Abstract:
A method of creating an AV fistula between adjacent first and second blood vessels, includes steps of cutting a hole through the adjacent walls of the first and second blood vessels and inserting a welding catheter into the first vessel, and through the hole into the second vessel, so that a distal end of the welding catheter is disposed within the second vessel. A portion of wall defining the welding catheter is then expanded radially outwardly, and the expanded wall portion is pulled proximally to engage the wall of the second blood vessel and to pull it toward the wall of the first blood vessel. Then, a portion of wall proximal to the first expanded wall portion and disposed in the first blood vessel is expanded radially outwardly, thereby capturing the walls of each of the second and first blood vessels between the two expanded wall portions. Cutting elements on the expanded wall portions are then energized to create a tissue welded elongate aperture between the first and second blood vessels.

Description:
This application is a divisional under 35 U.S.C. 120 of U.S. application Ser. No. 13/458,629, filed on Apr. 27, 2012 and entitled Systems and Methods for Creating Arteriovenous (AV) Fistulas, issued on Sep. 22, 2015 as U.S. Pat. No. 9,138,230, which application in turn claims the benefit under 35 U.S.C. 119(e) of the filing date of Provisional U.S. Application Ser. No. 61/480,638, entitled Systems and Methods for Creating Arteriovenous (AV) Fistulas, filed on Apr. 29, 2011. It is also related to U.S. application Ser. No. 13/161,182, entitled Systems and Methods for Creating Arteriovenous (AV) Fistulas, filed on Jun. 15, 2011, and U.S. application Ser. No. 13/161,356, entitled Intravascular Arterial to Venous Anastomosis and Tissue Welding Catheter, filed on Jun. 15, 2011. All of the foregoing applications are commonly owned and expressly incorporated herein by reference, in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In the body, various fluids are transported through conduits throughout the organism to perform various essential functions. Blood vessels, arteries, veins, and capillaries carry blood throughout the body, carrying nutrients and waste products to different organs and tissues for processing. Bile ducts carry bile from the liver to the duodenum. Ureters carry urine from the kidneys to the bladder. The intestines carry nutrients and waste products from the mouth to the anus. 
     In medical practice, there is often a need to connect conduits to one another or to a replacement conduit to treat disease or dysfunction of the existing conduits. The connection created between conduits is called an anastomosis. 
     In blood vessels, anastomoses are made between veins and arteries, arteries and arteries, or veins and veins. The purpose of these connections is to create either a high flow connection, or fistula, between an artery and a vein, or to carry blood around an obstruction in a replacement conduit, or bypass. The conduit for a bypass is a vein, artery, or prosthetic graft. 
     An anastomosis is created during surgery by bringing two vessels or a conduit into direct contact, and to create a leak-free blood flow path between them. The vessels are joined together with suture or clips, in an open surgical procedure. The anastomosis can be end-to-end, end-to-side, or side-to-side. In blood vessels, the anastomosis is elliptical in shape and is most commonly sewn by hand with a continuous suture. Other methods for anastomosis creation have been used including carbon dioxide laser, and a number of methods using various connecting prosthesis, clips, and stents. Such procedures are time consuming, clinician dependent (open to surgical error), and often result in strictures, or clotting of the vein or artery. 
     An arterio-venous fistula (AVF) is created by connecting an artery to a vein. This type of connection is used for hemodialysis, to increase exercise tolerance, to keep an artery or vein open, or to provide reliable access for chemotherapy. 
     An alternative is to connect a prosthetic graft from an artery to a vein for the same purpose of creating a high flow connection between artery and vein. This is called an arterio-venous graft, and requires two anastomoses. One is between artery and graft, and the second is between graft and vein. 
     A bypass is similar to an arteriovenous graft. To bypass an obstruction, two anastomoses and a conduit are required. A proximal anastomosis is created from a blood vessel to a conduit. The conduit extends around the obstruction, and a second distal anastomosis is created between the conduit and vessel beyond the obstruction. 
