Abstract:
Interventional catheters are disclosed for use in performing diagnostic and therapeutic procedures in vessels that are accessed retrograde to blood flow. The catheters include an elongated shaft slidably disposed within a sheath, a distal region having an end effector and a filter disposed proximal to the end effector to capture emboli liberated during the diagnostic or therapeutic procedure. The filter includes a plurality of struts that cooperate with an exterior surface of the catheter to define a reservoir to retain captured emboli, the reservoir configured so that advancement of the sheath contracts the filter without squeezing or dislodging captured emboli beyond a distal end of the filter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/945,729, filed Nov. 12, 2010, now U.S. Pat. No. 8,257,385, which is a continuation of U.S. patent application Ser. No. 11/315,463, filed Dec. 21, 2005, now U.S. Pat. No. 7,837,702, the entire contents of all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to catheters for performing interventional procedures, such as angioplasty and/or stenting, in vessels where there is a risk of the release of one or more emboli. In particular, the present invention is designed for use in instances where the target vessel is accessed distal to the lesion or in the so-called “retrograde” fashion as in the iliac arteries when approached via ipsilateral femoral access. 
     BACKGROUND OF THE INVENTION 
     Interventional techniques have been developed wherein catheters are used to perform diagnostic and therapeutic procedures, such as stenting and angioplasty. During such procedures, thrombus, plaque, or other material may be released into the bloodstream as emboli. If free to circulate through the body, emboli may become lodged in the smaller distal vessels often with serious consequences, thereby presenting a risk of life-threatening or limb threatening ischemia. 
     U.S. Pat. No. 5,011,488 to Ginsburg, for example, describes a catheter designed to remove frangible thrombus from a vessel, such as from a A-V fistula, to restore flow through the vessel and reduce the risk that thrombus may dislodge and migrate to other regions of the patient&#39;s vasculature. The catheter comprises three concentrically arranged flexible tubes, wherein the innermost tube has at its distal end an expandable body and the central tube has an expandable funnel-shaped member. In operation, the funnel-shaped member is deployed proximal of the thrombus while the innermost tube and expandable member are advanced to a position distal of the thrombus. The expandable member then is deployed to contact the vessel wall and retracted proximally to urge the thrombus into the funnel-shaped member. U.S. Pat. No. 5,102,415 to Guenther et al. describes another multi-catheter device for use in removing blood clots. 
     The devices described in the foregoing patents have several disadvantages that limit their utility. First, the presence of multiple concentric catheters increases the delivery profile and rigidity of the device. Second, the devices are configured primarily to remove frangible thrombus, and are expected to be unsuitable for removing calcified or dense lesions without inflicting trauma to the vessel endothelium. Third, the configuration of the funnel-shaped components and retractable innermost catheter are incompatible with dilatation or stent delivery functionality. 
     U.S. Pat. No. 5,549,626 to Miller et al. describes a vena cava filter including a self-expanding mesh basket affixed to the distal end of an inner catheter enclosed within a delivery sheath. Suction may be applied through the inner catheter to remove emboli captured in the basket. As in the Ginsburg and Guenther patents, the device described in Miller is not appropriate for use in connection with stent delivery or vessel dilatation. 
     U.S. Pat. No. 4,723,549 to Wholey describes a catheter having an expandable filter mounted to the catheter shaft distal to a dilatation balloon. The filter comprises a plurality of ribs that are preformed to stow against the catheter. A balloon located between the ribs and catheter causes the ribs to deploy radially outward when inflated. The ribs and filter return to the collapsed position when the balloon is deflated. 
     The device described in the foregoing Wholey patent contemplates antegrade blood flow, i.e., in a proximal to distal direction along the catheter shaft. Accordingly, the device described in the Wholey patent would not be suitable for capturing emboli in the retrograde access applications, such as in the iliac arteries. In addition, there is a risk that, when the balloon deflates and the ribs collapse against the catheter shaft, some of the emboli collected in the filter may be squeezed past the end of the filter and escape into the bloodstream. 
