Patent Publication Number: US-2007118165-A1

Title: System and method for removal of material from a blood vessel using a small diameter catheter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      The present application is a continuation-in-part of commonly assigned copending U.S. patent application Ser. No. 11/074,827, which was filed on Mar. 7, 2005, by Richard M. DeMello, et al. for a SMALL DIAMETER SNARE and is hereby incorporated by reference, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/551,313, which was filed on Mar. 8, 2004, by Richard M. DeMello et al., for a SMALL-DIAMETER SNARE and is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to surgical catheters, and more particularly to devices for removing thrombus, and other blockages and materials within blood vessels.  
      2. Background Information  
      Certain snare and similar devices have become available over recent years for retrieving malfunctioning or misplaced devices or blockages such as plaque and thrombus within the cardiovascular and non-vascular regions of the body. These typically consist of fairly large diameter sheaths, which house a movable central wire or wires whose distal ends are formed into a loop, plurality of loops or other purpose-built shape. The loop is used to ensnare and capture the desired object for withdrawal and removal from the body, while other shapes may be used to grasp or capture softer biological materials. In use, the snare or another distal tool is typically passed through a guiding catheter or other introducing catheter that is placed within the vasculature and is directed to the vessel or area where the misplaced or malfunctioning device is located. The snare/distal tool can then capture the intended device or material and retrieve it out of the body through the introducing catheter or by withdrawing both the snare and the introducing catheter in tandem.  
      Currently available snares and similar distal tools are designed using large diameter outer sheaths that require larger entry sites. This may result in complications such as excessive bleeding and/or hematomas. Additionally, because of the large diameter, it may be necessary to remove the existing catheters and exchange to other larger devices increasing the overall time and cost of the procedure. A third disadvantage of the old means is that the outer sheath, which is typically made of a plastic material, exhibits little or no torque control, which can make ensnaring the misplaced or malfunctioned device or removing other materials very difficult. Lastly, because of the size and stiff design of these snare/distal tool devices, they have a very sharp distal leading edge which cannot be safely advanced into small diameter vessels such as those in the coronary and cerebral vasculature without risking damage to the vessel wall. An exemplary small-diameter snare design that satisfies many of the concerns above is provided in commonly owned U.S. Pat. No. 6,554,842, entitled SMALL DIAMETER SNARE by Heuser, et al., the teachings of which are expressly incorporated herein by reference.  
      Devices, such as the exemplary Heuser design, are characterized by a small-diameter outer sheath that has a relatively thin wall (for example, approximately 0.0020 inch or less in wall thickness) so as to accommodate an axially movable/rotatable central core wire of approximately 0.008 inch. The structure allows a snare loop attached to the distal end of the core wire and housed within the open distal end of the sheath to be selectively extended from the sheath end, withdrawn and torqued. This sheath is at least partially composed of metal. The thinness of the tube, and its metallic content make it susceptible to splitting, fracturing and fatigue failure under stress. In addition, the metal section of the tubular outer sheath tends to experience permanent (plastic) deformation when bent, and once deformed, the central core wire will tend to bind upon the lumen of the sheath, rendering the device inoperable for its intended purpose. In addition, the outer wall of the metal tube section has a lubricious coating, such as PTFE (Teflon), which is typically approximately 0.0010 inch in thickness. This necessitates further downsizing of the sheath overall outer diameter thereby reducing the inner diameter available for accommodating the central core wire, thereby further increasing the risk of inadvertent failure of the device through breakage or plastic deformation.  
      Further considerations arise in the case of a non-snare device used to remove materials from blood vessels. Within the U.S. alone, approximately 700,000 strokes occur every year. The majority of these (83%) are ischemic strokes due to blood clots (thrombus) that become lodged in and block cerebral vessels. It has been documented that if the blockage can be eliminated within a short period of time (up to 8 hours), the patient can experience a full recovery from the stroke. Presently, clot-dissolving drugs can be administered to break up the clot and restore blood flow, however these drugs must be administered within 3 hours of symptom onset as they take considerable time to become effective. Unfortunately, not all patients are medically eligible to receive these drugs and most frequently patients, do not arrive for medical treatment within the 3 hour limit. In these patients, mechanical removal of the blood clot has been shown to have a significant positive outcome.  
      Several devices have been designed to break up and suction-out thrombus in the large vessels of the legs and coronary arteries. These use a variety of means to accomplish this such as water jets, mechanical maceration, ultrasound or photo-acoustic shock waves, and laser ablation. All of these devices however, have limitations when working in the cerebral vessels. First they tend to be large and bulky and very difficult or impossible to navigate above the skull base and secondly, their therapeutic means can be extremely vigorous resulting in damage to the delicate blood vessels in the brain. They also require removal of an already placed microcatheter from the patient in exchange for their device.  
      One device used to treat blood clots is a mechanical capture device whereby the blood clot is grasped and pulled out of the distal vessels of the brain. The MERCI retrieval device (available from Concentric Medical of Mountain View, Calif.) is a 0.014-inch guidewire that can be passed into the blood clot as a straight wire and then can be remotely shaped into a corkscrew configuration, becoming intertwined within the blood clot. The wire is then withdrawn from the distal cerebral vessel pulling the blood clot with it. Although this device addresses the ability to navigate above the skull base, it has one major shortcoming. That is the corkscrew segment of the wire must be very soft and flexible in order to navigate within the brain. This reduces the ability of the device to remain in the corkscrew shape as it is withdrawing the blood clot. During withdrawal, the wire can straighten and the blood clot can be partially or fully released resulting in greater injury to the patient through thromboembolism. A more effective tool for removal of thrombus reduced risk of release or breakup and the ability to navigate smaller blood vessels is highly desirable.  
