Implant for competing blood vessel to promote fistula maturation and method thereof

Abstract

An implant is used in a competing vein of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula. The implant includes a blood flow restrictor configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location. The blood flow restrictor enables blood in the competing vein to flow therethrough, while reducing a volumetric blood flow rate as the blood flows therethrough. The blood flow restrictor is biodegradable in the competing vein so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the longitudinal orifice increases.

Description

Attorney Docket No. A0012679W001IMPLANT FOR COMPETING BLOOD VESSEL TO PROMOTE FISTULA MATURATION AND METHOD THEREOFFIELD

[0001] The present technology is generally related to an implant for use in a competing vein of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula.SUMMARY

[0002] An arteriovenous (AV) fistula is a connection made between an artery and vein to enable hemodialysis therapy in patients with end stage renal disease. FIG. 1 shows a drawing of a known AV fistula in a subject. The AV fistula must first be created using surgical or endovascular techniques, and then allowed to mature for a period of weeks. During this maturation period flow driven vascular remodeling leads to vein luminal growth and wall thickening, readying the vein for high volume flow capable of two needle cannulation and cycling of the blood through the dialysis machine.

[0003] Unfortunately, many AV fistulas fail to mature independently, with the vein remaining too small and thin walled to be usable for dialysis. Many reports estimate the rate of early fistula failure (in which the fistula never matures) is 30-40%. In these instances, a variety of interventions can be performed to promote maturation including angioplasty to dilate the vein and treat stenosis, surgical banding, and embolization to divert flow away from other outflow pathways and into the fistula.

[0004] One reason why the fistulas fail to mature is caused by a lack of sufficient flow through the fistula. Embolization to divert flow away from other outflow pathways (i.e., competing vein) and into the fistula helps maturation of the AV fistula. However, the known techniques render the competing vein(s) permanently unusable.SUMMARY

[0005] The techniques of this disclosure generally relate to an implant and a method of using the implant in a competing vein of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula. In particular, the implant enables a reducedAttorney Docket No. A0012679W001 volumetric blood flow through the competing vein and is at least partially biodegradable over time to enable restoration of volumetric blood flow.

[0006] In one aspect, the present disclosure provides an implant for use in a competing vein of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula. The implant comprises a blood flow restrictor to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location. The blood flow restrictor has opposite longitudinal ends and a length extending therebetween. The blood flow restrictor defines a longitudinal orifice extending along the length of the blood flow restrictor and through the opposite longitudinal ends to enable blood in the competing vein to flow therethrough. The longitudinal orifice is sized and shaped to reduce a volumetric blood flow rate as the blood flows therethrough. The blood flow restrictor is biodegradable in the competing vein to enlarge the longitudinal orifice so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the longitudinal orifice increases.

[0007] In another aspect, the disclosure provides an implant for use in a competing vein of primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula. The implant comprises a blood flow restrictor configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location. The blood flow restrictor having opposite longitudinal ends and a length extending therebetween. The blood flow restrictor enables blood in the competing vein to flow longitudinally therethrough at an initial reduced volumetric blood flow rate. An entirety of the blood flow restrictor is biodegradable in the competing vein so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the blood flow restrictor increases from the initial reduced volumetric blood flow rate to fully restore volumetric blood flow rate in the competing vein.

[0008] Methods of using the implant are also disclosed.

[0009] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims.Attorney Docket No. A0012679W001BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 shows a schematic illustration of an arteriovenous (AV) fistula.

[0011] FIG. 2 is a schematic illustration of an implant including a blood flow restrictor positioned within a competing vein.

[0012] FIG. 3 is a schematic illustration of a vascular system having an AV fistula and multiple competing veins.

[0013] FIG. 4 is similar to FIG. 3, but including the implants positioned within competing veins.

[0014] FIG. 5 is a schematic illustration of another embodiment of an implant including a blood flow resistor.

[0015] FIG. 6 is a schematic illustration of another embodiment of an implant including a blood flow resistor.

[0016] FIG. 7 is a schematic illustration of another embodiment of an implant including a blood flow resistor.

