Every Day
January - April 2006 Issue
Stroke News: Advanced Device Lets Doctors Pull Out Clots
Sam O. Zaidat, MD, MScMedical College of Wisconsin
Neuro-Interventional Stroke Critical Care Specialist
In 2004, the FDA approved a new device to remove clots from blocked arteries. Known as the Merci® Retriever, the device enables interventionalists to extract stroke-causing blood clots in the same way you uncork a bottle of wine.
Q. First of all, what is an ischemic stroke?The majority of the time, an ischemic stroke is the result of blockage in one of the major brain arteries. The area of the brain that is supplied by that artery suffers from immediate loss of blood supply and, consequently, is deprived of oxygen and glucose. Brain cells cannot tolerate a long time without blood and they eventually die.
Q. What are the symptoms of ischemic stroke?Symptoms of stroke can be weakness on one side of the body, slurred speech, loss of vision, double vision, loss of sensation, sometimes loss of balance, and sometimes a feeling of vertigo or motion sickness. If those symptoms last more than six hours, the damage that happens may not be reversible. The only way to reverse this damage is to try to open the blocked artery within the first six hours.
Q. That’s where the new clot-retrieval device comes in. How does it compare to the clot-busting medications we are familiar with?Clots are often resistant to clot-busting medications. So people have come up with the idea that if the clot does not respond to medication, maybe we can take it out mechanically. That’s how the idea of the Merci® Retriever was born.
Q. How does the Merci® Retriever work?
The Merci® device features a series of loops, like a corkscrew.To deploy the device, you first pass a catheter through a groin arteryup to the brain artery that's clogged. Next, you advance the retriever (with loops closed) through the clot. You open two loops behind the clot, then come back into the middle of the clot and open another three loops. You then engage the clot by rotating the device so that it kind of grabs on tight.
The next step is to inflate a balloon to stop the blood flow momentarily so the clot does not flow downstream while you are retracting it outside the artery. You then start pulling gently on the device to bring the clot down to a larger catheter in the neck. Finally, you suck the clot into the catheter and deflate the balloon. If you managed to retract the entire clot, the blood flow will resume and the brain willreceive blood again.
Q. Can the retriever reach every clot?No. The Merci® Retriever will not be effective in a small branch of artery that makes many turns and loops. You need to use the device in a straight moderate size arterial segment, and usually those are at the beginning of the big arteries. But that means you can usually use it if the stroke is severe. In a major stroke, where the clot is big, that’s where the retriever is effective.
Q. What risks are associated with the retriever?The main risk is a brain bleed. One other risk is perforating the artery. Occasionally delayed reestablishment of blood flow when more than six hours has lapsed from the symptoms onset may lead to bleeding into the brain – if the brain has been dead for a while, the sudden gush of blood can create an intracranial bleed.
Q. How many people could this device impact?I would say that about 15 percent of emergency stroke patients can benefit from this device. The retriever has been studied for use up to eight hours after onset of symptoms. Six hours is more optimal to get more of a response, but there is still some response up to eight hours. The Merci® Retriever would improve the outcome for those 15 percent of patients if they came within that time window.
Q. Can the retriever be used in combination with other therapies?If a patient arrives within two hours of initial symptoms and he is a candidate for receiving clot-busting medication through the artery, they would be started on a less invasive treatment with clot busting medications. If the stroke was severe enough and there is no response to medications, we may proceed to perform a brain angiogram to obtain a picture of the arteries and identify any clot. If a clot is seen and big enough and has not been dissolved by the medication, clot retrieval may be used. The clot retrieval may not be considered immediately if the patient presents very early from the stroke onset. But in severe stroke cases, you need to give the patient the benefit of all the treatment modalities. In that scenario, you can offer a combination of clot-busting medications and mechanical clot-retrieval therapies.
Q. How does this new device fit into the “big picture” for stroke care?I believe you have to think of stroke care as a continuum. There are five elements: One, initial care that encompasses EMS service who encounter the patient first hand, and then emergency room physician and a well trained stroke neurologist taking care of the patient within the first hour of their presentation. Two, you have a neuro-interventionalist who can proceed to the next options, administering clot-busting medications directly into the clot itself or taking the clot out using the retriever device. Three, you have to have a specialized neurosurgeon with you on the team to deal with any complications that happen. Four, you want to have a specialized neurointensivist and neuro critical care team to take care of the patient after the procedure in a specialized neuro intensive care unit. Five, neuro rehabilitation and stroke rehabilitation specialists who would provide after care and maximize patient recovery and integration back into the community is important for quality outcomes.
A hospital that has all five elements can take emergency stroke patients through the whole continuum of care. Froedtert & Medical College of Wisconsin has all of the elements and is well equipped to provide complete stroke care.
Author: Sam O. Zaidat, MD, MSc Source: Every Day Date: January - April 2006 Issue |