Patent Publication Number: US-2009240238-A1

Title: Clot Retrieval Mechanism

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a clot retrieval and removal system for percutaneous removal of clots or other emboli from a body lumen. 
     BACKGROUND OF THE INVENTION 
     Human blood vessels often become occluded (blocked) or stenotic (narrowed) by plaque, thrombi, deposits, or other substances, which reduce the blood carrying capacity of the vessel. For instance, a stenosis may be formed by an atheroma which is typically a harder, calcified substance which forms on the lumen walls of the blood vessel. Also, the stenosis can be formed of a thrombus material which is typically much softer than an atheroma, but can nonetheless cause restricted blood flow in the lumen of the blood vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, or even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected. 
     Percutaneous interventional procedures developed to treat occlusive vascular disease, such as angioplasty and stenting, often dislodge material from the vessel walls. This dislodged material, known as emboli, enters the bloodstream, and may be large enough to occlude smaller downstream vessels, potentially blocking blood flow to tissue. The resulting ischemia poses a serious threat to the health or life of a patient if the blockage occurs in critical tissue, such as the heart, lungs, or brain. In order to reduce the risk of embolization, guidewire filter devices or embolic protection devices that can be temporarily placed within the vascular system to collect and retrieve plaque, thrombus and other embolic particulate, which may be dislodged during angioplasty, stenting or other procedures, are known. 
     Another method of treating stenotic vasculature is removal of the stenosis by thrombectomy or atherectomy. During thrombectomy and atherectomy, the stenosis is mechanically cut or abraded away from the vessel. However, such procedures often require the use of some type of embolic protection device to capture emboli released from the treatment site. 
     In certain presentations, it may be appropriate or desirable to remove an emboli or thrombi in one operation, for example, removal of a cerebral thrombosis and/or other emboli blocking blood flow to the brain that are associated with ischemic stroke. In another example, removal of an emboli or thrombi in one operation may be desirable when the blockage occurs in a narrow or tortuous portion of the vasculature, which multiple more complex medical devices cannot easily access, or when the stenosis is of a softer thrombus composition. In addition, a medical device for removing thrombi or emboli from within a vascular system that eliminates the need for an additional filtering device would be desirable. As such embodiments of the present invention are directed to a medical device that provides a low profile self-expanding vascular device useful for thrombectomy and embolectomy that does not include a filtering element. 
     BRIEF SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to a clot retrieval device for removing thrombi or other emboli from a body lumen. The clot retrieval device includes an elongate shaft portion, a self-expanding snare disposed at a distal end of the shaft portion and a flexible bag portion attached to the self-expanding snare. The snare may be a loop or circlet formed in a distal end of the elongate shaft portion or may be a separate component attached thereto. Preferably at least the self-expanding snare is formed of a shape memory material. An opening of the bag portion for receiving the thrombi or emboli there through faces proximally when the snare is fully deployed. The bag portion is made of a flexible, non-porous material, such as a balloon-type or elastomeric material, that is foldable or otherwise collapsible to achieve a low-profile for tracking through the body lumen. 
     Embodiments of the present invention are directed to methods of using the clot retrieval device described in the previous paragraph. In an embodiment, a method of removing a clot or other emboli from a body lumen includes the steps of tracking a clot retrieval device having an elongate shaft portion, a self-expanding snare and a non-porous bag portion to a treatment site within the body lumen proximate the clot. The clot retrieval device is then deployed distal of the clot to allow the snare to reach an expanded configuration such that an opening of the bag portion faces proximally toward the clot. The snare is manipulated to envelope the clot within the bag portion of the clot retrieval device for subsequent removal from the body lumen. The method may include drawing the snare proximally over the thrombi or emboli and/or using a secondary device tracked proximal of the clot to push the thrombi or emboli through the snare into the bag portion of the device. In another embodiment, a balloon catheter may be used to restrict or prevent blood flow through the treatment site to aid in easing the snare over the clot or emboli. In addition, a balloon of the balloon catheter may be inflated within the body lumen to be in contact with the clot and act as a “stop” to prevent proximal migration of the clot during capture by the snare of the clot retrieval device. Such a method may help to prevent damage to a wall of the body lumen. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The foregoing and other features and advantages of the invention will be apparent from the following description of the invention as illustrated in the accompanying drawings. The accompanying drawings, which are incorporated herein and form a part of the specification, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. The drawings are not to scale. 
