US20040162543A1 - Intravascular catheter with multiple axial fibers - Google Patents

Abstract

An intravascular catheter having a shaft, at least a portion of which includes a braid reinforcement with a plurality of axial members disposed between the helical members that form the braid. The axial members provide a number of advantages including: maintaining one-to-one correspondence in axial manipulation; maintaining uniform flexibility in several planes of flexure; reducing the likelihood of causing a curling effect; increasing the strength of connections between shaft segments; uniformly increasing stiffness of the catheter; and increasing the burst strength of the catheter. By positioning the axial members between the helical members, the axial members do not create a protrusion and do not become fixed to any adjacent polymer layer. Thus, the benefits of axial members are retained, without creating the undesirable effects of friction caused by an axial protrusion and without creating the undesirable effects of limited flexure caused by an adjacent polymer layer becoming fixed to the axial member.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• The present invention is related to U.S. patent application Ser. No. 09/234,203, filed Jan. 20, 1999, entitled “INTRAVASCULAR CATHETER WITH COMPOSITE REINFORCEMENT”; and U.S. patent application No. (unknown), filed on even date herewith, entitled “INTRAVASCULAR CATHETER WITH AXIAL FIBER”, the entire disclosures of which are hereby incorporated by reference.[0001]
FIELD OF THE INVENTION
• The present invention generally relates to intravascular catheters. More specifically, the present invention relates to intravascular catheters having braid reinforcement.[0002]
BACKGROUND OF THE INVENTION
• Intravascular catheters are used in a wide variety of relatively non-invasive medical procedures. Such intravascular catheters may be used for diagnostic or therapeutic purposes. Generally, an intravascular catheter allows a physician to remotely perform a medical procedure by inserting the catheter into the vascular system of the patient at a location that is easily accessible and thereafter navigating the catheter to the desired target site. By this method, virtually any target site in the patient's vascular system may be remotely accessed, including the coronary, cerebral, and peripheral vasculature.[0003]
• The distance between the access site and the target site is often in excess of 100 cm. The inside diameter of the vasculature at the access site is often less than 2 cm, and the inside diameter of the vasculature at the target site is often less than 0.5 cm. Accordingly, intravascular catheters must be relatively long and thin. Furthermore, in order to navigate through the patient's tortuous vascular system, intravascular catheters must be very flexible. It is also desirable that intravascular catheters be relatively soft in order to minimize the probability of damaging vascular tissue.[0004]
• Intravascular catheters typically have a radiopaque portion and are guided through the patient's vascular system with the assistance of x-ray fluoroscopy. A physician may manipulate the proximal end of the catheter and fluoroscopically monitor the corresponding movement of the distal end of the catheter. It is desirable that intravascular catheters be sufficiently radiopaque along their length and particularly at their distal end such that the physician is able to clearly monitor the progress of the catheter as it is being advanced from the vascular access site to the vascular target site.[0005]
• After the intravascular catheter has been navigated through the patient's vascular system with the distal end thereof adjacent the target site, the catheter may be used for various diagnostic and/or therapeutic purposes. Frequently, diagnostic and therapeutic techniques require the infusion of fluids through the catheter. For example, it may be desirable to inject radiopaque contrast media through the catheter to provide enhanced fluoroscopic visualization for diagnostic purposes, or to inject pharmaceutical solutions (i.e., drugs) to the target site for therapeutic purposes. In order to maintain a fluid path, it is desirable that intravascular catheters be sufficiently resistant to kinking. In addition, because such fluids are delivered under pressure, it is also desirable that intravascular catheters be sufficiently resistant to bursting.[0006]
• To satisfy some of these desirable features, prior art intravascular catheters have utilized a reinforcement structure such as a braid or coil disposed between an inner tubular polymer layer and an outer tubular polymer layer. A braid reinforcement structure may provide high resistance to bursting and improve the connection integrity between individual shaft segments. A coil reinforcement structure may provide adequate resistance to ovaling and kinking.[0007]
