Patent Abstract:
Apparatus for occluding a vessel and enhancing blood flow within a catheter are provided, wherein a catheter comprises a multi-section self-expanding wire weave forming a radially expandable body and an occlusive distal section, covered with an elastomeric polymeric coating, and disposed within an outer sheath. Methods of using the apparatus of the present invention to remove emboli also are provided.

Full Description:
REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/418,727, filed Oct. 15, 1999, now U.S. Pat. No. 6,423,032 which is a continuation-in-part of U.S. patent application Ser. No. 09/333,074, filed Jun. 14, 1999, now U.S. Pat. No. 6,206,868 which is a continuation-in-part of International Application PCT/US99/05469, filed Mar. 12, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to apparatus and methods for protecting against embolization during vascular interventions and improving flow characteristics within a catheter. More particularly, the apparatus and methods of the present invention facilitate blood flow within a catheter by providing a catheter having a radially expandable main body section. 
     BACKGROUND OF THE INVENTION 
     Catheters are commonly manufactured using materials that do not substantially change in cross-sectional area. It is highly desirable that the initial cross-sectional catheter area be relatively small compared to the vasculature for patient comfort and ease of transluminal guidance. However, catheters in which the working diameters remain relatively small have several disadvantages during interventional procedures. 
     A primary disadvantage of a small cross-sectional catheter area is increased flow resistance within the catheter. A high volume of blood flow being forced through a relatively small lumen may cause damage to blood cells. During interventional procedures involving the removal of emboli, the flow may be further constrained when aspirating large emboli in addition to blood. It therefore would be advantageous to provide a catheter having a small delivery cross-sectional area for transluminal insertion, but which is capable of expanding to a larger cross-sectional area, thus reducing flow resistance within the catheter. 
     Heretofore, no reliable expandable catheters have been available. U.S. Pat. No. 5,102,401 to Lambert et al. describes a catheter comprising a thermoplastic elastomeric hydrophilic polyurethane coated on at least the outside surface with a hydrophobic polymer. The catheter expands to a larger lumen size in about 3 to 15 minutes when contacted with an aqueous liquid. Additional publications have further discussed catheters which soften upon being raised to a temperature approaching body temperature. 
     There are several drawbacks associated with such previously known expandable catheters. Such catheters can soften when deployed, resulting in kinking or deformation of the proximal section of the catheter, thereby cutting off flow. Additionally, such catheters require a wait of up to several minutes for the desired expansion to occur. Accordingly, there remains a need for a structurally durable, rapidly expandable catheter. 
     Previously-known apparatus and methods are known that employ a mechanically expandable occlusive element disposed at the distal end of a catheter. Commonly assigned U.S. Pat. No. 6,206,868 to Parodi discloses an occlusive element comprising a self-expanding wire mesh basket covered with an elastomeric polymer coating. The catheter is initially surrounded by a movable sheath, and is inserted transluminally with the sheath at a distalmost position. The sheath is retracted proximally to cause the basket to deploy, and the basket is again collapsed within the sheath by moving the sheath to its distalmost position. 
     The occlusive basket described in the Parodi patent is advantageous because it provides a rapidly expandable basket that is substantially flush with the vessel wall to enhance emboli removal. However, emboli then may be funneled into a relatively small cross-sectional area lumen that extends from the site of the stenosis to the vascular entry site. For many procedures, this distance may comprise the vast majority of the overall catheter length. Accordingly, blood flow is potentially constrained throughout the majority of the catheter. 
     In view of these drawbacks of previously known catheters, it would be desirable to provide apparatus and methods for radially varying the size of a catheter so that the catheter can be maneuvered within the body at a contracted delivery diameter and then self-expands to a larger diameter to facilitate blood flow. 
     It also would be desirable to provide apparatus and methods for enhancing the flow of blood and emboli within a catheter by expanding the cross-sectional area of the catheter that extends from the site of the stenosis to the vascular entry site. 
     It still further would be desirable to provide apparatus and methods for rapidly expanding the cross-sectional area of a catheter without relying on chemical or thermal transformations. 
     It still further would be desirable to provide apparatus and methods for an expandable catheter whereby the structural integrity is not compromised upon expansion. 
     It still further would be desirable to provide apparatus and methods for efficiently removing emboli by means of an occlusive member that is substantially flush with the vessel wall. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide apparatus and methods for radially varying the size of a catheter so that the catheter can be maneuvered within the body at a contracted delivery diameter and then self-expands to a larger diameter in situ to facilitate blood flow. 