         FIG. 1  illustrates a side view of a medical device according to an embodiment of the present invention. 
         FIG. 2  illustrates an expanded, partial cross-sectional view of a distal portion of the medical device of  FIG. 1  tracked proximate a clot within a body lumen. 
         FIG. 2A  depicts an end view of a clot retrieval device depicted in  FIG. 2  in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a clot retrieval device according to an embodiment of the present invention partially deployed distal of the clot of  FIG. 2 . 
         FIG. 4  illustrates the clot retrieval device of  FIG. 3  in a fully deployed configuration. 
         FIG. 5  illustrates the clot retrieval device of  FIG. 3  enveloping the clot. 
         FIG. 6  illustrates a side view of a clot retrieval device in accordance with another embodiment of the present invention. 
         FIG. 6A  depicts an end view of the snare of the clot retrieval device of  FIG. 6  in an unexpanded configuration. 
         FIG. 7  is a flow chart depicting various methods in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Specific embodiments of the present invention are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements. The terms “distal” and “proximal” are used in the following description with respect to a position or direction relative to the treating clinician. “Distal” or “distally” are a position distant from or in a direction away from the clinician. “Proximal” and “proximally” are a position near or in a direction toward the clinician. 
     The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Although the description of the invention is in the context of treatment of blood vessels such as the coronary, carotid and renal arteries, the invention may also be used in any other body passageways where it is deemed useful. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. 
       FIG. 1  illustrates a side view of a system for retrieving a clot or emboli from a body lumen in accordance with an embodiment of the present invention, with  FIG. 2  illustrating an enlarged partial cross-sectional view of a distal portion of the system situated within a body vessel  201  proximate a clot or other emboli  203 . The system includes a single-lumen guide catheter  100  having a hub  102  for attaching to a Tuohy-Borst adapter (not shown) at the site of entry into a body lumen, as would be known to one of ordinary skill in the art. Suitable guide catheters that may be used in embodiments of the present invention include those shown and described in U.S. Pat. No. 5,902,287 to Martin and U.S. Pat. No. 5,964,971 to Lunn, which are hereby incorporated by reference in their entirety. A single-lumen delivery or sheath catheter  104  is slidably received within the lumen of guide catheter  104  and has a proximal end  108  that remains proximal of hub  102  and a distal end  106  that is tracked through the vasculature to the point of treatment, i.e., the site of the thrombi or emboli  203  to be removed. Suitable delivery or sheath catheters that may be used in embodiments of the present invention include those shown and described in U.S. Patent Publ. No. 2007/0032815 to DeVaux and U.S. Patent Publ. No. 2005/0004553 to Douk, which are hereby incorporated by reference in their entirety. 
     A clot retrieval device  110  is shown slidably received within lumen  205  of sheath catheter  104  and includes a proximal end  112  that remains outside the patient proximate hub  102  and a distal end  114  that is positionable at the point of treatment proximal of clot  203 . In  FIG. 1 , distal end  114  of clot retrieval device  110  is shown protruding slightly from distal end  106  of sheath catheter  104 , but it should be understood that this is for illustrative purposes only and that during use while sheath catheter  104  is being advanced through the vasculature clot retrieval device  110  would be maintained within lumen  205  until deployment. In  FIG. 2 , distal end  114  of clot retrieval device  110  is shown being advanced distally from lumen  205  of sheath catheter  104  in the direction of arrow X, such that distal end  114  pierces and passes through clot  203  while clot retrieval device  110  is still in an unexpanded configuration. 
     In another embodiment, clot retrieval device  110  may utilize a restraining or delivery sheath to maintain the device in its collapsed configuration, in addition to or instead of sheath catheter  104 , such that once a distal end of the restraining sheath is retracted by the clinician or the sheath is otherwise removed, the expandable or deployable portion of the device will transform into its fully expanded configuration, as will be explained in greater detail below with reference to  FIGS. 3 and 4 . In an embodiment, an RF energy source may be used to cut through the restraining sheath to allow expansion of the device. 
