Patent Description:
A fistula is generally 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 hemodialysis patients. Specifically, 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 effective hemodialysis. Generally, fistula formation requires the surgical dissection of a target vein, transecting and moving the vein for surgical anastomosis to the artery. These fistulas typically have a primary failure rate (failure before the patient receives dialysis) of about <NUM>-<NUM>%, and take between <NUM> and <NUM> months (e.g., <NUM>-<NUM> weeks) before the fistula is usable for dialysis. It may be useful to find improved ways to form a fistula between two blood vessels.

<CIT> discloses a system for creating fistula between two blood vessels of a patient comprising a first catheter and a second catheter, which comprise one or more fistula-forming elements. The first and second catheters comprise one or more magnets, which may be used to assist in bringing the first and catheters in closer proximity to facilitate fistula formation.

In one embodiment, a system for forming a fistula includes a first catheter configured to be advanced through a first vessel, a second catheter configured to be advanced through a second vessel, one or more magnetic field sensors, a user output device configured to output a ready signal, and a control unit communicatively coupled to the one or more magnetic field sensors and the user output device. The first catheter includes one or more first catheter magnetic elements and a fistula-forming element. The second catheter includes one or more second catheter magnetic elements. The one or more first catheter magnetic elements and the one or more second catheter magnetic elements are configured to draw the first catheter and the second catheter together. The one or more magnetic field sensors are configured to output a magnetic field signal indicative of a magnitude of a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements. The control unit is configured to receive the magnetic field signal from the one or more magnetic field sensors, determine a distance of separation of the first catheter from the second catheter based the magnetic field signal from the one or more magnetic field sensors, and output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element.

In another embodiment, a system for forming a fistula includes a first catheter configured to be advanced through a first vessel, a second catheter configured to be advanced through a second vessel, a probe configured to be positioned external to a treatment site, a user output device configured to output a ready signal, and control unit communicatively coupled to the one or more magnetic field sensors and the user output device. The first catheter included one or more first catheter magnetic elements and a fistula-forming element. The second catheter includes one or more second catheter magnetic elements. The one or more first catheter magnetic elements and the one or more second catheter magnetic elements are configured to draw the first catheter and the second catheter together. The probe is configured to be positioned external to a treatment site and includes one or more magnetic field sensors configured to output a magnetic field signal indicative of a magnitude of a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements. The control unit is configured to receive the magnetic field signal from the one or more magnetic field sensors, determine a distance of separation of the first catheter from the second catheter based the magnetic field signal from the one or more magnetic field sensors, and output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element.

In yet another embodiment, a method for forming a fistula includes advancing a first catheter through a first vessel, wherein the first catheter comprises one or more first catheter magnetic elements and a fistula-forming element, advancing a second catheter through a second vessel, wherein the second catheter comprises one or more second catheter magnetic elements, aligning the one or more first catheter magnetic elements with the one or more second catheter magnetic elements, detecting a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements with one or more magnetic field sensors, determining a distance of separation of the first catheter from the second catheter based on a magnetic field signal from the one or more magnetic field sensors, generating a ready signal with user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter, and forming the fistula with the fistula-forming element in response to the ready signal.

Embodiments provided herein are directed to systems and methods for forming a fistula. Systems according to the present disclosure generally include a first catheter configured to be advanced through a first vessel and a second catheter configured to be advanced through a second vessel. At least one of the first catheter and the second catheter includes a fistula-forming element, such as an electrode. Additionally, the first and second catheters include one or more magnetic elements configured to draw the first catheter and the second catheter toward one another. By drawing the first and second catheters together tissue of the first and second vessels may become impinged therebetween and operation of the fistula-forming element may be used to form an opening (i.e., a fistula) between the first vessel and the second vessel. However, ensuring proper alignment and distance of the first catheter and the second catheter relative to one another may be challenging. For example, fluoroscopy may be used to indicate positions of the first and second catheters. However, fluoroscopy provides visual feedback in a <NUM>-dimensional plane, which may make it difficult to ensure proper <NUM>-dimensional alignment.