• Some types of prior art intravascular catheters also utilize longitudinal or axial members to impart stiffness to the catheter shaft. For example, U.S. Pat. No. 5,057,092 to Webster discloses an intravascular catheter having a braid reinforcing mesh and longitudinal warp members. The longitudinal warp members are intended to provide increased bending stiffness and thus permit reductions in the wall thickness and/or softer materials for the inner and outer tubes. The warp members are interwoven with the braid such that warp members alternate under or over the braid mesh. Because the braid reinforcing mesh is disposed between an inner polymeric layer and an outer polymeric layer, portions of the longitudinal warp members are disposed between the braid reinforcing mesh and the adjacent polymeric layer.[0008]
• With this arrangement, the adjacent polymeric layer may conform to the longitudinal warp members so as to create radial protrusions running the length of the catheter. A protrusion along the inside surface of the catheter may not be desirable because it may create friction or bias with devices inserted therein (e.g., guidewires). A protrusion along the outside surface of the catheter may not be desirable because it may create friction, bias or prevent adequate sealing with devices that the catheter is inserted into (e.g., introducer sheaths, compression fittings, etc.).[0009]
• Also with this arrangement, the adjacent polymeric layer may become fixed to the longitudinal warp members as it conforms thereto. Fixing the longitudinal warp members to the adjacent polymeric layer may not be desirable because it may limit relative movement and flexure therebetween. Limiting relative movement and flexure may cause excessive stiffness in one or more planes of flexure. This may cause difficulties in manipulating and navigating the catheter through tortuous vasculature, which is clearly undesirable.[0010]
• Accordingly, it is desirable to provide the advantages of a longitudinal or axial member without creating a protrusion and without fixing the axial member to the adjacent polymeric layer.[0011]
SUMMARY OF THE INVENTION
• The present invention overcomes these disadvantages by providing an intravascular catheter that includes a braid reinforcement with a plurality of axial wires or fibers disposed between the helical members that form the braid. By placing the axial members between the helical members, the axial members do not create a protrusion on either side of the braid. In addition, the axial members do not become fixed to any polymer layer adjacent the braid. Thus, the present invention maintains the benefits of axial members, but without the undesirable effects of friction caused by an axial protrusion and without the undesirable effects of limited flexure caused by an adjacent polymer layer becoming fixed to the axial member.[0012]
• In addition to avoiding the disadvantages discussed above by positioning the axial members between the helical members, the present invention provides several benefits by utilizing a plurality of axial members. First, the axial members prevent elongation of the shaft of the catheter thereby maintaining one-to-one correspondence in axial manipulation of the catheter, even when the shaft is placed in tension. Second, by equally spacing the axial members about the circumference of the catheter, the shaft maintains uniform flexibility in several planes of flexure thereby facilitating precise control of the catheter as it is navigated through tortuous vasculature. Third, as compared to a single axial member, uniformly spacing the axial members about the circumference of the catheter reduces the likelihood of causing the catheter to curl when the lumen of the catheter becomes clogged and the catheter is pressurized. Fourth, the strength of the connections between adjacent shaft segments is increased significantly. Fifth, the stiffness of the catheter may be uniformly increased thereby potentially reducing the profile of the catheter by allowing the wall thickness and/or hardness of the polymer layers to be reduced. Sixth, the burst strength of the catheter may be significantly increased by virtue of the axial members limiting radial expansion of the shaft.[0013]
• An intravascular catheter in accordance with one embodiment of the present invention includes an elongate shaft having a lumen extending therethrough. The shaft includes an inner polymer layer, a reinforcement layer disposed about the inner layer and an outer polymer layer disposed about the reinforcement layer. The reinforcement layer comprises a tubular braid having two or more interwoven helical members. The reinforcement layer also includes a plurality of axial members disposed between the helical members such that the axial members are retained within the tubular braid structure for at least a length thereof. The axial members may be wires, fibers, filaments, cables or the like, but are generically referred to herein as axial members.[0014]
• The axial members are preferably uniformly spaced about the circumference of the shaft. Virtually any number of axial members may be utilized, depending on the particular characteristics desired. For example, four or eight axial members may be utilized wherein the axial members are uniformly spaced apart by 90° or 45°, respectively, about the circumference of the shaft. In addition, only a portion of the shaft may include a plurality of axial members. For example, the distal shaft portion may have fewer axial members than the proximal shaft portion such that the distal shaft portion is more flexible.[0015]