     As noted above, in current medical practice, it is desirable to connect arteries to veins to create a fistula for the purpose of hemodialysis. The process of hemodialysis requires the removal of blood from the body at a rapid rate, passing the blood through a dialysis machine, and returning the blood to the body. The access to the blood circulation is achieved with catheters placed in large veins, prosthetic grafts attached to an artery and a vein, or a fistula where an artery is attached directly to the vein. 
     Fistulas for hemodialysis are required by patients with kidney failure. The fistula provides a high flow of blood that can be withdrawn from the body into a dialysis machine to remove waste products and then returned to the body. The blood is withdrawn through a large access needle near the artery and returned to the fistula through a second large return needle. These fistulas are typically created in the forearm, upper arm, less frequently in the thigh, and in rare cases, elsewhere in the body. It is important that the fistula be able to achieve a flow rate of 500 ml per minute or greater. Dialysis fistulas have to be close to the skin (&lt;6 mm), and large enough (&gt;4 mm) to access with a large needle. The fistula needs to be long enough (&gt;6 cm) to allow adequate separation of the access and return needle to prevent recirculation of dialysed and non-dialysed blood between the needles inserted in the fistula. 
     To create a fistula, it is necessary to carefully dissect an artery and vein from their surrounding tissue, and to join them to create a leak-free blood flow path between them. This is typically done by suturing the vein to the artery in an open surgical procedure, using fine suture or clips. The vein is either attached by an end to end anastomosis, end to side anastomosis, or a side to side anastomosis. The procedure is time consuming, clinician dependent (open to surgical error), and often times results in strictures, or clotting of the vein or artery. It is highly desirable to be able to make the anastomosis quickly, reliably, with less dissection, and with less pain. It is important that the anastomosis is the correct size, is smooth, and that the artery and vein are not twisted. 
     SUMMARY OF THE INVENTION 
     The present disclosed invention eliminates the above described open procedures, reduces operating time, and allows for a consistent and repeatable fistula creation. 
     It is well known that heat, whether its source is Radio Frequency (RF), resistance, or laser, will attach and weld tissue or vessels upon direct pressure and contact over the targeted weld area. This is often done with jaw-type, compression heat delivery devices. It is also well known that radially expandable devices such as balloons, metal cages, and baskets are often coupled with energy in the form of RF, or in the case of balloons, heated saline, and used intraluminally to ablate tissue, stop bleeding, or create a stricture. 
     The present invention uses two pair of opposable, collapsible slits on the main catheter body that extend outwards and trap with compression the surrounding vessel walls between them. Heat is then applied to the tissue using RF energy or resistance heat through the exposed woven wire elements. The woven wire elements are actually a component of the coaxial wire mesh embedded into the main catheter body. This coaxial mesh serves two purposes. One is to increase the torqueability of the main catheter, and a second is to supply energy to the exposed electrodes. The electrodes are created by scathing a desired amount of the encapsulating layer of polymer over the wire mesh. Heat from the device travels internally through the vessel walls to the adventitia which surrounds the vessels. With the combination of heat and clamping force, the vessels are joined together. 
     More particularly, there is provided a device for creating an arteriovenous (AV) fistula, which comprises a welding catheter comprising an elongate tube having a circumferential wall. The first portion of the wall is actuatable between a collapsed orientation wherein the distal portion is axially aligned with remaining portions of the circumferential wall and a radially expanded orientation. A second portion of the wall, spaced proximally from the first wall portion, is actuatable between a collapsed orientation wherein the distal portion is axially aligned with remaining portions of the circumferential wall and a radially expanded orientation. Tissue cutters are disposed on the circumferential wall on and adjacent to the first and second portions thereof. The first wall portion further comprises a plurality of circumferentially spaced slots disposed therein, which in one embodiment comprises a pair of circumferentially opposed slots. The second wall portion also comprises a plurality of circumferentially spaced slots disposed therein, which in one embodiment also comprises a pair of circumferentially opposed slots. 
