Abstract:
A system may comprise a clot engagement element having a collapsed delivery configuration and an expanded configuration for engaging with a clot and for dislodging the clot from a first vessel segment. An elongate member may be configured to apply a pull force to the clot engaging element to dislodge the clot from the first vessel segment. A clot removal catheter may include a lumen at its distal end sized to receive the clot and configured to maintain a stable position in a second blood vessel segment proximal of and larger in diameter than the first blood vessel segment. A distal end of the elongate member may be configured to protect a third blood vessel segment between the first and second blood vessel segments from tractive forces transmitted by the elongate member during clot dislodgement from the first vessel segment.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/780,422, filed Mar. 13, 2013, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to endovascular medical devices which are retracted through a portion of the vasculature while in contact with the vessel wall as part of their typical method of use. In particular this invention is of benefit to mechanical thrombectomy devices, vena cava filters, embolic filters, stents and similar devices. For example, it is relevant to clot retrieval devices which are used to retrieve blood clots in the case of ischemic stroke, or in another example, stents which are used to relieve stenosis. 
       BACKGROUND 
       [0003]    Mechanical thrombectomy devices such as stentrievers are frequently used to recanalize blocked cerebral arteries in patients suffering from acute ischemic stroke. The method of use of such a device involves introducing a guidewire endovascularly and advancing it through the vasculature until it is distal of the obstructive clot. A guide catheter is then passed over the guidewire to a location proximal of the clot. A microcatheter is passed over the guidewire through the guide catheter to a location distal of the clot. The guidewire is then withdrawn proximally to allow for the introduction of the clot retrieval device in the collapsed configuration through the microcatheter. A generic clot retrieval device is comprised of an elongate member and a clot engaging body connected to the distal end of the elongate member. The clot retrieval device is advanced distally within the microcatheter until is it situated within the clot. At this stage the microcatheter is withdrawn and the device will expand. In its expanded configuration the device exerts a radial force on the clot thus capturing the clot against the walls of the vessel. Once the clot has been captured by the engaging body of the device and aspirating has commenced, the device and the clot are withdrawn towards the guidecatheter. The device and the clot are withdrawn into the guidecatheter and removed from the vasculature. 
         [0004]    The force required to retract the device may have undesired consequences. In order to dislodge the clot from the vessel a force must be applied to it through the stentriever device. This force is effectively applied to the vessel in which the clot is lodged and to the distal vascular bed, placing these vessels in tension and placing the vessels proximal of the clot in compression. Once the clot begins to move there is relative movement between the stentriever device and shaft and the vessel wall. This relative movement can cause abrasion and damage to the endothelia and underlying layers of the vessel wall, which may result in a dissection or perforation, or could give rise to the subsequent formation of thrombus which could then be liberated to create an additional stroke. 
         [0005]    The force that must be applied to dislodge and retract the clot is dependent not only on how well lodged the clot is in the vessel, but also on the frictional losses that occur where the stentriever device contacts vessel walls or the inner surface of the catheter through which it passes. Thus it would be advantageous to have the use of a device which acts as a shield between the elongate shaft and the vessel wall. In the preferred embodiment the invention would remain in situ in the vessel as the elongate shaft is being retracted and absorb the tension which would normally be exerted on the shaft and the vessels. Preferably the invention would have a low friction inner surface and a higher friction outer surface. This would allow the shaft to move more fluidly within the device while the device remained in the vessel. The present invention includes these features and improves upon the methods of clot retrieval previously discussed. 
       SUMMARY OF THE INVENTION 
       [0006]    The disclosed designs overcome the disadvantages of existing mechanical thrombectomy solutions. In one embodiment a tubular member is slidably disposed on the shaft of a thrombectomy device. The device captures the clot in the engaging body. Once the clot has been captured the device is withdrawn proximally through the vasculature. The withdrawal of the device places pressure on the surrounding vessels and causes abrasion on the inner walls of the vessels. This is the stage at which the highest loads are applied. However the use of a slider tube reduces these forces. 
         [0007]    As it is slidably disposed on the elongate shaft of the thrombectomy device and the coefficient of friction between the tube and elongate shaft is lower than that between the slider tube and the vessel, the slider tube remains in situ as the shaft is retracted. The force that the elongate shaft would normally exert on the vessels is spread over the outer surface area of the tube. Therefore there is less friction within the vessels and this reduces the effects of abrasion. 