The present concept is directed to using one or more magnetic field sensors that detect the magnetic field produced between the magnetic elements of the first and second catheters. Based on the detected magnetic field, a control unit may determine distance and/or alignment of the first and second catheters. When the appropriate distance and alignment has been reached, a signal may be output by the control unit, which alerts an operator that the first and second catheters are correctly positioned for fistula formation. In some embodiments, the control unit may be operable to prevent operation and/or activation of the fistula-forming element when the control unit determines that the first and second catheters are not positioned within an appropriate distance of one another or otherwise improperly aligned. Various embodiments of the testing device and the operation of the testing device will be described in more detail herein.

Any suitable catheter or catheters may be used to form fistulas using the methods and/or systems described here. The systems and methods described herein may use one or more of the devices as described in <CIT>, entitled "DEVICES AND METHODS FOR FORMING A FISTULA," <CIT> (published as <CIT>, entitled "DEVICES AND METHODS FOR FORMING A FISTULA," <CIT> (published as <CIT>, entitled "FISTULA FORMATION DEVICES AND METHODS THEREFOR," <CIT> (published as <CIT>, entitled "Fistula Formation Devises and Methods Therefor," <CIT> (published as <CIT>, entitled "DEVICES AND METHODS FOR FORMING A FISTULA," and <CIT> (published as <CIT>, entitled "SYSTEMS AND METHODS FOR ADHERING VESSELS".

In some variations, a fistula may be formed using a first catheter placed in a first vessel (e.g., an artery) and a second catheter placed in a second vessel (e.g., a vein). <FIG> illustrates one variation of a system <NUM> that may be used to form a fistula between the first vessel and the second vessel. As shown there, system <NUM> includes a first catheter <NUM> and a second catheter <NUM>. The first catheter <NUM> includes a catheter body <NUM> and a fistula-forming element <NUM>. The fistula-forming element <NUM> may be advanced or biased out of an opening <NUM> in the catheter body <NUM>. For example, the fistula-forming element <NUM> may be positioned proximal to a tip <NUM> of the first catheter <NUM> and may be extendable from a sidewall <NUM> of the first catheter <NUM> of the catheter body <NUM>. In other embodiments, the fistula-forming element <NUM> may not be moveable relative to the catheter body <NUM>.

The fistula-forming element <NUM> may be any device operable to form an opening between a first vessel (e.g., a vein) and a second vessel (e.g., an artery). For example, the fistula-forming element <NUM> may be any cutting, puncturing, and/or ablating device, such as a knife, needle, and/or an electrode. In the illustrated embodiment, the fistula-forming element <NUM> includes an electrode <NUM>. Current may be passed through the electrode <NUM> to ablate or otherwise remove tissue contacted by the electrode <NUM>. In some variations, the first catheter <NUM> may have an insulated housing <NUM> (e.g., a ceramic housing or the like) within the catheter body <NUM>, which may help protect other components of the first catheter <NUM> from heat that may be generated by the electrode <NUM> during tissue removal/ablation. In embodiments, the electrode <NUM> may be selectively moved from a position in which the electrode <NUM> is retained or otherwise held within the catheter body <NUM> to a position in which the electrode <NUM> extends away from a sidewall <NUM> of the catheter body <NUM> (such as shown in <FIG>). The electrode <NUM> may also be selectively moved back to a retracted/low-profile position (either the same or a different position as the previous retracted position) following ablation of tissue. In some variations, the electrode <NUM> may be biased toward an extended position when not otherwise restrained by the catheter body <NUM>.

While a fistula-forming element <NUM> including an electrode <NUM> is shown in <FIG>, it should be appreciated that the embodiments may include a catheter having any suitable fistula-forming element <NUM> (e.g., one or more electrodes/electrocautery mechanisms, one or more mechanical cutting mechanisms such as blades, lances, needles, or the like, one or more chemical devices, cryogenic-cautery devices, laser ablation devices, combinations thereof and the like), such as those described in more detail in <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), and <CIT> (published as <CIT>).