     The first and second portions of the wall are each biased toward their respective radially expanded orientations. The elongate tube further comprises an axial through hole and an inner tube disposed in the axial through hole, wherein the elongate tube and the inner tube are attached to one another distally of the first and second wall portions. An actuator is disposed on a handle proximal to the elongate tube, for actuating the first and second wall portions between their radially expanded and collapsed orientations. The actuator has a first position for radially expanding only the first portion of the wall and a second portion for also radially expanding the second portion of the wall. In the disclosed embodiments, the actuator functions to actuated the radially expanding first and second portions by pulling the inner tube proximally. 
     An outer sheath is axially positionable to cover both of the radially expanding first and second wall portions, and is alternatively axially positionable to selectively expose only the first wall portion or both of the first and second wall portions. 
     A power source is provided for selectively energizing the tissue cutters, which, in certain embodiments, are energized by RF energy. In the illustrated embodiments, the tissue cutters comprise wire mesh electrodes. 
     In another aspect of the invention, there is disclosed a method of creating an AV fistula between adjacent first and second blood vessels, which comprises steps of cutting a hole through the adjacent walls of the first and second blood vessels and inserting a welding catheter into the first vessel, and through the hole into the second vessel, so that a distal end of the welding catheter is disposed within the second vessel. A portion of wall defining the welding catheter is then expanded radially outwardly, and the expanded wall portion is pulled proximally to engage the wall of the second blood vessel and to pull it toward the wall of the first blood vessel. Then, a portion of wall proximal to the first expanded wall portion and disposed in the first blood vessel is expanded radially outwardly, thereby capturing the walls of each of the second and first blood vessels between the two expanded wall portions. Cutting elements on the expanded wall portions are then energized to create a tissue welded elongate aperture between the first and second blood vessels. 
     An additional method step following the foregoing steps involves collapsing the first and second expanded wall portions and withdrawing the welding catheter from the blood vessels. The energizing step, in certain embodiments, comprises energizing electrodes, which may comprise wire mesh electrodes, with RF energy. 
     The hole cutting step may be performed, in accordance with the inventive method, by inserting a needle into the first blood vessel, extending an obturator through a lumen in the needle until a tip thereof contacts the wall of the first blood vessel, and energizing a cutting tip of the obturator to cut the hole. 
     Preferably, an outer sheath is disposed over an elongate tube comprising the welding catheter, and the inventive method further comprises a step of withdrawing the outer sheath proximally to expose the first wall portion prior to the first expanding step. The method further comprises a step of withdrawing the outer sheath proximally to expose the second wall portion prior to the second expanding step. 
     The invention, together with additional features and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying illustrative drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view showing the first step of an inventive method for creating an A-V fistula in accordance with the principles of the present invention; 
         FIG. 2  is a view similar to  FIG. 1 , wherein a needle has been inserted into a vessel in the hand of a patient; 
         FIG. 3  is a view illustrating the insertion of a guidewire through the needle into the vessel; 
         FIG. 4  is a view similar to  FIG. 3  wherein the needle has been withdrawn and removed; 
         FIGS. 5-18  are sequential views illustrating one method of utilizing the inventive system; 
         FIG. 19  is a cross-sectional view of a multilumen catheter and associated structure; 
         FIGS. 19 a -19 c    illustrate alternative distal work pieces for the needle and associated cutting features of the inventive system; 
         FIG. 19 d    is a cross-sectional view taken through lines A-A of  FIG. 19 ; 
         FIG. 20  is an isometric view of a welding catheter constructed in accordance with the principles of the present invention; 
         FIGS. 20 a  and 20 b    illustrate a distal portion of the welding catheter of  FIG. 20  in sequential modes; 
         FIG. 21  is a view similar to  FIG. 20 b   , showing an alternative embodiment; 
         FIG. 21 a    is an end view of the device shown in  FIG. 21 ; 
         FIG. 22  is a view similar to  FIG. 20 b   , illustrating another alternative embodiment; and 
         FIG. 22 a    is an isolation view showing still another alternative embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now particularly to  FIGS. 19-22 , a particular embodiment of a system for creating an A-V fistula, in accordance with the principles of the present invention, will be described. A welding catheter  10  ( FIG. 20 ) comprises, in a presently preferred embodiment, a 3-4 f (French) (70-80 shore A) elongate tube or outer sheath  12 , having a through hole  14  for accommodating a 2-3 f inner tube  16  and a standard 0.014 diameter guidewire. A distal end  18  is tapered with a softer (40-50 shoreA) polymer tip which is in the range of 1-2 inches in length. This is to allow atraumatic ease of entry into and through the vessels. The inner tube  16  is preferably constructed of a flexible material such as a polymer in the range of 70-90 shoreA or a thin-walled nitinol metal. The distal end of the main catheter tube  12  features four (4) slots  20 ,  20   a.    