         [0008]    The device reduces the friction within the vessel and it also reduces the overall force required to withdraw the elongate shaft. As the level of friction is reduced the forces of compression on the surrounding vasculature are consequently reduced. The slider tube may contain low diameter regions and/or highly flexible regions as described below and these regions increase the flexibility of the tube and thus further reduce the forces on the neighbouring vascular bed. Therefore the overall force required to remove the clot is reduced, which in turn reduces the forces on the vascular bed. Therefore the key benefit of the present invention is a significant reduction in rubbing of the elongate shaft against vessel walls during the initial dislodgement and retraction of the clot. 
         [0009]    An additional benefit of the present invention is the prevention of accidental retraction of the clot retrieval device into the distal end of the microcatheter and subsequent loss of the clot. This could occur should a physician attempt to use the microcatheter in the manner of a slider tube, namely withdraw the clot retrieval device as far as the microcatheter and withdraw the microcatheter a little further and so forth. This increases the possibility of the device being withdrawn into the microcatheter and resuming its collapsed configuration and therefore losing control of the clot. If a slider tube is used the microcatheter is withdrawn a significant distance and the slider tube will automatically start to advance proximally with the device once the distal end of the slider tube contacts the shaft. The process functions thus as there is less energy expended as the device shaft slides through the slider tube compared to the slider tube moving through the vessel. This effect is influenced by the difference in the coefficient of friction between the slider tube and shaft and between the slider tube and vessel, and also by the relative lateral stiffnesses of shaft and slider tube. 
       Statement of the Invention 
       [0010]    One embodiment of this invention comprises a system for dislodging an occlusive clot from a first blood vessel segment the system comprising: a clot retrieval device and a clot removal catheter, the clot retrieval device comprising a clot engaging element and an elongate member, the clot engagement element having a collapsed delivery configuration and an expanded configuration for engaging with the clot and for dislodging the clot from the first vessel segment, the elongate member configured to apply a pull force to the clot engaging element to dislodge the clot from the first vessel segment, the clot removal catheter comprising a lumen at its distal end sized to receive said clot and configured to maintain a stable position in a second blood vessel segment, said second blood vessel segment being proximal of and larger in diameter than said first blood vessel segment, a third blood vessel segment between said first and second blood vessel segments, the distal end of the elongate member configured to protect the third blood vessel segment from tractive forces transmitted by the elongate member during clot dislodgement from the first vessel segment.
       Wherein the system further comprises an elongate structural element and a slider tube, the slider tube configured to slide relative to the elongate structural element.   wherein the elongate member is configured so that the slider tube slides over a distal section of the elongate structural element.   wherein the slider tube comprises a proximal position and a distal position.   wherein the slider tube can slide freely over the surface of the elongate member between a proximal position and a distal position.   wherein the clot retrieval device is delivered to the occlusion site in the first vessel segment through a catheter and the advancement of the clot retrieval device through the lumen of the delivery catheter biases the slider tube in a proximal position.   wherein the slider tube comprises an inner lumen and an outer surface and the inner lumen is sized to slide freely over at least the surface of a distal portion of the elongate structural element.   wherein the slider tube inner lumen comprises a first material and the slider tube outer surface comprises a second material.   wherein the slider tube first material comprises a lower coefficient of friction than the slider tube second material.   wherein the slider tube comprises a distal abutment surface and a proximal abutment surface.   wherein the elongate structural element comprises a distal stop and a proximal stop to limit the sliding movement of the slider tube.   wherein the proximal stop and/or the distal stop of the elongate structural element comprise an abutment surface, a collar, a tube end, a spring end, a tether, a tapered shaft section, a diameter change, or a surface projection.   wherein elongate member is at least partially a nitinol material or a stainless steel material.   wherein a distal end of the elongate member is connected to the clot engaging element and the proximal end of the elongate member extends exterior of the patient.   wherein the slider tube encircles the elongate structural element over at least a distal portion of its length.   wherein the tractive forces acting on the third blood vessel segment comprise a combination of normal forces acting on the vessel wall and tangential forces acting along the third blood vessel segment wall.   wherein the tractive forces acting on the third blood vessel segment comprise dynamic forces associated with relative movement between the third segment vessel wall and the elongate member.   wherein the elongate member comprises an elongate structural element and a slider tube the slider tube configured to allow relative movement between the elongate structural element and the slider tube during clot dislodgement.   wherein the system comprises a microcatheter for delivering the clot removal device to the occlusive clot in the first vessel segment, the microcatheter comprising a lumen sized to receive the clot engagement element in its collapsed configuration.   wherein retraction of the microcatheter effects deployment of the clot engagement element.   wherein the microcatheter lumen is configured to slidably receive the slider tube.   wherein the slider tube outer diameter is at least as small as the diameter of the clot engagement element in its collapsed configuration.       