[0017] FIG. 8A-B is a schematic illustration of another embodiment of an implant including a blood flow resistor.

[0018] FIG. 9 is a schematic illustration of an implant delivery system including a catheter positioning an implant including a blood flow resistor in a competing vein.

[0019] FIG. 10 is a schematic illustration of a vascular system having an AV fistula and blood flow resistors positioned in a competing vein.

[0020] FIG. 11 is similar to FIG. 10, showing the vascular system after complete degradation of the blood flow resistors and full restoration of the competing veins.DETAILED DESCRIPTION

[0021] The present disclosure describes an implant and a method of using the implant in a competing vein (broadly, competing blood vessel) of a primary vein (broadly, main blood vessel) of an arteriovenous (AV) fistula (broadly, a blood vessel fistula) to promote maturation of the AV fistula.

[0022] Referring to FIG. 2, an embodiment of an implant for use in a competing vein of primary vein of an arteriovenous (AV) fistula to promote maturation of an AV fistula is generally indicated at reference numeral 10. In FIG. 2, the implant 10 is shown schematically implanted in the competing vein CV of a primary vein of the AV fistula.Attorney Docket No. A0012679W001Figure 3 is a schematic representation of a vasculature or vascular system including the competing vein CV (i.e., one or more competing veins), the AV fistula AVF, an artery A of the AV fistula, and the primary vein PV of the AV fistula. Figure 4 illustrates two of the implants 10 in two separate competing veins CV, although one implant may be used for one of the competing veins or more than two implants may be used for more than two competing veins. It is understood that broadly, the primary vein PV and the artery A may be broadly considered first and second blood vessels, the competing vein CV may be considered a competing blood vessel of the first blood vessel, and the AV fistula AVF may be considered a fistula of the first and second blood vessels. Accordingly, in one or more other embodiments, the implant 10 may be suitable for other types of blood vessel fistulas for promoting maturation of the fistula.

[0023] The implant 10 includes a biocompatible, biodegradable blood flow restrictor 12 sized and shaped to be delivered to a selected location of the competing vein CV, such as by using a delivery system described below. The blood flow restrictor 12 may be any size and shape that is suitable to be inserted into a subject's competing vein CV. In a suitable embodiment, at least a portion of the implant 10, for example the blood flow restrictor 12, is expandable in at least a radial or transverse direction from a collapsed configuration to an expanded configuration. In the collapsed configuration, the implant 10 is sized and shaped to be delivered to the competing vein through vasculature of the subject, such as by using a delivery catheter of the delivery system. Once at the implant site in the competing vein CV, the implant (e.g., the blood flow restrictor 12) is expanded to its expanded configuration. In one example, the implant 10 expands to a size and shape such that the implant 10 (e.g., blood flow restrictor 12) engages (e.g., sealingly engages) the wall of the competing vein. The implant 10 may seal against the wall of the competing vein CV to inhibit blood flow between the wall and the implant. The implant 10 may also include other components or structures, such as anchoring elements (e.g., biodegradable anchors) configured to facilitate anchoring the blood flow restrictor 12 to the wall of the competing vein. These additional components may also be biocompatible and biodegradable so that the entirety of the implant 10 is biodegradable in the competing vein CV over time.

[0024] Referring back to FIG. 2, in one example the blood flow restrictor 12 may have a generally cylindrical shape. The blood flow restrictor 12 has opposite longitudinal endsAttorney Docket No. A0012679W00114 and a length extending therebetween. In the illustrated embodiment, a cross-sectional dimension of the blood flow restrictor 12 may be generally uniform along its length, or may be non-uniform. For example, the blood flow restrictor 12 and / or one or both longitudinal ends 14 thereof may have a diameter that may be from about 1 to about 10 millimeters. The diameter or other cross-sectional dimension of the blood flow restrictor 12 and / or one or both longitudinal ends 14 thereof may be variable based on the size of the location of the competing vein CV, such that the size and shape of the blood flow restrictor and / or one or both longitudinal ends thereof may vary depending on the dimension of the competing vein CV. The length of the blood flow restrictor 12 may be any length that is suitable for the intended use, as described below. For example, the longitudinal length may be from about 2 millimeters to about 2 centimeters. In one or more other embodiments, the blood flow restrictor 12 may be configured generally as "one size fits all," so that a single size and shape of the blood flow restrictor 12 is suitable for various different sizes and shapes of competing veins CV.