     It is another object of the present invention to provide apparatus and methods for enhancing the flow of blood and emboli within a catheter by expanding the cross-sectional area of the catheter that extends from the site of the stenosis to the vascular entry site. 
     It is another object of the present invention to provide apparatus and methods for rapidly self-expanding the cross-sectional area of a catheter without relying on chemical or thermal transformations. 
     It is yet another object of the present invention to provide apparatus and methods for an expandable catheter whereby the structural integrity is not compromised upon expansion. 
     It is another object of the present invention to provide apparatus and methods for efficiently removing emboli by means of an occlusive member that is substantially flush with the vessel wall. 
     These and other objects of the present invention are accomplished by providing apparatus and methods suitable for removing emboli and facilitating blood flow within a catheter. The apparatus preferably comprises a catheter having a wire weave configuration, an elastomeric polymer coating covering the weave to provide a blood impermeable membrane, and an outer sheath covering the catheter in a contracted state. The catheter preferably comprises an occlusive distal section, a radially expanding main body, and a fixed diameter proximal section that passes through the vascular entry site. 
     In a preferred method, the catheter is advanced through the femoral artery and the distal end is positioned proximal to a lesion. As the outer sheath covering the catheter is retracted proximally, the occlusive distal section expands to a predetermined shape to form an occlusive seal against the vessel wall. As the outer sheath is further retracted, the main body of the catheter expands radially to a larger diameter. The outer sheath is further retracted proximally toward the vascular entry site, e.g., the arteriotomy. 
     The occlusive distal section occludes antegrade flow, and retrograde flow may be induced at the site of the stenosis, e.g., via negative pressure in a venous return line. An interventional procedure, such as angioplasty, stenting or atherectomy, then may be performed to treat the lesion. Emboli generated during the procedure are directed via the retrograde flow into the enlarged lumen of the catheter for subsequent removal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments, in which: 
     FIG. 1 is a side view of apparatus constructed in accordance with the present invention in a collapsed delivery state; 
     FIGS. 2A-2C are schematic illustrations of the expandable features of the catheter; 
     FIG. 3 is a side view of a catheter constructed in accordance with the present invention in a fully deployed state; 
     FIGS. 4A-4D depict method steps of using the catheter of the present invention; 
     FIGS. 5A-5B illustrate alternative configurations of the expandable body of the catheter; and 
     FIGS. 6A-6D describe a mechanism for enabling proximal retraction of the outer sheath of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, embolic protection apparatus  20  constructed in accordance with principles of the present invention is described. Apparatus  20  comprises catheter  21 , outer sheath  22 , venous return line  32 , tubing  29  and optional blood filter  30 . 
     Catheter  21  comprises lumen  40  that communicates with hemostatic port  23 , e.g., a Touhy-Borst connector and blood outlet port  28 . Tubing  29  couples blood outlet port  28  to filter  30  and blood inlet port  31  of venous return line  32 . 
     Outer sheath  22  preferably comprises clip  25 , longitudinal slit  27  and solid distal section  35 . Clip  25  is affixed to the proximal end of outer sheath  22  and may engage catheter  21  in a locked state, as shown in FIG. 1, or may disengage from catheter  21  when a force is applied. As described hereinbelow, longitudinal slit  27  permits outer sheath  22  to disengage from catheter  21 , to allow proximal retraction of outer sheath  22  without interfering with blood outlet port  28  or hemostatic port  23 . 
     Hemostatic port  23  and lumen  40  are sized to permit interventional devices, such as balloon angioplasty catheters, atherectomy devices and stent delivery systems, to be advanced through lumen  40  to the site of the occlusion. 
     Venous return line  32  includes hemostatic port  33 , blood inlet port  31  and a lumen that communicates with ports  33  and  31  and tip  34 . Venous return line  32  may be constructed in a manner per se known for venous introducer catheters. Tubing  29  may comprise a suitable length of a biocompatible material, such as silicone. Alternatively, tubing  29  may be omitted and blood outlet port  28  of catheter  21  and blood inlet port  31  of venous return line  32  may be lengthened to engage either end of filter  30  or each other. 
     Referring to FIG. 2, the expandable features of catheter  21  are described in greater detail. FIG. 2A depicts catheter  21  having lumen  40  in a contracted state within outer sheath  22 . The device may be transluminally inserted and positioned within a vessel V in the contracted state. The distal section of catheter  21  may be constructed in an expandable wire weave configuration. In a preferred embodiment, the wire weave comprises a shape-memory retaining material, for example, a Nickel Titanium alloy (commonly known in the art as Nitinol). 
