Abstract:
An apparatus and method for treating cerebral blood vessels such as carotid arteries. The system generally includes an apparatus and method for safely and easily deploying a self-expanding stent in a vessel while preventing embolic migration using a filter.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of surgical instruments. Specifically, the present invention relates to an emboli-capture device for treating cerebral blood vessels such as carotid arteries. 
     Stenting and angioplasty in stenosed cerebral vessels (e.g., carotid arteries) pose risks of dislodging thrombus or friable plaque. The thrombus or plaque can become lodged in the brain or arteries and cause serious injury such as a stroke. If such embolic material is dislodged during a stenting procedure, it is necessary to collect the material before the it migrates and causes injury. A previous invention, U.S. Pat. No. 4,921,478, “Cerebral Balloon Angioplasty System,” Solano et al., employs an occlusion catheter carrying a relatively large inflatable occlusion balloon to repair vessels. The balloon is capable of being formed into a funnel while simultaneously sealing a vessel and establishing retrograde blood flow. The balloon is bulky and difficult to refold and withdraw from lesions within the vessels. The withdrawal is prone to causing extensive tissue damage and dislodging more emboli. Moreover, the balloon-type system will not work effectively without a complete and perfect seal between the balloon and the vessel wall. Moreover, Solano et al. contemplates no occlusion in conjunction with the deployment of a self-expanding stent. Furthermore, although the prior art filtered the blood, sometimes excess emboli remained when the device was removed from blood vessels. 
     What has been needed and heretofore unavailable is a means to deliver and implant a stent in conjunction with a safe and easy-to-use device and method of use for stenting blood vessels while minimizing the risk of embolic migration. The present invention satisfies this need. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus and method for treating stenosed cerebral blood vessels such as carotid arteries. The system generally includes an apparatus and method for safely and easily deploying a self-expanding stent in a vessel while preventing embolic migration. 
     In a preferred embodiment, a system for percutaneously delivering a stent within a vessel while preventing embolic migration includes: a restraining sheath that is capable of both expanding and retracting whereby minimal friction is created between the restraining sheath and the stent during deployment of the stent; a filter for trapping and retaining embolic material, the filter being located relative to the restraining sheath such that the filter will trap any embolic material flowing into the restraining sheath; a stent delivery catheter having a proximal end open to atmospheric pressure and a distal end connected to a proximal end of the restraining sheath; and a stent that initially is in a collapsed state and positioned within the restraining sheath. 
     The filter may consist of one of many devices already in use, e.g., a strainer device comprised of a plurality of wires. The expansion of the restraining sheath may be accomplished by mechanically pushing a composite sheath using a design similar to that of an umbrella. 
     In another preferred embodiment, expansion of the filter may be accomplished by using a wedge and spine mechanism to open the restraining sheath from a closed position. 
     In another preferred embodiment, the expansion of the filter may be accomplished by releasing a plurality of bent wires that are restrained in a straightened position. 
     The sheath design provides optimal deployment of the self-expanding stent because the sheath both expands in a radial direction and retracts in a proximal direction simultaneously. Therefore, due to the angle of incidence created between the sheath and the stent during deployment there is a low coefficient of friction between the sheath and the stent. This is an ideal configuration for recapturing a partially deployed stent because contact is constantly maintained between the sheath and the undeployed part of the stent. 
     A desired site within a vessel is first accessed with the system. The restraining sheath is then deployed while being moved proximally. The restraining sheath, as it expands, forms an occlusive conical member or catch basin at a proximal end of the stent. The stent, being self-expanding, is automatically deployed as the restraining sheath expands. A temporary seal is created between the stent and the restraining sheath. An outer edge of a distal end of the restraining sheath may include a material taken from the group of materials consisting of soft plastic, rubber, and a gel, in order to ensure a proper seal between the sheath and the stent. Therefore, unlike the situation where a balloon exerts pressure on a vessel wall to cause a seal, in the present invention vessel damage is minimized. 
     The filter is located within the restraining sheath at the occlusion site in another embodiment. 
     In yet another preferred embodiment, the filter may be located within the stent delivery catheter. Alternatively, the filter may be located outside of the patient&#39;s body. 
     Due to the occlusion of the vessel at the proximal end of the stent, a pressure differential is created between the more distal arteries (pressurized at blood pressure plus atmospheric pressure) and a lumen of the stent delivery catheter (pressurized at atmospheric pressure). Therefore, retrograde blood flow is induced and blood and embolic particles are flushed into the filter where the embolic particles are captured. 
     In another preferred embodiment, a vacuum apparatus may be included in the system if the occlusion is not adequate to induce sufficient retrograde blood flow or to ensure that the maximum number of embolic particles are aspirated into the filter. The restraining sheath is then collapsed to its original size, thereby trapping any remaining embolic material. The system is then removed from the patient. 
     Other features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment, depicting in a closed position an apparatus of a composite design similar to that of an umbrella for expanding a restraining sheath wherein expansion is accomplished by mechanically pushing the sheath. 