[0025] The blood flow restrictor 12 defines a longitudinal orifice 18 (i.e., at least one longitudinal orifice) extending along the length and through the opposite longitudinal ends 14 of the blood flow restrictor 12. The orifice 18 enables blood in the competing vein CV to flow therethrough and is sized and shaped to reduce the volumetric flow rate (designated as Q) of blood as the blood flows through the orifice. For example, a CV having a volumetric blood flow from about 500 to about 1000 ml / min with no device may have a reduced volumetric blood flow from about 100 to about 200 ml / min with the presence of the blood flow restrictor, or may the volumetric flow rate may be reduced from about 60% to about 90%. The volume of the orifice 18 may be proportional to the volume of the blood flow restrictor 12 such that the orifice volume is between 20% to 80% the blood flow restrictor volume. The proportional volume of the orifice 18 may depend on the desired volumetric flow rate of the blood in the competing vein CV. For example, the defined orifice 18 having a volume that is 50% of the blood flow restrictor 12 volume will enable a greater volumetric blood flow compared to an orifice 18 having a volume that is 20% of the blood flow restrictor 12 volume.

[0026] The blood flow restrictor 12 of FIG. 2, more specifically a body or wall 17 of the restrictor, defines a single longitudinal orifice 18 with a cylinder shape (i.e., uniform dimension) extending along the length of the blood flow restrictor 12. In this embodiment,Attorney Docket No. A0012679W001 the openings through the longitudinal ends 14 may be the same size, as shown. In one or more other embodiments, the longitudinal orifice 18 may be non-uniform along its length. For example, referring to FIG. 5, the blood flow restrictor 12 may define a cone shaped orifice 18' along the length of the blood flow restrictor. The downstream longitudinal end 14 may be smaller than the upstream longitudinal end. The orifice 18, 18' may have other shapes. In these embodiments, the blood flow restrictors 12 may be generally non-porous other than the orifice 18, 18' such that the only flow of blood through the blood flow restrictor is through the orifice. Moreover, as also explained below, the implant 10 may be implanted in the competing vein CV such that blood does not flow between the vein wall and the implant 10, whereby substantially all of the blood flow is directed through the orifice 18 18' of the blood flow restrictor 12.

[0027] The blood flow restrictor 12 is biodegradable in the competing vein CV to enlarge the longitudinal orifice 18 so that as the blood flow restrictor 12 biodegrades in the competing vein CV over time, the volumetric blood flow rate through the longitudinal orifice 18 increases. The blood flow restrictor 12 may be made of biodegradable polymeric material such as PGA, PLGA, or any copolymers based on glycolic acid and other monomers such as lactic acids, e-caprolactone, trimethylcarbonate, or dioxanone, and any combinations thereof. The blood flow restrictor 12 may be made of polydyroxyalcanoates (PHAs) such as PH3B and PH4B, or any copolymers thereof or mixtures therefore. The blood flow restrictor 12 can also be produced by including biopolymers such as collagen, chitosan, hyaluronic acid, cellulose derivatives - notably bioresorbable ones -, and alginate - notably partially oxidized. These biopolymers are formulated in such a way as to provide a sufficient residence time to achieve a satisfactory degree of fistula maturation, particularly through chemical or physical cross-linking or structuring processes. The mentioned biopolymers can also be advantageously combined with the aforementioned resorbable polymers. Other suitable biocompatible, biodegradable materials may be used.

[0028] In one example, the entirety of the blood flow restrictor is biodegradable and made from the biodegradable material. Thus, the blood flow restrictor 12 may consist of or essentially consist of the biodegradable material. In such examples, the entirety of the blood flow restrictor 12 biodegrades over time to enable full restoration of the competing vein CV. In addition, any other components or structures of the implant 10 may also beAttorney Docket No. A0012679W001 biodegradable and configured to degrade over time like the blood flow restrictor to enable fully restoration of the competing vein CV.