     The use of Nitinol generally requires the setting of a custom shape in a piece of Nitinol, e.g., by constraining the Nitinol element on a mandrel or fixture in the desired shape, and then applying an appropriate heat treatments, which are per se known. 
     Catheter  21  preferably is enclosed by elastomeric polymer  45 , such as latex, polyurethane or polyisoprene. The shape of catheter  21  is initially constrained by outer sheath  22 . As outer sheath  22  is retracted proximally, wires  43  and lumen  40  expand radially and may expand linearly to form occlusive distal section  42  having mouth  52 , as shown in FIG.  2 B. Elastomeric polymer  45  stretches to conform to the expanded shape. The predetermined configuration preferably comprises angled taper  44  and hoop  47 . 
     The radial expansion of occlusive distal section  42  is such that its outer diameter is substantially flush with the intima of vessel V to occlude antegrade flow. Additionally, the surface contact between occlusive distal section  42  and vessel V may effectively anchor the device. 
     Angled taper  44  facilitates direction of blood and emboli from mouth  52  into main body  46  of catheter  21 . Additionally, angled taper  44  permits outer sheath  22  to slide distally over occlusive distal section  42  to effectively collapse that section within the sheath. 
     Hoop  47  may be used to separate occlusive distal section  42  from main body  46 , as the two sections preferably have distinct expanded diameters. Main body  46  comprises a wire configuration that is initially compressed circumferentially within outer sheath  22 . As outer sheath  22  is further retracted proximally, main body  46  expands radially within vessel V, as shown in FIG.  2 C. Wires  48  expand radially to a predetermined shape that may be established, for example, by heat treating a shape-memory alloy as described hereinabove. Exemplary wire configurations for main body  46  are described in FIG. 5 hereinbelow. 
     Referring now to FIG. 3, a schematic side view of catheter  21  is depicted in a fully deployed state. Catheter  21  comprises occlusive distal section  60 , main body  66 , proximal section  70 , and angled tapers  62  and  68 . Occlusive distal section  60  and main body  66  comprise expanded diameters d 1  and d 2 , respectively, while proximal section  70  comprises transluminal insertion diameter d 3 . 
     Occlusive distal section  60  and main body  66  are initially collapsed within outer sheath  22  such that their contracted diameters are substantially equal to the transluminal insertion diameter d 3  of proximal section  70 . Catheter  21  then may be percutaneously and transluminally inserted into the body and maneuvered within the vasculature at diameter d 3  until deployed, as depicted in FIG.  2 . 
     In the deployed state, d 1  is sized to occlude blood flow in the targeted vessel (other than through mouth  61 ). Diameter  1 , may expand to occlude flow in a range of vessels. Occlusive distal section  60  facilitates removal of large emboli via mouth  61 . Angled taper  62  assists in directing blood and emboli from occlusive distal section  60  into main body  66 . Blood and emboli then are directed proximally at transport diameter d 3 . 
     Advantageously, the enlarged lumen provided by main body  66  transports blood from a location near the lesion to a location slightly distal to vascular entry site I, a distance that preferably spans the majority of the overall length of catheter  21 . Accordingly, flow resistance may be reduced throughout the majority of the catheter. 
     Angled taper  68  funnels blood from main body  66  into proximal section  70 . Proximal section  70  preferably remains fixed at transluminal insertion diameter d 3  and extends from blood outlet port  28  to a location slightly distal to vascular entry site I. 
     Referring to FIGS. 4A-4D, use of apparatus in accordance with the present invention is described. In FIG. 4, lesion S is located within a vessel V of the body. In a first step, catheter  88 , initially compressed within outer sheath  86 , is inserted either percutaneously and transluminally or via a surgical cut-down, to a position proximal to lesion S, as shown in FIG.  4 A. As described hereinabove, outer sheath  86  then is retracted proximally to cause occlusive distal section  92  to deploy, as shown in FIG. 4B, and further retracted proximally to radially expand main body  98 . 
     Venous return line  32  then may be introduced into the patient&#39;s femoral vein, either percutaneously or via a surgical cut-down. Filter  30  then is coupled between blood outlet port  28  of catheter  21  and blood inlet port  31  of venous return line  32  using tubing  29 , and any air is removed from the line. Once this circuit is closed, negative pressure in venous return line  32  during diastole will establish a low rate continuous flow of blood through lumen  90  of catheter  21 . As shown in FIG. 4B, the deployment of occlusive distal section  92  occludes antegrade flown in vessel V, while the negative pressure through lumen  90 , e.g., from venous return line  32 , induces retrograde flow at the site of the lesion. 
