WO2024223036A1

WO2024223036A1 - A catheter for use in a system for forming a fistula between two vessels

Info

Publication number: WO2024223036A1
Application number: PCT/EP2023/060954
Authority: WO
Inventors: Ciaran GILES; Alan Kavanagh; Michael Whelan; John O'shea
Original assignee: ClearStream Technologies Ltd
Current assignee: ClearStream Technologies Ltd
Priority date: 2023-04-26
Filing date: 2023-04-26
Publication date: 2024-10-31
Anticipated expiration: 2025-10-26

Abstract

The present disclosure relates to a catheter for use in a system for forming a fistula between two vessels comprising a catheter shaft having a longitudinal axis; a backstop coupled to the catheter shaft and having an electrode engagement surface for receiving a fistula-forming electrode; and a guidewire lumen extending from a distal end of the catheter to an opening in the backstop.

Description

A Catheter for Use in a System for Forming a Fistula between Two Vessels

Technical Field

The present disclosure relates to a catheter for use in a system for forming a fistula between two vessels .

Background

The accumulation of atherosclerotic plaque in blood vessel walls can often result in blood flow blockages , which can cut or reduce arterial circulation to limbs and lead to peripheral arterial disease . Resulting conditions can include infection, tissue death and in some cases total limb necrosis .

Alleviating peripheral arterial disease can make use of minimally invasive treatments including angioplasty and atherectomy, whereby catheters are inserted to respectively widen the blood vessel with a balloon or remove plaque from the vessel wall . Other types of procedures include endovascular bypass procedures or deep vein arteriali zation ( DVA) procedures . Both of these procedures require the creation of a fistula between a vein and artery . For an endovascular bypass procedure , a vascular bypass graft is placed from a location proximal to the blockage to a location distal to the blockage in order to provide an unobstructed path for the blood to circumvent the diseased area . For a deep vein arteriali zation procedure , a fistula is created between a peripheral artery and a deep vein with the intent of "arteriali zing" the veins . Arterial blood can then flow through the vein and bypass the blockage in the artery to thereby provide adequate blood flow to the target tissue .

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 . The catheters may have a rapid exchange ("RX" ) tip at the distal end to allow the catheter to be introduced over and tracked along a guidewire . The RX tip avoids the need for excessively long guidewires when exchanging catheters and al lows a physician to easily hold the guidewire in place whilst removing or introducing a catheter . However, the distal RX tip increases the length o f the catheters by approximately 20mm or more and can make it di f ficult to form a fistula close to an occlusion or obstruction in a vessel . Furthermore , the increased length can make it more di f ficult to manoeuvre these catheters through tortuous vessel anatomy, such as the anterior tibial vessel , for example .

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 .

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 .

Summary

According to a first aspect of the disclosure , there is provided a catheter for use in a system for forming a fistula between two vessels . The catheter comprises a catheter shaft having a longitudinal axis , a backstop coupled to the catheter shaft and having an electrode engagement surface for receiving a fistula- forming electrode , and a guidewire lumen extending from a distal end of the catheter to an opening in the backstop . In some embodiments , this may result in a catheter for use in a system which can form a fistula closer to an occlusion or obstruction in the blood vessel .

In some embodiments , this may result in a catheter for forming a fistula which can more easily be manoeuvred through the vessel anatomy .

Throughout this disclosure , the term ' fistula' refers to a passageway or connection, for example between an artery and a vein .

The backstop may comprise a through-hole forming part of the guidewire lumen, the through-hole ending in the opening .

The backstop may have a recessed portion positioned on the opposite side of the backstop from the electrode engagement surface .

In some embodiments , this may result in a backstop having a reduced profile which may allow it to more easily be manoeuvred through the vessel anatomy .

The opening may be positioned in the recessed portion .

In some embodiments , this may allow the catheter to move over or track the guidewire more easily . In some embodiments , this may further allow the catheter to be deployed in a smaller diameter vessel .

The recessed portion may comprise a substantially V-shaped part .

In some embodiments , this may allow the guidewire to smoothly exit through the opening and may avoid the guidewire catching on any edges . In some embodiments , this may further help to maintain the structural integrity of the backstop . The substantially V-shaped part may have a first surface and a second surface . The first surface may be positioned substantially perpendicular to the longitudinal axis of the catheter whilst the second surface may be positioned at an angle of between 45 to 80 degrees from the first surface .

The recessed portion may further comprise a longitudinally elongated part positioned proximally of the substantially V- shaped part .