• The helical members that form the braid may each comprise polymeric material, a metallic material, or a combination thereof. Similarly, the axial members may comprise a polymeric material or a metallic material. If a polymeric material is utilized for the helical members or the axial members, then each member may comprise a plurality of monofilaments such as LCP. The monofilaments may be held together statically thereby eliminating the need for a binding material that might otherwise add to the profile of the members. To further minimize profile, the monofilaments may be arranged side-by-side to collectively define a flat ribbon or cable.[0016]
• An intravascular catheter in accordance with another embodiment of the present invention includes an elongate shaft having a reinforcement layer. The reinforcement layer comprises a tubular braid including two or more interwoven helical members and a plurality of axial members disposed between the helical members. Optionally, the catheter may include inner and/or outer polymer layers disposed on either side of the reinforcement layer. Each of the inner and/or outer layers may comprise a single layer of polymeric material or multiple layers of polymeric materials.[0017]
• The present invention also provides a method of making such a catheter. The manufacturing method includes the steps of braiding two or more helical members about a plurality of axial members such that the axial members are disposed between the helical members. The axial members are preferably uniformly spaced about the circumference of the shaft. The helical members may be braided over a carrier such as a mandrel that is later removed or a polymeric tubular member that becomes the inner layer of the catheter shaft. After the reinforcement layer is woven about the carrier, another polymeric tubular member may be disposed about the reinforcement layer to become the outer layer of the catheter shaft.[0018]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a plan view of an intravascular catheter in accordance with the present invention;[0019]
• FIG. 2 is fragmentary partially sectioned side view of the shaft of the catheter illustrated in FIG. 1; and[0020]
• FIG. 3 is a cross-sectional view taken along line[0021]3-3 in FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
• The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention.[0022]
• FIG. 1 illustrates intravascular catheter[0023]10 in accordance with the present invention. Catheter10 includes anelongate shaft12 having aproximal region14 and adistal region16. The catheter10 includes a lumen18 (as best seen in FIG. 3) extending through the entire length of theelongate shaft12 to an opening at thedistal end20 of theshaft12. Catheter10 may have, for example, a length of 80-150 cm and an outside diameter of approximately 3F.
• A[0024]manifold24 is connected to theproximal end22 of theshaft12 which includes an interior (not visible) in fluid communication with thelumen18 of theelongate shaft12. The manifold24 includes astandard fitting26 for connection to a fluid source such as a syringe. Astrain relief28 is disposed between the manifold24 and theproximal end22 of theshaft12 in order to reduce the tendency of the shaft to kink therebetween. Theproximal end22 of theelongate shaft12 may extend through thestrain relief28 for connection to themanifold24. Alternatively, the distal end of thestrain relief28 may be connected to theproximal end22 of theelongate shaft12 with the proximal end of thestrain relief12 connected to themanifold24.
• With either arrangement, the intravascular catheter[0025]10 provides a fluid path from the fitting26 of the manifold24 to thedistal end20 of theelongate shaft12 by way of the interior (not visible) of the manifold24 and thelumen18 of theelongate shaft12. Intravascular catheter10 may be intravascularly navigated over a guide wire (not shown) and used to deliver diagnostic and/or therapeutic fluids to a desired vascular target site using conventional techniques.
• [0026]Elongate shaft12 includes aproximal region14 and adistal region16. Theproximal region14 is typically more stiff than thedistal region16 in order to provide more pushability for advancing thedistal region16. Thedistal region16 is usually more flexible than theproximal region14 to provide more trackability for navigating tortuous vasculature. A multi-layer construction may be used in either theproximal region14 or both the proximal14 and distal16 regions, depending on the pushability, trackability, and other characteristics desired for each region.
• The multi-layer construction is best seen in FIGS. 2 and 3. In FIG. 2, the[0027]outer layer30 has been removed to expose thebraid reinforcement layer50 comprising helical members32 (individually designated as32A and32B) and the axial members34 (individually designated as34A,34B,34C and34D). The helical members32 and theaxial members34 are each shown as a set ofmonofilaments40, but may also comprise asingle monofilament40. The multi-layer construction includes the innerlubricious polymer layer36 surrounded by thebraid reinforcement layer50 which, in turn, is surrounded by theouter layer30. Atie layer38 may be provided between thebraid reinforcement layer50 and the innerlubricious layer36.