     FIG. 2 is a perspective view of the apparatus of FIG. 1 depicted in an open position. 
     FIG. 3 is a perspective view of another embodiment depicting an apparatus in a closed position for expanding the restraining sheath wherein expansion is accomplished by using a wedge and spine mechanism to open the restraining sheath from a closed position. 
     FIG. 4 is a perspective view of the apparatus of FIG. 3 in a partially expanded position. 
     FIG. 5 is a perspective view of the apparatus of FIG. 3 in a fully expanded position. 
     FIG. 6 is a perspective view of another preferred embodiment depicting an apparatus in a closed position for expanding the restraining sheath wherein expansion is accomplished by releasing bent wires that are restrained in a straightened position. 
     FIG. 7 is a perspective view of the apparatus of FIG. 6 in a fully expanded position. 
     FIG. 8 is a cross-sectional view of a restraining sheath in a closed position. 
     FIG. 9 is a perspective view of a restraining sheath that has been partially expanded by the apparatus of FIG.  3 . 
     FIG. 10 is a perspective view of a restraining sheath that has been partially expanded by the apparatus of FIG.  6 . 
     FIG. 11 is an elevational view of the present invention, partially in cross-section, after advancement to a desired vessel site and just prior to commencement of stent deployment. 
     FIG. 12 is an elevational view, partially in cross-section, depicting the present invention during stent deployment. 
     FIG. 13 is an elevational view, partially in cross-section, depicting the present invention after the stent has been fully deployed. 
     FIG. 14 is an elevational view, partially in cross-section, depicting the resent invention after the stent has been fully deployed, including an optional vacuum apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in the exemplary drawings, the present invention may be embodied in various ways. Where common elements occur in more than one embodiment, the same reference numerals will be used. Referring to FIG. 1, depicting one preferred embodiment, apparatus  10  of a composite design similar to that of an umbrella for expanding a restraining sheath is shown. The restraining sheath is omitted for clarity. A stent delivery catheter  12  is coaxially positioned within apparatus  10 . Expansion of the restraining sheath is accomplished by mechanically pushing the sheath via expansion of expandable cage  14 . The cage  14  consists of spines  16  each of which have bend  18 . The spines  16  are secured by fixed support ring  20  at the proximal end of spines  16 . A distal end of control wire  22  is fixed to collar  24  that is slidably mounted about the delivery catheter. The cage is expanded by pulling the collar proximally via the control wire which causes secondary spines  26  (see FIG. 2) to press against the larger spines  16 . One end of each secondary spine  26  is pivotally secured to collar  24 . The opposing end of each secondary spine  26  is pivotally secured to larger spine  16 . Likewise, the proximal end of each larger spine  16  is pivotally secured to the fixed control ring  20 . As a result, cage  14  pushes outwardly on the sheath membrane and the sheath thus expands at a distal end and forms a catch basin. 
     In another preferred embodiment, apparatus  30  provides expansion for the sheath membrane (omitted for clarity), as shown in FIG. 3. A plurality of spines  32  project distally and function to support the sheath. The spines  32  are pivotally secured at their proximal ends to stent delivery catheter  12 . Wedge  15  is slidably mounted on the stent delivery catheter and may be moved axially relative to the catheter and spines  32  by a control wire (omitted for clarity) or other means. 
     As shown in FIG. 4, when wedge  15  is moved proximally relative to the spines, the wedge forces the spines to protrude outwardly in a radial direction. FIG. 5 depicts the spines in a fully expanded position. The wedge has been moved as far as possible in a proximal direction. 
     As shown in FIG. 6, apparatus  40  for expanding the sheath membrane (omitted for clarity) provides yet another preferred embodiment. A plurality of bent wires  42  are restrained in a straightened position by fixed restraint ring  44  at a proximal end of apparatus  40  and slidably mounted restraint ring  46  at a distal end of the apparatus. The slidably mounted restraint ring is initially positioned at the distal ends of wires  42 . Catheter  12  is coaxially positioned within wires  42  and rings  44 , 46 . A second control wire  48  is attached to the slidably mounted restraint ring. 
     Referring to FIG. 7, the slidably mounted restraint ring  46  has been moved proximally via the second control wire. The wires  42  have thus been released and have sprung into their resting bent positions. This action serves to fully expand a restraining sheath. 
     Turning to FIG. 8, restraining sheath  50  is depicted and is supported by spines  52 , or alternatively wires. The restraining sheath in a closed position may consist of folds  54 . An alternative to providing folds  54  is to construct a restraining sheath of a material that is capable of being stretched in a radial direction. This alternative would require less material but would require more force to expand the material in a radial direction than would be required if folds were implemented. A restraining sheath may be formed from a material selected from the group of materials consisting of polyethylene, polyester and polyamide. The material, which has a low coefficient of friction, may be obtained in varying grades of softness. 
     As shown in FIG. 9, restraining sheath  56  may be expanded by apparatus  30  of FIG. 3 such that the diameter at the distal end is larger than the diameter at the proximal end. 
