Endovascular Therapy: Future of Stroke Treatment?
With stroke treatment, timing is everything. For nearly 20 years, one drug—tissue plasminogen activator (tPA)—has been the gold standard of treatment for people who suffer an acute ischemic stroke.
Typically, the sooner tPA is started, the better the patient’s outcome will be. But only about 8 percent of stroke patients who arrive at a hospital are eligible for tPA. Even when patients arrive within the therapeutic window, tPA isn’t always the best treatment. Delivered intravenously over the course of about an hour, tPA doesn’t always effectively dissolve clots in major arteries, where the most severe and debilitating types of stroke originate.
Endovascular therapy: A viable option?
Because of limits on the use of tPA, options to this treatment are needed. For decades, researchers have been investigating endovascular therapy to treat stroke. Until now, results of endovascular therapy clinical trials have been mixed, to the disappointment of many stroke specialists.
But the results reported in 2015 from five significant international trials (most funded by makers of the devices used in the intervention) have shown that aspects of the technique have improved enough to consider the therapy a major player in future stroke treatment, especially for severe and potentially disabling strokes.
During endovascular therapy, often referred to as intra-arterial therapy, a neurovascular surgeon inserts a catheter into an incision in the patient’s groin, threading it to the blocked blood vessel.
A stent retriever, or stentriever, a device that’s attached to the catheter, grabs the clot, and the surgeon pulls it out through the incision. tPA is typically administered intravenously before endovascular therapy is performed. A variation of the procedure, however, delivers tPA through the catheter and directly into the clot.
The intervention works best on large blood clots in major arteries, called large vessel occlusions (LVOs), which cause the most severe strokes. In the latest clinical continued trials, the degree to which patients could regain function and independence at 90 days after interventions was consistently better among patients treated with endovascular therapy, usually combined with tPA, than in patients treated with intravenous tPA alone.
Death rates were lower in the endovascular therapy group as well. Complications, such as cerebral hemorrhage, were rare in both groups. Researchers cut short several trials because of endovascular therapy’s positive results in carefully selected patients.
As with tPA, time remains a critical element in endovascular therapy. Surgeons must perform the procedure within six hours after stroke onset, a slightly longer time window than with tPA.
The latest round of clinical trials has resulted in better outcomes than the disappointing batch of trials that ended as recently as 2013. The first of the most recent trials, a Dutch study aptly called MR CLEAN (Multicenter Randomized Clinical Trial of Endovascular Treatment for Acute Ischemic Stroke in the Netherlands), involved patients who were within six hours of stroke onset.
Almost all patients received intravenous tPA and were then assigned to either usual care or further intervention with endovascular therapy. Those who received endovascular treatment had a significant increase in their ability to function after three months, with no evidence of brain hemorrhage and no increase in death rate.
One key to the latest success of endovascular therapy is likely the improvement in imaging technology that’s used to select patients who’ll benefit from the procedure.
The first step in treating stroke is to identify the type of stroke a patient is having, either ischemic or hemorrhagic, using a computed tomography (CT) scan or a CT scan with angiography. Hemorrhagic stroke patients can’t be treated with tPA or endovascular therapy, which could cause more brain damage.
The CT scan can also reveal the clot’s size and location and the extent of damage to the brain. The best candidates for endovascular therapy are those with an LVO and limited damage to brain tissue in a region of the brain called the penumbra. If significant damage appears on the CT scan, it’s too late to perform the therapy.
Most of the studies used basic imaging and some form of imaging of the blood vessels: CT with angiography, MRI with angiography or studies called perfusion imaging, which accurately show how much blood is getting to the brain.
Another reason for better outcomes, according to experts, is the introduction of improved clot-busting mechanical devices like stentrievers used in endovascular therapy. These devices entrap and remove clots, restoring blood flow.
First-generation devices like the Merci Retriever, which ensnares the clot with a corkscrew-shaped device, and the Penumbra System, which uses a vacuum tip to remove the clot, have been largely replaced by newer, faster and more reliable wire-mesh stentrievers like Solitaire and Trevo.
Though tPA continues to be the optimal initial treatment for ischemic stroke, the American Heart Association/American Stroke Association also recommends stent retrieval device for certain patients experiencing acute ischemic stroke, including patients who:
• Had no significant disability before the current stroke
• Received tPA within 4.5 hours of symptom onset
• Have a clot blocking a large artery supplying blood to the brain
• Are at least 18 years old
• Experienced an acute, severe stroke
• Have no permanent damage in more than half the brain on the affected side
• Can have the procedure start within six hours after symptom onset
The response time to treat stroke victims has improved in recent years as well. The benefits of tPA and endovascular surgery depend on the time it takes to treat a stroke. The heightened awareness of the need for fast-acting treatment by emergency responders and clinicians has made endovascular therapy a more viable alternative.
The ideal “door-to-needle” time—the time from which a stroke patient enters the hospital, is evaluated and tPA administered—is 60 minutes or less. This rapid response should also benefit endovascular therapy results.
Barriers to endovascular therapy
A major benefit of endovascular therapy is that it can extend the therapeutic window for patients who arrive at the hospital too late for tPA. Yet, if endovascular therapy sounds too good to be true, it may be, at least for now.
Few U.S. hospitals are equipped to perform the procedure. Surgeons must be specially trained in endovascular therapy, and protocols for the therapy must be developed. For the most part, the intervention is currently available in stroke centers that took part in the clinical trials. It’s also used more often at teaching hospitals in urban areas than in other locations.
One tactic some emergency services are using to work around the spotty availability of endovascular therapy is to get stroke patients to the nearest hospital that offers tPA within the four-and-a-half-hour time frame. Once a patient is evaluated and tPA administered, he or she can be safely transported to a stroke center where endovascular therapy can be performed.