     U.S. Pat. No. 6,042,598 to Tsugita et al. describes a variety of percutaneous catheter-based embolic filters. That patent discloses a number of filters that may be deployed from a distal end of a catheter. Like the filter in the aforementioned Wholey patent, however, such filters are not suitable for retrograde access applications, because the emboli are generally released downstream of the filters. In addition, FIG. 10 of Tsugita et al. depicts a catheter for use in retrograde access applications in which the filter assembly is coupled directly to the outer surface of the catheter. Such an arrangement is undesirable because it permits movements of the catheter to be directly transferred to the filter, thus creating the risk that emboli may escape past the outer edge of the filter. More importantly, however, the filter described with respect to FIG. 10 does not provide any mechanism for preventing large amounts of embolic material from being squeezed out of the filter by the sheath during filter contraction and removal of the catheter. 
     U.S. Patent Application Publication No. US2002/0095172 to Mazzocchi et al. describes various embolic filters that attempt to prevent emboli from escaping filters when they are contracted for removal. The filter of FIGS. 13-15 comprises a basket having a cover slidably disposed to engage the basket and thereby retain emboli within the filter. However, the relative complexity of the filters described in that application would appear to limit the utility of those designs. 
     In view of the foregoing, it would be desirable to provide a catheter for use in an interventional procedure in retrograde access applications, such as the iliac vessels, wherein the catheter has an embolic protection capability and provides a reduced insertion profile. 
     In view of the foregoing, it would be desirable to provide a catheter for use in an interventional procedure in retrograde access applications, such as the iliac vessels, wherein the catheter has an embolic protection capability and a simple design that avoids the use of multiple concentric catheters. 
     It further would be desirable to provide a catheter for use in an interventional procedure in retrograde access applications, wherein the catheter has an embolic protection capability and does not require suction or aspiration, thereby obviating the need to provide a suction or aspiration lumen and enabling a smaller insertion profile. 
     It also would be desirable to provide a catheter for use in an interventional procedure in retrograde access applications, wherein the catheter has an embolic protection capability and reduces the risk that emboli will be dislodged from the device during filter contraction and removal of the catheter. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide a catheter for use in an interventional procedure that requires retrograde access, such as the iliac vessels, wherein the catheter has an embolic protection capability and provides a reduced insertion profile. 
     It is another object of the present invention to provide a catheter for use in an interventional procedure in retrograde access applications, such as the iliac vessels, wherein the catheter has an embolic protection capability and a simple design that avoids the use of multiple concentric catheters. 
     It is also an object of this invention to provide a catheter for use in an interventional procedure in retrograde access applications, wherein the catheter has an embolic protection capability and does not require suction or aspiration, thereby obviating the need to provide a suction or aspiration lumen and enabling a smaller insertion profile. 
     It is a further object of the present invention to provide a catheter for use in an interventional procedure in retrograde access applications, wherein the catheter has an embolic protection capability and reduces the risk that emboli will be dislodged from the device during contraction and removal of the catheter. 
     These and other objects of the present invention are accomplished by providing an interventional catheter for use in retrograde access applications, such as the iliac arteries, having a filter that captures and securely retains emboli within a reservoir when the filter is collapsed for removal from the vessel. In a preferred embodiment, the catheter comprises a catheter having a therapeutic or diagnostic end effector, e.g., a balloon for dilatation or stent delivery, a filter disposed on the catheter shaft proximal of the end effector and a reservoir disposed between the filter and the end effector. The device preferably further comprises a delivery sheath that surrounds the catheter and assists in retracting the filter to its delivery configuration. 
     When used to treat stenotic lesions occurring in an artery that requires retrograde access, such as an iliac artery being treated from the ipsilateral femoral artery, the catheter is advanced through the artery until the end effector is disposed within the lesion, as may be determined by radiography. The sheath then is withdrawn proximally beyond the end effector and filter, allowing the filter to deploy. The end effector then is actuated to perform a desired diagnostic or therapeutic function, e.g., a balloon is inflated to dilate the lesion and/or deploy a stent and restore patency to the vessel. 