The longitudinally elongated part of the recessed portion may have a longitudinal surface which may be substantially longitudinally arranged and proximally adj acent the second surface of the V-shaped part .

The through-hole may be straight and extend longitudinally .

In some embodiments , this may avoid kinking of the guidewire . In some embodiments , this may further result in simple manufacture of the backstop .

The opening may be a lateral opening in the backstop .

In some embodiments , this may improve the structural integrity of the backstop .

The lateral opening may be positioned on the opposite side of the backstop from the electrode engagement surface .

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

The through-hole may have a curved longitudinal profile .

In some embodiments , this may allow the guidewire to smoothly pass through the through-hole and may avoid kinking of the guidewire . In some embodiments , this may result in improved structural integrity of the backstop as it avoids edges in the through-hole .

The through-hole may comprise a proximal portion and a distal portion . The proximal portion and the distal portion may further be positioned at an angle relative to each other .

In some embodiments , this may result in easier manufacturing of the backstop . In some embodiments , this maintains structural integrity of the backstop .

The distal portion of the through hole may be aligned with a longitudinal axis of the catheter .

The proximal portion may be positioned at an angle of 10 to 60 degrees relative to the distal portion .

In some embodiments , this may allow the guidewire to pas s through the through-hole smoothly .

The backstop may be a non-conductive backstop .

In some embodiments , this may prevent arcing between the fistula- forming electrode and the backstop and result in more controlled fistula formation .

The backstop may, at least partially, be made from a ceramic material .

In some embodiments this may al low the backstop to better withstand the heat and plasma generated by the fistulaforming electrode .

The electrode engagement surface may comprise a recessed portion . The recessed portion may have a concave shape . In some embodiments , this may result in improved engagement between the fistula- forming electrode and the backstop and compression of the vessel walls , resulting in more ef fective fistula formation .

The backstop may further comprise protrusions on either side of the recessed portion .

In some embodiments this may result in a more secure engagement of the fistula- forming electrode with the backstop and added stability when creating a fistula .

The catheter may further comprise a distal set of magnets , disposed distally of the backstop .

In some embodiments this may assist in aligning of the fistula- forming electrode with the backstop .

The distal set of magnets may further comprise a through-hole forming part of the guidewire lumen .

In some embodiments , this may allow alignment of the fistulaforming electrode and backstop whilst reducing catheter length .

The catheter may further comprise a proximal set of magnets , disposed proximally of the backstop .

According to a second aspect of the disclosure , there is provided a system for forming a fistula . The system comprises a first catheter according to any of the above and a second catheter . The second catheter comprises a housing and a fistula- forming electrode extending radially from the housing . The fistula- forming electrode may be disposed at least partially within the housing .

In some embodiments this may better protect the fistulaforming electrode and help to better direct the energy generated by the fistula- forming electrode .

The fistula forming electrode may have a convex-shaped portion . The fistula- forming electrode may further comprise a ribbon wire .

In some embodiments this may result in more ef fective fistula creation .

The system may further comprise a distal set of magnets disposed on the second catheter, distally of the housing . The system may further comprise a proximal set of magnets disposed on the second catheter, proximally of the housing . In some embodiments this may assist in the aligning of the fistula- forming electrode with a backstop .

The housing may, at least partly, be made from a ceramic material . In some embodiments this may allow the housing to better withstand the heat and plasma generated by the electrode .

The system may further comprise an RF energy generator for supplying energy to the fistula- forming electrode .

These and other features of the concepts provided herein will become more apparent to those of skill in the art in view of the accompanying drawings and the following description, which describe particular embodiments of such concepts in greater detail .

Brief Description of the Drawings For a more complete understanding of the present disclosure , reference is now made , by way of example only, to the accompanying drawings . These drawings are used to illustrate only typical embodiments of this disclosure and are not to be considered limiting on its scope . The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness .

Identical reference numbers do not necessarily indicate an identical structure . Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers .

Fig . 1 is a schematic representation of a catheter system for forming a fistula between two vessels , according to one or more embodiments shown and described herein;

Fig . 2A shows a catheter having a backstop for use in a system for forming a fistula according to one or more embodiments of the present disclosure , according to one or more embodiments shown and described herein;

Fig . 2B shows a perspective view of the backstop of the catheter of Figure 2A, according to one or more embodiments shown and described herein;

Fig . 2C shows a cross-sectional side view of the backstop of the catheter of Figure 2A, according to one or more embodiments shown and described herein;

Fig . 3A shows a catheter system being introduced into an artery and a vein, according to one or more embodiments shown and described herein; Fig . 3B shows the catheter system of Fig . 3A during a fistula formation process between the artery and the vein, according to one or more embodiments shown and described herein;

Fig . 3C is a schematic representation of blood flow through the artery and vein after the fistula creation process , according to one or more embodiments shown and described herein;

Fig . 4 shows an alternative embodiment of a backstop for a catheter according to one or more embodiments of the present disclosure ;

Fig . 5 shows an alternative embodiment of a backstop for a catheter according to one or more embodiments of the present disclosure .

Detailed Description

The embodiments described herein are provided as exemplary and non-limiting embodiments of the present disclosure .

Directional terms as used herein— for example up, down, right , left , front , back, top, bottom are made only with reference to the figures as drawn and are not intended to imply absolute orientation .

Throughout this disclosure , the terms "proximal" and "distal" refer to the proximal and distal directions in relation to the catheter, unless otherwise speci fied . Speci fically, "proximal" refers to a point on the catheter which is intended to be closer to a physician when the catheter is in use , i . e . , closer to the handle , while "distal" refers to a point on the catheter which is intended to be further away from a physician when the catheter is in use , i . e . , closer to the tip . With reference to Figure 1 , there is illustrated a system 10 for forming a fistula comprising a first catheter 100 and a second catheter 200 . A handle 170 may be attached to the proximal end of the first catheter 100 . The first catheter 100 includes a catheter shaft 110 , which may have a tubular shape . The second catheter 200 also includes a catheter shaft 210 , which may have a tubular shape .

The catheter body 110 of the first catheter 100 may have a fistula- forming electrode 130 which may extend radially from the catheter body 110 for contacting a vessel wall , such as a wall of a vein or artery, and forming a fistula . The fistulaforming electrode 130 may be in the form of a ribbon wire and have an arc shape which is convex with respect to the longitudinal axis of the catheter body 110 . The fistulaforming electrode 130 may be made from a number of suitable materials such as tungsten, molybdenum, niobium, tantalum, rhenium, or combinations and alloys thereof .

The fistula- forming electrode 130 may be positioned at least partially within an electrode housing 120 . The electrode housing 120 may form part of the catheter body 110 , for example , by being embedded within the catheter body 110 . The electrode housing 120 may be made from a non-conductive material , such as a ceramic material , which may allow the electrode housing 120 to better withstand the heat from the plasma generated by the fistula- forming electrode 130 . The fistula- forming electrode 130 may have a radially expanded configuration shown in Figure 1 and a radially contracted configuration shown in Figure 3A.

In the radially expanded configuration of Figure 1 , the fistula- forming electrode 130 may extend radially further away from the electrode housing 120 than in the radially contracted configuration of Figure 3A. In the radially contracted configuration shown in Figure 3A, the fistulaforming electrode 130 may be fully disposed in the housing 120 , or it may extend from the housing 120 by a small distance . The fistula- forming electrode 130 may take the form of a leaf spring which may allow the fistula- forming electrode 130 to bend and thereby ef fectively move between the radially contracted and radially expanded configurations .

There are a number of di f ferent ways in which the fistulaforming electrode 130 may be moved between the radially contracted configuration and the radially expanded configuration . For example , a distal end of the fistulaforming electrode 130 may be free to move within the electrode housing 120 . The fistula- forming electrode 130 can then be moved from the radially expanded configuration ( see Figure 1 ) to the radially contracted configuration ( see Figure 3A) by pushing down on the fistula- forming electrode 130 , for example , through the use of a sheath (not shown) . When the sheath is removed, the fistula- forming electrode 130 will regain its original shape and expand from the radially contracted configuration to the radially expanded configuration .

In another example , the distal end of the fistula- forming electrode 130 can be fixed relative to the electrode housing 120 . The proximal end of the electrode 130 , which may be connected to a connecting element 131 , can be longitudinally moveable relative to the electrode housing 120 . A user may then push or pull the proximal end of the fistula- forming electrode 130 via the connecting element 131 in order to move the fistula- forming electrode 130 between the radially contracted configuration and the radially expanded configuration . For example , a user may push the connecting element 131 and the proximal end of the fistula- forming electrode 130 in order to move the fistula- forming electrode 130 from the radially contracted configuration to the radially expanded configuration . Similarly, a user may pull the connecting element 131 and the proximal end of the fistula- forming electrode 130 in order to move the fistula- forming electrode 130 from the radially expanded configuration to the radially contracted configuration .