[0029] The degradation rate of the blood flow restrictor 12 and / or implant 10 can be tunable to align with the typical maturation time period of the AV fistula of 4 to 6 weeks. For example, the blood flow restrictor 12 degradation rate may be adjusted by modifying the features of the polymer such as stereochemistry, crystallinity, porosity, and molecular weight. The porosity will enable compaction and deliverability through a catheter. The porosity can be adjusted to have the optimal balance between compaction (deliverability), flow reduction, and degradation rate.

[0030] Other similar embodiments of the blood flow restrictor 12 are shown in FIGS. 6-8B. Components and structures that are the same or similar to the prior blood flow restrictor are indicated by corresponding reference numerals. Unless indicated otherwise, the teachings and description of the blood flow restrictor 12 applies equally to the other blood flow restrictors, including the blood flow restrictors being biocompatible and biodegradable in the competing vein CV.

[0031] In FIG. 6, another embodiment of a blood flow restrictor is indicated at reference numeral 112. Unlike the blood flow restrictor 12, the wall 17 of the blood flow restrictor 112 defines pores 20 in addition to the longitudinal orifice 18, making the wall of the blood flow restrictor porous. The pores 20 extend from the upstream longitudinal end 14 to the downstream longitudinal end to enable blood flow longitudinally through the blood flow restrictor. The pores 20 may be in fluid communication with the longitudinal orifice 18 or may be free from communication, at least initially. The pores provide additional or supplemental blood flow through the blood flow restrictor 112, which may increase the volumetric blood flow compared to the prior blood flow restrictor 12 that did not include pores and only enabled blood flow through the longitudinal orifice.

[0032] Referring to FIG. 7, another embodiment of a blood flow restrictor is indicated at reference numeral 212. In this embodiment, the blood flow restrictor does not define a longitudinal orifice. Instead, the wall 17 of the blood flow restrictor 112 defines pores 20 extending from the upstream longitudinal end 14 to the downstream longitudinal end to enable blood flow longitudinally through the blood flow restrictor. The pores provide the primary or only volumetric blood flow through the blood flow restrictor. As the blood flowAttorney Docket No. A0012679W001 restrictor 212 biodegrades, the sizes of the pores increase and therefore the volumetric flow through the pores increases.

[0033] Referring to FIGS. 8A-8B, another embodiment of a blood flow restrictor is indicated at reference numeral 312. In this embodiment, the blood flow restrictor is made of a flowable biodegradable slurry that solidifies when positioned within the competing vein CV. Referring to FIG. 8A, the slurry is positioned within the competing vein CV by use of, for example, a balloon backstop 37. Other suitable forms of positioning may be used. Referring to FIG. 8B, once positioned within the competing vein CV, the slurry solidifies forming the blood flow restrictor 312.

[0034] A method of promoting maturation of an arteriovenous (AV) fistula or another blood vessel fistula using any of the biodegradable blood flow restrictors 12, 112, 212 312 will now be described. The method comprises evaluating the maturity of the AV fistula AVF. FIG. 3 shows a schematic drawing of an AV fistula AVF wherein an artery A and a vein V are connected via the AV fistula AVF allowing blood to flow through the AV fistula AVF. The AV fistula AVF may be created by any suitable method. The disclosed method may be conducted on side-to-side, end-to-end, or end-to-side AV fistulas.

[0035] The maturity of the AV fistula AVF may be evaluated collecting and analyzing any suitable date or information including, but not limited to, determining the size of the primary vein PV, determining the blood flow rate within the primary vein PV, and characterizing a magnitude of a thrill produce by the existing AV fistula AVF. The primary vein PV is the vein where the primary outflow path is located. The evaluation may be conducted using any suitable techniques including, but no limited to, ultrasound, venography, or analyzing a fistulagram. The suitable time of evaluation is after the creation of the AV fistula AVF. For example, the evaluation may take place between about 1 week to about 4 weeks after the creation of the AV fistula.