     In accordance with the principles of the present invention, emboli released during actuation of the end effector are captured in the filter and directed into the reservoir. Upon completion of the interventional procedure, the sheath and inner catheter are moved relative to one another to collapse the filter, thereby sealing the emboli within the reservoir and reducing the risk of an inadvertent release of particles. The catheter then is removed from the patient. 
     In one embodiment, the reservoir constitutes a reduced diameter section of the catheter shaft. In this embodiment, when the filter is contracted against the catheter shaft by advancement of the sheath, the filter spans the reduced diameter section of the shaft and imparts no squeezing motion to the captured embolic material. Accordingly, the captured embolic material cannot be squeezed past the distal end of the filter and is securely retained in the reservoir. 
     In an alternative embodiment, filter mesh has an amphora shape wherein the distal ends of the struts that support the filter mesh include a concave indentation, so that the proximal portion of the filter defines a reservoir. The indentation is configured so that when the sheath is advanced to contract the struts, the distal ends of the filter contact the catheter shaft before more proximal portions of the struts, and prevent embolic material from being dislodged from the filter in a distal direction. 
     Methods of using devices constructed in accordance with the present invention also are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and advantages of the present invention will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like referenced characters refer to like parts throughout, and in which: 
         FIGS. 1A and 1B  are side views of a prior art catheter for use in retrograde access applications depicting some of the shortcomings of such designs; 
         FIG. 2  is a side view of an exemplary embodiment of an interventional catheter of the present invention; 
         FIGS. 3A and 3B  are side sectional views of the device depicted in  FIG. 2  taken along the line A-A when in a contracted and a deployed state, respectively; 
         FIGS. 4A and 4B  are side views of an embodiment of a self-expanding member in closed and open states, respectively; 
         FIGS. 5A to 5F  are side views illustrating steps of using the device of  FIG. 2 ; and 
         FIGS. 6A and 6B  are side sectional views of an alternative embodiment of a filter suitable for use in the catheter of the present invention, deployed within a vessel and in a contracted state, respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to an interventional catheter for use in the retrograde access applications, such as the iliac arteries, that includes an embolic protection system. In an iliac stenting procedure, for example, an interventional catheter is inserted percutaneously or through a cut-down in the patient&#39;s groin in the region of the femoral artery, whereby the blood flows towards the device along the catheter shaft, i.e., from the distal end of the device towards its proximal end. A catheter that incorporates a filter element located distal to the dilatation or stent delivery balloon, such as the above-described U.S. Pat. No. 4,723,549 to Wholey, cannot practically be used in such a procedure, since any emboli liberated will be carried away from the filter. 
     Referring to  FIG. 1A , the stent delivery system and filter arrangement depicted in FIG. 10 of the foregoing U.S. Pat. No. 6,042,598 to Tsugita et al. is reproduced. Stent delivery system  10  comprises catheter  11  having stent  12  disposed on balloon  13 , filter  14  and sheath  15  slidably disposed on catheter  11 . Filter  14  comprises filter mesh  16  affixed to self-expanding struts  17 . Sheath  15  retains struts  17  contracted against the shaft of catheter  11  during insertion of the catheter. Sheath  15  then is retracted proximally so that struts  15  self-expand and deploy filter mesh  16  to the funnel shape depicted in  FIG. 1A . To ensure that emboli do not escape past the outer edge of filter  14 , open end  18  of the filter contacts the vessel wall. 
     Stent delivery system  10  provides a filter suitable for use in retrograde access applications, i.e., where blood flows from the distal to the proximal catheter direction, as indicated by arrow A. Emboli E liberated during the stent delivery and dilatation procedure are captured in filter mesh  16 . Upon completion of the interventional procedure, sheath  15  is advanced distally to collapse the filter and permit retrieval of the catheter. Alternatively the filter may have an atraumatic outer surface such that the catheter may be retracted into the sheath to close the filter. 
     Referring to  FIG. 1B , a principal drawback of the foregoing prior art catheter system is described. In particular, when sheath  15  is advanced forward, it causes struts  17  and filter mesh  16  to collapse against the shaft of catheter  11  in a proximal to distal direction. This is expected to squeeze captured embolic material distally towards open end  18  of filter  14 , where it can escape from the filter into the bloodstream. The present invention is directed to solving this problem. 