These configurations of the electrode 130 may be advantageous for a more ef ficient fistula-creating process , in that the fistula- forming electrode 130 can be advanced through the vessel anatomy in the radially contracted configuration having a low profile , and subsequently expanded to create a fistula in the radially expanded configuration .

The catheter body 110 may further comprise a proximal set of magnets 140 disposed proximally of the fistula- forming electrode 130 . The catheter body 110 may also further comprise a distal set of magnets 150 disposed distally of the fistula- forming electrode 130 . The magnets may be used to assist in aligning the fistula- forming electrode 130 with the second catheter 200 , which acts as a backstop catheter . In some configurations , a single set of magnets may suf fice . The number of magnets disposed within the set of magnets 140 and 150 is variable and any suitable number of magnets may be used .

The first catheter 100 may also comprise a rapid exchange tip 160 (RX tip ) at the distal end of the catheter body 110 . The rapid exchange tip 160 may comprise a guidewire lumen 161 , for accommodating a guidewire 115 , which extends between a first proximal opening 163 and a second distal opening 162 . The rapid exchange tip 160 may enable a faster exchange of the first catheter 100 . The RX tip 160 avoids the need for excessively long guidewires when introducing or exchanging the first catheter 100 and allows a physician to easily hold the guidewire 115 in place whilst removing or introducing the catheter 100 .

The first electrode connecting element 131 may extend along the length of the catheter body 110 and may be in the form of a wire or cable , for example . The electrode connecting elements 131 may connect the fistula- forming electrode 130 to a source of RF energy, which may be in the form of an ESU pencil ( examples of which include a Bovie® Pen Generators ) , such that RF energy can be supplied to the fistula- forming electrode 130 . The electrode connecting element 131 may be conductive and configured to carry an RF current , so as to allow supply of RF energy to the fistula- forming electrode 130 .

A handle 170 may be disposed at a proximal end of the first catheter 100 . Handle 170 may comprise a braided catheter end 171 which is connected to the distal end of catheter body 110 . The braided catheter end 171 may facilitate operation of the first catheter 100 by providing grip, thus stabilising the first catheter 100 . The electrode connecting element 131 may extend within the catheter body 110 , and inside braided catheter end 171 up to a toggle switch 180 . Toggle switch 180 may be positioned on the grip handle 173 and may comprise a toggle switch button 181 . The toggle switch 180 may be configured to switch the power supplied to the fistulaforming electrode 130 on and of f by moving the toggle switch button 181 between a first and second configuration . Grip handle 173 may have a bulbous or otherwise conveniently manoeuvrable shape and is connected at a distal end to the braided catheter end . The proximal end of grip handle 173 may include an aperture 174 through which a second connecting element 172 passes . Second connecting element 172 may be connected directly at a distal end to toggle switch 180 , and indirectly to electrode connecting element 131 via the toggle switch 180 . The second connecting element 172 may be connected proximally to the source of RF energy, which may be in the form of a generator or ESU pencil (not illustrated) . The second connecting element 172 may be in the form of a wire , rod or cable , for example .

Figure 1 also shows the second catheter 200 as part of system 10 for forming a fistula between two blood vessels . Second catheter 200 may comprise a catheter body 210 and a backstop 220 having an electrode engagement surface 230 , which may be concave and recessed with respect to the catheter body 210 . Protuberances 231 and 232 may protrude radially outward from the catheter body 210 on either side of the electrode engagement surface 230 and assist in creating a concave geometry for the electrode engagement surface 230 . The concave geometry may be complementary to the shape of the electrode 130 and may help to induce a deformation of the vessel wall when forming a fistula . The backstop 220 may be made from a non-conductive material , such as a ceramic material , to prevent unwanted arcing between the fistulaforming electrode 130 and the backstop 220 and help the backstop 220 better withstand the heat from the plasma generated by the electrode 130 .

The catheter body 210 may further comprise a distal set of magnets 240 disposed distally of the backstop 220 . The catheter body 210 may further comprise a proximal set of magnets 250 disposed proximally of the backstop 220 . The sets of magnets 240 , 250 may be used for aligning the backstop 220 of the second catheter 200 with the electrode 130 of the first catheter 100 . In some configurations a single set of magnets may suf fice . The number of magnets disposed within each set of magnets 240 and 250 is variable .

