have now transported about 600 patients.

Other US centers have also started mobile stroke unit programs, including the Cleveland Clinic; University of Colorado, Denver; Capital Health New Jersey; Rush University; University of Tennessee, Memphis; Columbia/Cornell in New York City; and Mercy Health, Toledo, Ohio.

The BEST MSU trial has included mostly patients in Houston so far, but is now expanding to include data from other US centers as well. The trial has a "1 week on, 1 week off" design, so the mobile stroke unit is available to attend suspected stroke patients for 1 week, and then the next week it is off duty, during which time alerts are still received, but normal emergency medical services teams are dispatched and the patient receives standard care. Approximately 300 patients have been treated with tPA so far in the study: half in the mobile unit and half in the standard pathway.

Dr Grotta explained that in Houston, the mobile stroke unit has a team of four staff members: one paramedic, one computed tomography technician, one nurse, and a vascular neurologist (Dr Grotta himself). "We are transitioning to a team of three and using telemetry so the stroke neurologist does not have to be in the unit."

He says on average, they receive four or five calls a day, with four or five patients each week actually being transported in the mobile unit and two or three of these receiving tPA.

"The unit operates within a 20-mile radius of the hospital, and the average call is 8 miles from the base station. But we often rendezvous with the first responder [emergency medical services] ambulance halfway."

Dr Nour pointed out that these programs are difficult to set up logistically and are expensive, at around $1 million per unit, but there is no central funding available, so the money has to come from the hospital or philanthropic donations.

Another report at the ISC meeting outlined the work involved in setting up a mobile stroke unit in New York City, which is the first such unit on East Coast of the United States. In a poster presentation, Benjamin Kummer, MD, from New York-Presbyterian/Weill Cornell Medical Center in New York City, described the "tremendously complex process" of establishing the program.

The first steps were securing donor funds to build the unit and assembling a multidisciplinary team. Local stakeholders, including the Fire Department of New York (which runs the emergency services) and the Regional Emergency Medical Services of New York City, were engaged to integrate the mobile stroke unit into the New York City emergency dispatch system. And then collaboration was needed from many different departments, including neurology, emergency medicine, emergency medical services, radiology, laboratory services, information technology, nursing, and pharmacy.

Dr Kummer explained that the mobile unit is based at either Columbia or Cornell and is staffed by two paramedics, one radiology technologist, and a vascular neurologist. It is operational on weekdays from 7 AM to 3 PM. Similar to the Houston program, they are planning to move to teleneurology in time, so that the neurologist does not have to be in the mobile unit.

The unit began operating in October 2016, after 2 years of planning. Dr Kummer said barriers to implementation included building an operational information technology infrastructure, establishing a functional prenotification system between the mobile unit and accepting hospitals, and integrating the unit into institutional workflows for electronic documentation, order entry, and hospital registration.

The mobile unit has evaluated 30 patients so far and treated 9 patients with tPA. The median time to treatment from symptom onset is 94 minutes compared with between 129 and 151 minutes for patients treated in the two affiliated hospitals.

Dr Kummer commented: "As we only have a very small number of patients, this has to be taken with a large grain of salt, but it certainly looks promising."

"The most important thing is the time from symptom onset to treatment. If we can reach patients sooner and cut out transportation time and [emergency department] delays, then we should improve outcomes."

He added: "I firmly believe mobile stroke units are going to take off and will eventually be the norm throughout the US — there are many such programs in in planning now."

He pointed out that although the prime objective of these units is to get tPA in quicker, they will also facilitate getting the right patients to the right hospitals faster. "The [computed tomography] scan on board will help to identify patients suitable for endovascular treatment who can then be to taken straight to a comprehensive center."

Dr Nour added that in the future, they may be used not just for patients with stroke, but also for patients with any neurologic emergency: traumatic brain injury, seizures, and so on. "They are a platform for delivery of care for patients who need treatment very fast."

International Stroke Conference (ISC) 2017: Abstracts 119 and LBP14. Presented February 22 and 23, 2017.

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