     The slots  20 ,  20   a  are arranged so that there are two slots  20 ,  20   a  in series on each side of the tube  12 , with each set of two slots  20 ,  20   a  opposed 180 degrees from one another about the circumference of the tube. Thus, there is a set of distal opposed slots  20 , and a second set of proximal opposed slots  20   a . The slots  20 ,  20   a  are preferably within a range of 0.030-0.060 inches long, and are biased to be axially collapsed, as shown in  FIG. 20 , when tension is applied to the inner tube  16 . The inner tube  16  must have enough column strength to activate the collapsible wings (described below) into their radially expanded orientation when it is pulled proximally. To clarify terminology used throughout this application, when the slots are axially collapsed, the wings are radially expanded. Likewise, when the slots are axially expanded, the wings are radially collapsed. The inner 3 f tube  16  is attached to the inner diameter (ID) of the outer 4 f tube  12  near the distal end. A 4-5 f elongate tube  22  extends over the tube  12  and is slidably attached at the proximal end thereof. The outer tube  12  is attached to a handle  24  at a proximal end  26 , and is fixed in place. Wire mesh  28  of the outer tube  12  is exposed, as shown, and a conductor wire  30 , preferably in a range of 16-20 Ga. (Gauge) is attached to the mesh, as shown, at one end, and has a standard banana connector  32  at the opposite end for attachment to an RF generator. The inner tube  16  is attached at the distal end by the slidable actuator handle  24 . The actuator handle  24  has two positions. A first position  31   a  ( FIG. 20 ), actuates the axial collapse of the distal set of slots  20 , so that first radially protruding wings  34  are formed by expanding radially outwardly, as shown in  FIG. 20 a   . A second position  31   b  ( FIG. 20 ), actuates the further collapse of the proximal set of slots  20   a , as shown in  FIG. 20 b   , to form second radially protruding wings  36 , proximally of the first wings  34 . These two sets of wings  34 ,  36 , when the slots  20 ,  20   a  are collapsed, have an expanded width of approximately 3-6 mm. The inner tube  16  has a through lumen  38  to allow passage over a guidewire. 