[0036] The method further comprises selecting a competing vein in fluid communication with the primary vein. The method may also comprise determining the volumetric blood flow rate in the competing vein(s) CV.

[0037] In response to the evaluation of the maturity of the AV fistula AVF, one of the implants including one of the blood flow restrictors 12, 112, 212, 312 described above is selected to be delivered to the competing vein CV. For example, in some embodiments, the determination may be that increasing the volumetric blood flow through the primary veinAttorney Docket No. A0012679W001PV will accelerate the maturity of the AV fistula AVF. For example, the volumetric blood flow through the primary vein PV may be less than about 600 ml per minute, 500 ml per minute, or 400 ml per minute. In other embodiment, the determination may be that increasing the primary vein PV size will promote AV fistula AVF maturity. For example, the diameter of the primary vein PV is desired to be at least 4 mm, at least 5 mm, or at least 6 mm.

[0038] Reference is made to FIG. 4 showing the implant 10 and associated blood flow restrictor 12 for ease of description and explanation, with the understanding that the method may be similar to identical when using the other embodiments of the implants and blood flow restrictors. The implant 10 is positioned within the selected competing vein CV. The blood flow restrictor 12 of the implant 10 size and the orifice volume is selected based on the evaluation of the AV fistula AVF maturity, the desired blood flow in the primary vein PV, and the desired blood flow reduction in the competing vein(s) CV. The blood flow restrictor 12 is selected such that the reduced blood flow in the competing vein CV is no less than 100 ml per minute, at least 200 ml per minute, or at least 300 ml per minute. Maintaining blood flow through the competing vein(s) CV will prevent the veins being rendered unusable in the future.

[0039] Another aspect of the disclosed method is delivering the blood flow restrictor 12 to the competing vein. The blood flow restrictor 12 may be delivered to the competing vein CV though any suitable technique. For example, in some embodiments, the delivery is conducted using a delivery system including a catheter. Referring to FIG. 9, shows a schematic drawing of a catheter 35 delivering the implant 10 to a competing vein CV.

[0040] When the implant 10 is placed in the competing vein CV, the blood is diverted to the primary vein PV. This results in the primary vein PV experiencing an increased volumetric blood flow and the primary vein grows in size. The implant 10 and / or blood flow restrictor 12 is biodegradable (e.g., entirely biodegradable) so that the blood flow restrictor biodegrades in the competing vein over time and the volumetric blood flow rate through the longitudinal orifice increases. Simultaneously, the primary vein grows in size, the AV fistula matures, and the blood flow restrictor(s) biodegrade.

[0041] Referring to FIG. 10, the primary vein PV is larger and the blood flow restrictors 12 are partially degraded. In some embodiments, the blood flow restrictor 12 is entirely biodegradable such that the blood flow in the competing vein is completelyAttorney Docket No. A0012679W001 restored. The degradation rate of the blood flow restrictor 12 can be tunable to align with the typical maturation time period, for example, of about 4 to 6 weeks. Referring to FIG.11, the blood flow restrictors 12 are completely degraded and the volumetric blood flow in the competing veins CV is no longer restricted.

[0042] From the foregoing it will be seen that this invention is one well adapted to attain all ends and objectives herein-above set forth, together with the other advantages which are obvious and which are inherent to the invention.

[0043] Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matters herein set forth OPT or shown in the accompanying drawings are to be interpreted as illustrative, and not in a limiting sense.