The second catheter <NUM> may have any suitable elements or combination of elements to aid in forming a fistula between it and the first catheter <NUM>. For example, the second catheter <NUM> may comprise a catheter body <NUM> having a recess <NUM> extending therein. The recess <NUM> may be coated by an insulating material (not shown), which may act as a backstop to receive and contact the electrode <NUM> (or other fistula-forming element <NUM>) of the first catheter <NUM> without damaging one or more components of the second catheter <NUM>. Additionally or alternatively, the second catheter <NUM> may include one or more fistula-forming elements, which may be the same as or different from the fistula-forming element of the first catheter <NUM>.

Each of the first and second catheters <NUM>, <NUM> includes one or more alignment elements, which may help to position catheters within the vasculature. The one or more alignment elements help to bring two catheters (and with them, associated blood vessels) in closer approximation so that a fistula may be formed between associated blood vessels. Additionally or alternatively, the one or more alignment elements may be used to position the one or more catheters in a specific rotational configuration relative to the blood vessels and/or the other catheters. Additionally or alternatively, the one or more alignment elements may be used to position one or more catheters axially within a blood vessel or blood vessels. For example, the one or more alignment elements may be configured to position a fistula-forming element <NUM> of a catheter relative with the first vessel and the second vessel such that activation of the fistula-forming element <NUM> directs fistula formation between the two vessels.

The one or more alignment elements may include one or more magnetic elements (e.g., magnetic elements <NUM> and/or <NUM>). Examples of magnet arrangements for use with the catheters described here may be found in <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), <CIT> (published as <CIT>), and <CIT> (published as <CIT>). These magnetic alignment elements may be attracted to one or more additional elements (e.g., one or more portions of a second catheter <NUM>, one or more magnets or other components placed externally from the body) to help position or align the catheter within a vessel. For example, one or more magnets placed outside of the body may interact with the magnetic alignment components of a catheter to help facilitate advancement of the catheter through the vasculature. Additionally or alternatively, one or more magnetic elements of a first catheter <NUM> may interact with one or more magnetic elements of a second catheter <NUM> to attract the first and second catheters <NUM>, <NUM> toward each other, and/or to bias the first and second catheters <NUM>, <NUM> toward a specific rotational and/or axial alignment.

For example, in the variation of system <NUM> shown in <FIG>, the first catheter <NUM> includes one or more first catheter magnetic elements <NUM> and the second catheter <NUM> includes one or more second catheter magnetic elements <NUM>. These magnetic elements <NUM>, <NUM> may be configured to bias the axial positioning of the first and second catheters <NUM>, <NUM> such that the opening <NUM> of the first catheter <NUM> axially aligns with the recess <NUM> of the second catheter <NUM>. The magnetic elements <NUM>, <NUM> may also be configured to bias the rotational positioning of the first and second catheters <NUM>, <NUM> such that the opening <NUM> of the first catheter <NUM> faces toward the recess <NUM> of the second catheter <NUM>. Accordingly, the one or more magnetic elements <NUM>, <NUM> may be used to help position the first and second catheters <NUM>, <NUM> within respective vessels (e.g., arteries/veins) such that the electrode <NUM> may extend from the opening <NUM> toward recess <NUM> of the second catheter <NUM> during fistula formation.

The one or more first catheter magnetic elements <NUM> may include one or more magnets or magnetic arrays positioned distal and/or proximal to the fistula-forming element <NUM>. For example, the one or more first catheter magnetic elements <NUM> may be positioned both proximal and distal to the fistula-forming element <NUM>, such that there are one or more magnets or magnetic arrays positioned on either side of the fistula-forming element <NUM>. Similarly, the one or more second catheter magnetic elements <NUM> may include one or more magnets or magnetic arrays positioned distal and/or proximal to the recess <NUM>. For example, the one or more second catheter magnetic elements <NUM> may be positioned both proximal and distal to the recess <NUM> and correspond to the one or more first catheter magnetic elements <NUM>. The one or more first catheter magnetic elements <NUM> and the one or more second catheter magnetic elements <NUM> may include temporary magnets, permanent magnets, and/or electromagnets.