     With reference to  FIGS. 3 and 4 , clot retrieval device  110  includes an elongate shaft portion  220 , a snare or wire circlet  216  and a balloon-type bag or pouch portion  218 . Elongate shaft portion  220  extends from proximal end  112  to snare  216  and may be a solid wire, a hollow tube or of another construction suitable for a guidewire. Elongate shaft portion  220  must be flexible enough to navigate the tortuous pathways of the vascular system and yet have pushability. As such to impart improved pushability to clot retrieval device  110 , elongate shaft portion  220  may be a solid core wire formed from a material such as stainless steel, a nickel-based super alloy, a spring steel alloy, particularly a composition sold under the trademark ELIGILOY, titanium, MP35N or nitinol. In addition, a core wire that forms elongate shaft portion  220  may be ground down and have several diameters in its profile in order to provide a transition in stiffness along its length. 
     In another embodiment, at least a proximal portion of elongate shaft portion  220  may be of a thin-walled, tubular structure of a metallic material, such as stainless steel, a spring steel alloy, particularly a composition sold under the trademark ELIGILOY, MP35N, titanium or nitinol. In an embodiment, a metallic tube commonly referred to as hypodermic tubing or a hypotube may be used. In an alternate embodiment, elongate shaft portion  220  may include a proximal tubular structure made from a polymeric material, such as polyethylene block amide copolymer, polyvinyl chloride, polyethylene, polyethylene terephthalate, polyamide, polyimide, polypropylene, polytetrafluoroethylene, polycarbonates, and polyurethanes, alone or in combination with a metal reinforced polymer shaft portion utilizing one or more of the aforementioned materials. 
     Snare  216  may be a loop formed in elongate shaft portion  220  proximate the distal end  114  of the clot retrieval device  110 . The transformation of snare  216  from a compressed, delivery configuration to an expanded, deployed configuration may be impelled by external mechanical means, such as in the manner of a lasso wherein the clinician distally feeds an additional length of shaft portion  220  until snare  216  achieves an expanded configuration, or by self-shaping memory to be self-expanding. Preferably, snare or circlet  216  is self-expanding, meaning that snare or circlet  216  has a mechanical memory to return to the expanded, or deployed configuration. Mechanical memory may be imparted to the metal of snare  216  by thermal treatment to achieve a spring temper in stainless steel, for example, or to set a shape memory in a susceptible metal alloy, such as nitinol. 
     In an alternate embodiment, the snare may be a separate component that is attached to a distal end of the elongate shaft portion. In such an embodiment, the snare may be formed from a different material than the remainder of the clot retrieval device. In certain instances, a separately formed snare may achieve manufacturing and/or performance advantages over an integral snare and shaft component. 
     Balloon-type bag or pouch portion  218  of clot retrieval device  110  is of a balloon or other flexible material that is nonporous and is formed in a conical or windsock-like shape. In accordance with embodiments of clot retrieval devices described herein, a nonporous material is a continuous material, such as a fabric or film, with a pore structure that is small enough so as to restrict transport of thrombi, leukocytes, erythrocytes, and similar solid blood constituents therethrough. In other words, the nonporous material has no openings or holes formed therein that would allow blood flow through the material. In an embodiment, bag portion  218  may be of a flexible, non-elastic or elastomeric material to include polymeric materials used in angioplasty balloons or covered grafts, such as polyamides, to include certain nylons, polyurethanes, polytetrafluoroethylene, polyesters, including Dacron, and polyimides. With reference to  FIG. 2A , bag portion  218  may be formed to fold around snare  216  in a predetermined manner, such as the spiral “star” shape shown, to achieve a low-profile and ease of deployment. In order to achieve a symmetrically consistent folded profile, bag portion  218  may be formed of material and in a manner as shown and described with respect to angioplasty balloons in U.S. Pat. No. 5,350,361 to Tsukashima et al., which is incorporated by reference herein in its entirety. 
