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Saving BrainsNew Endovascular Approaches to Stroke Preventionby Ruth SoRelle, M.P.H.
Tell this Baylor College of Medicine Chair of Radiology that stroke happens, and doctors just have to deal with the aftermath, and you would think you had walked into a buzz saw. "Of course we can try to beat stroke," he said. "We can definitely do something about it." He points to a photo of a stroke patient in intensive care on a respirator. "We have to do something before it's too late," he said. "This patient was devastated by a stroke. Somehow, we failed her." For Mawad, failure is not an option. The best medicine, and in the toughest cases the tools of endovascular radiology, can prevent the devastating aftermath of stroke. To understand Mawad's plan, you have to understand stroke. Between 80 and 85 percent of strokes are ischemic - a clot shuts off blood flow to the brain, and tissue begins to die. The others are hemorrhagic - caused by uncontrolled bleeding in the brain, usually as a result of an aneurysm, a weakened area of a blood vessel. "We need to recognize them before they rupture," he said. "Then they can be treated preemptively. We can prevent the stroke, and since almost all aneurysms are now treated endovascularly, we don't have to go in and do open surgery." Endovascular is similar to heart procedures such as balloon angioplasty in which a catheter or small tube is inserted into a blood vessel in the groin and fed up the vascular pathway until it reaches the coronary arteries of the heart. There, interventional cardiologists inflate balloons and insert stents to clear clogged arteries that nourish the heart muscle. For Mawad, failure is not an option. The best medicine, and in the toughest cases the tools of endovascular radiology, can prevent the devastating aftermath of stroke. "There are several levels of difficulty above interventional cardiology," said Mawad. "There are three main coronary arteries in the heart. There are 100 to 150 arteries in the brain. You spend 25 years doing this, and you start to know your way around." Endovascular means that Mawad inserts a tiny catheter in a blood vessel in the patient's groin area and painstakingly feeds it through the vascular system until it reaches the weakened area of the brain artery. Once there, he fills the aneurysm with a platinum coil, chosen because its shape and size fits the aneurysm. "It just obliterates the aneurysm," he said. "I tell patients it's as though you have a cavity and we are going to fill it. The cavity stays there, but it is filled." Over the years, he and others in his department have helped tailor the coils to fit the need. Some now have a modified surface that encourages the formation of scar and fibrous tissue - and that makes the repair more permanent. Sometimes the aneurysm's shape impedes repair. Then, he must insert a stent - a taut spring of metal that goes into the artery and strengthens it. Then working through this stent, he inserts the repair coil into the cavity of the aneurysm itself. Ischemic stroke - those that occur when blood flow to the brain is blocked by a clot - is more difficult. The most troubling for Mawad are the strokes that have already occurred. "We have to race against time to salvage brain function," he said. To him, such salvage therapy means an opportunity has already been lost. In some cases, direct infusions of clot-busters such as urokinase, tissue plasminogen activator or Reopro, a monoclonal antibody that inhibits the clumping of blood cells called platelets can clear the artery. Or Mawad can feed a catheter containing a tiny balloon up into the blood vessel and fragment the clot. In tough cases, he might have to use a spring-shaped stent to force his way through the clot. To preserve the brain, he may cool the patient by using cold saline in a catheter - a process called hypothermia. Or he may insert a large balloon in the abdominal cavity below the renal artery. As the heart pumps, this balloon shifts the flow to the head and increases the volume of blood that gets to the brain. It's all a furious attempt to save brain tissue before it dies from lack of blood. Mawad works hard to prevent disability. As far as he's concerned, however, the fact that the stroke has occurred represents failure. He wants to intervene much sooner. "We want to create a paradigm shift - from salvage to prevention," he said. "We want to identify patients at risk - the smokers, diabetics, hypertensives and those with a family history of stroke, women with atrial fibrillation (an abnormal heart rhythm) or those who are already having 'pre-stroke' symptoms such as transient ischemic attacks (mini-strokes)." Mawad believes these patients deserve to be studied with a CT scan, or an MRI (magnetic resonance imaging) or MRA (magnetic resonance angiography that looks at the blood vessels in the brain). Such tests will identify those who have atherosclerotic disease, which can clog their arteries. "If we identify them, and we know they are symptomatic, then the first step is maximal medical treatment," he said. "We treat their blood pressure with ACE inhibitors, we treat their lipid (blood fat) profile with statins (to reduce cholesterol) and we use anti-platelet therapy such as aspirin or Plavix (a so-called super-aspirin). "If we maximize their medical treatment and they continue to have symptoms, then we move on to revascularization procedures such as angioplasty and stent," continued Mawad. These are designed to open the narrowed arteries and keep them open with a stent that provides "ribs" to maintain the artery's architecture.
In this procedure, Mawad pushes a catheter up from the groin blood vessel into the carotid artery where he unsheathes a filter above the area of narrowing or stenosis. This prevents the remnants of the clot from migrating toward the brain. Then he inflates a balloon, crushing the material, called plaque, against the wall of the artery. Plaque is a fibrous buildup of tissue that narrows the artery. Next, he puts a stent in the artery to hold it open and prevent the artery from narrowing again. When he collapses the filter and pulls it out, he can actually find the minute particles of the clot collected in the material. "It works," said Mawad. "It's the same principle as angioplasty and stenting in the heart." He uses the same technique in stenosis of the vertebral artery, which carries blood to the brain stem. Mawad was among the first in his field to do this, and it is still considered experimental. Currently, it is done only on high-risk patients who do not respond to medical therapy. Feeding tiny wires no more than 1/12,000th of an inch into the arteries near and in the brain requires sophisticated pictures of the brain and its tree of blood vessels. Using three-dimensional pictures taken with his sophisticated machinery, Mawad can plan his procedures beforehand, measuring the size of the arteries on the tiniest scale and determining what size balloon and stent he needs. During the procedure, he watches the progress of the wire, balloon and stent on moving images displayed in the procedure area. Later, he uses the three-dimensional pictures again to check his work and make sure the artery is indeed open. "Three-dimensional imaging is an essential tool," said Mawad, who operates one of the busiest centers for this kind of treatment in the nation at St. Luke's Episcopal Hospital. He has participated in the development and refinement of many of the techniques in use here and in other major centers today. Combating stroke's deadly effects requires a team from many different disciplines - radiology, cardiology, neurology, neurosurgery, vascular medicine and more. This team can salvage brains when a stroke has occurred, and more important, prevent the event itself. His dream is to build a center where he can prevent stroke and other neurovascular disorders that threaten that most precious of organs - the brain. |
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Volume 1, Issue 2, Summer 2005 |
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| Last modified: October 10, 2008 |
Dr. Michel E. Mawad is on a mission to save brains.
Today, endovascular techniques such as those used by Mawad are the treatment of choice in patients who are at high risk of complications from surgery.