In some embodiments, the first and/or second catheters <NUM>, <NUM> may include one or more markers <NUM> for visualizing advancement and positioning thereof. In some variations, the marker <NUM> may be directly visualized. In other variations, the marker may be indirectly visualized (e.g., via ultrasound, fluoroscopy and/or X-ray visualization). Markers <NUM> may be located anywhere relative to the catheter, e.g., one or more surfaces of the catheter, inside of the catheter. In some variations, one or more portions of the catheter may be made from an echogenic or radiographic material. A marker may be attached to a catheter by any suitable method, for example, by mechanical attachment (e.g., embedded in a portion of the catheter, circumferential circumscription, or the like), adhesive bonding, welding, soldering, combinations thereof or the like. For example, in the variation of system <NUM> shown above in <FIG>, each of the first and second catheters <NUM>, <NUM> may include one or more markers <NUM>. These markers <NUM> may be visualized during advancement and/or positioning of the first and second catheters <NUM>, <NUM> to confirm that the catheters are properly positioned within the blood vessels. For example, in variations where the opening <NUM> of the first catheter <NUM> is axially aligned with the recess <NUM> of the second catheter <NUM> and/or the opening <NUM> of the first catheter <NUM> is rotationally aligned relative to the recess <NUM> of the second catheter <NUM>, the one or more markers <NUM> may be used, through one or more visualizing techniques (e.g., ultrasound, fluoroscopy and/or X-ray), to confirm this positioning of the first and second catheters <NUM>, <NUM> with the first and second vessels, prior to formation of the fistula.

However, as noted above, such visualizing techniques may be subject to error. For example, though the first and second catheters <NUM>, <NUM> may appear aligned under <NUM>-dimensional fluoroscopy, the first and second catheters <NUM>, <NUM> may not be aligned in <NUM>-dimensional space. As will be described in greater detail below, instead of the one or more markers <NUM> and/or in addition to the one or more markers <NUM>, the system <NUM> includes one or more magnetic field sensors <NUM>, which may be used to determine alignment and/or positioning of the first and second catheters <NUM>, <NUM> relative to one another.

<FIG> schematically illustrates modules of the system <NUM> that may be communicatively coupled to one another over a communication path <NUM>. The system <NUM> generally includes a control unit <NUM>, the one or more magnetic field sensors <NUM>, and a user output device <NUM>. In yet further embodiments, the system <NUM> may further include a power source <NUM> and/or a safety device such as a locking mechanism <NUM>.

The various electronic components of the system <NUM> are communicatively coupled to one another over the communication path <NUM>. The communication path <NUM> may be a bus, which connects the various components of the system <NUM>. The communication path <NUM> may be formed from any medium that is capable of transmitting a signal such as, for example, conductive wires, conductive traces, optical waveguides, or the like. Moreover, the communication path <NUM> may be formed from a combination of mediums capable of transmitting signals. In some embodiments, the communication path <NUM> includes a combination of conductive traces, conductive wires, connectors, and buses that cooperate to permit the transmission of electrical data signals between the various components of the components such as processors, memories, sensors, input devices, output devices, and communication devices. Additionally, it is noted that the term "signal" means a waveform (e.g., electrical, optical, magnetic, mechanical or electromagnetic), such as DC, AC, sinusoidal-wave, triangular-wave, square-wave, vibration, and the like, capable of traveling through a medium.

The control unit <NUM> can be any type of computing device and includes one or more processors and one or more memory modules. The one or more processors may include any device capable of executing machine-readable instructions stored on a non-transitory computer-readable medium, such as those stored on the one or more memory modules. Accordingly, each of the one or more processors may include a controller, an integrated circuit, a microchip, a computer, and/or any other computing device.