 
         [0032]    Another embodiment of this invention comprises a clot removal device for removing an occlusive clot form a distal blood vessel of a patient, the clot removal device comprising a clot engaging element, an elongate member and a tractive tubular member, the clot engagement element having a collapsed delivery configuration and an expanded configuration for engaging with the occlusive clot and for dislodging the occlusive clot from the distal blood vessel, the elongate member comprising a proximal section, an intermediate section and a distal section, a distal end of the distal section of the elongate member connected to the clot engaging element and the proximal end of the elongate member extending exterior of the patient, the elongate member further configured to transmit a pull force applied by the user to the clot engaging element to dislodge the clot from the distal blood vessel, the tractive tubular member configured to encircle the elongate member over at least a portion of the length of the elongate member distal section, the distal section of the elongate member being slidable and rotatable relative to the tractive tubular member, the elongate member distal section and the tractive tubular member configured to protect the proximal blood vessel from tractive forces transmitted by the elongate member during clot dislodgement from the distal vessel segment.
       wherein the tractive tubular member is slidable between a proximal position and a distal position along the distal section of the elongate member.   wherein the tractive tubular member comprises an inner lumen and an outer surface and a proximal abutment surface and a distal abutment surface.   Wherein the interface between the elongate member distal end and the tractive tubular member comprises the outer surface of the distal section of the elongate member and the inner surface of the lumen of the tractive tubular member.   wherein the interface between the elongate member distal section and the tractive tubular member is configured to facilitate low friction sliding of the tractive tubular member relative to the elongate member.   wherein the coefficient of friction of the inner surface of the tractive tubular member is less than the coefficient of friction of the outer surface of the tractive tubular member.   wherein the distal section of the elongate member comprises a polished surface or a buffed surface.   wherein the distal section of the elongate member comprises a longitudinally polished surface or a longitudinally buffed surface   wherein the clot removal device is delivered to the occlusion site in the distal blood vessel through a catheter and the advancement of the clot removal device through the lumen of the catheter biases the tractive tubular member towards the proximal end of the elongate member distal section.   wherein the tractive tubular member inner surface comprises a first material and the tractive tubular member outer surface comprises a second material.   wherein the tractive tubular member first material comprises a lower coefficient of friction than the tractive tubular member second material.   wherein the elongate member comprises a distal stop and a proximal stop, said distal and proximal stops configured to limit the distance of sliding of the tractive tubular member.   wherein the proximal stop and/or the distal stop of the elongate member comprise an abutment surface, a collar, a tube end, a spring end, a tether, a tapered shaft section, a diameter change, or a surface projection.   wherein elongate member is at least partially a nitinol material or a stainless steel material.   wherein the slider tube encircles the elongate member distal section over at least a portion of its length.   wherein the clot removal device comprises a sliding distance, said sliding distance comprising the distance along the elongate member that the tractive tubular element can slide without obstruction.
           wherein the sliding distance is at least as long as the length of the occlusive clot.   wherein the sliding distance is at least 10 mm.   wherein the sliding distance is at least 20 mm   wherein the sliding distance is at least 30 mm   wherein the sliding distance is at least 40 mm   wherein the sliding distance is at least 50 mm   wherein the sliding distance is less than 150 mm.   
           wherein the tractive forces acting on the proximal blood vessel comprise a combination of normal forces acting on the vessel wall and tangential forces acting along the proximal blood vessel wall.   wherein the tractive forces acting on the proximal blood vessel comprise dynamic forces associated with relative movement between the proximal blood vessel wall and the elongate member.   wherein the clot removal device comprises a microcatheter for delivering the clot removal device to the occlusive clot, the microcatheter comprising a lumen sized to receive the clot engagement element in its collapsed configuration.   wherein retraction of the microcatheter effects deployment of the clot engagement element.   wherein the microcatheter lumen is configured to slidably receive the tractive tubular member.   wherein the tractive tubular member outer diameter is at least as small as the diameter of the clot engagement element in its collapsed configuration.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]      FIG. 1 a    shows the conventional method for removing a clot. 