     SUMMARY OF THE INVENTION  
      This invention overcomes prior disadvantages by providing a small-diameter snare device and a device for removing thrombus and other materials from vascular lumens consisting of a hollow, elongate, thin-walled outer sheath. The sheath is constructed from polymer, at least at a distal part thereof for enhanced flexibility and can be metal at an adjoining proximal part for added strength. A single central core wire extends through the entire length of the sheath. The outer diameter of the core wire is sized close to the inner diameter of the sheath while allowing for axial sliding, in order to maximize the support to the body portion of the snare device. The distal end of the core wire has a tapered section of reduced diameter or cross section to provide a “guidewire-like” flexibility to the distal portion of the device. In one embodiment, a second wire of about fifty percent or less (approximately 30 percent in an illustrative embodiment) of the inner diameter of the sheath is shaped to form a snare loop and the two ends are attached to the distal most portion of the central core wire via welding, soldering, or brazing. In another embodiment, a tool tip for removal of thrombus is provided by joining one or more wires that are shaped to provide a radially expanded structure when deployed from the sheath. Both the snare and tool tip can be termed generally a “capture segment” herein After assembly of the core and sheath, a second short, hollow tube is fitted over the proximal end of the central core and attached thereto to provide an actuating handle to slideably move the central core within the sheath, thus exposing and retracting the snare loop from the open distal end of the sheath. The loop is typically circular or oval shaped and can also be multiplanar (for example, a twisted, figure eight shape) so as to increase the ability to ensnare and capture objects. The loop attachment to the core wire is facilitated and strengthened by a wrapped coupling coil formed typically of 0.001-inch platinum wire applied to secure the loop prior to soldering (brazing or other metal-flowing joining techniques), and through which solder flows to permanently secure the loop to the core wire. The tool tip can be single wire formed into a planar structure or a proximally directed cage that surrounds a central stalk. Alternatively, the tool tip can be a plurality of wires joined to the core wire and extending from an axial central stalk to a plurality of radially oriented positions. The wires can extend proximally to form a fish-hook-like arms that embed into the thrombus and allow it to be withdrawn by withdrawing the device proximally out of the vessel. The wires can be doubled with an end bend, each of the free ends of each bent wire being attached to the core wire.  
      Coatings can be applied to the outer surfaces of the core assembly and the tube assembly to reduce friction between the core and the tube as well as to enhance movement of the snare and thrombus removal device within a catheter. The entire device, when complete, can be made less than 0.014-inch in diameter, and is capable of being placed directly through a percutaneous transluminal coronary angioplasty (PTCA) balloon catheter or other small diameter (micro)catheter that may already be in place within the patient. Alternatively, the snare or thrombus removal device may be passed through the guiding catheter along side of the balloon or access catheter without the need to remove the prior device, and thus, lose temporary access to the site within the patient.  
      In use, the loop of the snare device is first withdrawn into the sheath by pulling on the actuating handle. The snare device is then advanced into the balloon or guiding catheter until the distal end of the snare has exited the distal end of the guiding catheter. The snare is then torqued and manipulated into place adjacent to the object to be retrieved. The snare loop is exposed from the tube by pushing the actuating handle forward; and through a combination of advancing, withdrawing, and rotating the entire device, the object is ensnared within the loop. The loop is then retracted back into the tube so that the ensnared object is grasped tightly within the loop and the snare with the object is withdrawn from the patient&#39;s body.  
      In use, the thrombus removal tool tip is first withdrawn into the sheath by pulling on the actuating handle. The device is then advanced into the balloon or guiding catheter until the distal end of the sheath has exited the distal end of the guiding catheter. The sheath is then directed into or through the thrombus so that it exits the opposite, distal side of the thrombus. The tool tip is then exposed from the sheath by pushing the actuating handle forward; and once withdrawn, the radially extended tool tip is moved proximally to engage the thrombus. In a planar configuration the tool tip mainly rests on the thrombus&#39; distal face. In a proximally projected (fish hook) configuration, the hooks embed themselves in the material. The device is the withdrawn is withdrawn from the patient&#39;s body through the vascular system with the thrombus engaged and dragged proximally by the tool tip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention description below refers to the accompanying drawings, of which:  
       FIG. 1  is a partial side cross section of a small-diameter snare device according to an illustrative embodiment of this invention;  
       FIG. 2  is a full cross section in the region of the attachment between the loop and core wire, taken along line  2 - 2  of  FIG. 1 ;  
       FIG. 3  is a cross section of a snare loop wire according to an alternate embodiment having a braided construction;  
       FIG. 4  is a partial side cross section of the small-diameter snare device including a manipulator handle assembly attached to the proximal end thereof;  
       FIG. 5  is a full cross section in the region of the slide actuator of the handle, taken along line  5 - 5  of  FIG. 4 ;  
       FIG. 6  is a cross section of a pair of D-shaped loop wire sections adjacent to the region of their connection to the core wire according to an alternate embodiment  
       FIG. 7  is a partial side cross section of the distal region of a small-diameter catheter for removal of thrombus and other materials according to an illustrative embodiment of this invention;  
       FIG. 8  is a perspective view of the distal end of the small diameter catheter of  FIG. 7  showing the distal tool deployed;  
       FIG. 9  is a perspective view of the distal end of the small diameter catheter generally in accordance with  FIG. 7  showing a deployed distal tool according to a first alternate embodiment;  
       FIG. 10  is a perspective view of the distal end of the small diameter catheter generally in accordance with  FIG. 7  showing a deployed distal tool according to a second alternate embodiment;  
       FIG. 11  is a perspective view of the distal end of the small diameter catheter generally in accordance with  FIG. 7  showing a deployed distal tool according to a third alternate embodiment;  
       FIG. 12  is a perspective view of the distal end of the small diameter catheter generally in accordance with  FIG. 7  showing a deployed distal tool according to a fourth alternate embodiment;  
       FIG. 13  is a perspective view of the distal end of the small diameter catheter generally in accordance with  FIG. 7  showing a deployed distal tool according to a fifth alternate embodiment;  
       FIG. 14  is a frontal view of the distal end of the small diameter catheter of  FIG. 13 ;  
       FIG. 15  is an exposed fragmentary view of a blood vessel with a thrombus showing the insertion thereinto of the distal end of the small diameter catheter of  FIG. 7  with distal tool retracted;  
       FIG. 16  is an exposed fragmentary view of the blood vessel with a thrombus of  FIG. 15  showing the deployment of the distal tool following insertion thereinto of the distal end of the small diameter catheter of  FIG. 7 ;  
       FIG. 17  is an exposed fragmentary view of the blood vessel with a thrombus of  FIG. 15  showing the withdrawing of the thrombus while engaged by the deployed distal tool of the small diameter catheter of  FIG. 7 ;  
       FIG. 18  is an exposed fragmentary view of a blood vessel with a thrombus showing the withdrawing of the thrombus while engaged by the deployed distal tool of the small diameter catheter of the embodiment of  FIG. 12 ; and  
       FIG. 19  is an exposed fragmentary view of a blood vessel with a thrombus showing the withdrawing of the thrombus while engaged by the deployed distal tool of the small diameter catheter of the embodiment of  FIG. 13 .  