The one or more memory modules of the control unit <NUM> are communicatively coupled to the one or more processors. The one or more memory modules may be configured as volatile and/or nonvolatile memory and, as such, may include random access memory (including SRAM, DRAM, and/or other types of RAM), flash memory, secure digital (SD) memory, registers, compact discs (CD), digital versatile discs (DVD), and/or other types of non-transitory computer-readable mediums. Depending on the particular embodiment, these non-transitory computer-readable mediums may reside within the control unit <NUM> and/or external to the control unit <NUM>. The one or more memory modules are configured to store logic (i.e., machine readable instructions) that, when executed by the one or more processors, allow the control unit <NUM> to determine a distance of separation of the first catheter <NUM> from the second catheter <NUM> and/or alignment of the first catheter <NUM> and the second catheter <NUM> and output a ready signal (e.g., with a user output device <NUM>) in response to determining that the distance of separation of the first catheter <NUM> from the second catheter <NUM> is within a predetermined threshold. In some embodiments, where the distance of separation is determined to be larger than the predetermined threshold (e.g., greater than about <NUM>, greater than about <NUM>, greater than about <NUM>, or other predetermined threshold distance) or the control unit <NUM> determines that the first and second catheters <NUM>, <NUM> are otherwise not in alignment, the logic executed by the one or more processors may prevent operation of the fistula-forming element <NUM>.

As noted above, the system <NUM> includes one or more magnetic field sensors <NUM>. The one or more magnetic field sensors <NUM> provide alignment information of the first catheter <NUM> and the second catheter <NUM> relative to one another. A magnetic field sensor <NUM> may include any device configured to output a magnetic field signal indicative of a magnitude of the magnetic field, e.g., the force of the magnetic field. Such magnetic field sensors <NUM> may include, but are not limited to Hall Effect sensors, magnetoresistive sensors, microelectromechanical systems (MEMs) magnetic field sensors <NUM>, superconducting quantum interference device (SQUID) sensors, or the like. <FIG> schematically illustrates magnetic field lines between a first catheter magnetic element <NUM> and a second catheter magnetic element <NUM>. As the first catheter magnetic element <NUM> moves closer to the second catheter magnetic element <NUM>, the force of the magnetic attraction between the first catheter magnetic element <NUM> and the second catheter magnetic element <NUM> increases. <FIG> graphically illustrates the logarithmic relationship between distance <NUM> on the x-axis and force <NUM> on the y-axis, as taught by Coulomb's law: <MAT> where F is force of attraction and r is the distance of separation between magnetic elements <NUM>, <NUM>. That is, force of attraction is inversely proportional to the square of the distance of separation. The magnetic field signal output by the one or more magnetic field sensors <NUM> provides a measurement indicative of the force of the magnetic attraction between magnetic elements <NUM>, <NUM>. In operation, the control unit <NUM> receives the magnetic field signal from the one or more magnetic field sensors <NUM>, and executes logic to determine the distance of separation of the first catheter <NUM> from the second catheter <NUM> using Coulomb's law, above. Once a predetermined distance of separation, A, is reached, the control unit <NUM> may provide a notification to an operator that the first and second catheter <NUM>, <NUM> are properly positioned.

Additionally, to provide increased attraction and alignment, the one or more first catheter magnetic elements <NUM> and the one or more second catheter magnetic elements <NUM> may be arranged with opposite poles facing one another. That is, for example, the one or more first catheter magnetic elements <NUM> may be arranged such that the north pole is aligned on the side of the catheter body <NUM> with the fistula-forming element <NUM> and the one or more second catheter magnetic elements <NUM> may be arranged such that the south pole is aligned on the side of the catheter body <NUM> with the recess <NUM> for receiving the fistula-forming element <NUM>, or vice versa. Accordingly, wherein the poles are not properly aligned for attraction, no magnetic field or a weaker magnetic field would be produced. Accordingly, the size of the magnetic field sensed based on the magnetic field signal may indicate both distance of the first catheter <NUM> from the second catheter <NUM> and alignment of the first catheter <NUM> and the second catheter <NUM>.