           [0062]      FIG. 1 b    shows the forces and abrasion on vessels during retraction of clot. 
           [0063]      FIG. 2  shows a detailed illustration of the present invention. 
           [0064]      FIG. 3 a    shows a novel method for clot retrieval. 
           [0065]      FIG. 3 b    shows the retrieval of clot using the present invention. 
           [0066]      FIG. 4  shows alternative embodiments of the present invention with stops. 
           [0067]      FIG. 5  shows alternative embodiments of the present invention with spring. 
           [0068]      FIG. 6  shows alternative embodiments of the present invention with tether. 
           [0069]      FIG. 7  shows an isometric view of an alternative embodiment of the present invention with stiff and rigid sections. 
           [0070]      FIG. 8 a    shows alternative embodiments of the present invention with flexible sections. 
           [0071]      FIG. 8 b    shows detail of the above in isometric view. 
           [0072]      FIG. 9  shows alternative embodiments of the present invention with sections of varying friction. 
           [0073]      FIG. 10  shows alternative embodiments of the present invention with sections of varying diameter. 
           [0074]      FIG. 11  a shows the method of use of the present invention. 
           [0075]      FIG. 11 b    illustrates the microcatheter being advanced in the vessel. 
           [0076]      FIG. 11 c    illustrates the clot retrieval device expanding within the clot. 
           [0077]      FIG. 11 d    illustrates the microcatheter being retracted and the slider tube being deployed. 
           [0078]      FIG. 11 e    illustrates the clot retrieval device being stopped by the distal mechanical stop and the slider tube. 
           [0079]      FIG. 11 f    illustrates the slider tube and the clot retrieval device and the clot being retracted. 
       
    
    
     DETAILED DESCRIPTION 
       [0080]    Specific embodiments of the present invention are now described in detail with reference to the figures, wherein identical reference numbers indicate identical or functionality similar elements. The terms “distal” or “proximal” are used in the following description with respect to a position or direction relative to the treating physician. “Distal” or “distally” are a position distant from or in a direction away from the physician. “Proximal” or “proximally” or “proximate” are a position near or in a direction toward the physician. The invention is applicable to any mechanical thrombectomy clot retrieval device, and a generic design of such a clot retrieval device is shown in the illustrations. 
         [0081]      FIG. 1 a - b    shows the conventional method of retrieving a clot from tortuous vasculature. A guidewire and microcatheter are inserted into the artery and are advanced across the occlusive clot  5 , which is lodged at a bifurcation using any conventionally know techniques. 
         [0082]    The guidewire is removed from the microcatheter to allow the clot retrieval device  1  to be advanced in a collapsed configuration until it is located within the clot  5 . The device  1  is deployed on retraction of the microcatheter  7 . The device comprises an elongate shaft  3 , having the distal end that extends interior of the artery and a proximal end that extends exterior of the artery. It has a clot engaging body  4  which is connected to the distal section of the elongate element  3 . On expansion, the device exerts a radial force upon the clot and captures the clot against the lumen of the vessel  2 . 
         [0083]    Once the clot retrieval device has captured the clot, the device is retracted proximally. The force which is pulling the device proximally also exerts a force  9  on the vessels in the immediate vicinity  8  thus pulling these vessels towards the microcatheter and potentially distorting the vasculature in the area as illustrated in  FIG. 1 b   . Furthermore, the proximal force  9  on the device also distorts the vessel  2  in which the elongate member  3  is being retracted. The force compels the vessel  2  to conform to the shape of the elongate member thus forcing it to straighten and lose its original shape. It compresses the vessels in the immediate vicinity of the elongate member  3 . In addition, the elongate member  3  may cause abrasion  10  within the lumen of the vessel  2  as it is retracted. As the vessel  2  distorts the elongate member is forced to contact the walls of the vessel which may cause the vessel to lose or damage the endothelia of the vessel at these points. 
         [0084]    The vessel distortion and abrasion could be avoided by leaving the microcatheter more distal (and closer to the clot retrieval device) when initially retracting the clot retrieval device, however this could easily result in the user retracting the clot retrieval device, thus collapsing the device within the microcatheter and liberating the clot. The slider tube design described in  FIG. 2  avoids vessel damage without the risk of inadvertent device retraction into the microcatheter. 