[0044] The invention may be further described by reference to the following numbered paragraphs:1. An implant for use in a competing vein of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula, the implant comprising: a blood flow restrictor configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location, the blood flow restrictor having opposite longitudinal ends and a length extending therebetween, wherein the blood flow restrictor defines a longitudinal orifice extending along the length of the blood flow restrictor and through the opposite longitudinal ends to enable blood in the competing vein to flow therethrough, wherein the longitudinal orifice is sized and shaped to reduce a volumetric blood flow rate as the blood flows therethrough, wherein the blood flow restrictor is configured to be biodegradable in the competing vein to enlarge the longitudinal orifice so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the longitudinal orifice increases.2. The implant set forth in paragraph 1, wherein an entirety of the blood flow restrictor is biodegradable in the competing vein.3. The implant set forth in any one of paragraphs 1 or 2, wherein the blood flow restrictor consists of biodegradable material.Attorney Docket No. A0012679W0014. The implant set forth in any one of paragraphs 1-3, wherein the blood flow restrictor is configured to gradually biodegrade in the competing vein over a period of 4 to 6 weeks.5. The implant set forth in any one of paragraphs 1-4, wherein the blood flow restrictor is configurable between a collapsed configuration, to enable delivery of the implant to the competing vein, and an expanded configuration, to enable the implant to sealingly engage a wall of the competing vein.6. The implant set forth in any one of paragraphs 1-5, wherein the longitudinal orifice consists of a single longitudinal orifice.7. The implant set forth in any one of paragraphs 1-5, wherein the longitudinal orifice comprises a plurality of longitudinal orifices.8. The implant set forth in any one of paragraphs 1-7, wherein the blood flow restrictor includes a porous wall defining a plurality of pores enabling blood flow through the porous wall through the longitudinal ends.9 The implant set forth in any one of paragraphs 1-7, wherein the blood flow restrictor includes a non-porous wall inhibiting blood flow through the non-porous wall through the longitudinal ends such that blood flows only through the longitudinal orifice.10. The implant set forth in claim any one of paragraphs 1-9, wherein the longitudinal ends include an upstream longitudinal end and a downstream longitudinal end, wherein an area of the longitudinal orifice at the upstream end is greater than an area of the longitudinal orifice at the downstream end.11. The implant set forth in paragraph 10, wherein the longitudinal orifice tapers from the upstream longitudinal end to the downstream longitudinal end.12. The implant set forth in paragraph 1, wherein the blood flow restrictor is formed from a flowable, biodegradable material injected into the competing vein over a mandrel and solidified into the blood flow restrictor.13. An implant for use in a competing vein of primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula, the implant comprising: a blood flow restrictor configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location, the blood flow restrictor having opposite longitudinal ends and a length extending therebetween,Attorney Docket No. A0012679W001 wherein the blood flow restrictor enables blood in the competing vein to flow longitudinally therethrough at an initial reduced volumetric blood flow rate, wherein an entirety of the blood flow restrictor is biodegradable in the competing vein so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the blood flow restrictor increases from the initial reduced volumetric blood flow rate to fully restore volumetric blood flow rate in the competing vein.14. The implant set forth in paragraph 13, wherein the blood flow restrictor includes a porous wall defining a plurality of pores enabling blood flow through the porous wall through the longitudinal ends.15. The implant set forth in any one of paragraphs 13 or 14, wherein the blood flow restrictor is configured to gradually biodegrade in the competing vein over a period of 4 to 6 weeks.16. A method of using the implant set forth in any one of paragraphs 1-15, comprising: determining the volumetric blood flow rate in at least one of the competing vein and the primary vein; and delivering the blood flow restrictor to the competing vein.17. The method set forth in paragraph 16, wherein the delivering the blood flow restrictor comprises using a catheter.18. The method set forth in any one of paragraphs 16 or 17, further comprising selecting, before the delivering the blood flow restrictor, the blood flow restrictor from a plurality of blood flow restrictor based, at least in part, on one or more of: a desired volumetric blood flow through at least one of the competing vein and the primary vein; and a diameter of the primary vein.19. The method set forth in paragraph 18, wherein the desired volumetric blood flow through the competing vein is no less than 100 ml per minute.20. The method set forth in paragraph 18, wherein the blood flow restrictor has a diameter of at least 4 mm.

[0045] It should be understood that various aspects disclosed herein may be combined in different combinations than the combinations specifically presented in the description and accompanying drawings. It should also be understood that, depending on theAttorney Docket No. A0012679W001 example, certain acts or events of any of the processes or methods described herein may be performed in a different sequence, may be added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device.

[0046] In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0047] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term “processor” as used herein may refer to any of the foregoing structure or any other physical structure suitable for implementation of the described techniques. Also, the techniques could be fully implemented in one or more circuits or logic elements.