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT  
      A. Small Diameter Snare Device and General Design Details  
       FIG. 1  shows a small diameter snare device  100  according to an embodiment of this invention. The device  100  includes of a hollow, elongate, thin-walled polymer outer sheath  102 . The sheath  102  may include a radiopaque marker located at or adjacent to the open distal end  104  for visualization under fluoroscopy. The polymer can be any one of a number of acceptable biocompatible polymers with sufficient structural strength to support a thin-walled (approximately 0.0020 inch maximum wall thickness TS) structure without rupture or other failure under normal use conditions.  
      In one embodiment, the sheath is constructed from polyimide with a tungsten filler for radiopacity. The radiopaque filler may be added to the sheath polymer during processing, or a radiopaque material may be added to the outer surface via vapor deposition, plating, ion implantation processes, or the like. Alternatively, radiopaque markers can be applied at the distal end and/or other known locations along the sheath, and thus, an overall tungsten filler/radiopaque coating can be omitted. As discussed further below, the outer surface can include thereon a polytetrafluoroethylene (PTFE or “Teflon”) coating upon some, or all, of its outer surface for enhanced lubricity. Alternatively, the outer sheath coating can be constructed form a hydrophilic material that provides lubricity, instead of a PTFE coating. The sheath polyimide material is commercially available for a variety of vendors and sources and is becoming accepted in a variety of medical device applications. It has the property of allowing a very strong, thin-walled cylindrical-cross section tube to be made therefrom, with wall thicknesses on the order of approximately 0.00075 inch to 0.010 inch in normal applications. Nevertheless, the resulting polyimide tube can withstand high pressures in excess of 750 PSI when employed in the size range of the sheath of this invention. Polyimide also resists high temperatures, as much as 1000 degrees F, or greater. Accordingly, polyimide is desirable as a sheath material based upon all of the above-described superior performance characteristics. Nevertheless, it is expressly contemplated that other equivalent plastic/polymer materials suitable for forming a thin-walled sheath tube with similar or better properties (e.g. high strength, thin wall-thickness limits, small diametric sizing) may also be employed as an acceptable “polymer” herein.  
      The outer sheath  102 , which forms the main support and outer framework of the device  100  has an overall length sufficient to traverse the body&#39;s varied vasculature, and is (for most applications) permissibly in a range of between approximately 20 cm and 500 cm (more typically between 120 cm and 300 cm). The outer diameter DSO of the sheath is permissibly (for most applications) in a range of between approximately 0.010 inch to 0.045 inch (more typically between 0.010 inch and 0.021 inch). In general, where the outer diameter is less than 0.35 inch, the device  100  may fit easily through a standard balloon catheter.  
      A single central core wire  110  extends through the entire length of the sheath  102 . The outer diameter DC of the core wire through most of the length of the sheath  102  (except near the distal end  104 ) is sized close to the inner diameter DSI of the sheath while allowing for axial sliding (double arrow  112 ), in order to maximize the support imparted by the core wire  110  to the body portion/sheath  102  of the snare device  100 . The distal end  114  of the core wire  110  has a tapered section  116  of reduced diameter or cross section to provide a “guidewire-like” flexibility to the distal portion of the device. A second (typically metal) wire  120  of about 50%-30% the inner diameter of the sheath is shaped to form a snare loop  122 , and the two ends  126  and  128  are attached to the distal-most portion  130  of the central core wire  110  via welding, soldering, brazing or another high-strength (typical metal-flowing). The loop  122  is typically circular or oval shaped and can also be multiplanar (a twisted “figure-eight” as shown, for example) so as to increase the ability to ensnare and capture objects. Where a multi-planar structure is shown, the entire structure can be referred to collectively as a loop or the two resulting oval perimeters in the figure-eight can be termed in the plural as “loops.” The loop or loops can have a permissible diametric range (their object-grasping inner circumference) of between approximately 1 mm and 100 mm, and typically have a range between 2 mm and 35 mm. However ranges outside the stated values are expressly contemplated.  
      Note, as used herein, the snare or any other tool tip that selectively extends from the end of the sheath can be termed a “capture segment.” 
      The central core wire  110  is made from metal for flexibility and strength. In one embodiment, the central core wire  110  may be made by connecting a proximal stainless steel portion, for support and stiffness, to a distal nitinol portion, for torqueability and kink resistance. Likewise, it can be made from 300 series stainless steel or a stronger, heat settable material such as 400 series stainless steel, alloy MP35N, a chromium-cobalt alloy such as Elgiloy, or nitinol in its super elastic or linear elastic state.  
      Note, because a thin-walled polymer sheath is employed, it advantageously allows for a maximized central core wire diameter, which in turn, provides stiffness for torque control and axial pushability in the body of the snare device.  