     With reference to  FIGS. 3 and 4 , clot retrieval device  110  is maneuvered to be distal of clot  203  such that the device achieves an expanded configuration distal of the clot or emboli. Bag portion  218  is shown attached to snare  216  such that an opening  328  of bag portion  218  faces proximally toward clot  203  when the snare  216  is fully deployed. In order to prevent over enlargement of snare  216 , a ring or circular clip  326  closely encircles the loop or winding that forms snare  216  to aid in defining or fixing a diameter of opening  328 . Ring  326  is secured to shaft portion  220 . In an embodiment, ring  326  may be sized to allow some expansion of the loop that forms snare  216  thereby allowing snare  216  to expand to conform to blood vessels of varying diameters. In another embodiment, ring  326  may restrict movement of the loop that forms snare  216  so that snare  216  may be preset in size such that when fully expanded snare  216  may not come into contact with the walls of vessel  201 . Alternatively, a tether or wire (not shown) may be attached to ring  326  to permit a clinician to manipulate the diameter of the loop to open or close snare  216 . 
     In an embodiment where snare  216  is of nitinol, bag portion  218  may be attached to snare  216  either by coating snare  216  with a biocompatible polymer or by surrounding snare  216  with a suitable polymeric sleeve such that a material of bag portion  218  may be thermally bonded thereto. In addition, webs  324  of a balloon or other flexible material may be attached between a proximal end of snare  216  and elongate shaft portion  220  to add structural support to snare  216  and aid in maintaining proper orientation of ring  326  and proximal opening  328  during capture of the clot. 
     A small flexible end wire or tail portion  222  may distally extend within bag portion  218 , from snare  216  to distal end  114  of clot retrieval device  110 , in order to maintain or define a length of bag portion  218  in its expanded configuration. In an alternate embodiment, as shown by the dotted line in  FIG. 4 , tail portion  222  may include a curved portion  222   a  that aids in defining an interior space of bag portion  218 . 
     In  FIG. 5 , clot retrieval device  110  is shown pulled proximally over clot  203  in vessel  210  such that clot  203  is enveloped within bag portion  218 . It should be understood that bag portion  218  is not necessarily of a transparent material and that clot  203  is viewable therethrough in  FIG. 5  for illustrative purposes only. 
       FIG. 6  illustrates a clot retrieval device  610  in accordance with another embodiment of the present invention, with  FIG. 6A  depicting an end view of clot retrieval device  610  in a spirally coiled, unexpanded configuration. Clot retrieval device  610  includes elongate shaft portion  620 , snare  616  and non-porous, balloon-type bag portion  618 , each of which may be made of the various materials previously described with reference to the embodiment of  FIGS. 2-5 . Elongate shaft portion  620  may be constructed as in the previous embodiment with a winding or loop forming snare  616  and tail portion  622 . However, as shown in  FIG. 6A , snare  616  is wound upon itself or spirally coiled to achieve the compressed or unexpanded configuration of clot retrieval device  610 . As such, snare  616  unwinds to the diameter of vessel  201  to achieve the expanded configuration of clot retrieval device  610 , as shown in  FIG. 6 . In this manner snare  616  is able to fit variable diameters of vasculature. Bag portion  618  may be bonded, such as by thermal bonding, to snare  616  in a manner as previously described such that bag portion  618  may be tightly coiled along with snare  618  to achieve a low-profile and for ease of deployment. 
     Tethers  630  are attached at each of their distal ends to snare  616  and have proximal ends (not shown) that extend out of the patient for manipulation and control by the clinician. In other words, tethers  630  proximally extending adjacent elongate shaft portion  620  for substantially the length of clot retrieval device  610 . In an embodiment where a proximal portion of elongate shaft portion  620  is a hollow tube, a distal port may be provided to allow a proximal length of tethers  630  to enter a lumen of elongate shaft portion  620  to be accessible to a clinician via a proximal port therein. Tethers  630  facilitate manipulation, clot retrieval, and extraction of clot retrieval device  610  by allowing a clinician additional control of the device. Tethers  630  may be thin metallic wires or strands of material. Although three tethers  630  are shown, it should be understood that fewer or more tethers may be utilized without departing from the scope of this embodiment of the present invention. 
     In another embodiment, in order to accommodate the unwinding of snare  616 , bag portion  618  may be slidably attached thereto via hem  632 . Hem  632  is sized and configured to allow the loop that forms snare  616  to enter and slidably extend through hem  632  unobstructed so that tail portion  622  sits within bag portion  618 . Tethers  630  may be attached to hem  632 , rather than snare  616 , in order to allow snare  616  to freely slide/uncoil within hem  632 . In an alternate embodiment wherein a tail portion is not utilized, hem  632  may be sized to accommodate unwinding/expansion of coiled snare  616  therein. 
