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Recieved: 14 July 2015/ Accepted: 20 August 2015/ Published online: 30 September 2015
Mechanical Blood Clot Retrievers
ABSTRACT
Stroke is one of the leading cause of death and serious longterm disability. There are two types of stroke - hemorrhaging and ischemic. The last one can be treated with clot-busting drugs such as tissue plasminogen activator (tPA) and urokinase, but drugs must be given to patients within 3 hours of the onset of stroke symptoms. Unfortunately, just a tiny fraction of patients enter the emergency room within first three hours. For those who are not eligible for clot busters scientists designed mechanical blood clot retrievers. There are some retrievers’ generations: first - MERCI (Mechanical Embolus Removal in Cerebral Ischemia) and Penumbra; second - Solitaire and TrevoPro. Retrievers are effective but they remove clots fragmentally and fragments can embolize arteries. To avoid this adverse reaction scientist invented new generation of retrievers - Lazarus Funnel and ReCover which are close to get wide use in clinical practice.
KEYWORDS
Stroke, Blood Coagulation, Thrombectomy, Equipment
INTRODUCTION
Stroke, or cerebrovascular insult (CVI), is disturbed circulation that starves neurons of oxygen. It results in neurons death which in turn causes specific stroke signs and symptoms. Here are some of them: 1) Loss of consciousness; 2) Loss of body balance; 3) Inability to control or feel one side of the body; 4) Blindness in one eye; 5) Problems with understanding what goes around; 6) Inability to speak clearly; 7) Ear tingling.
There are two types of stroke: 1) ischemic - caused by blood vessel occlusion that leads to ischemia distal to the obstruction;
2) hemorrhagic - caused by blood vessel rupture that result in the lack of oxygen all around the damaged
area of brain.
These two types of stoke are treated in a different way. Let me draw your attention to the treatment for ischemic stroke.
Currently, it is available two main directions for stroke treatment. The aim is to provide revascularization and restore the blood flow. It can be reached by using thrombolytics such as tissue plasminogen activator
Ekaterina Kochetova 1 ; http://orcid.org/0000-0001-7079-6380 E-mail: katerina15101994@gmail.com
1 Department of Pathological Physiology, I.M. Sechenov First Moscow State Medical University, Moscow, Russian Federation
(tPA), streptokinase or urokinase but drugs must be given to patients within 3 hours of the onset of stroke symptoms [1, 24-25]. However, a tiny fraction of patients with acute ischemic stroke is eligible for this kind of treatment due to the late enters to the hospitals [2]. Patients who don’t meet the requirements for clot buster therapy have got a chance of good outcomes with designing mechanical tools that are used in surgery to remove thrombi in a blocked area. Unfortunately, this innovative treatment is used not worldwide: only the USA, Canada, Japan and west Europe do thrombectomy in the brain arteries. Moreover, many medical students and some doctors in Russia are not familiar with mechanical blood clot retrievers: how they work, what benefit is to use them, what the difference between retrievers’ generations is. I hope the review will help to realize lots of useful and important data about mechanical blood clot retrievers.
MAIN BODY
Retrievers’ generations
There are some retrievers’ generations which are different in many indicators. The first generation is MERCI (full name is Mechanical Embolus Removal in Cerebral Ischemia) and Penumbra;
The second one - Solitaire and TrevoPro. Retrievers are very effective but they remove clots fragmentary and fragments can embolize arteries. To avoid this adverse reaction scientist designed new generation of retrievers - Lazarus Cover and Lazarus ReCover.
MERCI
The MERCI Retriever is a medical devised designed to remove emboli in cerebral arteries. It was the first devise improved by US Food and Drug Administration (FDA) in August 2004 to extract clots in patients who suffer from acute ischemic stroke [3].
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Picture 1. MERCI is in the process of thrombectomy Picture 2. Different Penumbra retrievers
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Picture 3. Solitaire stent retnever is inside of thrombus
The retriever is a long thin wire with a spiral coil formed at the distal end. The process starts when a catheter is snaking into the affected vessel from the femoral artery. Then MERCI heads upward through the catheter to the affected site of the brain. While the retriever is in a catheter tube the distal coil keeps straightened to fit the catheter shape [4].
The retriever is then fed through the catheter. When the retriever emerges at the clot site, a surgeon pulls back a catheter, then the wire reforms, wrapping around the clot with tiny loops and the clot can be pulled from the brain artery. At this time the balloon is inflated to prevent blood flow that could hinder the retrieval process. To prevent breaking off the clot while pulling it out, a balloon at the proximal end is inflated to stop blood flow through the artery. Once the clot is pulled out, the balloon is deflated and the blood flow is restored [5].