     In accordance with the principles of the present invention, the interventional catheter of the present invention includes a filter configured to cooperate with a reservoir to ensure that embolic material captured by the filter is not inadvertently released when the filter is contracted for removal. More preferably, the device of the present invention includes a filter that seals the reservoir to prevent embolic material from escaping the filter during contraction and removal of the filter from the patient&#39;s vessel. 
     Referring now to  FIG. 2 , exemplary catheter  20  constructed in accordance with the principles of the present invention is described. Illustratively, catheter  20  comprises a stent delivery system, although it should be understood that the system could alternatively comprise a dilatation system, atherectomy system or other interventional diagnostic or therapeutic system. 
     Catheter  20  comprises catheter shaft  21  having distal end  22  and proximal end  23 . Shaft  21  is slidably disposed within sheath  24  having distal end  25  and proximal end  26 . Catheter  20  further comprises a distal region carrying a diagnostic or therapeutic end effector, illustratively balloon  27 , inflation port  28  in communication with interior of the balloon, optional radiopaque markers  29 ,  30  and  31 , and filter  32 . Filter  32  comprises plurality of self-expanding struts  33  that support filter mesh  34 , as described herein below. 
     Catheter  20  further comprises a guide wire lumen through which guide wire  35  may be slidably disposed. For over-the-wire use, the guidewire lumen extends from the distal end  22  to a port at proximal end  23  of catheter  20 . Alternatively, rapid-exchange functionality, the guide wire lumen may extend from distal end  22  to a port comprising a lateral skive in the exterior surface of catheter shaft  21  about 8-10 centimeters proximal of filter  32 . In either case, the guidewire lumen extends through the distal region of catheter shaft  21  including filter  32  and the end effector. 
     Sheath  24  optionally may include radiopaque marker  36  disposed at distal end  25  to permit fluoroscopic confirmation of the location of the sheath. Illustratively, balloon  27  has plastically deformable stent  37  disposed on its exterior surface, although any suitable stent and delivery mechanism may be employed with the embolic protection system of the present invention. 
     Catheter shaft  21  and sheath  24  preferably are formed of flexible biocompatible materials, such as polyethylene, polyurethane, PEBAX, nylon and other polymers typically used in catheter construction. Catheter shaft  21  optionally may comprise carbon nanotubes or other additives for added strength. Sheath  24  likewise may be formed in a conventional manner from known catheter materials. Balloon  27  preferably comprises a non-compliant or semi-compliant material, such as polyethylene or nylon, and may be constructed using balloon molding techniques that are per se known. 
     Referring now also to  FIGS. 3A and 3B , which omits filter mesh  34  for clarity, catheter shaft  21  includes reduced diameter section  38  disposed adjacent to filter  32 . Reduced diameter section  38  is shorter than the length of struts  33 , so that when the struts are contracted against catheter shaft  21 , filter  32  and reduced diameter section  38  cooperate to form reservoir  39 . Accordingly, as depicted in  FIG. 3A , when struts  33  are contracted against the catheter shaft, the struts span the length of reduced diameter section  3 , and together with filter mesh  34 , positively seal reservoir  39 . This in turn prevents the escape of embolic material captured within the reservoir. 
     In addition, because struts  33  are not expected to deflect appreciably into reduced diameter section  38  during distal advancement of sheath  24 , advancement of the sheath will not squeeze or dislodge captured embolic material towards the open end of the filter. Consequently, the risk that emboli will be released from the filter into the blood flow during contraction and removal of the catheter is greatly reduced relative to previously-known catheter designs, such as depicted in  FIG. 1 . 
     In a preferred embodiment, sheath  24  has an inner diameter of 6.5 French and catheter shaft  21  has an outer diameter of approximately 5 French, narrowing to a diameter of about 3 French at reduced diameter section  40 . Catheter  20  preferably has a length appropriate for over-the-wire or rapid exchange use, as may be desired for a particular application. 