     A method of using a clot retrieval device in accordance with an embodiment of the present invention is described as follows, with reference to  FIGS. 3-5 . A guidewire (not shown) is advanced into the patient&#39;s vasculature until the intended treatment site, i.e., the clot or emboli  203 , is reached. A sheath or delivery catheter  104  is loaded with a clot retrieval device  110  in accordance with an embodiment of the present invention. The sheath catheter  104  is then back-loaded onto the guidewire and tracked thereover until a distal end  106  of the sheath catheter  104  is proximal of the clot or emboli  203  to be removed. The clot retrieval device  110  is then pushed distally from the sheath catheter lumen  205  to a position distal of the clot where the snare  216  of the device self-expands into its deployed configuration, as shown in  FIGS. 3 and 4 . With the snare  216  and bag portion  218  fully deployed within the vessel, the clot retrieval device  110  is manipulated, e.g., proximally retracted, such that the clot  203  is enveloped within the bag portion  218  of the device for removal. 
     Alternatively, as represented in the method depicted on the right side of the flow chart of  FIG. 7 , after the clot retrieval device  110  has been deployed the sheath catheter  104  may be advanced distally to push the clot  203  through the snare  216  into the bag portion  218  of the device for removal. In either manner, the clot retrieval device  110  with the clot therein may then be retracted back into the sheath catheter  104  for subsequent removal from the vasculature. It would be understood by one of ordinary skill in the art that the sheath catheter  104  may be removed prior to the manipulation of the clot retrieval device  110  over the clot, such that the clot retrieval device  110  with the clot therein is removed separately from the vasculature upon capture of the clot. 
     In a method according to another embodiment of the present invention, as represented in the method depicted on the left side of the flow chart of  FIG. 7 , the sheath catheter  104  may be removed from the vasculature after deployment of the clot retrieval device  110  and a balloon catheter (not shown) may be advanced over the guidewire, if still indwelling, or over the elongate shaft portion  220  of the clot retrieval device  110  until a distal end thereof is positioned in apposition with a proximal portion of the clot. One of ordinary skill in the art will recognize that any of a number of balloon catheters known in the art would be suitable for practicing this embodiment of the present invention. The balloon of the balloon catheter may then be inflated to a sufficient diameter to hold its longitudinal position within the vessel. The balloon may then act as a stop to prevent the clot from moving proximally away from the snare  216  and bag portion  218  of the clot retrieval device  110  to thereby ease the capture of the clot by the clot retrieval device  110 . Additional advantages of this method are that the balloon stops or dramatically restricts blood flow thereby preventing the blood from carrying distally small portions of thrombi or emboli, which may break-off during positioning of the clot retrieval device; it also quells a “water-hammering” effect, which may tend to break-up the clot; and in certain areas of the vasculature may effectively create a backflow helping to dislodge the clot and easing removal thereof. 
     In a method according to another embodiment of the present invention, as represented in the alternate method depicted on the left side of the flow chart of  FIG. 7 , a large lumen balloon catheter (not shown), rather than a simple sheath catheter, may be initially tracked over the guidewire to be positioned proximal of the clot. A clot retrieval device  110  in accordance with an embodiment of the present invention may then be slidably advanced through the balloon catheter lumen to penetrate and pass through, or alternatively pass by, the clot such that the snare  216  and bag portion  218  of the clot retrieval device  110  expands distal of the clot. A balloon of the balloon catheter is then inflated to substantially decrease or entirely stop blood flow as the clot retrieval device  110  is proximally advanced to envelope the clot within the bag portion  218  of the device for removal from the vasculature. A large lumen balloon catheter suitable for practicing this method of the present invention is shown and described in U.S. Pat. No. 6,702,782 to Miller et al., which is hereby incorporated by reference herein in its entirety. 
     While various embodiments according to the present invention have been described above, it should be understood that they have been presented by way of illustration and example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the appended claims and their equivalents. It will also be understood that each feature of each embodiment discussed herein, and of each reference cited herein, can be used in combination with the features of any other embodiment. All patents and publications discussed herein are incorporated by reference herein in their entirety.