During fistula formation, the distance of separation between the first catheter <NUM> and the second catheter <NUM> should be within a predetermined threshold for fistula formation. For example, the predetermined threshold may be about <NUM> or less, such as about <NUM> or less, <NUM> or less, or the like. The predetermined threshold or distance is any distance at which forming a fistula with the fistula-forming element <NUM> is or has been shown to be possible. For example, such predetermined distance may allow the fistula-forming element <NUM> to fully extend through a wall of a first vessel and through a wall of a second vessel to contact the recess <NUM> of the second catheter <NUM>, thereby forming an opening between the first vessel and the second vessel. Accordingly, and as will be explained in greater detail below, when the control unit <NUM> determines that the distance of separation between the first catheter <NUM> and the second catheter <NUM> is, for example, <NUM> or less between the portion of the first catheter <NUM> including the fistula forming element <NUM> and the portion of the second catheter <NUM> including the recess <NUM>, than the control unit <NUM> determines that proper distance and alignment has been achieved between the first catheter <NUM> and the second catheter <NUM>.

The one or more magnetic field sensors <NUM> may be mounted to and/or within the catheter body <NUM> of the first catheter <NUM>, the second catheter <NUM> or both, as illustrated in <FIG>. In some embodiments, one or more magnetic field sensors <NUM> may be instead mounted to an external probe <NUM>, as illustrated in <FIG>.

In the embodiment illustrated in <FIG>, the one or more magnetic field sensors <NUM> may be integrated into the first and/or the second catheter <NUM>, <NUM>. That is, the one or more magnetic field sensors <NUM> are advanced through the one or more vessels with the first and/or second catheter <NUM>, <NUM>. The one or more magnetic field sensors <NUM> may be positioned proximal and/or distal to the one or more magnetic elements <NUM>, <NUM> of the first and/or the second catheter <NUM>, <NUM>. For example, a magnetic field sensor <NUM> may be mounted to the first catheter <NUM> distal (e.g., closer to the tip <NUM>) of the one or more first catheter magnetic elements <NUM> and/or the fistula-forming element <NUM>. In some embodiments, a magnetic field sensor <NUM> may be located proximal to the one or more first catheter magnetic elements <NUM> and the fistula-forming element <NUM>. In some embodiments, a first magnetic field sensor may be associated with a first magnetic element of the first catheter <NUM> and a second magnetic field sensor may be associated with a second magnetic element of the first catheter <NUM> on either side of the fistula-forming element <NUM>.

In some embodiments, a magnetic field sensor <NUM> may only be incorporated into one of the first catheter <NUM> and the second catheter <NUM>. For example, the second catheter <NUM> may include a magnetic field sensor <NUM> mounted to the catheter body <NUM> of the second catheter <NUM> distal and/or proximal of the one or more magnetic elements <NUM> of the second catheter <NUM> and the recess <NUM>. In some embodiments, each of the first catheter <NUM> and the second catheter <NUM> include one or more magnetic field sensors <NUM>. It is noted that additional magnetic field sensors may provide greater sensitivity to alignment and separation distance. The one or more magnetic field sensors <NUM> may be closely situated to the one or more first catheter magnetic elements <NUM> and/or the one or more second catheter magnetic elements <NUM> (e.g., spaced about <NUM> or less from the one or more magnetic elements).

As noted above, and with reference to <FIG>, the one or more magnetic field sensors <NUM>, in addition to and/or instead of any catheter-mounted magnetic field sensors <NUM>, may be mounted to an external probe <NUM>. The external probe <NUM> may be a handheld probe or may be mounted to a robotic arm or other fixture configured to hold the probe proximate to a treatment portion of a patient. For example, <FIG>, illustrates an arm <NUM> of a patient with a first catheter <NUM> positioned within a first vessel <NUM> (e.g., a vein) and a second catheter <NUM> positioned within a second vessel <NUM> (e.g., an artery). The first and second catheters <NUM>, <NUM> are substantially similar to that described above with respect to <FIG>. The first and second catheters <NUM>, <NUM> are advanced through the first and second vessels to a treatment site (e.g., where a fistula is to be formed). When the first and second catheters <NUM>, <NUM> are positioned at or approximately at the treatment site, the external probe <NUM> may be advanced toward the treatment site to detect the strength of the magnetic field between one or more first catheter magnetic elements <NUM> of the first catheter <NUM> and the one or more second catheter magnetic elements <NUM> of the second catheter <NUM>. For example, the external probe <NUM> may be advanced so as to be within a sensing range (e.g., within about <NUM> meters, within about <NUM> meters, with about <NUM> meters, etc.) of the one or more magnetic field sensors <NUM> of the external probe <NUM>. The one or more magnetic field sensors <NUM> whether internal or external may automatically begin detecting the magnetic attraction between the first and second catheters <NUM>, <NUM> when the first catheter magnetic elements <NUM> and the second catheter magnetic elements <NUM> begin attracting one another.