     Filter mesh  34  preferably comprises a mesh having a pore size selected to allow the passage of blood, but not emboli, through the filter. Illustratively, filter mesh has a pore size less than 500 micrometers, and more preferably, 200 micrometers or less. Filter mesh  34  may be attached to struts  32  using a suitable adhesive, bonding, sonic welding, or other method known in the art. 
     Referring now also to  FIGS. 3 and 4 , struts  33  are coupled to mounting ring  40 , which is affixed to catheter shaft  21  proximal of reduced diameter section  38 . Struts  33  are provided in sufficient number so that the outer edge of the filter assumes a substantially circular shape that contacts the entire interior circumference of a target vessel when deployed. Preferably, the filter mesh is supported by at least four struts, and more preferably, six, eight or more struts. 
     Struts  33  may comprise wire elements that are bonded to mounting ring  40 . Alternatively, as depicted in  FIGS. 4A and 4B , struts  33  and mounting ring  40  are integrally formed from a tube or flat sheet of metal, e.g., by laser cutting or etching. Struts  33  and mounting ring  40  preferably comprise a resilient metal alloy, and more preferably, a superelastic shape memory alloy, such as a nickel-titanium alloy. Although struts  33  are depicted as having a generally rectangular shape, it should be appreciated that the size, shape, geometry, and number of struts  33  may be varied to suit different applications. 
     As depicted in  FIGS. 3A and 3B , catheter shaft  21 , including reduced diameter section  38 , may be integrally molded or machined from a tube of suitable biocompatible polymer. Alternatively, reduced diameter section  38  may comprise a short length of metal alloy hypotube, such as stainless steel, which is bonded at its proximal and distal ends to catheter shaft  21 . This alternative construction advantageously may provide additional strength to the catheter in the vicinity of the reduced diameter section, and enhance pushability of the distal end of the catheter, especially with respect to a lesion comprising dense plaque. 
     Struts  33  preferably self-expand from the closed position depicted in  FIG. 4A  to the open position depicted in  FIG. 4B  upon proximal retraction of sheath  24 . Struts  33  alternatively may comprise a shape memory alloy that is thermally actuated to transition between the open and closed position. For example, struts  33  may comprise a nickel-titanium alloy in which the expanded shape depicted in  FIG. 4B  has been impressed at high temperature. After placement of catheter  20  and retraction of sheath  24 , a bolus of warm water may be injected around catheter  20 , e.g., through the introducer catheter, to heat the struts to transition struts  33  and filter  32  to the deployed position. As a further alternative, mounting ring  40  and struts  33  may be resistively heated to transition the struts to the deployed position. In any of the foregoing embodiments, struts  33  are returned to the contracted position for removal by advancing sheath  24  to contact and collapse the struts against catheter shaft  21 . 
     Still referring to  FIGS. 4A and 4B , struts  33  may include radiopaque markers  41 , visible under a fluoroscope, to confirm deployment of the filter  32 . Markers  41  when deployed will have a substantially larger circumference than markers  29 ,  30 , and  31  on catheter shaft  21  and marker  36  on sheath  24 , thereby to facilitate rapid differentiation between filter  32 , sheath  24  and catheter shaft  21 . 
     Referring now to  FIGS. 5A-5F , a method of using catheter  20  of  FIG. 2  is described to protect against embolism during iliac stenting. With respect to  FIG. 5A , the patient is prepped and the femoral artery is accessed percutaneously or via cutdown and an introducer (not shown) is placed to establish access to the patient&#39;s vessel V. Guidewire  35  is placed across lesion L and catheter  20  then is advanced along the guidewire until the stent is disposed across lesion L, as determined by fluoroscopic visualization of markers  30  and  31 . Blood flow F is towards the operator, i.e., from the distal-to-proximal direction relative to device  10 . 
     Once the position of catheter  20  is confirmed, sheath  24  is retracted proximally while holding catheter shaft  21  stationary. As depicted in  FIG. 5B , sheath  24  is retracted to expose balloon  27 , stent  37  and filter  32 . As the sheath is retracted proximal to filter  32 , struts  33  cause the filter to deploy so that filter mesh  34  spans the vessel. Proper retraction of sheath may be confirmed by using a fluoroscope to determine the relative positions of markers  29  and  27 . 