      With reference also to  FIG. 2 , the central core wire distal-most portion  130  may be offset in one axis relative to the central axis  202  of the sheath  102 . This allows mounting of the loop ends  126  and  128  in a most efficient cross-sectional-space-saving manner. Surrounding the distal most portion and two loop ends  126 ,  128  is a helical wrap of platinum (in this embodiment) wire  140 . In one embodiment, the wire has a diameter of approximately 0.001 inch. It is applied to the interconnection between the loop and core wire prior to permanent joining-together of the structure. It thereby secures these components in a tight relationship while solder, weldment, brazing, etc. are applied, reducing the risk of unwanted separation/spreading or sliding of components relative to each other. This further ensures a predictable end diameter for the structure, allowing a tighter wall-thickness tolerance without risk of binding between the core wire assembly and inner wall of the sheath  102 . During assembly, solder, etc. passes through small gaps formed between wraps of wire  140  to pool in fillets  210  against the components  126 ,  128  and  130 .  
      In one embodiment, the snare loop  122  may be made from a 300 series or a heat settable material, such as 400 series stainless steel material, MP35N. Likewise, it may be made from a kink-resistant material, such as chromium-cobalt or nitinol alloy. The snare loop may have an optional radiopaque marker  148  located at the distal-most portion of the loop  122  to aid in fluoroscopic visualization. Alternatively, the snare loop(s) may be formed of a radiopaque material, such as platinum to aid in fluoroscopic visualization. Similarly, the snare loops may have a radiopaque coating applied via vapor deposition, plating, ion implantation processes, or the like, to aid in fluoroscopic visualization, or the snare loop(s) may be covered by a coil (not shown) wound from a radiopaque material, such as platinum to aid in fluoroscopic visualization.  
      In another embodiment (see  FIG. 3 ), the snare loop(s) may be formed of a wire  302  that defines a plurality of stranded or braided members  304  of an appropriate wire strand material, rather than a single, solid wire as shown above. This stranded or braided wire  302  may (in one or more embodiments) include at least one strand (or multiple strands)  306  of a radiopaque material, such as platinum to aid in fluoroscopic visualization. Alternatively, the snare loop(s) may be formed of a radiopaque material-cored tube, such as a tantalum filled chromium-cobalt material, or platinum filled nitinol material (not shown).  
      While the snare loops are shown as an independent component attached to a separate core wire end, it is expressly contemplated that the core wire and loops can be a unitary component. For example, in an alternate embodiment (not shown), the snare loops can be made from part of the central core by reducing the diameter of the end of the central core and doubling this free distal end over to form the loop. The free distal end is then joined to the more-proximal part of the narrowed distal end of the core wire. The joint can include wrapping with wire ( 130  above) and soldering, etc. to construct the finished loop structure.  
      After assembly of the core wire  110  with appropriate loop(s), and its insertion into the sheath  102 , a second short, hollow tube is fitted over the proximal end  152  of the central core wire  110  and attached thereto by a filler or adhesive  154  to provide an actuating handle  150  so as to slideably move the central core wire axially (double arrow  112 ) within the sheath  102 , thus selectively exposing and retracting the snare loop  122  from the open distal end  104  of the sheath  102 . In one embodiment, the actuating handle  150  may be sized with an outer diameter DOO similarly (or identically) in outer diameter DSO to the main body of the sheath  102 . The exposed proximal end  152  of the core wire  110  may include a narrowed-diameter end  160 , with a special connection so that an additional length of wire  166  can be attached to it, thereby extending the overall length of the snare device. This extension has a similarly sized outer diameter DA to that of the handle  150  (DOO) and sheath  102  (DSO). The attachment of this similarly small-diameter extension allows for the exchange of one catheter for another catheter over the body of the snare (and extension). The entire snare device when complete (including the actuating handle  150 ) can be made less than 0.014 inch in overall outer diameter, and is therefore capable of being placed directly through a PTCA balloon catheter or other small-diameter catheter  180  ( FIG. 1 ), having a sufficiently large inner diameter CD, that may already be in place within the patient (e.g. CD&gt;DSO). Since the actuating handle is equally small in diameter, it also passes through the small-diameter catheter with an extension piece joined behind the handle to the attachment end  160 , and thereby allowing the device to be guided even deeper into the patient when needed. The snare may also be passed through the guiding catheter along side of the balloon or access catheter without the need to remove the prior device and, thus, lose temporary access to the site within the patient. For example, the snare may be initially passed through the PTCA balloon catheter, which is already located within the target area. The balloon catheter can then be removed and replaced with a larger-inner diameter catheter to allow removal of the object.  
      The actuating handle  150  may consist of a metal or a polymer tube. In an alternate embodiment (not shown) the actuating handle may consist of a tube slideable within a second metal tube that is attached to the proximal end  170  of the sheath to maintain an axial orientation between the proximal end of the core wire  102  and sheath, thereby minimizing permanent bending or kinking of the core wire at or near this proximal location.  
      While the depicted actuating handle  150  is of similar outer diameter as the sheath  102 , it is expressly contemplated (where the handle will not be passed into another catheter) that the actuating handle may be made in a diameter significantly larger than the snare device so that it may also serve as a torquing handle, similar to those utilized in routine small-diameter guidewire placement.  FIG. 4  shows an overall version  400  of the snare device that includes an enlarged handle attachment  402  attachment to the previously described snare device of  FIG. 1  (with like components in  FIGS. 1 and 4  retaining like reference numbers). The handle attachment  402  may be made from a polymer material which (in an embodiment of this invention) is injection molded and mechanically attached onto the snare or (in another embodiment) may be over molded directly onto the snare. The handle attachment  402  includes a base ring  410  that is secured to the outer surface of the proximal end  170  of the sheath  102 . In a detachable-handle embodiment, the ring can consist of a conventional lockable collet structure in which turning of an outer element reduces the diameter of an inner locking element to deliver securing hoop stress to the distal end  170  outer surface of the sheath  102 . The base ring is connected to two or more ribs  412  and  414  that are also shown in cross section in  FIG. 5 .  