     This low rate continuous flow due to the difference between venous pressure and arterial pressure will continue throughout the interventional procedure. Specifically, blood passes through lumen  90  and blood outlet port  28  of catheter  21 , through biocompatible tubing  29  to filter  30 , and into blood inlet port  31  of venous return line  32 , where it is reperfused into the remote vein. Continuous blood flow (except during inflation of any dilatation instruments) with reperfusion in accordance with the present invention provides efficient embolic removal with significantly reduced blood loss. 
     Referring to FIG. 4C, with occlusive distal section  92  deployed and retrograde flow established in vessel V, an interventional procedure to treat lesion S may be performed. The procedure may be any commonly known in the art. For example, balloon angioplasty may be applied whereby conventional angioplasty balloon catheter  101  having balloon  102  may be loaded through hemostatic port  23  and lumen  90 , then positioned within lesion S. Hemostatic port  23  then is closed, and balloon  102  is inflated to treat lesion S. Balloon  102  then is deflated upon satisfactory removal or disruption of lesion S. 
     Referring to FIG. 4D, emboli E generated during the procedure are directed into lumen  90  via the established retrograde flow. Angled taper  96  funnels blood and emboli E into main body  98 . Blood and emboli E travel proximally within catheter  21 , and emboli E may be subsequently removed via filter  30 . 
     Upon completion, outer sheath  86  may be advanced distally along the length of catheter  21  to collapse main body  98  and occlusive distal section  92  within the sheath, which in turn causes antegrade flow to become re-established in vessel V. Catheter  21  then may be retracted transluminally and the apparatus may be removed from the patient&#39;s vessel. 
     Referring to FIG. 5, alternative configurations of the radially expanding main body in accordance with the present invention are described. In FIG. 5A, a hoop configuration is shown wherein main body  110  of catheter  21  comprises several individual hoops  116 . Individual hoops  116  are designed such that they may be compressed circumferentially by a compressive force F, e.g., the force provided by outer sheath  22 , as depicted in region  112 . When compressive force F is removed, hoops  116  expand to a larger, predetermined diameter. In a preferred embodiment, hoops  116  are manufactured from a shape-memory material, e.g, Nitinol, according to methods described hereinabove. 
     Individual hoops  116  preferably are enclosed within elastomeric polymer coating  113  to form an expandable, blood impermeable membrane. Individual hoops  116  may be connected to adjacent hoops via linkages  118  for additional structural stability. 
     Alternatively, main body  110  may comprise a plurality of compressible, spiral-shaped wires. As shown in FIG. 5B, wires  126  and  128  are angled such that they form long, continuous spirals along the length of main body  110 . The compressible, spiral-shaped wires preferably comprise a shape memory material and may be coated with elastomeric polymer  113 . Linkages  122  may be used to provide additional support between adjacent spirals. 
     Referring now to FIG. 6, a mechanism for allowing proximal retraction of outer sheath  140  is described. Outer sheath  140  comprises clip  142 , longitudinal slit  144  and solid distal section  146 , as shown in FIG.  6 A. 
     Clip  142  is sized to engage catheter  141  in a locked state, as shown in FIG.  6 B. Clip  142  preferably comprises a compliant rubber-like material that may deform when a force F is applied in the direction indicated, i.e., a manual force applied by the physician. Walls  148  of clip  142  may part to allow clip  142  to disengage from catheter  141 . 
     Longitudinal slit  144  of outer sheath  140  preferably comprises flaps  152  and  154 . In a contracted state, flaps  152  and  154  overlap to enclose catheter  141 , as shown in FIG. 6C from a sectional view through section line A—A of FIG.  6 A. As a force F is applied, flaps  152  and  154  disengage from catheter  141 , as shown in FIG. 6D from a sectional view through section line A—A. 
     Solid distal section  146  guides outer sheath  140  as it is further retracted proximally. When the procedure is completed, outer sheath  140  is advanced distally such that flaps  152  and  154  once again overlap. In this overlapping state, outer sheath  140  retracts catheter  141  within the sheath as the sheath is advanced distally. Clip  142  then may re-engage catheter  141 . 
     While preferred illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.

Technology Classification (CPC): 0