         [0085]      FIG. 2  shows a detailed illustration of a clot retrieval device of the present invention. The device  51  has an elongate shaft  53  having a distal end that extends interior of the artery and a proximal end that extends exterior of the artery, a clot engaging body  54  configured at the distal end of the elongate shaft, tethers  52  having distal ends connected to the proximal end of the clot engaging body  54  and proximal ends connected to the elongate element  53 . A coil  66  is slidably disposed around the elongate member  53 , the distal end of which is located proximal of a distal stop  63  and the proximal end is located within the lumen of the slider tube  61 . The tubular member  61  is slidably disposed around the elongate shaft  53 . The distal end of the slider tube extends over the coil  66  and the proximal end is located distal of the proximal stop  64 . The slider tube itself may comprise a range of constructions, some of which are shown in  FIGS. 4-10 . The slider tube  61  is a solid tube composed of flexible material such that it may be retracted through tortuous vasculature without deforming it. In the preferred embodiment the slider tube  61  is composed of a polymer such as PEN, PET, UHMWPE, LCP or Aramid. 
         [0086]    In the preferred embodiment the elongate member  53  has a lower coefficient of friction while being retracted through the slider tube  61  when compared to that between the slider tube and the vessel. As a result, the slider tube remains in situ as the elongate shaft is retracted and during dislodgment of the clot thereby protecting the walls of the vessel from abrasion. 
         [0087]    The overall effect of the slider tube  61  is to spread the pressure and tension that the elongate member normally exerts on the vessel across the entire surface area of the tube thus reducing the tension from accumulating in any one particular area in the vessel. 
         [0088]    In addition, the use of a slider tube  61  is a more secure form of prevention of abrasion than a microcatheter. If the microcatheter was used to prevent abrasion of the inner walls of the vessel the device may potentially re-enter the microcatheter. If this occurred the device would compress into its collapsed configuration and it may lose control of the clot. The clot would then be free to travel to the more distal vasculature and occlude a smaller vessel. As the distal stop  63  and the slider tube  61  are located between the device  51  and the microcatheter this occurrence is prevented. 
         [0089]      FIG. 3 a - b    illustrates the preferred method of retrieving a clot from tortuous vasculature using the present invention. A guidewire and microcatheter are inserted into the artery and are advanced across the occlusive clot  105 , which is lodged at a bifurcation using any conventionally know techniques. The guidewire is removed from the microcatheter to allow the clot retrieval device  101  to be advanced within the microcatheter in a collapsed configuration until it is located within the clot. The device  101  is deployed on retraction of the microcatheter  107 . The device has an elongate shaft  103 , having the distal end that extends interior of the artery and a proximal end that extends exterior of the artery. On expansion, the device exerts a radial force upon the clot and captures the clot against the lumen of the vessel  102 . 
         [0090]    On further retraction of the microcatheter  107 , the distal stop  113  is deployed. This is followed by the deployment of the slider tube  111  and the distal stop. The distal and proximal stops are connected to the elongate member  103  at the distal and proximal ends of the slider tube. The tubular member  111  is slidably disposed along the elongate member  103 . Upon the deployment of the slider tube  111 , the clot retrieval device  101  is then retracted proximally by means of the elongate member  103 . The device  101  is retracted until the distal stop reaches the distal end of the slider tube  111 . When it reaches the slider tube  111 , the slider tube  111  is automatically withdrawn as the clot retrieval device  101  and the clot  105  are withdrawn proximally into the guidecatheter  106 . 
         [0091]      FIG. 4  illustrates another alternative embodiment of the present invention. The device  151  having distal end that extends interior of the artery and proximal end that extends exterior of the artery, a clot engaging body  154  and control tethers  165 . The distal ends of the control tethers are attached to the proximal end of the engaging body  154  and the proximal ends are attached to the distal end of the elongate member  153 . 
         [0092]    The slider tube is slidably disposed around the elongate member  153 . The distal stop  163  is affixed to the distal end of the elongate member  153 . The proximal stop  164  is affixed to the elongate member proximal of the slider tube  161 . The slider tube  161  is held in place by the distal  163  stop and the proximal stop  164 . The device  151  is advanced through the microcatheter in a collapsed configuration until it is within the clot. Once the device is deployed it expands and captures the clot by exerting a radial pressure on the clot. As the device is being retracted, the slider tube  161  is automatically be withdrawn as the clot retrieval device  151  is withdrawn proximally into the guidecatheter. 