Second catheter 200 may comprise a similar rapid exchange tip 260 (RX tip ) to that of the RX tip 160 of first catheter 100 , located at the distal end of the catheter body 210 . The rapid exchange tip 260 may comprise a guidewire lumen 261 for accommodating a guidewire 215 which extends from a distal opening 262 to a proximal opening 263 . The distal opening 262 may be a longitudinal opening at the distal tip of the catheter body 210 whilst the proximal opening may be a lateral opening positioned distally of the backstop 220 and magnets 250 . The RX tip 260 may enable a faster exchange o f the second catheter 200 . The RX tip 260 avoids the need for excessively long guidewires when introducing or exchanging catheter 200 and allows a phys ician to easily hold the guidewire 215 in place whilst introducing or removing the catheter 200 .

However, the RX tip 260 may have a length in the range of approximately 20mm to 30mm and therefore increases the length between the electrode engagement surface 230 of the backstop 220 and the distal end of catheter shaft 210 . This can make it di f ficult to form a fistula close to an obstruction or occlusion in a vessel .

Figures 2A shows a second catheter 300 according to an embodiment of the disclosure . Throughout this disclosure , the same reference numerals are used to refer to features which are identical across di f ferent embodiments . The second catheter 300 in Figures 2A-2C is similar to the second catheter 200 of Figure 1 in that it is shown to include a catheter shaft 310 , a proximal set of magnets 340 , a distal set of magnets 350 , and a backstop 320 having an electrode engagement surface 330 with proximal and distal protuberances 331 and 332 positioned on either side of the electrode engagement surface 330 , though a greater of fewer number of components are contemplated and possible . The electrode engagement surface 330 may have a concave shape and form a first recessed portion of the backstop 320 .

However, the second catheter 300 di f fers from second catheter 200 in that it does not have a separate RX tip 260 . Instead, the second catheter 300 comprises a guidewire lumen 361 which extends from a distal opening 362 at a distal end of the catheter 300 to an opening 321 in the backstop 320 . As shown in FIG . 2A, the backstop may comprise a second recessed portion 322 positioned on the opposite side of the backstop

320 to the electrode engagement surface 330 , with the opening

321 positioned within the second recessed portion 322 . The guidewire 315 may pass via the distal opening 362 through the guidewire lumen 361 and exit through the opening 321 in the backstop 320 . The guidewire lumen 361 passes through the distal magnets 350 and may include a longitudinally arranged through-hole 323 formed in the backstop 320 which ends in the opening 321 . The opening 321 may be in the form of a circular or elliptical hole . This arrangement still allows for rapid exchange of the second catheter 300 and avoids both the use of excessively long guidewires and the need for a separate rapid exchange guidewire tip .

Figure 2B illustrates a perspective view of the backstop 320 and FIG . 2C illustrates a cross-sectional side view of the backstop 320 which illustrate the shape and arrangement o f the backstop 320 in more detail . The second recessed portion 322 may have a V-shaped part 324 and an elongated part 325 which may be substantially rectangular, for example , and positioned proximally of the V-shaped part . The V-shaped part 324 may form a deeper recess in the backstop 320 than the elongated part 325 . The peak 324C of the V-shaped portion 324 may be positioned at substantially the same longitudinal position as the distal protuberance 332 . The V-shaped part 324 of the second recessed portion 322 may have a first surface 324A and a second surface 324B positioned proximally of the first surface 324A. The first surface 324A may be positioned substantially perpendicular to the longitudinal axis of the second catheter 300 while the second surface 324B may be positioned at an angle of between 45 to 80 degrees from the first surface 324A. The opening 321 may be formed in the first surface 324A of the V-shaped part 324 . The elongated part 325 of the recessed portion 325 may have a longitudinal surface 325A which is substantially longitudinally arranged and proximally adj acent the second surface 324B of the V-shaped part 324 . The V-shaped part 324 of the second recessed portion 322 may allow the guidewire 315 to smoothly exit through the opening 321 without kinking or catching on the backstop 320 , whilst maintaining structural integrity of the backstop 320 . As shown in FIG . 2C, the through-hole 323 may be straight and extend longitudinally through backstop 320 , such as parallel to a longitudinal axis of the catheter shaft 310 . The combination of a through-hole 323 and the second recessed portion 322 enable the removal of the RX tip, and thus , a shortening of the second catheter 300 when compared to second catheter 200 found in Figure 1 . As illustrated with respect to Figures 3A-3C, this allows the second catheter to be used to form a fistula closer to an occlusion, or obstruction, in the blood vessel . The reduced length of the second catheter 300 also allows it to be manoeuvred through the vessel anatomy more easily .