     Balloon  27  then may be inflated by infusing contrast, saline or carbon dioxide through the inflation port and into balloon  27 . As balloon  27  inflates, stent  37  is expanded into contact with lesion L, compressing the lesion against the vessel wall and restoring patency to the vessel. During stent deployment, pieces of plaque are released from lesion L, forming emboli E. Emboli E are carried downstream by blood flow F and are captured by filter  32  and are deposited in reservoir  38 , as depicted in  FIG. 5C . 
     Referring now to  FIG. 5D , after deployment of stent  37 , balloon  27  is deflated. This process may release addition emboli E that are captured in filter  32 . Sheath  24  is then advanced distally to cause struts  33  and filter mesh  34  to collapse and seal reservoir  38 . As depicted in  FIG. 5E , as sheath  24  is further advanced in the distal direction to cover balloon or the balloon is retracted, emboli are retained within the reservoir and cannot escape into the blood flow. 
     Referring to  FIG. 5F , once sheath  24  has been advanced over filter  32  and/or balloon  27 , catheter  20  may be removed, followed by removal of guide wire  35 . Once catheter  20  is removed from the patient, emboli E collected in reservoir  38  may be examined. It should be appreciated that the foregoing method may be employed without stent  37  present on catheter  20 , in case a simple dilatation procedure is desired. 
     Referring now to  FIGS. 6A and 6B , an alternative embodiment of a filter suitable for use in the catheter of the present invention is described. In particular, filter  50  may be directly substituted for filter  32  in catheter  20  of  FIG. 2 . In the following description, except where specifically noted, primed reference numbers refer to the corresponding structure of the embodiment of  FIG. 2 . Thus, for example, catheter  20 ′ of  FIG. 6A  is shown disposed in vessel V and includes catheter shaft  21 ′ slidably disposed within sheath  24 ′. Balloon  27 ′ carries stent  37 ′ for deployment within lesion L. 
     Filter  50  comprises plurality of struts  51  coupled at their proximal ends to catheter shaft  21 ′. The distal ends of each of struts  51  includes a concave indentation  52  which slopes outward to define opening  53  of the filter. Struts  51  are covered with filter mesh  54 , for example, ePTFE having a multiplicity of pores  55 , sized as described hereinabove. As depicted in  FIG. 6A , concave indentations  52  form neck  56  that give the filter an amphora shape in the deployed position. In accordance with the principles of the present invention, the portion of filter  50  proximal of neck  56  defines reservoir  57  that retains emboli E captured by filter  50  during deployment of stent  37 ′. 
     Struts  51  operate in a manner similar to that described above for filter  32 . In particular, struts  51  are held in a contracted delivery position by sheath  24 ′, and self-expand radially outward to the amphora shape illustrated in  FIG. 6A  when sheath  24 ′ is retracted proximally. Preferably, struts  51  comprise a shape memory alloy that has been trained, using known techniques, to retain concave indentations  52 . The sloping surface of opening  53  is shaped so that embolic material liberated by actuation of the end effector, illustratively deployment of stent  37 ′ by balloon  27 ′, are funneled past neck  56  into the proximal portion of the filter. 
     Struts  51  are configured to collapse towards the exterior surface of catheter shaft  21 ′ when sheath  24 ′ is advanced distally upon completion of actuation of the end effector to return filter  50  to its delivery position. In accordance with one aspect of the present invention, concave indentations  52  of struts  51  contact the exterior surface of the catheter shaft  21 ′ before the portion of the filter proximal to neck  56 . In this manner, as sheath  24 ′ is advanced distally, the struts seal reservoir  57 , thereby preventing embolic material captured within the reservoir from being expelled past neck  56  of the filter. Accordingly, further advancement of sheath  24 ′ over filter  50  cannot squeeze embolic material from the filter, reducing the risk of embolization during contraction and removal of the catheter. 
     Although preferred illustrative embodiments of the present invention are described above, it will be evident to one skilled in the art that various changes and modifications may be made without departing from the invention. It is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.