         [0093]      FIG. 5  illustrates another alternative embodiment of the present invention. The device  201  having a distal end that extends interior of the artery and a proximal end that extends exterior of the artery, a clot engaging body  204  and control tethers  215 . The distal ends of the control tethers  215  are attached to the proximal end of the engaging body  204  and the proximal ends are attached to the distal end of the elongate member  203 . The slider tube  211  contains the elongate member  203  at the distal end of the elongate member  203 . The device contains a spring  218  having distal ends attached to the distal end of the elongate member  203  and proximal end attached to the elongate shaft distal. In this embodiment of the invention, there is no requirement for a distal stop as the spring  218  functions as a distal stop. As the clot retrieval device is retracted the slider tube  211  automatically begins to withdraw as soon as the proximal end of the spring  218  contacts the distal end of the slider tube  211 . 
         [0094]    In the preferred embodiment the spring is a soft spring and therefore the spring  218  also has the effect of reducing the tension between the device  201  and the elongate member  203  and the slider tube  211  during retraction of the device  201 . The proximal stop  213 , which is located at the proximal end of the slider tube  211 , prevents the slider tube  211  from retracting further into the microcatheter upon deployment. 
         [0095]      FIG. 6  illustrates another alternative embodiment of the present invention. The device  251  having a distal end that extends interior of the artery and a proximal end that extends exterior of the artery, a clot engaging body  254  and control tethers  265 . The distal ends of the control tethers  265  are attached to the proximal end of the engaging body  254  and the proximal ends are attached to the distal end of the elongate member  253 . The slider tube  261  is slidably disposed around the elongate member  253  at the distal end of the elongate member  253 . A distal stop  263  is located at the distal end of the elongate member  253 . An elongate tether  269 , having distal end affixed to the distal end of the elongate member  253  and proximal of the distal stop and proximal end attached to the slider tube  261 , has the effect of tying the slider tube  261  to the device while allowing it to move within the vasculature thus reducing the overall friction of the device during retraction. The elongate tether  269  functions as a proximal stop for the slider tube. 
         [0096]      FIG. 7  is an isometric view of a section of an alternative embodiment of this invention. The slider tube  311  comprises an atraumatic design wherein alternative sections of the tube are composed of regions of stiff material  312 , which are punctuated by flexible joint regions or articulation regions  313 . This design allows the tube to articulate with the vasculature without distorting the vessels or causing abrasion to the walls of the vessels. The slider tube  311  is slidably disposed around the elongate member and contains the elongate member during retraction and prevents it from causing abrasion or distorting the vessels. This embodiment also reduces the compression of the vessels proximal of the device. Any number of flexible joints and stiff regions can be used at any section along the tube and can be used in conjunction with any tubular device disclosed elsewhere in this document. 
         [0097]      FIG. 8 a    is an isometric view of a section of an alternative embodiment of the present invention. The slider tube  361  comprises an atraumatic design wherein the tube is punctuated by flexible regions  362  alternated with rigid regions  363 . The flexible regions  362  are composed of sections of tubing in which sections of the tubing have been removed. These slits  364  allow the slider tube to be more flexible as it reduces the outer surface area of the tube and allows it bend at smaller angles. During retraction this reduces the effect of abrasion of the vessels and prevents distortion and compression of the vessels proximal of the device thus enhancing the device performance.  FIG. 8 b    is an isometric view of the slits  414  in the slider tube  411 . The slits may be of any shape and size and number and they may be located at any section across the tube. Such slits may be used in conjunction with any other tubular designs disclosed elsewhere in this document. 
         [0098]      FIG. 9  is an isometric view of a section of an alternative embodiment of the present invention. The slider tube  461  is comprised of an atraumatic design wherein the tube is comprised of alternating low friction regions  462  and high friction regions  463 . The low friction regions may be created by electropolishing the tube to obtain a smooth outer surface and the high friction regions may be created by fashioning slight protrusions which emanate from the outer surface of the tube. The protrusions may be of any shape or size or number. In the preferred embodiment the effect of the varying regions of high and low friction would be to spread the pressure and tension that the elongate member exerts on the vessel across the entire surface area of the tube thus reducing the tension from accumulating in any one particular area in the vessel. The slight increase in friction of these alternating regions will increase the efficiency of the elongate element as it moves through the slider tube. This effect is due to the higher coefficient of friction between the slider tube and the vessel compared to the lower coefficient between the elongate element and the slider tube. The result is that the slider tube remains in situ as the elongate shaft is retracted thus protecting the vessel walls from abrasion. Any number of low friction regions and high friction regions can be used at any section along the tube and can be used in conjunction with any tubular device disclosed elsewhere in this document. 