      An actuating ring  420  is secured onto the actuating handle  150  either permanently or detachably. Where it is detachable, it may also utilize a locking collet structure (not shown) as described above. At least two apertures  430  and  432  allow passage of the respective ribs  412  and  414  so that the ring  420 , actuating handle  150  and core wire  110  can be slid axially (double arrow  440 ) with respect to the sheath  102  based upon slideable movement of the actuating ring  420 . The ribs secure the ring  420  and interconnected core wire  110  and handle  150  against rotation relative to the sheath. The connection is sufficiently strong so that rotation of the handle assembly  402  causes torquing of the entire device so as to rotate the loop(s)  122  into a desired rotational orientation. In an alternate embodiment, the ring may be a non-circular structure. In another alternate embodiment (also not shown), the ring  420  may also allow at least limited rotation of the core wire relative to the sheath by utilizing arcuate slots at the ribs.  
      The handle assembly  402  includes a rear gripping member  450 . It forms the opposing attachment location for the ribs  412  and  414 , opposite the base ring  410 . The gripping member can be any acceptable size that provides ergonomic support for a practitioner during a procedure. In one embodiment the member  450  has an outer diameter of approximately ½ to ¾ inch and an external length of approximately 4 to 5 inches. However, it is expressly contemplated that both these dimensions are widely variable outside the stated ranges herein. The member  450  defines an inner cylindrical barrel  452  having an inner diameter sized to slideably receive and guide the proximal end of the actuator handle  150 . The barrel  452  has a sufficient length relative to the inner wall  462  of its end cap  460  so that the end  160  of the device does not strike the wall  462  at maximum withdrawal (as approximately shown) of the loop(s)  122  into the sheath  102 .  
      Coatings can be applied to the outer surfaces of the core assembly and the sheath assembly to reduce friction between the core and the tube as well as to enhance movement of the snare device within a catheter. In one embodiment, a lubricious coating, such as PTFE (Teflon), hydrophilic, or diamond-like coating (DLC) may be applied to the outer surface of the sheath to reduce friction. Likewise, one of these coatings may be applied to the outer surface of the core wire to reduce friction with respect to the sheath. Since the coating adds a quantifiable thickness to the thickness of the sheath and/or diameter of the core wire, the overall size of components should be adjusted to compensate for the thickness of any lubricating coating. For example, the outer diameter of the sheath may need to be reduced to maintain a desired 0.035-inch or less outer diameter. Likewise, the thickness of the uncoated wall of the sheath may be reduced to maintain the desired inner diameter and create a final wall thickness, with coating, of approximately 0.0020 inch.  
      According to an alternate embodiment, as shown in  FIG. 6 , the loop wire strand  602  (solid in this example) may be made from a half-round or “D-shaped” profile, at least in the vicinity of its joint with the core wire. Note that the advantages of this structure are particularly advantageous in the embodiment described above where the core wire distal end actually forms the loop strand and is joined back on itself so that a separate overlapping core wire end (joined to two separate loop ends) is not present. This D-shaped profile allows for maximizing the cross sectional area of the loop wire thereby increasing its overall breaking strength. For example, a tube with a 0.008-inch inner diameter can accommodate two 0.004-inch diameter round wires stacked together, or the equivalent of a single 0.008-inch (approximately diameter wire if two “D-shaped” wires are stacked. For a given overall desired diameter of DW, the wire strands are half-circular cross sections joined at a line, each having the individual width ½ DW taken through a center point  606  and normal to the joint line between halves. The total cross sectional area of a 0.004-inch diameter wire is 0.000013 square inch, whereas the joined “D-shaped” wire has a cross sectional area of 0.000025 square inch. This results in a doubling of the cross sectional area, and likewise, doubling of the breaking strength of the wire.  
      Having described the general structure of the snare device and its various alternate embodiments, the operation of the snare device is now briefly described. In use, the loop  122  of the snare device is first withdrawn (proximally) into the sheath  102  by pulling on the actuating handle  150 . The snare is then advanced into a balloon or guiding catheter (not shown) until the distal end  104  of the snare device has exited the distal end of the catheter. The snare device is then torqued and manipulated into place adjacent to an object to be retrieved. The snare loop  122  is then exposed (extended) from the open distal end  104  of the sheath  102  by pushing the actuating handle  150  forward (distally), and through a combination of advancing (distally), withdrawing (proximally), and rotating the entire device, the object is ensnared within the loop. The loop is then retracted/withdrawn back into the sheath so that the ensnared object is driven against the distal end  104  of the sheath and grasped tightly within the remaining exposed loop. With the object so-grasped, the snare device with the object is withdrawn (proximally) from the patient&#39;s body.  
      Having described the structure of a snare device according to various embodiments herein and some exemplary techniques for employing the device the following advantages, among others of the above-described invention should be clearer. Namely, this invention provides a small-diameter snare device, less than 0.035 inch in diameter that is capable of fitting through existing balloon or guiding catheters. The body of the snare consists of a thin-walled polymer sheath, which allows for a maximized central core wire diameter, which in turn, provides stiffness for torque control and pushability in the body of the snare device. This device enables addition of one or more extensions onto the proximal end of the snare to allow for exchanging catheters directly over the snare if desired. Portions or all of the sheath and the snare loops can be radiopaque to aid in fluoroscopic visualization. Finally, lubricious coatings can be applied to the outer surface of the core wire and sheath to reduce friction and aid in movement.  
      B. Small Diameter Device for Thrombus Removal  
      With reference now to  FIG. 7 , a device  700  for removing thrombus is shown in partial side cross section. The device  700  is a small diameter catheter having a hollow, elongate, thin-walled polymer outer sheath  702  that is substantially similar in materials, structure, and function to the sheath  102  described above for the snare device of  FIG. 1 . As such, the proximal end (not shown) of the device  700  can be similar or identical in form and structure to the proximal end of the snare device  100  described above. In general, the sheath  702  can be coated with a lubricious coating, such as PTFE, DLC, or hydrophilic polymer material. One material contemplated for the sheath is a polyimide plastic, but a variety of alternate materials displaying the above-described performance characteristics are expressly contemplated. The overall sheath length is in a range of 20 cm to 500 cm (more typically between 120 cm and 300 cm), depending upon (among other factors) the location of the insertion point into the body cavity/vasculature, and the location of the target thrombus, or other material, to be acted upon by the device  700 . The outer diameter of the device sheath ODS is in a range of approximately 0.010 inch to 0.045 inch (more typically between 0.010 inch and 0.021 inch). It has a wall thickness of approximately 0.00075 to 0.010 inch in most applications. As described above, a sheath outer diameter less that 0.35 inch enables the device  700  to fit through the lumen of a standard balloon or microcatheter (typically with luminal diameter of 0.014 inch, or less). As described above the core wire&#39;s diameter is sized relatively close along the majority of its length (except the distal end) to the inner diameter IDS of the sheath  702 .  