     Now referring particularly to  FIGS. 19, 19   a ,  19   b , and  19   c , there is shown a multilumen catheter  40 , preferably having a 4-5 f diameter. A central lumen  42  accommodates the passage of a standard 0.018 diameter guidewire  44 . A second lumen  46  accommodates a pre-bent cannulated needle  48 , having a 0.015 inside diameter to accommodate a 0.014 diameter guidewire. The angle  50  of the bent needle  48  is preferably within the range of 30-45 degrees, and includes a removable pencil point tip obturator  52 . The obturator  52  is fabricated of nitinol or other suitable material, and insulated  54 , as shown in  FIG. 19 b   , with only the tip  56  exposed. Heat is applied to the tip  56  from an RF energy source connected to the distal end. The catheter  40  is preferably made of a polymer in the range of 60-75 shoreA. The needle  48  is preferably made of nitinol, with an OD in the range of 0.019-0.021. The memory characteristics of nitinol allow the needle to deform and nest while in the catheter lumen. The distal end of the catheter is tapered to allow ease of entry into the vessel.  FIGS. 19 a , 19 b , and 19 c    show alternative obturator designs.  FIG. 19 b    is the presently preferred embodiment, already discussed above, while  FIG. 19 a    shows a cold tip without RF heat, and  FIG. 19 c    shows a corkscrew or auger design which allows traction during penetration into the vessel. The guidewire  44  can be run through the corkscrew device. 
     With particular reference now to  FIGS. 1-18 , to begin the inventive method of creating an AV fistula, the practitioner selects an appropriate procedural site having each of a first vessel  58  and a second vessel  60  in close proximity to one another. In currently preferred approaches, the first vessel  58  comprises a vein, and the second vessel  60  comprises an artery, but the invention is not necessarily limited to this arrangement. As illustrated in  FIG. 1 , one presently preferred location is the hand  62  of a patient. Then, generally employing principles of the Seldinger technique, as shown in  FIG. 2 , the first vessel  58  is punctured by a needle  64 , which is inserted therein, in the direction of an arrow  66 . A first guidewire  68 , preferably a standard 0.014 diameter guidewire, is then inserted through a lumen of the hollow needle  64  into the vessel  58 , and advanced in the direction of an arrow  70  ( FIG. 3 ). Following this, as shown in  FIG. 4 , the needle  64  is removed, by withdrawing it in the direction of an arrow  72 . 
     The vessel access catheter  40  is placed over the first guidewire  68  and inserted over the guidewire into the first vessel  58 , in the direction of arrow  74 , as shown in  FIG. 5 . As illustrated in  FIG. 6 , the pre-bent cannulated needle  48  is then extended out of the catheter  40  from a side port  76  and into contact with the second vessel  60 . The obturator ( FIG. 19 )  52 , with its cutting tip is extended through the needle  48 , and RF energy is applied to the needle, as shown in  FIG. 7 , preferably in the range of 10-20 W monopolar, creating a hole in the vessel walls and allowing the needle  48  to extend in the direction of arrow  78  farther into the second vessel  60 . Then, as shown in  FIG. 8 , the obturator cutting element  52  is removed, and the second guidewire  44  is passed through the lumen of the needle  48 , distally in the direction of arrow  80  ( FIG. 9 ). This second guidewire  44  creates the access path for the welding catheter  10  ( FIG. 20 ). The access needle  48  is retracted in the direction of arrow  82  ( FIG. 10 ), and the welding catheter  12  is passed over the guidewire  44  distally into the first vessel, and then into the second vessel, as shown in  FIGS. 11 and 12 . 
     The outer tube or sheath  12  is retracted proximally to expose the underlying catheter, as shown in  FIG. 13 , sufficiently to expose the first pairs of opposed slots  20 . The inner tube  16  ( FIG. 20 ) is retracted by the activation lever  24  to first position  1 , thereby causing the first pair of slots  20  to collapse and extend outwardly ( FIG. 14 ). Once locked in place, the catheter is pulled back, causing the second vessel  60  to come into contact with the first vessel  58  ( FIG. 15 ). 
     At this juncture, the outer sheath  12  is retracted further, to expose the second set of slots  20   a  ( FIG. 16 ). The activation lever  24  is then retracted from the first position  31   a  to the second position  31   b , which causes the second pair of slots  20   a  to collapse and extend outwardly, forming the second radially protruding wings  36 , trapping the surrounding wall of the first vessel and second vessel between them ( FIG. 16 ). RF energy is then applied, and the mesh electrodes  28  on both extended members create the weld between the first and second vessels. More particularly, the RF energy functions to burn and fuse or weld the vessels together, creating an elongate aperture  84  through the opposing walls of each of the first vessel  58  and second vessel  60 , as well as any intervening tissue. This elongate aperture  84  is shown in  FIGS. 17 and 18 . Alternative cutting approaches, such as resistive heat (hot wire), ultrasonic, laser, or mechanical approaches, may be used instead of RF energy, if desired. The wings  34 ,  36  are then collapsed by returning the activation lever  24  back to its original position, and the catheter  12  is removed ( FIG. 17 ). 
     As formed, the elongate aperture  84  will typically resemble a slit. However, as pressurized flow  86  ( FIG. 18 ) begins to occur through the slit or aperture  84 , which creates a communicating passage between the first vessel  58  and the second vessel  60 , the aperture widens responsive to the pressure, taking the shape of an ellipse as it opens to form the desired fistula. The edges of the aperture are cauterized and welded. 
     Tissue welding of the type intended to occur in the practice of these inventive methods is discussed in U.S. Pat. No. 6,908,463, to Treat et al., which is herein expressly incorporated by reference, in its entirety. 
       FIGS. 21, 21   a ,  22 , and  22   a  illustrate alternative configurations of the inventive device. In  FIGS. 21 and 21   a , multiple slots are illustrated for forming multiple wings  34 , which may be four, six, or eight. Coated wire expandable mesh tubing to form two conformable cones  88 , with the internal facing surfaces exposed to create an electrode ( FIG. 22 ).  FIG. 22 a    illustrates that the RF energy source may also be bipolar, which localizes the heat and welded area. 
     In yet another unillustrated embodiment, two pair of opposable slits may be mounted on separate coaxial elongate bodies. The second coaxial body with a pair of collapsible slits allows for a predetermined force or pressure on the tissue that is to be welded. This force can be either by manual operator “feel” or by use of a spring or tensioning means. The spring tension can also be manually manipulated by rotating the housing, which will vary the compressive spring force, thus allowing the operator to “tune” the compression or force depending on the distance and composition of fat and tissue between the artery and vein. 
     In still another unillustrated embodiment, the slits on the coaxial bodies are positioned 90 degrees apart. This arrangement in a bipolar mode allows for the dispersion of energy equally around the circumference of the anastomosis thus creating a symmetrical weld. The slits on the first body will house the electrode for the first pole and the slits on the second body with house the electrode for the second pole. 
     In another embodiment, the second coaxial body is a coaxial tube with an circumferential electrode exposed only at the distal end. 
     Alternative configurations of the mounting of the electrodes on the collapsible slits are possible, wherein the electrodes are comprised of round or square stainless steel or nitinol wires in the range of 0.002-0.015 diameter communicated to the openings in the expanded slits through lumens in the elongate bodies. This configuration also allows for the electrodes to be in the bipolar configuration without having to be on separate coaxial bodies. A singe electrode may be exposed along the length of the expanded slit. Multiple parallel electrodes, may be utilized, wherein the electrodes are exposed as segmented parallel diameters. This configuration may also comprise staggered squares, rectangles or ovals, depending on the desired weld and associated vessels to be welded. Various electrode configurations can be attached at the proximal end and sequenced by use of a microprocessor or switching means. The electrodes are configured in opposable pairs to allow one pair to weld tissue until a predetermined resistance or impedance is recognized, the pair of electrodes will then shut off and the second pair is energized until the impedance or resistance level again reaches the predetermined amount and then this pair will shut off. This can be repeated for a multiple of electrodes. This will allow for controlled welding of the tissue and limit potential charring and necrosis at the weld site. 
     Accordingly, although an exemplary embodiment and method according to the invention have been shown and described, it is to be understood that all the terms used herein are descriptive rather than limiting, and that many changes, modifications, and substitutions may be made by one having ordinary skill in the art without departing from the spirit and scope of the invention.