In some embodiments, the one or more magnetic elements <NUM> of the first and second catheters <NUM>, <NUM> may include electromagnets. In such embodiments, an external magnetic field generator, not shown may be used to excite the electromagnets. Additionally, the electromagnets of the first and second catheters <NUM>, <NUM> may be communicatively coupled to the control unit <NUM> and output electrical signals to the control unit indicative of their location in <NUM>-dimensional space within the magnetic field produced by the magnetic field generator. For example, each of the electrical signals may be indicative of a location of the electromagnet relative to the magnetic field generator. Based on this information, the control unit <NUM> may execute logic to determine the locations of the first and second catheters <NUM>, <NUM> relative to one another. Accordingly, the one or more magnetic elements <NUM> of the first and second catheters <NUM>, <NUM> may act as location sensors or magnetic field sensors <NUM>.

Referring again to <FIG>, the system <NUM> further includes a user output device <NUM> communicatively coupled to the control unit <NUM> over the communication path <NUM>. The user output device <NUM> may include any visual, tactile, or audible feedback device configured to output a ready signal when the control unit <NUM> determines, based on the magnetic field signal from the one or more magnetic field sensors <NUM>, that the first and second catheters <NUM>, <NUM> are within a proper distance and/or have proper alignment for fistula formation. For example, the user output device <NUM> may include a light indicator (e.g., a florescent light, an LED light, or the like) mounted to the external probe <NUM> or a handle of the first catheter <NUM> and/or the second catheter <NUM>. The light indicator may be turned on by the control unit <NUM> in response to detecting that the first and second catheters <NUM>, <NUM> are properly positioned relative to one another. In some embodiments, the light indicator may be a green light when it is determined that the first and second catheters <NUM>, <NUM> are properly positioned. In some embodiments, the light indicator, or a separate indicator light, may be a red light when it is determined that the first and second catheters <NUM>, <NUM> are not properly aligned. In some embodiments, an audible sound may be emitted from a speaker in response to achieving proper alignment.

In some embodiments, the system <NUM> may include a locking mechanism <NUM> that prevent activation of the fistula forming element <NUM> when it is determined that the first and second catheters <NUM>, <NUM> are improperly aligned (e.g., not within the predetermined separation range). For example, the locking mechanism <NUM> may be communicatively coupled to the control unit <NUM> over the communication path <NUM> so as to be operable by the control unit <NUM>. For example, the locking mechanism <NUM> may be a switch that electrically couples to fistula forming element <NUM> to a power source <NUM>. It may be that the locking mechanism <NUM> is positioned to prevent flow of energy from the power source <NUM> to the fistula-forming element <NUM> (e.g., an electrode <NUM>) in response to determining that the first and second catheters <NUM>, <NUM> are improperly aligned. In some embodiments, the locking mechanism <NUM> may be positioned to prevent flow of energy to from the power source <NUM> to the fistula-forming element <NUM> until the control unit <NUM> determines that the first and second catheters <NUM>, <NUM> are properly aligned. Other contemplated locking mechanisms may include, but are not limited to, magnetic locking mechanisms, relays, solenoids, interlock actuators, or the like.

In some embodiments, the power source <NUM> may be communicatively coupled to the control unit <NUM> such that the control unit <NUM> may selectively operate the power source <NUM> (e.g., a battery, an RF generator, an outlet, or the like). In such embodiments, the control unit <NUM> may be configured to prevent operation of the power source <NUM> from energizing the fistula-forming element <NUM> when it is determined that the first and second catheters <NUM>, <NUM> are not properly aligned.