      In this an other embodiments described herein the sheath can be all polymer along its entire length, or can be constructed from a combination of polymer and metal. For example, the distal part  705  of the sheath  702  can be the above-described polyimide material (or another appropriate polymer), while the proximal part  707  can be constructed from 300 series stainless steel or any other appropriate metal. This affords the desired flexibility in the distal part, while providing greater strength and rigidity against buckling in the proximal part. Flexure is required less and beam strength (so as to assist in driving the device distally) is required more in the proximal part  707 . The distal part  705 , is joined to the proximal part  707  at a joint  709  located at a predetermined distance along the device. The joint  709  can be accomplished using adhesive or any other acceptable joining technique. In one example, the polymer distal part is approximately 40 centimeters in length, while the metal proximal part is approximately 140 centimeters in length. These measurements are widely variable depending upon the overall length of the sheath  702 , the purpose of the device (e.g. where it will be inserted) and the distance of the distal part in which high flexibility is required.  
      The same actuating handle attachment  402  can be employed to move the distal tool  720  of the device  700  into and out of (proximally and distally—double arrow  706 ) the distal end  704  of the sheath  702 .  
      As with the above-described snare device  100 , the device  700  employs a central core wire  710  that moves distally and proximally within the sheath under bias of a handle assembly (handle  402 , for example) attached at the sheath&#39;s proximal end. The core wire  710  can be constructed from 300 series stainless steel or a stronger, heat settable material, such as 400 series stainless steel, alloy MP35N, a chromium-cobalt alloy, such as El-giloy, or nitinol in its super elastic or linear elastic shape. Like that of the snare device, the core wire  710  can be constructed by connecting a proximal stainless steel portion, for support and stiffness, to a distal nitinol portion, for torqueability and kink resistance.  
      The distal region of the core wire  710  is defined by a tapered section  716  as described above. The tapered section necks to a reduced diameter, generally cylindrical distal most portion  730 . This narrowed distal area of the core wire  710  affords the above-described guidewire-like flexibility to the distal portion of the device  700 . The dimensions for each wired portion can be similar or identical to those described above for the core wire  110 .  
      Notably the capture segment in this embodiment is a distal tool tip  720  consisting of a plurality of wires  740  (in this example, four wires at right angles-as shown in  FIG. 8 ), each formed into a predetermined shape. In this embodiment, the shape is an open loop in the form of a “fish hook” that extends distally from the sheath tip  704  in a stalk  732 , thereafter opening up and curving radially outwardly from the device center axis  742 , and then proximally to end in a radially inward hooked tip. This shape can be loosely termed a “grappling hook” or “umbrella” shape.  
      Each wire  740  is sized so that the bundle can be drawn inwardly, fully through the distal tip  704  of the sheath  702 . The wires  740  are constructed from a metal having substantial flexibility, kink resistance and memory of its shape. Acceptable metals include, but are not limited to, 300 series stainless steel, a heat settable material, such as 400 series stainless steel or another material, such as cobalt-chromium alloy (Elgiloy, nitinol, etc). The wires  740  each include proximal ends  744  that are formed to closely conform to the narrowed distal most portion  730  of the core wire  110 . The wires  740  and/or the portion  730  can be formed with flats, half-rounds or steps to more-closely pack the wires  740 . In this embodiment, the wires can be offset in accordance with the cross section of  FIG. 2 . The wires  740  may include a variety of cross sectional shapes, similar to the D-shape shown in  FIG. 6 . In particular, where four closely conforming wires are employed, as in  FIGS. 7 and 8 , the wire cross sections can be a quarter of a circle (a right-angled pie piece), so that all four wires, when stretched out along the axis  742  and packed together can form an approximate circular cross section. In this embodiment, the wires  740  are secured to the core wire  710 , using welds, solder, brazing, adhesives in combination with a wrapped, helical coil of platinum wire  750  as shown and also described above (refer to wire  140  in  FIG. 1 ). The coil wire  750  has a diameter of approximately 0.001 inch in this embodiment. As described above solder can be flowed between the wire gaps during assembly to fill the spaces therebetween, and render the connection strong and permanent.  
      The range of radial extension of a fully-deployed tool tip or other capture segment is highly variable. It can be anywhere from 1 millimeter to 100 millimeters in various embodiments. This radial sizing depends partly upon the size of the space into which the capture segment is being inserted. More typically, a capture segment will have maximum radial extension between approximately 2 millimeters and 35 millimeters.  
      As described above one or more of the wires  770  can include an applied radiopaque marker (tungsten, for example)  760  at any location or a plurality of locations thereon. In this example a marker  760  is applied to each wire tip. The projecting distal-to-proximal length LT is highly variable. In other embodiments described herein below, the distal-to proximal projection can be approximately zero. The dimension should be sufficient in particular designs to ensure appropriate grasping and capture of a thrombus (described further below). The radial projection RT of each wire  740  or the distal tool tip  720  as a whole from the axis  742  should be sufficient to cover the approximate dimension of the cross section to be cleared, while remain smaller than the inner lumen of any vessel through which the deployed tool is expected to carry. This helps to reduce the chance of injury to vascular walls. Also the packed, axially directed stalk section  732  should be long enough to allow the bundle to fully deploy from the sheath tip  740  and exhibit sufficient space from the sheath tip  704  so that the sheath tip does not interfere with the engagement of the tool tip  720  with a thrombus or other target structure.  