• The[0028]inner layer36 may be formed of a lubricious polymer such as PTFE or HDPE and preferably has a relatively thin wall to minimize profile.Inner layer26 has an inside diameter sufficiently large to accommodate a conventional guidewire and to accommodate the delivery of fluids therethrough at a sufficient flow rate. For example, the inside diameter of theinner layer36 may be approximately 0.027 inches and the wall thickness of theinner layer36 may be approximately 0.0005 inches. Theinner layer36 may be formed, for example, by coating or extruding a lubricious polymer such as PTFE over a removable mandrel, or by using other known manufacturing techniques.
• The[0029]tie layer38 may be utilized to secure the helical members32 to the innerlubricious layer36. Thetie layer38 enhances the bond between the innerlubricious layer36, the helical members32, and theouter layer30.Tie layer38 also fills any micro-pores that may form in theinner layer36 to thereby increase burst strength. Further,tie layer38 maintains the position of the helical members32 on theinner layer36 during the manufacturing process. The thickness of thetie layer38 may be approximately 0.0003 inches to reduce the corresponding increase in profile. An example of a suitable material fortie layer38 is polyurethane, which may be coated onto the innerlubricious layer36.
• As seen in FIGS. 2 and 3, the helical members[0030]32 are interwoven to form a tubular braid. For purposes of illustration, only twohelical members32A and32B are shown. Those skilled in the art will recognize that the braided helical members32 may vary in number, pattern, pick-count, etc., without departing from the scope of the present invention. The helical members32 may comprise a polymeric material, a metallic material or a combination thereof. Polymeric helical members32 provide superior flexibility and softness, metallic helical members32 provide superior radiopacity and kink resistance, and a combination of polymeric and metallic helical members32 provide all these attributes.
• If metallic materials are utilized, the helical members[0031]32 may comprise stainless steel, nickel-titanium alloy, or a highly radiopaque material such as gold, tungsten, iridium, or an alloy thereof. If a plurality of metallic helical members32 are utilized, one or more of the metallic helical members32 may comprise stainless steel to provide superior strength and one or more of the other metallic helical members32 may comprise a highly radiopaque material to provide enhanced radiopacity. Although stainless steel provides higher radiopacity relative to most polymers, a more dense material such as those identified above are preferred for purposes of radiographic visualization. The metallic helical members32 may have a rectangular cross-section or a circular cross-section, depending on the desired mechanical characteristics and the desired effect on profile. For example, metallic helical members32 may have a circular cross-section with a diameter of approximately 0.0016 inches.
• If polymeric materials are utilized, the helical members[0032]32 may comprise asingle monofilament40 or a plurality ofmonofilaments40 as shown. The plurality ofmonofilaments40 may be unfused or fused together depending on the desired characteristics.Unfused monofilaments40 may be held together statically thereby eliminating the need for a binding material that might otherwise add to the profile of theshaft12. To further minimize profile, themonofilaments40 may be arranged side-by- side to collectively define a flat ribbon or cable, as best seen in FIG. 3.
• Fused[0033]monofilaments40 provide the helical members32 with mechanical characteristics similar to that of a solid rod.Unfused monofilaments40 held together statically provide the helical members32 with mechanical characteristics similar to that of a cable. A cable, as opposed to a solid rod, is more flexible and is able to withstand more fatigue from repeated bending. As such, helical members32 comprising a plurality ofmonofilaments40 held together statically provide ashaft12 that is more flexible and more durable. These features are significant because the catheter10 must be able to navigate tortuous vasculature and withstand harsh handling conditions.
• The[0034]monofilaments40 may be made of a liquid crystal polymer (LCP) available under the trade name VECTRAN. Eachmonofilament40 may have a circular cross-section having a diameter of 0.0007 inches. Each helical member32 may comprise two (2) to ten (10), and preferably five (5)monofilaments40 which, as stated previously, may be fused or unfused. Themonofilaments40 are preferably unfused and arranged side-by-side to essentially define a flat cable or ribbon. It is possible, however, that themonofilaments40 be arranged in any manner to collectively define any other desired geometry.