Figures 3A-3C illustrate a method of using the first catheter 100 and the second catheter 300 to form a fistula between the vein V and an artery A to allow blood to flow past a blockage B in the artery .

Figure 3A shows a cross-sectional side view of the first catheter 100 disposed in a vein V and the second catheter 300 disposed in an artery A, the first and second catheters 100 , 300 being advanced to a treatment site where a fistula is to be formed .

Firstly, the first catheter 100 is introduced into a vein V of a patient through an access site and advanced along guidewire 115 towards the treatment site in a first direction dl . The first direction dl may be a proximal direction with respect to the body of the patient . To facilitate introduction into and advancement of the first catheter 100 along vein V, the electrode 130 of the first catheter 100 may be in the radially contracted configuration . The first catheter 100 may be introduced into the vein V and advanced to the treatment site inside a sheath (not shown) . A second access site is formed in the artery A to allow introduction of the guidewire 315 and the second catheter 300 into the artery A. The guidewire 315 may be introduced first through the access site into artery A and advanced to the treatment site in second direction d2 . The second direction d2 may be a distal direction with respect to the body of the patient . Once the guidewire 315 is positioned at the treatment site , the second catheter 300 may be introduced into the artery A and advanced to the treatment site by advancing it along the guidewire 315 . To that end, the proximal end of the guidewire 315 is inserted into the guidewire lumen 361 through distal opening 326 and exits the guidewire lumen through opening 321 . The catheter 300 can then be advanced in direction d2 to track the guidewire 315 through the artery A to the treatment site .

Due to the shortened length of the guidewire lumen 361 compared to an over-the-wire catheter, the length of the guidewire 315 can be minimised . Furthermore , this allows a physician to easily and securely hold the guidewire 315 in place whilst introducing the catheter 300 .

Figure 3B shows a cross-sectional side view of the catheter system with the first catheter 100 in a second position inside the vein V at the treatment site . The second catheter 300 is also positioned at the treatment site in the artery A. Due to the reduced length of the second catheter 300 , and speci fically the reduced length between the backstop 320 and the distal end of catheter shaft 310 , the backstop 320 can be positioned closer to blockage B such that the fistula can be formed closer to blockage B . The proximal set of magnets 140 of the first catheter 100 may be aligned with the distal set of magnets 350 of the second catheter 300 . The distal set of magnets 150 of the first catheter 100 may be aligned with the proximal set of magnets 340 of the second catheter 300 . This results in the convex-shaped electrode 130 becoming aligned with the complimentary concave-shaped electrode engagement surface 330 . The magnets may further have the ef fect of reducing the distance between the vein V and artery A and compressing the vessel walls of the vein V and artery A between the fistula- forming electrode 130 and backstop 320 .

The electrode 130 is moved from the radially contracted configuration to the radially expanded configuration . In the radially expanded configuration, the electrode 130 extends from the electrode housing 120 and comes into contact with the venous wall . The user may then press toggle switch button 181 on handle 170 or otherwise activate the electrode 130 .

Thereafter, a radiofrequency (RF) current , for example , may be supplied to the electrode 130 through electrode connecting element 131 , which causes the electrode 130 to heat up and generate a plasma . The plasma causes rapid dissociation o f the molecular bonds in the organic compounds and allows the electrode 130 to cut through the walls of the vein V and artery A until it reaches the electrode engagement surface 330 , thereby creating a fistula connecting vein V to artery A. The first and second catheters 100 , 300 may then be withdrawn from the vein V and artery A, respectively .

Figure 3C is a cross-sectional view of the vein V and artery A after the first and second catheter 100 , 300 have been withdrawn . Figure 3C shows a fistula which has been formed between the vein V and artery A, proximal of the blockage B . Blood may therefore flow in the direction of the arrows d3 , d4 and d5 , from the artery A through the fistula, into the vein V, and in a retrograde direction through vein V .

When performing a deep vein arteriali zation ( DVA) procedure , a stent may be placed within the fistula to stabilise the fistula . When performing an endovascular bypass procedure , a second fistula may be formed distally of the blockage B in a similar manner as explained with respect to Figure 3B above . A stent graft may then be placed through the first and second fistulas via the vein V, such that the blood flow can circumvent the blockage B .