A method of forming a fistula between a first vessel <NUM> and a second vessel <NUM> will now be described. With reference to <FIG>, the method includes advancing the first catheter <NUM> through the first vessel <NUM> to a treatment site and advancing the second catheter <NUM> through the second vessel <NUM> to the treatment site. As the one or more magnetic elements <NUM> of the first and second catheters <NUM>, <NUM> approach one another so as to be aligned within one another, the one or more or magnetic field sensors <NUM> (e.g., either internal or external magnetic field sensors <NUM>, may automatically begin detecting the magnetic field produced between the one or more first catheter magnetic elements <NUM> of the first catheter <NUM> and the one or more second catheter magnetic elements <NUM> of the second catheter <NUM>. The control unit <NUM> may receive the signal from the one or more magnetic field sensors <NUM> and execute logic to determine the distance of separation of the first catheter <NUM> from the second catheter <NUM> (e.g., the axial offset distance, D, of the one or more magnetic elements <NUM> of the first catheter <NUM> from the one or more magnetic elements <NUM> of the second catheter <NUM>). Once it is determined that the distance of separation of the first catheter <NUM> from the second catheter <NUM> is within a predetermined range (e.g., <NUM> or less) and/or the proper rotational alignment is achieved, the control unit <NUM> may generate a ready signal with the user output device <NUM>. At that point, the operator of the system <NUM> may form a fistula with the fistula-forming element <NUM> between the first and second vessels. For example, the operator may advance the electrode <NUM> or may cause energy to flow through the electrode <NUM> to ablate tissue of the first vessel <NUM> and the second vessel <NUM> impinged between the first catheter <NUM> and the second catheter <NUM>. As noted above, where it is determined that proper alignment and distance have not been achieved, the control unit <NUM> may operate a locking mechanism <NUM> or the power source <NUM> to prevent fistula formation until proper alignment is achieved.

In some embodiments, additional visual confirmation with fluoroscopy, ultrasound, or the like may be used.

It should now be understood that embodiments described herein are directed to using one or more magnetic field sensors that detect the magnetic field produced between the magnetic elements of the first and second catheters. Based on the detected magnetic field, a control unit may determine distance and/or alignment of the first and second catheters. When the appropriate distance and alignment has been reached, a signal may be output by the control unit, which alerts an operator that the first and second catheters are correctly positioned for fistula formation. In some embodiments, the control unit may be operable to prevent activation of the fistula-forming element where the control unit determines that the first and second catheters are not positioned within an appropriate distance of one another or otherwise improperly aligned. Such systems provided several clinical benefits including the use of less or no fluoroscopy, as magnetic sensing may provide confirmation to both separation distance and rotational alignment. The system also minimizes operator subjectivity when reading fluoroscopy, or other <NUM>-dimensional, images.

It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

Claim 1:
A system (<NUM>) for forming a fistula comprising:
a first catheter (<NUM>) configured to be advanced through a first vessel, the first catheter comprising one or more first catheter magnetic elements (<NUM>) and a fistula-forming element (<NUM>);
a second catheter (<NUM>) configured to be advanced through a second vessel, the second catheter comprising one or more second catheter magnetic elements (<NUM>), wherein the one or more first catheter magnetic elements and the one or more second catheter magnetic elements are configured to draw the first catheter and the second catheter together; characterised in that the system further comprises
one or more magnetic field sensors (<NUM>) configured to output a magnetic field signal indicative of a magnitude of a magnetic field produced between the one or more first catheter magnetic elements and the one or more second catheter magnetic elements;
a user output device (<NUM>) configured to output a ready signal; and
a controller communicatively coupled to the one or more magnetic field sensors and the user output device, wherein the controller is configured to:
receive the magnetic field signal from the one or more magnetic field sensors;
determine a distance of separation of the first catheter from the second catheter based on the magnetic field signal from the one or more magnetic field sensors; and
output the ready signal with the user output device in response to determining that the distance of separation of the first catheter from the second catheter is a predetermined distance or less, wherein the ready signal is indicative of proper alignment and position of the first catheter and the second catheter to form the fistula with the fistula-forming element.