• The[0035]axial members34 are disposed between thehelical members32A and32B.Axial members34 may comprise any of the same or similar structures and materials as helical members32. Preferably, eachaxial member34 comprises a plurality ofLCP monofilaments40 arranged side-by-side as a flat cable as best seen in FIG. 3.
• The[0036]axial members34 limit elongation of theshaft12 when the catheter10 is placed in tension. The catheter10 may be placed in tension when the catheter10 is retracted in the proximal direction or withdrawn from a patient's vascular system and some resistance to movement is encountered. If the resistance to movement is encountered distal of theproximal end22, thecatheter shaft12 is placed in tension. When significant tension is applied to theshaft12, theaxial members34 limit elongation of the shaft. Further, theaxial members34 maintain one-to-one correspondence between axial manipulation of theproximal end22 and axial movement of thedistal end20 of theshaft12, even when the catheter10 is placed in tension. By maintaining one-to-one correspondence in axial manipulation, theaxial members34 maintain precise control of the catheter10.
• Not only do the[0037]axial members34 limit elongation of theshaft12 and maintain precise control of the catheter10, but by positioning theaxial member34 between thehelical members32A and32B, theaxial members34 do not create a radial protrusion or become fixed to an adjacent polymer layer, both of which may create undesirable effects.
• Specifically, if the[0038]axial members34 were placed over or under the helical members32, radial protrusions may extend along the length of theinner layer36 or theouter layer30. Such protrusions along the inside surface of the catheter10 may not be desirable because they may create friction or bias with devices inserted into thelumen18. In addition, protrusions along the outside surface of the catheter10 may not be desirable because they may create friction, bias, or prevent adequate sealing with devices that the catheter10 is inserted into. By positioning theaxial members34 between thehelical members32A and32B, no protrusions are formed thereby maintaining low friction and adequate sealing.
• Further, if the[0039]axial members34 were positioned under or over thehelical members32A and32B, theinner layer36 or theouter layer30 may become fixed to theaxial members34, thereby limiting relative movement and flexure therebetween. Limiting relative movement and flexure may cause excessive stiffness in one or more planes of flexure. This may cause difficulties in manipulating and navigating the catheter10 through tortuous vasculature. By positioning theaxial members34 between thehelical members32A and32B, relative movement therebetween is permitted thereby maintaining some amount of flexibility.
• In addition to preventing axial elongation of the[0040]shaft12 thereby maintaining one- to-one correspondence and axial manipulation of the catheter10, theaxial members34 provide a number of other advantages. By equally spacing theaxial members34 about the circumference of theshaft12, theshaft12 maintains uniform flexibility in several planes of flexure corresponding to the number of axial members used. The greater the number of axial members used, the greater number of planes of uniform flexibility. Uniform flexibility provides precise control of the catheter10 as it is navigated through tortuous vasculature.
• As compared to a single axial member, uniform spacing of the[0041]axial members34 about the circumference of theshaft12 also reduces the likelihood of causing the catheter to curl when thelumen18 of the catheter10 becomes clogged and the catheter10 is pressurized. This may be encountered, for example, if the catheter10 is utilized to deliver embolic material that unintentionally occludes thelumen18. By reducing the likelihood of curling, the likelihood of causing trauma to the interior of the vessel wall is also reduced.
• The[0042]axial members34 also increase the strength of the connections between adjacent shaft segments and the burst strength of theshaft12. The axial members further provide additional stiffness to thecatheter shaft12 such that the wall thickness and/or hardness of the polymer layers30 and36 may be reduced.
• The[0043]outer layer30 may be formed of any suitable polymer such as polyether block amide having a wall thickness of approximately 0.0025 inches. Theouter layer30 may be loaded with a radiopaque contrast material such as barium sulfate, preferably loaded at 30% by weight. Theouter layer30 may be formed by interrupted layer coextrusion (ILC) as described in U.S. Pat. No. 5,622,665 to Wang, which is hereby incorporated by reference. Theouter layer30 may include a proximal portion formed of a relatively high durometer polymer and a distal portion formed of a relatively low durometer polymer. For example, the proximal ILC portion may be formed of PEBAX™ 7233, which has a durometer of 72D and the distal ILC portion may be formed of PEBAX™ 3533 having a durometer of 35D. By virtue of the ILC process, theouter layer30 gradually transitions from the relatively high durometer polymer to the relatively low durometer polymer, thereby gradually decreasing stiffness distally.