       FIG. 9  details a device tip  900  according to an alternate embodiment. The sheath  902  is constructed similarly to that of  FIGS. 7 and 1 . Likewise the internal core wire (not shown, is also constructed in accordance with the above described embodiment ( FIGS. 1 and 7 ). The tool tip in this embodiment is constructed from three wires  940 . They can be joined to the core wire&#39;s narrowed distal most portion using helical wraps and solder as described above. The proximal stalk can be closely packed and each wire can define a cross section that, when extended along the central axis, defines a complete circle with each wire  940  defining a third-of-a-circle pie piece (120 degrees) in this example. Note that in any of the embodiments herein the tool tip wires can alternatively define a circular cross section or another regular polygon. In the embodiment of  FIG. 9 , the three wires  940  define loops that extend radially outward in a narrowed spiral, and lie substantially within a plane perpendicular to the central axis  942 . This arrangement acts collectively as a perforated plate member that is deployed ahead of a thrombus and then engages it from behind. This activity is described more fully below.  
       FIG. 10  is a device  1000  according to another alternate embodiment. This shape is a version of the “grappling hook” or “umbrella” design that employs loops of continuous wire to define each separate hook member. This device comprises a sheath  1002  also similar to those described above. The tool tip  1020  projects from the sheath distal end to define four wire assemblies. In this embodiment, the wire assemblies  1040  extend radially and proximally, similarly to the embodiment of  FIG. 8 . These wire assemblies  1040  are formed as narrow pairs of wires  1044  that terminate proximally in a curved joint  1046 . This multi-wire arrangement affords greater surface area to the overall tool, which is helpful in ensuring an appropriate grasp on a thrombus or other material. The curved joint ends  1046  also blunt the leading edges of the tool, which engage the material, reducing the chance of the tool passing proximally through the material and also puncturing or scraping vascular walls. The individual wires (eight wires total) of the proximal stalk  1032  are arranged to surround the core wire in a manner that allows the entire tool tip to move into and out of the sheath  1002 . The wires can have a cross section shape along all or part of their length, which better facilitates this packing (e.g. ledges, pie piece shapes, etc.).  
       FIG. 11  details a device  1100  according to another alternate embodiment in which the tool tip  1120  that exits the distal end of the sheath  1102  includes four looped wire assemblies  1140  similar to the embodiment of  FIG. 10  that essentially define a “flower petal” shape. These wire assemblies extend from a proximal stalk of eight wires, like that of  FIG. 10 . The distal ends of the wire assemblies  1140  are arranged substantially in a plane, generally perpendicular to the axis  1142  of the sheath distal end. This and other tool tips herein are said to lie substantially within a plane because it is recognized that wires must often overlap each other as they are formed into the desired shape, thereby taking then slightly out of a common plane. The wire assemblies  1140  comprise a pair of wires  1144  that are joined at a radially outermost corner  1146 . The wires  1144  tend to bow away from each other between the corners  1146  and the central stalk  1132 . This stalk  1132  comprises eight wire ends that are all secured to the core wire in a manner described above (refer to  FIG. 10  description).  
       FIG. 12  defines a device with a sheath  1202  and tool tip  1220 . This tool tip defines, in essence a “potato masher” shape employing one continuous wire  1240  that starts and ends in the proximal stalk  1232 . The stalk, thus, contains only two wire shafts  1236  joined to the core wire, similar in interconnection to the snare device of  FIG. 1 . The wire  1249  is formed into a multi-layer spiral as shown. The spiral all lies substantially in a plane perpendicular to the sheath distal end axis  1242 . The Spiral affords a high degree of surface area for engaging a thrombus or other material. It also defines an approximately circular outer perimeter that better conforms to the shape of a vascular lumen. Likewise, this outer perimeter shape is less likely to scrape or damage the vascular wall. As in any of the tool tip designs described herein, the maximum outer diameter/radial extension of then tip is selected to conform to the luminal dimensional of the blood vessel in which the tip is deployed.  
      Another embodiment of a device  1300  is detailed in  FIGS. 13 and 14 . The device  1300  includes a sheath  1302  for which is deployed a tool tip  1320  that, like the tip of  FIG. 12 , is constructed from a continuous wire  1340  that begins and ends at the core wire ( 1450  in  FIG. 14 ) within the sheath  1302 . These wire ends can be connected to the core wire in the manner described above (refer to description of  FIGS. 1 and 12 ). The stalk  1332  of the tool tip  1320  extends along the distal end axis  1342  of the device  1300 , and then deviates radially as shown in  FIG. 14  in a connecting wire section  1460 . The wire  1320  extends from the connecting section  1460  in a series of proximally directed undulations  1360 . The undulations extend in a distal-to-proximal direction and are joined by alternating distal and proximal bend joints  1362  and  1364 , respectively. The overall tool tip structure defines a circle around the sheath  1302  and stalk  1332  that is like a cylindrical cage.  
      Note that each of the tool designs described herein is by way of example. These designs represent various classes of designs that can be employed. Some tool tips employ a continuous wire ( FIGS. 12-14 ). Some reside wire arrangements substantially within a single perpendicular plane ( FIGS. 9, 11  and  13 ). Some terminate in free end tips ( FIGS. 8 and 9 ). Some extend both radially and proximally ( FIGS. 8, 10  and  13 - 14 ). Some employ a series of continuous wires having bent tip ( FIGS. 10 and 11 ). Some are combinations of these alternative features. The size of the loops, bends and spirals can be varies based upon the size of the target vessel, as well as the size and characteristics of the material being engaged.  
      As in the snare device, each discrete “wire” in the tool tips described herein can be composed of a plurality of individual strands, collectively defining a cable. One or more strands can be radiopaque (refer to the description of  FIG. 3 ). Notably, the capture segments described herein can be formed in a variety of ways with markers as appropriate. In one example, the capture segment can be formed of a stranded or braided material, with multiple strands of kink-resistant material and at least one strand of a radiopaque material, such as platinum. Alternatively, the capture segment can be formed from a radiopaque-cored tube, such as tantalum filled with chromium-cobalt material, or platinum-filled nitinol material. In a further alternative, the capture segment may be formed unitarily with the distal end of the core wire, by reducing the diameter of the distal end of the core wire to form an appropriate capture segment within this region.  