     Turning to FIG. 10, restraining sheath  58  may be expanded by the apparatus of FIG. 6 such that the diameter at the distal end is larger than the diameter at the proximal end. 
     The sheath design provides optimal deployment of the self-expanding stent because the sheath both expands in a radial direction and retracts in a proximal direction simultaneously. Therefore, due to the angle of incidence created between the sheath and the stent during deployment, there is a low coefficient of friction between the sheath and the stent. This is an ideal configuration for recapturing a partially deployed stent because contact is constantly maintained between the sheath and the undeployed part of the stent. 
     Turning to FIGS. 11-13, in a preferred method, a desired site within vessel  60  is first accessed with the system, via a percutaneous technique. A stent delivery catheter  62  has its proximal end open to atmospheric pressure and its distal end running into the proximal end of restraining sheath  64 . Self-expanding stent  66  is initially in a collapsed state and partially disposed within the restraining sheath. The restraining sheath  64  is attached to and deployed by an apparatus such as the apparatus  40  shown in FIGS. 6-8. A plurality of bent wires  42  are restrained in a straightened position by a fixed restraint ring  44  at the proximal end of the apparatus  40  and a slidably mounted restraint ring  64  near the distal end of the apparatus. A control wire (not shown) or other means for moving the restraint ring  46  can be attached to the slidable mounted restraint ring  46  to enable the plurality of bent wires  42  to be deployed. As the bent wires  42  are deployed, the restraining sheath  64  is in turn deployed within the patient&#39;s vasculature. The restraining sheath is then deployed, and as it expands, forms occlusive conical member  68  or catch basin at the proximal end of the stent. The stent, being of the self-expanding type, is automatically deployed as the restraining sheath expands. A temporary seal is created between the stent and the restraining sheath. The outer edge of the distal end of restraining sheath  64  may include a material consisting of soft plastic, rubber, or a gel, in order to ensure a proper seal between the sheath and the stent. Therefore, unlike the situation where a balloon exerts pressure on a vessel wall to cause a seal, in the present invention vessel damage is minimized. As is shown in FIG. 12, when the restraining sheath  64  is expanded by the outward movement of the wires  42 , it also is simultaneously retracted back to allow a portion of the self-expanding stent  66  to expand and contract a portion of the stenosis  80  formed in the vessel  60 . The self-expanding stent  60  will begin to expand and contact more area of the stenosis  80  as the restraining sheath  64  is retracted via the action of the wires  42 . It also should be appreciated that the delivery catheter  62  may have to be retracted back away from the stenosis  80 , as is shown in FIG. 13, to allow the entire self-expanding stent  66  to be deployed across the stenosis  80  since the length of retraction of the restraining sheath  64  may be somewhat limited by the action of the particular apparatus used to expand and retract the sheath  64 . 
     A filter  70  for trapping and retaining embolic material or particles  72  is located within the lumen of the stent delivery catheter and relative to restraining sheath  64  such that the filter will trap any embolic material flowing into the restraining sheath. Such filters are known in the art and may include a strainer device comprised of a plurality of wires. The filter may be located within the restraining sheath at the occlusion site in one embodiment. In another embodiment, filter  70  may be located within the lumen of the stent delivery catheter  62 , at a location outside of the restraining sheath  64  as shown in phantom in FIG.  13 . In yet another preferred embodiment, the filter may be placed within the lumen of the catheter at a location outside of the patient&#39;s body (not shown). 
     Due to the occlusion of vessel  60  at the proximal end of stent  66 , a pressure differential is created between the more distal arteries (pressurized at blood pressure plus atmospheric pressure) and a lumen of the stent delivery catheter (pressurized at atmospheric pressure). Therefore, retrograde blood flow is induced and blood and embolic particles are flushed into filter  70  where the embolic particles are collected. An opening in the delivery catheter (not shown) distal to the filter provides an entrance to the lumen of the catheter which draws the embolic material into the opened restraining sheath  64  and into the filter  70 . 
     Turning to FIG. 14, in another preferred embodiment an aspiration system consisting of vacuum device  74  with optional valve  76  may be included in the system if the occlusion is not adequate to induce sufficient retrograde blood flow or to ensure that the maximum number of embolic particles  72  are aspirated into filter  70 . Alternatively, in another embodiment, an aspiration system consisting of a luer lock (not shown) capable of accepting a syringe may be used. The restraining sheath  64  is then collapsed to its original size, thereby trapping any remaining embolic material or particles  72 . The restraining sheath  64  is collapsed by simply moving the slidable mounted restraint ring  46  distally to retract the plurality of bent wires  42 . The system is then removed from the patient. Thus, a self-expanding stent is deployed safely and easily without the risk of embolic migration. 
     While the invention has been illustrated and described herein in terms of its use as a safe and easy-to-use apparatus and method for treating blood vessels while minimizing the risk of embolic migration, it will be apparent to those skilled in the art that the invention can be used in other instances. Other modifications and improvements may be made without departing from the scope of the invention.