Figure 4 shows an alternative embodiment of a backstop 420 . The backstop 420 is similar to backstop 320 of Figures 2B-2C in that it may include proximal and distal protuberances 431 and 432 on either side of an electrode engagement surface 430 which may form a convex recessed portion . Backstop 430 may also comprise an opening 421 and a through-hole 423 forming a guidewire lumen for accommodating a guidewire 315 . However, backstop 420 di f fers from backstop 320 in that it does not have a second recessed portion opposite the electrode engagement surface 430 . Rather, the opening 421 is a lateral opening, i . e . opening in a radial and not axial direction, which is positioned on the backstop 420 on the opposite side to the electrode engagement surface 430 . The through-hole 423 of backstop 420 has a curved longitudinal profile , such that guidewire 315 can move smoothly through the through-hole 423 without catching on any edges of the through-hole . The lack of a second recessed portion may also improve the structural integrity of the backstop 420 .

The backstop 420 may be used as part of second catheter 300 in a system to form a fistula . The method of using the backstop 420 as part of second catheter 300 to form a fistula is the same as described above with respect to Figures 3A-3C .

Figure 5 shows an alternative embodiment of a backstop 520 . The backstop 520 is similar to backstop 420 of Figure 4 in that it may include proximal and distal protuberances 531 and 532 on either side of an electrode engagement surface 530 which may form a convex recessed portion . Backstop 530 also may include an opening 521 and a through-hole forming a guidewire lumen for accommodating a guidewire 315 . However, backstop 520 di f fers in that the through-hole comprises a proximal portion 523 and a distal portion 524 , positioned at an angle relative to each other . The angle may range from 120 to 170 degrees . In this embodiment , the distal portion 523 of the through hole is aligned with a longitudinal axis of the backstop 520 . The backstop 520 may be easier to manufacture as it does not require the formation of a curved through- hole . Furthermore , the lack of a second recessed portion may also improve the structural integrity of the backstop 520 .

The backstop 520 may be used as part of second catheter 300 in a system to form a fistula . The method of using the backstop 520 as part of second catheter 300 in order to form a fistula is the same as described above with respect to Figures 3A-3C .

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

The second recessed portion 322 is not limited to a V-shaped part 324 and an elongated part 325 but can take any other suitable shape . For example , the second recessed portion 322 may comprise a rectangular part , a hemispherical part , a V- shaped part or any combination thereof .

The opening 321 may be positioned at any suitable location within the second recessed portions 322 .

The second recessed portion 322 may be positioned distally, proximally or at the same longitudinal position as the electrode engagement portion 330 .

The opening 321 , 421 , 521 may be positioned distally, proximally or at the same longitudinal position as the electrode engagement surface 330 , 430 , 530 .

The backstop may not have a second recessed portion 322 .

The through-hole 323 , 423 and 523 may take any suitable geometry which allows the guidewire to exit via an opening in the backstop. For example, the through-hole may be straight or curved, and may be longitudinally positioned or angled with respect to the longitudinal axis.

The electrode-engagement surface 330, 430, 540 of the backstop 320, 420, 520 is not limited to having a concave portion and is not limited to having a shape that is complimentary to the electrode 130. The backstop 230 may have any suitable shape, such as a protruding or recessed rectangular shape, or a protruding convex shape, for example.

The backstop 320, 420, 520 may not have any protuberances 331, 332, 431, 432, 531, 532.

The electrode 130 is not limited to having a convex shape but may take any other suitable shape such as a triangular or rectangular shape. The electrode 130 is further not limited to being a ribbon wire but may be a wire having any other suitable shape, such as a circular, oval or square wire.

The electrode 130 may be made from any suitable material which can conduct an electric current. The electrode 130 may not have a radially contracted and a radially expanded configuration. Rather, the first electrode may only have one fixed configuration.

The first catheter 100 may not comprise a rapid exchange tip 160. The first catheter 100 may not be connected to a handle 170.

The electrode housing 120 and the backstop 230, 330, 430, 530 are not limited to being made from ceramic materials. They can be made from any suitable materials which can withstand the heat and plasma generated by the electrode 130. For example, the electrode housing 120 and the backstop 230, 330, 420, 530 may be made from heat-resistant polymers such as polyimide or PEEK. The electrode 130 may be powered by means other than a generator and other than with RF energy . For example , the electrode may be supplied with AC or DC current to heat up the electrode 130 .