Penumbra
The Penumbra System is the second FDA-approved device specifically designed for the purpose of re-canalization in acute brain ischemia [7]. The Penumbra is used for endovascular thromboaspiration. The system provides dual options: the first one is debulking thrombus, and the second - aspiration of clots that have appeared during the debulking.
Mechanism pretty differs from MERCI system. Once the Penumbra system achieved an appropriate position which is proximal to the clot, an aspiration pump is turned on to start reduction and aspiration of the clot [8-10].
Solitaire
The Solitaire is a self-expanding stent made with plenty of thin wires. Solitaire is a combination of a stent (a tube used to expand narrowed blood vessels)
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and a retriever (a trap-device used to remove any kind of emboli) [11-13]. This combination allows the Solitaire to be extremely effective in opening up intracranial vessels in acute ischemic stroke [14].
Thrombectomy starts when a guidewire is placed into the femoral artery and directed up into the blocked brain artery. Guidewire should be placed distal of thrombus. A microcatheter is then fed up to and through the blockage. Next step is to pull out guidewire and place The Solitaire through the microcatheter. Pulling back the microcatheter, solitaires is expended in the area of the clot and grasp it. The clot is disrupted and can be pulled out by the device [15].
Picture 4. Lazarus Recover while pulling out the clot
Lazarus Funnel
Stent retrievers have created dramatically growth in acute stroke therapy but they remove clot fragmentary and these emboli can obturate arteries [16].
To decrease this possible unfavorable reaction scientist invented new generation of retrievers. Lazarus Effect is a name of a company that designed new innovative retrievers for thrombectomy. Two devices (Lazarus Cover and Lazarus ReCover) have already got CE-marked and widely use in European countries, however, Lazarus Effect official site says that these devices are not available for sale in the United States [17-18]. Moreover, the company gives a data that three new retrievers are under development (Lazarus Lynx, Lazarus Funnel and Lazarus Locket) [18]. All these devices are a combo of stent retriever
and a funnel which prevent artery embolization [19]. Clinical trials MERCI vs Solitaire
Most popular devices in clinical use are MERCI and Solitaire. 113 patients with acute ischemic stroke admitted to hospital within 8 hours of stroke symptoms took part in clinical trials. The researches randomly divided patients into two groups. The first group was treated with MERCI, the second one -with Solitaire.
According to the Solitaire with the Intension for Thrombectomy (SWIFT) trial published online in Lancet in August 2012, Solitaire was totally better than MERCI [22].
The results showed that:
1. Solitaire was effective in 61% of patients (it opened blocked vessels without causing symptomatic bleeding in or around the brain) vs 24% in the Merci group.
2. Mortality rate three months after a stroke was lower in the Solitaire group (17,2%) than in the Merci group (38,2%);
3. 11% of the MERCI group had bleeding in the brain compared with 2% in the Solitaire group.
4. 58% of the Solitaire group had good mental and motor functioning at 90 days, compared with 33% in the MERCI group. (Fig.1)
Solitaire vs Lazarus proximal Funnel and Lazarus distal Funnel
A cerebral flow model was used as in vitro simulator thrombectomy procedures to estimate efficacy of Lazarus Funnel. There were three cohorts: control is Solitaire retriever + guide catheter; proximal Funnel placement + control; and distal Funnel placement + control [23].
Successful re-canalization was more effective on 25% and reduction in distal emboli on 20% when proximal Funnel was used; and a 200% increase in successful re-canalization and a 60% reduction in emboli using distal Funnel [23]. (Fig.2)
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Picture 5.Devices with fragments of thrombus
Fig.1 Comparison outcomes and effectiveness In MERCI and Solitaire groups
CONCLUSION
We can see that devices for thrombectomy in acute ischemic stroke play a great role in a quick and an effectual rehabilitation. Patients treated with Solitaire stents had better revascularization rate, clinical outcome and lower complication rate than patients treated with the Merci retriever. The Lazarus Funnel resulted in a significant increase in re-canalization and
significant reduction in distal emboli without increase in time to re-canalization.
I truly believe in the near future this technique in acute ischemic stroke treatment will be used worldwide.
ACKNOWLEDGEMENTS
The author thanks MD-PhD Z.S.Manasova, Department of Pathological physiology, I.M.
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Sechenov First Moscow State Medical University, Moscow, Russian Federation, for her advices and help.
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