      C. Procedures for Withdrawal of Thrombus and Other Materials  
      Having described a number of different tool tip designs, the procedure of removing a thrombus or other material from a blood vessel is now described in further detail.  FIG. 15  shows the insertion of the device  700  of the embodiment of  FIG. 7  into a blood vessel  1500  containing a thrombus, or other internal blockage (natural or man-made). Initial insertion can be made via the aorta or another great blood vessel. The thrombus material is sufficiently accretive to itself so that it can be grasped and withdrawn without fragmentation-which could lead to a thromboembolism or another undesirable effect. As shown, the individual wires  740  (shown partially in phantom) are fully with-drawn/retracted proximally into the distal end of the sheath  702 . The wires  740  have sufficient resilience/flexibility to be forcibly drawn into the sheath, and out of their normal hooked, proximally directed shape due to the nature of the material from which they are constructed. As such they are arrayed in a proximal-to-distal alignment against the restraining force of the inner luminal wall of the sheath. Note that the wires are anchored to the core wire  710  in a manner generally described above.  
      In accordance with  FIG. 15 , the sheath  702  is directed distally (arrow  1510 ) so as to pierce fully through the thrombus  1502  as shown, exiting the distal side  1504  of the thrombus  1502 . The distal tip  704  is sufficiently small in diameter so that it can pierce the thrombus without significant effort. In alternate embodiment, the tip  704  can contain another chamfer so as to form a piercing chisel point, or another structure that facilitates piercing of the thrombus.  
      Once pierced, the handle (refer above to the description of  FIG. 4 ) is actuated to drive the core wire  710  distally (arrow  1610 ) so that the wires  740  are directed out (arrows  1620 ) of the distal tip  704  of the sheath  702 . The memory properties of the wire material cause them to each assume the preformed, proximally and radially directed hook shape of the deployed tool tip  720  as shown. At this time the stalk causes the tool tip  720  to reside at a distance distally spaced from the distal face  1504  of the thrombus  1502 . As such, the tool tip  720  can fully deploy without interference from the thrombus  1502 . In this embodiment, the radial extension of the wires  740  is slightly smaller than the luminal diameter LDV of the vessel  1500  so that the tool tip  720  can fully deploy without engaging or scraping the vessel wall.  
      Once deployed, the position of the core wire  710  with respect to the sheath  702  can be locked using, for example the above-described handle lock mechanism. The device  700  is then drawn proximally (arrow  1710 ) until the tool tip  720  begins to implant itself into the distal face  1504  of the thrombus  1502 . The wires  740  are shaped so that they flex appropriately upon engagement with the thrombus  1502 , thereby preventing them from passing proximally fully through the thrombus  1502 . As such all or a large portion of the thrombus is captured and can be withdrawn proximally (arrows  1720 ) with the device  700 . The thrombus  1502  is held to the tip  720  due to the embedding of the wires  740  so that the thrombus remains intact as it is passed out of the vessel  1500 , and into wider diameter blood vessels as it is directed out of the body via the device&#39;s point of entry (typically a major vein).  
      The tool tip  720 , and associated procedure described in  FIGS. 15-17  entails the embedding of the tool tip into the thrombus upon withdrawal. In alternate embodiments, the tool tip may not be particularly embedded during withdrawal. Reference is made to  FIG. 18  in which the device  1200  ( FIG. 12 ) has been driven distally into a vessel  1800  and through a thrombus  1802  in a manner described with reference to  FIGS. 15 and 16 . The tool tip  1220  has now been deployed from the distal end of the sheath  1202 , and taken its preformed shape. The wide and planar shape of the tip  1220  causes it to rest upon the distal face  1804  of the thrombus  1802  without passing substantially into the material. As shown, when withdrawing the device  1200  proximally (arrow  1810 ), the engaged tool tip  1220  bears forcibly against the distal face  1504  of the thrombus  1802 , and withdraws it proximally (arrows  1820 ).  
      Referring now to  FIG. 19 , the sheath  1302  of the device  1300  ( FIG. 13 ) has been driven at least part of the way through a thrombus  1902  in the vessel  1900 . The distal-to proximal undulating “cage” design of this tool tip  1320  makes it possible to deploy from inside the thrombus  1902 . This entails the cage shape being radially compressed along its undulations in its retracted state and thereafter expanding radially when freed from the end of the sheath. The expansion occurs within the thrombus body, thereby anchoring the tool tip  1320  within its center as shown. Alternatively, this cage-shaped tool tip  1320  can be deployed distally of the distal thrombus face  1904  in a manner described above. After either type of deployment, the device  1300  is withdrawn proximally (arrow  1910 ), thereby pulling the anchored thrombus  1902  along with it.  
      The above-described insertion procedures can be modified to accommodate the characteristics of the particular tool tip shape and size. A variety of additional tools and/or internal scanning devices can be employed to facilitate the procedure in accordance with known medical techniques. In addition, any of the materials or construction techniques described in connection with the thrombus-removal devices herein can be applied to the above-described snare device. In particular, the materials used to form tool tips herein can be used to form the snare. Note also that the proximal end of the thrombus-removal and snare device described herein includes a proximal end that allows removal of the actuator handle and addition of a small-diameter extension. When the extension is added, the practitioner can pass another catheter over the inserted device sheath, thereby using the device as a guide for the larger diameter catheter.  
      The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope of this invention. For example, while specified materials are described, it is expressly contemplated that similar or superior materials may be employed if and when available for the described components of this invention. In particular, a variety of metals, polymers, composite, nano-materials and the like having desirable memory characteristics can be employed for snares, tool tips and other components herein. Likewise, alternate techniques and materials can be employed for joining components. In addition further attachments can be provided to the devices described herein, with appropriate mounting hardware and locations to facilitate other, non-described procedures using the device. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of the invention.