ANAHEIM, Calif., Feb. 7 -- Time and distance may prevent a significant portion of the U.S. population from access to specialists trained to administer a clot-dissolving drug directly into brain arteries to stop a stroke within the presently accepted three-hour treatment window, University of Michigan researchers reported here today at the American Heart Association's 22nd International Joint Conference on Stroke and Cerebral Circulation.
In June 1996 the Food and Drug Administration approved giving TPA (tissue plasminogen activator) through a vein in the arm within three hours of the onset of stroke symptoms to stop a stroke in progress. However, researchers are looking for more effective ways to administer clot-dissolving drugs. One technique involves delivering the drug directly into the brain artery housing the clot. However, this requires more specialized facilities and personnel than is needed for intravenous administration. Also, clinical trials do not yet show if administering TPA directly into the artery is any more effective than injecting it into a vein.
Intra-arterial administration of TPA requires a smaller dose of the drug than delivering it through a vein, said Phillip A. Scott, M.D., of the University of Michigan in Ann Arbor, and this could potentially reduce the risk of bleeding complications. The procedure also allows physicians to physically disrupt the clot with a catheter if the clot doesn't dissolve.
But a major limitation of the intra-arterial approach is the extra time needed to assemble a team of medical personnel with special expertise and training. The American Heart Association Guidelines for Stroke favor further testing of this approach, noted Scott, but only by physicians "who are experienced in neurointerventional techniques and in centers with neurological expertise."
If current clinical trials show intra-arterial administration of TPA is a highly effective way to treat stroke, you then have to ask: "If you've got a great therapy, but you can only do it at medical centers with special personnel and facilities, and have a very short time to deliver it, how many people can it benefit and how do you increase its availability?" said Scott.
The three-hour window to provide stroke treatment with TPA currently excludes a majority of the U.S. population from access to the intra-arterial treatment, he added. He and his colleagues said today that only 36 percent of the U.S. population would have access to this therapy.
The scientists assumed that one of the three hours is necessary for transport of the patient to an emergency room. The other two hours are needed for the patient or family to recognize stroke symptoms, be evaluated by physicians in the emergency room, obtain a brain scan, perform and check essential lab tests, assemble the treatment team and prepare the room where the clot-dissolving drugs are administered.
"All of these things must be done before we are ready to actually do something to dissolve the clot in the patient's brain circulation," said Scott. "This leaves only 60 minutes for patient transport." In addition, he noted, current guidelines for administering TPA via a vein call for delivering it within 60 minutes after a patient walks through the emergency room door. An additional 30 to 60 minutes is needed to set up for intra-arterial administration, but patients still need to get the drug within three hours of stroke symptom onset.
The one-hour limit for patient transport creates a relatively confined geographic area from which patients might come. "We can go about 20 miles by ambulance in 60 minutes in most metropolitan emergency medical systems, and about 40 miles by air (helicopter) in 90 minutes," he said.
To identify medical centers with specialists capable of providing intra-arterial stroke treatment, the researchers used membership lists of the American and World Societies of Interventional Neuroradiology. They identified 82 centers and determined the populations around each center at the specified distances.
Scott said he and his co-workers were pleased to find that the percentage of Americans with access to treatment "was not as low as we were afraid it might be." In addition, they found that 52 percent of African-Americans live within 20 miles of a hospital identified with an interventional neuroradiologist. "This is particularly significant because of the higher incidence of stroke in the African-American community," he explained.
Regions identified with difficult emergency access to intra-arterial treatment included rural areas of the central plains, Montana, Idaho, Nevada, Maine and Georgia.
If new neuroprotective stroke therapies prove successful in delaying brain cell injury and/or the time window expands to six hours instead of three, you can extend the treatment radius around each medical center to 200 miles with helicopter transport, Scott said. That additional window of time would provide access to intra-arterial stroke therapy for 95 percent of the nation's population, he added.
Scott's colleagues at the University of Michigan section of emergency medicine are Mark J. Lowell, M.D., and Karl Longstreth, M.L.S.