         [0099]      FIG. 10  is an isometric view of a section of an alternative embodiment of the present invention wherein the slider tube  511  is composed of regions of small  512  and large diameter  513 . The regions of small diameter  512  may alternate with regions of large diameter  513  thus creating a low profile device. The atraumatic design reduces the force and tension on the vasculature as it increases the flexibility of the tubular device and it decreases the risk of abrasion. In the preferred embodiment the effect of the varying regions of smaller and larger diameter would be to spread the pressure and tension that the elongate member exerts on the vessel across the entire surface area of the tube thus reducing the tension from accumulating in any one particular area in the vessel. Any number of small diameter regions and large diameter regions can be used at any section along the tube and can be used in conjunction with any tubular device disclosed elsewhere in this document. 
         [0100]    Use of a slider tube of the present invention in conjunction with a clot retrieval device of the present invention in removing an obstructive clot  555  from an intracranial artery  552  is depicted in  FIG. 11 a - f   . A guidewire  566  and microcatheter  557  are inserted in the artery  552  by means of a guidecatheter  556  and are advanced across an obstructive clot  555  using any conventionally known techniques. The guidewire  566  is removed from the microcatheter  557  to allow the clot retrieval device  551  and the slider tube  561  to be advanced through the microcatheter in the collapsed configuration until the clot retrieval device  551  is within the clot  555 . The device has an elongate shaft  553 , having the distal end that extends interior of the artery and a proximal end that extends exterior of the artery, distal stop  563  which is located at the proximal end of the ring elements and proximal stop  564  which is located at the proximal end of the slider tube  561 . It has a clot engaging body  554  which is connected to the elongate element  553 . 
         [0101]    The microcatheter is retracted to deploy the clot retrieval device  551  within the clot in a manner that the engaging portion of the clot retrieval device is positioned across the clot. The engaging section of the clot exerts a gentle radial force on the clot while maintaining the integrity of the clot and avoiding its dissection. The microcatheter is then further retracted proximally to deploy the mechanical stops  563  and  564  and the slider tube  561  within the vessel  552 . Once the clot retrieval device  551  has engaged the clot  555  the device  551  is retracted proximally by means of the elongate member  553  to which the device is affixed. The device is retraced proximally until the distal stop  563  makes contact with the slider tube  561 . When the distal stop  563  has contacted the slider tube  561 , the slider tube  561  will automatically be withdrawn as the device  551  and the microcatheter  557  are withdrawn proximally into the distal end of the guidecatheter  556 . 
         [0102]    During this process the tension and the force that the elongate element  553  would normally exert on the inner lining of the vessel is absorbed by the slider tube  561  and spread across the entre outer surface of the slider tube  561 . Therefore the slider tube prevents excessive distortion of the vessel and prevents abrasion of the inner walls of the vessel. 
         [0103]    Furthermore, the slider tube  561  is a more secure form of prevention of abrasion when compared to a microcatheter  557 . If the microcatheter  557  was used in the manner of a slider tube  561 , the device  551  may unintentionally withdraw into the microcatheter. Should this happen the device  551  would compress into its collapsed configuration and the clot  555  would escape from the device and leaving open the possibility that it might advance distally through the vessel and occlude a smaller vessel at another junction in the vasculature. As the slider tube  561  and the mechanical stops  563  and  564  are located between the device  551  and the microcatheter  557  this reduces the possibility of this occurring. 
         [0104]    The slider tube  561  may be comprised of slits or rigid and flexible regions and/or high and low friction regions or any combination of the above as disclosed elsewhere in this document. It may be attached to the elongate member by the means described previously such as by a tether or a spring. It may also be held in situ around the elongate member by proximal and/or distal stops. Preferably the slider tube  561  is composed of a polymer such as PEN, PET, UHMWPE, LCP or Aramid. The slider tube  561  may be used in conjunction with any mechanical thrombectomy device such as stentrievers. 
         [0105]    Modification and additions can be made to the embodiments of the invention described herein without departing from the scope of the invention. For example, while the embodiments described herein refer to particular features, the invention includes embodiments having different combinations of features. The invention also includes embodiments that do not include all of the specific features described. 
         [0106]    The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail.