A catheter for forming a fistula

Abstract

A catheter for forming a fistula between two vessels. The catheter comprises a catheter body having a longitudinal axis; an electrode extending radially from the catheter body for contacting a vessel wall and forming the fistula; and a radiopaque loop disposed distally of the electrode. The radiopaque loop is configured for penetration by a needle.

Description

[0001] A Catheter for Forming a Fistula

[0002] Technical Field

[0003] The present disclosure relates to a catheter for forming a fistula between two vessels and a method of using a catheter to form a fistula between two vessels .

[0004] Background

[0005] A fistula denotes a passageway formed between two internal organs . Forming a fistula between two blood vessels can have one or more beneficial functions . For example , the formation of a fistula between an artery and a vein may provide access to the vasculature for haemodialysis patients . Speci fically, forming a fistula between an artery and a vein allows blood to flow quickly between the vessels while bypassing the capillaries . Needles , catheters , or other cannulas may then be inserted into the blood vessels near the fistula to draw blood from the circulatory system, pass it through a dialysis machine , and return it to the body . The quickened flow provided by the fistula may provide for ef fective haemodialysis .

[0006] The formation of a fistula may also be helpful in the treatment of peripheral arterial disease ( PAD) , for example . PAD can result from the occlusion of arteries in the legs and lower extremities such as the feet . Typically, such occlusion is brought about by atherosclerosis , whereby calci fied plaque deposited on the walls of an arterial vessel causes narrowing and blockage of the vessel lumen . Treatment for PAD in severe cases may include deep vein arterialisation ( DVA) , whereby a fistula may be formed between a diseased artery and a nearby deep vein to route the blood flow from the diseased artery to the deep vein in order to supply the extremity with blood . Another possible treatment for PAD is an endovascular bypass procedure , whereby two fistulas are formed either side of a blockage in a diseased artery . The blood flow is routed out of the artery and back into the artery by a conduit that circumvents the blockage . That conduit may, for example , be a stent graft placed within an adj acent vein .

[0007] Systems and methods for forming a fistula using an endovascular approach exist . Examples of these systems may comprise a first catheter having an electrode and a second catheter having a backstop . The electrode and backstop may be aligned via respective proximal and distal magnetic alignment elements positioned on each catheter . However, the large number of distal magnets can make it di f ficult to form a fistula close an occlusion or obstruction in a vessel . Furthermore , due to the large number of magnets , it can be di f ficult to manoeuvre these catheters through tortuous vessel anatomy, such as the anterior tibial vessel , for example . The large number of magnets can also make the device di f ficult and expensive to manufacture .

[0008] There is hence a need in the art for a new catheter for forming a fistula which can form a fistula closer to an occlusion or obstruction in the blood vessel .

[0009] Furthermore , there is a need in the art for a new catheter for forming a fistula which can more easily be manoeuvred through the vessel anatomy .

[0010] Furthermore , there is a need for a new catheter for forming a fistula which can be manufactured more easily and at a lower cost . Summary

[0011] In a first aspect of the present disclosure , there is provided a catheter for forming a fistula between two vessels . The catheter comprises a catheter body having a longitudinal axis ; an electrode extending radially from the catheter body for contacting a vessel wall and forming the fistula ; and a radiopaque loop disposed distally of the electrode . The radiopaque loop is configured for penetration by a needle .

[0012] In some embodiments , this may result in a catheter which can form a fistula closer to an occlusion or obstruction in the blood vessel and more easily be manoeuvred through the vessel anatomy .

[0013] Throughout this disclosure , the term "radiopaque" will be used to denote the ability of a material to block x-rays and therefore be visible under fluoroscopy . Speci fically, "radiopaque" in this context means more radiopaque than the organic tissue of the body . In some embodiments , the radiopaque loop may have a radiodensity greater than 5000 Houns field units (HU) . In some embodiments , the radiopaque loop may have a radiodensity greater than 10000 Houns field units (HU) .

[0014] The radiopaque loop may comprise a radiopaque wire .

[0015] The diameter of the radiopaque loop may be adj ustable .

[0016] In some embodiments , this may make it easier to advance the catheter through a blood vessel i f the diameter of the radiopaque loop is reduced . In some embodiments , this may make it easier to penetrate the radiopaque loop with a needle i f the diameter of the radiopaque loop is increased . The radiopaque loop may be connected to a pull wire extending along the length of the catheter body . The diameter of the radiopaque loop may be adj ustable by longitudinally moving the pull wire .

[0017] In some embodiments , this may provide a simple and ef fective way to adj ust the diameter of the radiopaque loop .

[0018] The electrode may be radially expandable .

[0019] In some embodiments , this may result in better fistula formation by the electrode .

[0020] The catheter body may comprise an electrode housing with at least one opening .

[0021] The radiopaque loop may be positioned adj acent to the electrode housing .

[0022] In some embodiments , this may reduce the overall length of the catheter .

[0023] The electrode may be at least partially positioned within the electrode housing .

[0024] In some embodiments , this may direct the RF energy towards the vessel wall , resulting in more ef fective and safer fistula formation .

[0025] The electrode may be configured to extend radially from the opening of the electrode housing .

[0026] The electrode may comprise a distal portion, a proximal portion and an intermediate portion .

[0027] The distal portion of the electrode may be moveable inside the electrode housing for moving the electrode between a radially contracted configuration and a radially expanded configuration .

[0028] In some embodiments , this may allow the electrode to be moved more easily between the radially contracted configuration and the radially expanded configuration .

[0029] Throughout this disclosure , the term ' radially expanded configuration' will be used to refer to a configuration of the electrode where the electrode has a greater radial extent than in the ' radially contracted configuration' .

[0030] The distal portion of the electrode may be fixed inside the electrode housing and the proximal portion of the electrode is moveable for moving the electrode between a radially contracted configuration and a radially expanded configuration

[0031] In some embodiments , this may allow the electrode to be moved more easily between the radially contracted configuration and the radially expanded configuration .

[0032] In some embodiments , this may further allow the amount o f radial expansion of the electrode to be controlled .

[0033] The electrode housing may be at least partially made from a ceramic material .

[0034] In some embodiments , this may provide the electrode housing with good resistance against the heat and plasma generated by the electrode .

[0035] The electrode may have a convex shape with respect to the catheter body .

[0036] In some embodiments , this may result in ef fective fistula formation . The electrode may comprise a leaf spring .

[0037] In some embodiments , this may allow the electrode to be bent and flexed without breaking .

[0038] Throughout this disclosure , the term ' leaf spring' will be used to refer to a flexible curved strip of material which can be bent but will regain its original shape when released .

[0039] The electrode may comprise a ribbon wire .

[0040] In some embodiments , this may result in ef fective fistula formation .

[0041] A system for forming a fistula between two vessels may comprise : a first catheter according to any of the preceding statements ; and a second catheter comprising a backstop for the electrode .

[0042] The second catheter may comprise a second radiopaque loop configured for penetration by a needle .

[0043] In some embodiments , this may provide a simple and ef fective way to align the electrode of the first catheter and the backstop of the second catheter .

[0044] The second radiopaque loop may be positioned distally of the backstop .

[0045] In some embodiments , this may allow the electrode and backstop to be aligned in a parallel configuration .

[0046] The second radiopaque loop may be positioned proximally o f the backstop . In some embodiments , this may allow the electrode and backstop to be aligned in an anti-parallel configuration .

[0047] The second radiopaque loop may be positioned adj acent the backstop .

[0048] The second radiopaque loop may comprise a radiopaque wire .

[0049] The diameter of the second radiopaque loop may be adj ustable .

[0050] In some embodiments , this may make it easier to advance the second catheter through a blood vessel i f the diameter of the radiopaque loop is reduced . In some embodiments , this may make it easier to penetrate the radiopaque loop with a needle i f the diameter of the radiopaque loop is increased .

[0051] The second radiopaque loop may be connected to a wire extending along the length of the second catheter . The diameter of the second radiopaque loop may be adj ustable by longitudinally moving the wire .

[0052] In some embodiments , this may provide a simple and ef fective way to adj ust the diameter of the radiopaque loop .

[0053] The backstop may have a portion shaped complimentary to the electrode .

[0054] In some embodiments , this may allow the electrode to better engage the backstop therefore resulting better fistula formation .

[0055] The backstop may have a concave portion .

[0056] The first catheter may further comprise a set of magnets positioned proximally of the electrode . The first catheter may not comprise any magnets positioned distally of the electrode .

[0057] The second catheter may further comprise a set of magnets positioned proximally or distally of the electrode .

[0058] In some embodiments , this may assist in alignment of the electrode with the backstop .

[0059] The system may further comprise a radiofrequency generator for supplying radiofrequency power to the electrode .

[0060] The system may further comprise a needle .

[0061] The needle may comprise a guidewire lumen for accommodating a guidewire .

[0062] The system may further comprise a guidewire disposed within the guidewire lumen of the needle .

[0063] The system may further comprise a sheath disposed over at least a portion of the catheter body of the first catheter and is slidably moveable along the longitudinal axis of the catheter body .

[0064] In some embodiments , this may assist in advancing the first catheter through tortuous vessel anatomy .

[0065] The sheath may be slidable to move the electrode between a radially contracted configuration and radially expanded configuration .

[0066] In a second aspect of the present disclosure , there i s provided a method of forming a fistula between two vessels using a catheter, the catheter having a catheter body, an electrode extending radially from the catheter body, and a radiopaque loop disposed distally of the electrode , The method comprises : inserting the catheter into a blood vessel and advancing it to a site where the fistula is to be formed; locating the radiopaque loop under fluoroscopy; piercing the radiopaque loop with a needle ; pulling or pushing the catheter to push the electrode against a wall of the blood vessel ; and supplying RF energy to the electrode to form the fistula .

[0067] Penetrating the radiopaque loop with a needle may further comprise inserting a guidewire through the needle and the radiopaque loop .

[0068] Pulling or pushing the catheter may cause the radiopaque loop to slide along the guidewire to push the electrode against a wall of the blood vessel .

[0069] Brief Description of the Drawings

[0070] To enable better understanding of the present disclosure , and to show how the same may be carried into ef fect , reference will now be made , by way of example only, to the accompanying drawings , in which :

[0071] FIG . 1 shows a first catheter and a second catheter for forming a fistula according to one or more embodiments of the disclosure ;

[0072] FIG . 2A shows the first catheter and second catheter of FIG . 1 being introduced into a vein and artery where a fistula is to be formed;

[0073] FIG . 2B shows the first catheter and second catheter being positioned at the treatment site where a fistula is to be formed . FIG . 2C shows a needle being introduced and penetrating a radiopaque loop of the first catheter and a radiopaque loop of the second catheter ;

[0074] FIG . 2D shows first catheter and the second catheter of FIG . 1 being aligned;

[0075] FIG . 2E shows the first catheter and the second catheter of FIG . 1 during the fistula formation process ;

[0076] FIG . 2 F shows the first catheter and the second catheter of FIG . 1 after the fistula formation process ;

[0077] FIG . 2G shows the first catheter and the second catheter of FIG . 1 being removed from the vein and artery;

[0078] FIG . 2H shows the fistula formed between the vein and artery;

[0079] FIG . 3 shows an alternative embodiment of a second catheter for forming a fistula according to one or more embodiments of the disclosure ; and

[0080] FIG . 4 shows the first catheter of FIG . 1 and the second catheter of FIG . 3 in the process of forming a fistula .

[0081] Detailed Description

[0082] FIG . 1 shows a system 10 for forming a fistula comprising a first catheter 100 and a second catheter 200 . The system 10 may, for example , be used for forming a fistula between two blood vessels , such as an arteriovenous fistula or a veno- venous fistula .

[0083] The first catheter 100 has a catheter body 110 which defines a longitudinal axis LI , and an electrode 130 which radially extends from the catheter body 110 . The electrode 130 is configured for contacting a vessel wall and forming a fistula . The first catheter 100 further has a first radiopaque loop 140 positioned distally of the electrode 130 .

[0084] The catheter body 110 may be elongated and substantially cylindrical in shape with a longitudinal axis LI . The catheter body 110 may have an electrode housing 120 near or at a distal end of the catheter body 110 . The electrode housing 120 may have an opening with the electrode 130 at least partially disposed in the electrode housing 120 and extending out of the opening . The first catheter 100 may also comprise a first proximal set of magnets 111 disposed proximally of the electrode housing 120 . The first proximal set of magnets 111 may comprise any suitable number o f magnets , such as in the range of 1 to 50 magnets . The first catheter 100 may not have any magnets positioned distally o f the electrode housing 120 .

[0085] As shown in FIG . 1 , the electrode 130 may have a proximal portion 131 , an intermediate portion 132 and a distal portion 133 . A conducting element 134 may be connected to the proximal portion 131 and may extend along the catheter body 110 of the first catheter 100 . The proximal end of the conducting element 134 may be connected to an RF energy source 160 , for example an ESU pencil or ESU unit , to allow RF energy to be supplied to the electrode 130 . The proximal portion 131 may be fixed to the electrode housing 120 , for example , with a clamping mechanism or an adhesive . The intermediate portion 132 may extend out of the opening of the electrode housing 120 which may allow it to contact a vessel wall for forming a fistula . The electrode 130 may be in the form of a leaf spring with the intermediate portion 132 having a convex shape which extends away from the electrode housing 120 . The distance between the top of the intermediate portion 132 and the electrode housing 120 is the height of the electrode 130 . The distal portion 133 may not be fixed and may move longitudinally relative to the electrode housing 120 . This may allow the electrode 130 to move between a radially contracted configuration and a radially expanded configuration . In the radially expanded configuration, the electrode 130 may extends radially further from the electrode housing 120 than in the radially contracted configuration .

[0086] The electrode 130 may be in the form of a ribbon wire and may be made from a number of suitable materials , such as one or more refractory metals . For example , the electrode 130 may comprise tungsten, molybdenum, niobium, tantalum, rhenium, or combinations and alloys thereof . The electrode housing 120 may be made from a non-conductive ceramic material which can withstand the heat and plasma generated by the electrode 130 .

[0087] The first radiopaque loop 140 may be positioned distally adj acent to the electrode housing 120 . The first radiopaque loop 140 may be in the form o f a wire and the si ze or diameter of the radiopaque loop 140 may be adj ustable . One end of the radiopaque loop 140 may be fixed to the electrode housing 120 whilst the other end of the radiopaque loop 140 may be connected to a pull wire 141 . The pull wire 141 may extend through the housing 120 and along the length of the catheter body 110 . The pull wire 141 may be longitudinally moveable relative to the catheter body 110 such that proximal movement of the pull wire 141 will reduce the si ze or diameter of the radiopaque loop 140 , whilst distal movement of the pull wire 141 will increase the si ze or diameter o f the radiopaque loop 140 . The first radiopaque loop 140 may be made from any suitable radiopaque material , such as platinum, gold, tantalum, stainless steel or nitinol , and may be suf ficiently rigid to extend di stally from the electrode housing 120 without falling down or collapsing . The first radiopaque loop 140 may be visible under fluoroscopy and may be open such that it can be penetrated by a needle .

[0088] The second catheter 200 may also comprise a catheter body 210 having a longitudinal axis L2 , and a backstop housing 220 having a backstop 230 disposed at or near a distal end of the catheter body 210 . The backstop 230 may have a concave portion which is shaped complimentary to the convex portion of the electrode 130 . The backstop housing 220 and the backstop 230 may also be made from a non-conductive ceramic material to withstand the heat and plasma generated by the electrode 130 . The second catheter 200 also comprises a second proximal set of magnets 211 disposed proximally of the backstop housing 220 . The second proximal set of magnets 211 may comprise any suitable number of magnets , such as in the range of 1 to 50 magnets . The second catheter 200 may not have any magnets positioned distally of the backstop housing 220 .

[0089] The second catheter 200 may also have a second radiopaque loop 240 positioned distally adj acent the backstop housing 220 and the backstop 230 . The second radiopaque loop 240 may be substantially similar to the first radiopaque loop 140 . For example , the second radiopaque loop 240 may also be in the form of a wire and the si ze or diameter of the radiopaque loop 240 may be adj ustable . One end of the second radiopaque loop 240 may be fixed to the backstop housing 220 whilst the other end of the radiopaque loop 240 may be connected to a pull wire 241 . The pull wire 241 may extend through the backstop housing 220 and along the length of the catheter body 210 . The pull wire 241 may be longitudinally moveable relative to the catheter body 210 such that proximal movement of the pull wire 241 will reduce the si ze or diameter of the radiopaque loop 140 , whilst distal movement of the pull wire 141 will increase the si ze or diameter of the radiopaque loop 140 . The second radiopaque loop 240 may be made from any suitable radiopaque material , such as platinum, gold, tantalum, stainless steel or nitinol , and may be suf ficiently rigid to extend distally from the backstop housing 220 without falling down or collaps ing . The second radiopaque loop 240 may be visible under fluoroscopy and may be open such that it can be penetrated by a needle . FIGS . 2A to 2H illustrate a method of using the system 10 of FIG . 1 to form a fistula between an artery A and a vein V . The aim of forming an arteriovenous fistula between artery A and vein V, may, for example , be to allow blood flow to circumvent a chronic total occlusion ( CTO) in the artery A. The fistula may be formed, for example , as part of a deep vein arteriali zation procedure or an endovascular bypass procedure . However, the present system 10 may also be used in any other fistula forming applications .

[0090] In order to form a fistula between two vessels , such as artery A and vein V, the first catheter 100 may be introduced into the venous system through a venous access site and the second catheter 200 may be introduced into the arterial system through an arterial access site . As shown in FIG . 2A, the first catheter 100 and the second catheter 200 may then be advanced through vein V and artery A, respectively, to the treatment site where the fistula is to be formed . The first catheter 100 and second catheter 200 may be advanced to the treatment site from the same direction . The treatment site may be adj acent to the chronic total occlusion ( CTO) in the artery A. The first catheter 100 may be advanced to the treatment site inside a sheath 150 . The sheath 150 may compress the electrode 130 such that it is in the radially contracted configuration . This may allow the first catheter 100 to more easily advance through the vessel due to the lower profile .

[0091] As shown in FIG . 2B, once the first catheter 100 and the second catheter 200 are positioned at the treatment site , the sheath 150 may be removed which may cause the electrode 130 to move to the expanded position . The first catheter 100 and second catheter 200 may then be aligned under fluoroscopy and with the help of the first proximal set of magnets 111 and the second set of proximal magnets 211 . The first proximal set of magnets 111 and the second set of proximal magnets 211 may be attracted to each other to help roughly align the electrode 130 with the backstop 230 and the first radiopaque loop 140 with the second radiopaque loop 240 .

[0092] Once the first catheter 100 and second catheter 200 are substantially aligned, a medical practitioner may identi fy the first and second radiopaque loops 140 , 142 under fluoroscopy and then pierce the skin of the patient with a needle 300 and penetrate the first radiopaque loop 140 and second radiopaque loop 240 with the needle 300 . The needle 300 may be introduced at an angle , speci fically, the needle 300 may be angled partially in a distal direction during introduction . As shown in FIG . 2C, a guidewire 310 may then be introduced through a lumen of the needle 300 into the vein V .

[0093] The needle 300 may then be removed, leaving the guidewire 310 in the vein V and passing through the first radiopaque loop 140 and the second radiopaque loop 240 . As shown in FIG . 2D, the si ze or diameter of the first radiopaque loop 140 and the second radiopaque loop 240 may then be reduced by pulling the pull wire 141 and pull wire 241 proximally . The larger initial first and second radiopaque loops 140 , 240 may make it easier to visualise the radiopaque loops under fluoroscopy and may help a medical practitioner to more easily penetrate the first and second radiopaque loops 140 , 240 with the needle 300 . By reducing the si ze or diameter of the first and second radiopaque loops 140 , 240 , the first and second radiopaque loops 140 , 240 ef fectively snare the guidewire 310 resulting in more ef fective alignment and compression of the vessel walls between the first catheter 100 and the second catheter 200 .

[0094] As shown in FIG . 2E , the first catheter 100 may then be pulled proximally in direction DI whilst the second catheter 200 may be pushed distally in direction D2 . Due to the angle of the guidewire 310 and the fact that the guidewire 310 i s snared by the first radiopaque loop 140 and the second radiopaque loop 240 , this will result in the first catheter 100 moving upwards along the guidewire 310 towards the venous wall whilst the second catheter 200 moves downwards along the guidewire 310 towards the arterial wall . The guidewire 310 may be suf ficiently rigid to allow the first radiopaque loop 140 and the second radiopaque loop 240 to slide and move upwards and downwards along the guidewire 310 . The electrode 130 becomes aligned with the backstop 230 and the arterial and venous wall are compressed between the electrode 130 and the backstop 230 . The combination of the first and second proximal sets of magnets 111 , 211 together with the distal first and second radiopaque loops 140 , 240 which are aligned via guidewire 310 , results in accurate and ef fective alignment between the first catheter 100 and second catheter 200 and ef fective compression of a localised section of the arterial and venous walls between the electrode 130 and backstop 230 .

[0095] The electrode 130 may then be activated, for example , by supplying a radiofrequency (RF) current to the electrode 130 from RF energy source 160 . The RF current causes the electrode 130 to heat up and generate a plasma . The plasma causes rapid dissociation of molecular bonds in organic compounds and allows the electrode 130 to cut through the venous and arterial vessel walls until it hits the backstop 230 to form the fistula . FIG . 2 F shows the first catheter 100 and second catheter 200 in the vein V and artery A, respectively, after the formation of the fistula .

[0096] The guidewire 310 may then be removed and the sheath 150 may be advanced over the first catheter 100 to force the electrode 130 to move from the radially expanded configuration to the radially contracted configuration . As shown in FIG . 2G, the first catheter 100 and second catheter 200 may then be pulled proximally and removed from the vein V and artery A, respectively . FIG . 2H shows the artery A and vein V connected with the fistula, after removal of the first catheter 100 and second catheter 200 . The arrows indicate the flow of blood B which may flow from the artery A through the fistula into the vein V and thereby circumvent the chronic total occlusion CTO in the artery A.

[0097] The present system 10 therefore allows a fistula to be formed with a first catheter 100 and a second catheter 200 having no distal sets of magnets . This means that the first and second catheters 100 , 200 are cheaper and simpler to manufacture . The reduced number of magnets also improves trackability of the first and second catheters 100 , 200 , as they can more easily manoeuvre through tortuous vessel anatomy . The lack of distal magnets and reduced length of the first catheter 100 and second catheter 200 may also allow a fistula to be formed much closer to an obstacle in the vessel , such as a chronic total occlusion, for example .

[0098] FIG . 3 shows an alternative embodiment of a second catheter 400 which may be used together with first catheter 100 to form a fistula . The second catheter 400 is similar to second catheter 200 and also comprises a catheter body 410 having a longitudinal axis L2 , and a backstop housing 420 having a backstop 430 disposed near a distal end of the catheter body 210 . The backstop 430 is substantially the same as backstop 230 and may have a concave portion which is shaped complimentary to the convex portion of the electrode 130 . The backstop housing 420 and the backstop 430 may also be made from a non-conductive ceramic material to withstand the heat and plasma generated by the electrode 130 .

[0099] However, second catheter 400 di f fers from second catheter 200 in that the second catheter 400 comprises a second radiopaque loop 440 which is disposed proximally of the backstop housing 420 and a set of magnets 411 which is disposed distally o f the backstop housing 420 . The distal set of magnets 411 may comprise any suitable number of magnets , such as in the range of 1 to 50 magnets . The second catheter 400 may not comprise any magnets positioned proximally of the backstop 430 .

[0100] The second radiopaque loop 440 may be positioned proximally adj acent the backstop housing 420 and the backstop 430 and may be formed as part of the catheter body 410 . The second radiopaque loop 440 may be formed as a radiopaque ring and may not be adj ustable . However, the radiopaque loop 440 may be rotatable relative to the catheter body 410 about longitudinal axis L2 , for example , via a rotating hinge or pivot . The second radiopaque loop 440 may be made from any suitable radiopaque material , such as platinum, gold, tantalum, stainless steel or nitinol . The second radiopaque loop 440 may be visible under fluoroscopy and may be open such that it can be penetrated by a needle .

[0101] FIG . 4 illustrates a method of forming a fistula between an artery A and vein V using first catheter 100 and second catheter 400 . The method is substantially the same as explained for above with respect to FIGS . 2A to 2H, except that by having the second radiopaque loop 440 disposed proximally of the backstop housing 420 , the second catheter 400 and the first catheter 100 can be introduced from opposite sides when forming a fistula .

[0102] The first catheter 100 and second catheter 400 are introduced into the vein V and artery A through respective access sites but advanced to the treatment site from opposite directions . The first catheter 100 and second catheter 200 may be aligned with the help of the proximal set of magnets 111 and the distal set of magnets 411 . A needle 300 may then penetrate the second radiopaque loop 440 and first radiopaque loop 140 and guidewire 310 may be inserted through the needle 300 and pass through the first radiopaque loop 140 and second radiopaque loop 440 . As shown in FIG . 4 , the first catheter 100 may then be pulled proximally in a direction DI whilst the second catheter 200 may be pulled distally in direction D2 . Due to the angle o f the guidewire 310 and the fact that the guidewire 310 is captured by the first radiopaque loop 140 and the second radiopaque loop 440 , this will result in the first catheter 100 moving upwards along the guidewire 310 towards the venous wall whilst the second catheter 400 moves downwards along the guidewire 310 towards the arterial wall . The electrode 130 becomes aligned with the backstop 230 and the arterial and venous wall are compressed between the electrode 130 and the backstop 430 . The combination of the first proximal set of magnets 111 and the distal set of magnets 211 together with the first and second radiopaque loops 140 , 440 which are aligned via guidewire 310 , results in accurate and ef fective alignment between the first catheter 100 and second catheter 400 and ef fective compression of a localised section of the arterial and venous walls between the electrode 130 and backstop 430 .

[0103] The electrode 130 may then be activated, for example , by supplying a radiofrequency (RF) current to the electrode 130 from RF energy source 160 to form the fistula .

[0104] Various modi fications will be apparent to those skilled in the art .

[0105] The first catheter 100 may not have a proximal set of magnets 111 .

[0106] The si ze or diameter of the first radiopaque loop 140 may not be adj ustable . Rather, the si ze or diameter of the first radiopaque loop 140 may be fixed .

[0107] The first radiopaque loop 140 may not be positioned directly adj acent the housing 120 . A further element , such as a portion of the catheter body 110 , for example , may be positioned between the housing 120 and the first radiopaque loop 140 .

[0108] The first radiopaque loop 140 is not limited to being a wire but may take any suitable form, such as a solid ring, for example .

[0109] The first catheter 100 may not have an electrode housing 120 and the electrode 130 may not be positioned within the electrode housing 120 but may be positioned directly on the catheter body 110 , for example .

[0110] The electrode 130 is not limited to being a convex shape but may take any suitable shape , such as a V-shape or a rectangular shape , for example .

[0111] The electrode 130 is not limited to being in the form of a ribbon wire but may take any other suitable form, such as a round wire , oval wire or square wire , for example .

[0112] The distal end of the electrode 130 may be fixed inside the electrode housing 120 and the proximal portion of the electrode 130 may be movable relative to the housing to move the electrode between the radially contracted configuration and the radially expanded configuration .

[0113] The electrode 130 may not be expandable and may not have a radially contracted configuration and a radially expanded configuration . Rather, the electrode may have a fixed height , for example .

[0114] The electrode housing 120 and backstop housing 220 , 420 are not limited to being made from a ceramic material and may be made from any other suitable type of material , such as a heat-resistant polymer, for example . The second catheter 200 may not have a proximal set of magnets 211.

[0115] The size or diameter of the second radiopaque loop 240 may not be adjustable. Rather, the size or diameter of the second radiopaque loop 240 may be fixed.

[0116] The second radiopaque loop 240 may not be positioned directly adjacent the backstop housing 220. A further element, such as a portion of the catheter body 210, for example, may be positioned between the backstop housing 220 and the second radiopaque loop 240.

[0117] The second catheter 200, 400 may not have a backstop housing 220, 420. Rather, the backstop may be directly disposed on the catheter body 210, 410.

[0118] The backstop 230, 430 may not be shaped complimentary to the electrode 130.

[0119] The backstop 230, 430 is not limited to being a concave shape but may take any other suitable shape, such as a flat surface, a V-shape or a rectangle shape, for example. The backstop 230, 430 may also be a protruding backstop, for example .

[0120] The second catheter 400 may not have a distal set of magnets

[0121] 411.

[0122] The second radiopaque loop 440 may not be positioned directly adjacent the backstop housing 420. A further element, such as a portion of the catheter body 2410, for example, may be positioned between the backstop housing 420 and the second radiopaque loop 440.

[0123] All of the above are fully within the scope of the present disclosure and are considered to form the basis for alternative embodiments in which one or more combinations of the above-described features are applied, without limitation to the speci fic combination disclosed above .

[0124] In light of this , there will be many alternatives which implement the teaching of the present disclosure . It is expected that one skilled in the art will be able to modi fy and adapt the above disclosure to suit its own circumstances and requirements within the scope of the present disclosure , while retaining some or all technical ef fects of the same , either disclosed or derivable from the above , in light of his common general knowledge in this art . All such equivalents , modi fications or adaptations fall within the scope of the present disclosure .

Claims

Claims :

1. A catheter for forming a fistula between two vessels, comprising : a catheter body having a longitudinal axis; an electrode extending radially from the catheter body for contacting a vessel wall and forming the fistula; and a radiopaque loop disposed distally of the electrode, wherein the radiopaque loop is configured for penetration by a needle.

2. The catheter of claim 1, wherein the radiopaque loop comprises a radiopaque wire.

3. The catheter of claim 1 or 2, wherein the diameter of the radiopaque loop is adjustable.

4. The catheter of claim 3, wherein the radiopaque loop is connected to a pull wire extending along the length of the catheter body and wherein the diameter of the radiopaque loop is adjustable by longitudinally moving the pull wire.

5. The catheter of any preceding claim, wherein the electrode is radially expandable.

6. The catheter of any preceding claim, wherein the catheter body comprises an electrode housing with at least one opening.

7. The catheter of claim 6, wherein the radiopaque loop is positioned adjacent the electrode housing.

8. The catheter of claim 6 or 7, wherein the electrode is at least partially positioned within the electrode housing.9 . The catheter of any of claims 6 to 8 , wherein the electrode is configured to extend radially from the opening of the electrode housing .10 . The catheter of any of claims 6 to 9 , wherein the electrode comprises a distal portion, a proximal portion and an intermediate portion .11 . The catheter of claim 10 , wherein the distal portion of the electrode is moveable inside the electrode housing for moving the electrode between a radially contracted configuration and a radially expanded configuration .12 . The catheter of claim 10 , wherein the distal portion of the electrode is fixed inside the electrode housing and the proximal portion of the electrode is moveable for moving the electrode between a radially contracted configuration and a radially expanded configuration13 . The catheter of any of claims 6 to 12 , wherein the housing is at least partially made from a ceramic material .14 . The catheter of any preceding claim, wherein the electrode has a convex shape with respect to the catheter body .15 . The catheter of any preceding claim, wherein the electrode comprises a leaf spring .16 . The catheter of any preceding claim, wherein the electrode comprises a ribbon wire .17 . A system for forming a fistula between two vessels comprising : a first catheter according to any of the preceding claims ; a second catheter comprising a backstop for the electrode .

18. The system of claim 17, wherein the second catheter comprises a second radiopaque loop configured for penetration by a needle.

19. The system of claim 18, wherein the second radiopaque loop is positioned distally of the backstop.

20. The system of claim 18, wherein the second radiopaque loop is positioned proximally of the backstop.

21. The system of any of claims 18 to 20, wherein the second radiopaque loop is positioned adjacent the backstop.

22. The system of claim 18, 19 or 20, wherein the second radiopaque loop comprises a radiopaque wire.

23. The system of any of claims 18 to 22, wherein the diameter of the second radiopaque loop is adjustable.

24. The system of claim 23, wherein the second radiopaque loop is connected to a wire extending along the length of the second catheter and wherein the diameter of the second radiopaque loop is adjustable by longitudinally moving the wire .

25. The system of any of claims 17 to 24, wherein the backstop has a portion shaped complimentary to the electrode.

26. The system of any of claims 17 to 25, wherein the backstop has a concave portion.

27. The system of any of claims 17 to 26, wherein the first catheter further comprises a set of magnets positioned proximally of the electrode.28 . The system of any of claims 17 to 26 , wherein the second catheter further comprises a set of magnets positioned distally of the electrode .29 . The system of any of claims 17 to 28 , further comprising a radiofrequency generator for supplying radiofrequency power to the electrode .30 . The system of any of claims 17 to 29 , further comprising a needle .31 . The system of claim 30 , wherein the needle comprises a guidewire lumen for accommodating a guidewire .32 . The system of claim 31 , further comprising a guidewire disposed within the guidewire lumen of the needle .33 . The system of any of claims 17 to 32 , further comprising a sheath disposed over at least a portion of the catheter body of the first catheter and is slidably moveable along the longitudinal axis of the catheter body .34 . The system of claim 33 , wherein the sheath is slidable to move the electrode between a radially contracted configuration and radially expanded configuration .35 . A method of forming a fistula between two vessels using a catheter, the catheter having a catheter body, an electrode extending radially from the catheter body, and a radiopaque loop disposed distally of the electrode , the method comprising : inserting the catheter into a blood vessel and advancing it to a site where the fistula is to be formed; locating the radiopaque loop under fluoroscopy; penetrating the radiopaque loop with a needle ; pulling or pushing the catheter to push the electrode against a wall of the blood vessel ; andsupplying RF energy to the electrode to form the fistula .36 . The method of claim 35 , wherein penetrating the radiopaque loop with a needle further comprises inserting a guidewire through the needle and the radiopaque loop .37 . The method of claim 36 , wherein pulling or pushing the catheter causes the radiopaque loop to slide along the guidewire to push the electrode against a wall of the blood vessel .

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