Individualizing the treatment of stroke
Time is of the essence for stroke victims. The longer the brain is deprived of oxygen, the greater the risk of permanent damage. Dr. Michael Hill wants to extend the existing treatment window on the basis of the individual patient's circumstances.
Story by Laura Ly/Photo by Veer
You have probably heard it said that "time is money". But what about the phrase "time is brain"? The expression is commonly used by experts to refer to the sense of urgency involved in treating stroke.
Ischemic stroke (the most common type) occurs when a blood vessel in the brain becomes blocked, usually by a clot, and blood flow to the brain is interrupted. If blood flow is not restored, brain cells start dying and brain function becomes impaired. Patients generally have only a few hours to receive treatment before damage to the brain is irreparable. AHFMR Health Scholar Dr. Michael Hill is investigating ways to extend the treatment time frame.
Doctors use thrombolysis—a treatment that Dr. Hill describes as "Drano for the brain"—to dissolve blood clots. "Most commonly, we give an intravenous infusion of a clot-busting drug such as tPA so that it flows with the blood. The whole body gets exposed to it, but enough gets into the brain clot that it dissolves and blood flow is restored," explains Dr. Hill.
Since the brain is being deprived of essential oxygen, access to treatment is critical; the sooner treatment is administered, the better the outcome for the patient. Most stroke patients are already ineligible for tPA (tissue plasminogen activator) treatment before they reach the hospital, because it must be given within four and a half hours. This is known as the safety window: the length of time following the onset of a stroke in which treatment can be administered with minimum risk and maximum benefit. A patient receiving tPA more than six hours after a stroke is at increased risk for bleeding in the brain. "On average, once you get three or four hours beyond the onset of stroke, it starts to become unsafe to dissolve the clot, and of no benefit to dissolve it because the damage has already occurred," notes Dr. Hill.
However, that three- to four-hour window is an average marker. Some patients have shown improvement when drugs were administered as late as 12 hours after the onset of stroke; other patients have shown brain impairment after only 90 minutes. "The individual variation in physiology is important. Sometimes people can have a clot in the brain, but they have lots of other blood vessels bringing blood—so the actual area of brain threatened is very small. And some people can have a huge area of brain threatened by one blocked artery," says Dr. Hill.
Using imaging technology such as MRI (magnetic resonance imaging) and CT scans (computerized tomography), Doppler ultrasound, and neurovascular imaging, doctors can determine the severity of brain damage. Dr. Hill explains, "By looking at pictures of the blood vessels, we can understand exactly where and what the problem is. If a patient has a clot in an artery, I need to know which artery, where, how much, and how it is affecting the brain—in order to decide the best approach to therapy."
Dr. Hill wants to move away from a time-window method of treating stroke patients; instead, he wants to treat patients on the basis of their individual "tissue window", as determined by brain imaging. "The four-and-a-half-hour window is a population average. But the average doesn't necessarily apply to the individual person. For example, I can do an MRI on a patient eight hours after the onset of stroke and see that the brain isn't dead. There is salvageable brain, and if I bring the blood flow back, there might be a big improvement for this patient."
"If we start to treat people individually, based on their physiology, it should open up treatment to a greater number of patients. My hope is that we can treat more stroke patients with thrombolysis, to prevent more disability and save people from the tragedy that is stroke."
Stroke in the Cinema
In February, AHFMR hosted its first Science in the Cinema event at the Plaza Theatre in Calgary: a screening of The Diving Bell and the Butterfly. The movie depicts the true story of Jean-Dominique Bauby, who suffered a stroke that paralyzed his entire body—apart from his left eye and eyelid. Using his one controllable eyelid, Bauby blinked his memoirs to a team of helpers who read the letters of the alphabet aloud.
Following the movie, Dr. Michael Hill led an audience discussion about a wide range of related topics, including ethics, stroke prevention, and the evolution of stroke treatments during the past decade. "It was kind of like a book club. You watch the movie, then you discuss it, and there's an exchange of ideas. It was a good experience for the audience, and it was fun for me," adds Dr. Hill.
For more information on upcoming Science in the Cinema events visit www.ahfmr.ab.ca/communications/scienceinthecinema.php