Claims

Attorney Docket No. A0012679W001WHAT IS CLAIMED IS:

1. An implant (10) for use in a competing vein (CV) of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula, the implant comprising: a blood flow restrictor (12) configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location, the blood flow restrictor having opposite longitudinal ends (14) and a length extending therebetween, wherein the blood flow restrictor defines a longitudinal orifice (18) extending along the length of the blood flow restrictor and through the opposite longitudinal ends to enable blood in the competing vein to flow therethrough, wherein the longitudinal orifice is sized and shaped to reduce a volumetric blood flow rate as the blood flows therethrough, wherein the blood flow restrictor is configured to be biodegradable in the competing vein to enlarge the longitudinal orifice so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the longitudinal orifice increases.

2. The implant (10) set forth in claim 1, wherein an entirety of the blood flow restrictor (12) is biodegradable in the competing vein (CV).

3. The implant (10) set forth in any one of claims 1 or 2, wherein the blood flow restrictor (12) consists of biodegradable material.

4. The implant (10) set forth in any one of claims 1-3, wherein the blood flow restrictor (12) is configured to gradually biodegrade in the competing vein (CV) over a period of 4 to 6 weeks.

5. The implant (10) set forth in any one of claims 1-4, wherein the blood flow restrictor (12) is configurable between a collapsed configuration, to enable delivery of theAttorney Docket No. A0012679W001 implant to the competing vein (CV), and an expanded configuration, to enable the implant to sealingly engage a wall of the competing vein.

6. The implant (10) set forth in any one of claims 1-5, wherein the longitudinal orifice (18) consists of a single longitudinal orifice.

7. The implant (10) set forth in any one of claims 1-5, wherein the longitudinal orifice (18) comprises a plurality of longitudinal orifices.

8. The implant set forth in any one of claims 1-7, wherein the blood flow restrictor (112) includes a porous wall (17) defining a plurality of pores (20) enabling blood flow through the porous wall.9 The implant (10) set forth in any one of claims 1-7, wherein the blood flow restrictor (12) includes a non-porous wall (17) inhibiting blood flow through the non- porous wall through the longitudinal ends (14) such that blood flows only through the longitudinal orifice (18).

10. The implant (10) set forth in claim any one of claims 1-9, wherein the longitudinal ends (14) include an upstream longitudinal end and a downstream longitudinal end, wherein an area of the longitudinal orifice at the upstream end is greater than an area of the longitudinal orifice at the downstream end.

11. The implant (10) set forth in claim 10, wherein the longitudinal orifice (18) tapers from the upstream longitudinal end (14) to the downstream longitudinal end.

12. The implant (10) set forth in claim 1, wherein the blood flow restrictor (12) is formed from a flowable, biodegradable material injected into the competing vein (CV) over a mandrel and solidified into the blood flow restrictor.Attorney Docket No. A0012679W00113. An implant (10) for use in a competing vein (CV) of a primary vein of an arteriovenous (AV) fistula to promote maturation of the AV fistula, the implant comprising: a blood flow restrictor (12) configured to be delivered to a selected location in the competing vein and engage a wall of the competing vein at the selected location, the blood flow restrictor having opposite longitudinal ends (14) and a length extending therebetween, wherein the blood flow restrictor enables blood in the competing vein to flow longitudinally therethrough at an initial reduced volumetric blood flow rate, wherein an entirety of the blood flow restrictor is biodegradable in the competing vein so that as the blood flow restrictor biodegrades in the competing vein over time, the volumetric blood flow rate through the blood flow restrictor increases from the initial reduced volumetric blood flow rate in the competing vein.

14. The implant (10) set forth in claim 13, wherein the blood flow restrictor (112) includes a porous wall (17) defining a plurality of pores (20) enabling blood flow through the porous wall.

15. The implant (10) set forth in any one of claims 13 or 14, wherein the blood flow restrictor (12, 112) is configured to gradually biodegrade in the competing vein (CV) over a period of 4 to 6 weeks.

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