The first and second catheters 100 , 300 may not comprise any magnets . The alignment of the first and second catheters 100 , 300 may be achieved through other means such as by fluoroscopy or with sensors embedded in the catheter shaft 110 , 310 , for example .

The handle 170 may not comprise a braided catheter portion 171 . The handle 170 may further not comprise a toggle switch 180 or toggle switch button 181 . Another mechanism may be used to activate the electrode 130 , for example , a button, a slider or a touch screen interface .

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 .

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

1 . A catheter for use in a system for forming a fistula between two vessels comprising : a catheter shaft having a longitudinal axis ; a backstop coupled to the catheter shaft and having an electrode engagement surface for receiving a fistulaforming electrode ; and a guidewire lumen extending from a distal end of the catheter to an opening in the backstop .

2 . The catheter of claim 1 , wherein the backstop comprises a through-hole forming part of the guidewire lumen, the through-hole ending in the opening .

3 . The catheter of claim 1 or 2 , wherein the backstop has a recessed portion positioned on the opposite side of the backstop from the electrode engagement surface .

4 . The catheter of claim 3 , wherein the opening is positioned in the recessed portion .

5 . The catheter of claim 3 or 4 , wherein the recessed portion comprises a substantially V-shaped part .

6 . The catheter of claim 5 , wherein the substantially V- shaped part has a first surface and a second surface , wherein the first surface is positioned substantially perpendicular to the longitudinal axis of the catheter and the second surface is positioned at an angle of between 45 to 80 degrees from the first surface .

7 . The catheter of claim 5 or 6 , wherein the recessed portion further comprises a longitudinally elongated part positioned proximally of the substantially V-shaped part .

8 . The catheter of claim 7 , wherein the elongated part of the recessed portion has a longitudinal surface which is substantially longitudinally arranged and proximally adj acent the second surface of the V-shaped part .

9 . The catheter of any of claims 2 to 8 , wherein the through-hole is straight and extends longitudinally .

10 . The catheter of claim 2 , wherein the opening is a lateral opening in the backstop .

11 . The catheter of claim 10 , wherein the lateral opening is positioned on the opposite side of the backstop from the electrode engagement surface .

12 . The catheter of claim 10 or 11 , wherein the through-hole has a curved longitudinal profile .

13 . The catheter of any of claims 10 or 11 , wherein the through-hole comprises a proximal portion and a distal portion, and wherein the proximal portion and the distal portion are positioned at an angle relative to each other .

14 . The catheter of claim 13 , wherein the distal portion of the through hole is aligned with a longitudinal axis of the catheter .

15 . The catheter of claim 13 or 14 , wherein the proximal portion is positioned at an angle of 10 to 60 degrees relative to the distal portion .

16 . The catheter of any preceding claim, wherein the backstop is a non-conductive backstop .

17 . The catheter of any preceding claim, wherein the backstop is , at least partially, made from a ceramic material .

18. The catheter of any preceding claim, wherein the electrode engagement surface comprises a recessed portion.

19. The catheter of claim 18, wherein the recessed portion has a concave shape.

20. The catheter of claim 18 or 19, wherein the backstop further comprises protrusions on either side of the recessed portion .

21. The catheter of any preceding claim, further comprising a distal set of magnets, disposed distally of the backstop.

22. The catheter of claim 21, wherein the distal set of magnets comprise a through-hole forming part of the guidewire lumen .

23. The catheter of any preceding claim, further comprising a proximal set of magnets, disposed proximally of the backstop .

24. A system for forming a fistula, the system comprising: a first catheter according to any preceding claim; and a second catheter comprising a housing and a fistulaforming electrode extending radially from the housing.

25. The system of claim 24, wherein the fistula-forming electrode is disposed at least partially within the housing.

26. The system of claim 24 or 25, wherein the fistulaforming electrode has a convex shaped portion.

27. The system of any of claims 24 to 26, wherein the fistula-forming electrode comprises a ribbon wire.

28. The system of any of claims 24 to 27, further comprising a distal set of magnets disposed on the second catheter, distally of the housing.

29. The system of any of claims 24 to 28, further comprising a proximal set of magnets disposed on the second catheter, proximally of the housing.

30. The system of any of claims 24 to 29, wherein the housing is, at least partly made from a ceramic material.

31. The system of any of claims 24 to 30, further comprising an RF energy generator for supplying energy to the fistulaforming electrode.