• A radiopaque marker band (not shown) may be provided at the[0044]distal end20 of theshaft12. Such a radiopaque marker band may be formed of gold, tungsten, iridium, or an alloy thereof. The radiopaque marker band may be disposed over thebraid50 and encapsulated by theouter layer30. The radiopaque marker may be swaged onto or adhesively secured to thebraid layer50. A radiopaque marker band facilitates radiographic visualization and navigation as discussed previously.
• The catheter[0045]10 may be manufactured by a number of suitable manufacturing processes including the process described hereinafter. Theinner layer36 and thetie layer38 may be obtained prefabricated from a suitable vendor, such as H.V. Technologies, and provided as discrete tubes or on a spool as a continuous tube. The helical members32 are then braided over a carrier (e.g., the tube comprising theinner layer36 and tie layer38) with theaxial members34 therebetween as described in greater detail hereinafter. The braided subassembly is subsequently cut to the desired length. A marker band is slid over thebraid reinforcement layer50 into position adjacent thedistal end20 of theelongate shaft12. Theouter layer30 comprising a prefabricated ILC tube is slid over thebraid reinforcement layer50. A heat shrink tube (e.g., FEP) is then placed over theshaft12 components and the composite subassembly is pulled through a heated die. The die is heated to 380°-430° F. causing the components of theshaft12 to be fused and compressed together by the combined heat and compressive radial force. The heat shrink tube is then removed, exposing the completedshaft12 subassembly. The manifold24 and thestrain relief28 are then attached to theproximal end22 of theelongate shaft12 using conventional techniques. Thedistal end20 of theelongate shaft12 is then trimmed to the desired length and a soft tip is thermally fused thereto. A lubricious coating is then applied to the exterior of thecatheter shaft12.
• As mentioned above, the helical members[0046]32 are braided over a carrier with theaxial members34 therebetween. Although braiding helical members is well known in the art, positioning axial members between the helical members requires some modification to conventional braiding machines. For example, a conventional Steeger braiding machine may be modified to incorporate individual bobbin carriers that deliver theaxial members34 through a horn gear shaft. Theaxial member34 carriers are retrofitted onto the horn gear. With this arrangement, one of thehelical member32A carriers is allowed to pass under and the otherhelical member32B carrier is allowed to pass over theaxial members34. The net result is abraid reinforcement structure50 comprising two or more interwoven helical members32, withaxial members34 disposed therebetween.
• From the foregoing, it should be apparent to those skilled in the art that the present invention provides both a novel intravascular catheter[0047]10 and a novel method of manufacture thereof. The catheter10 comprises anelongate shaft12 including abraid reinforcement50 withaxial members34 disposed between helical members32 that form thebraid50. By positioning theaxial members34 between the helical members32, theaxial members34 do not create the undesirable effects of friction caused by radial protrusions and further do not create the undesirable effects of limited flexure caused by anadjacent polymer30 or36 becoming fixed to theaxial members34. The axial members provide a number of advantages including: maintaining one-to-one correspondence in axial manipulation; maintaining uniform flexibility in several planes of flexure; reducing the likelihood of causing a curling effect; increasing the strength of connections between shaft segments; uniformly increasing stiffness of the catheter; and increasing the burst strength of the catheter.
• Those skilled in the art will recognize that the present invention may be manifested in a variety of forms other than the specific embodiments described and contemplated herein. Accordingly, departures in form and detail may be made without departing from the scope and spirit of the present invention as described in the appended claims.[0048]

Claims (32)

What is claimed is:

1. An intravascular catheter comprising an elongate shaft having a lumen extending therethrough, the shaft including an inner polymer layer, a reinforcement layer disposed about the inner layer and an outer polymer layer disposed about the reinforcement layer, the reinforcement layer comprising a tubular braid having a first helical member interwoven with a second helical member and a plurality of axial members disposed between the first helical member and the second helical member, wherein the elongate shaft has a circumference and wherein the axial members are spaced apart about the circumference of the shaft.

2. An intravascular catheter as inclaim 1, wherein the axial members are uniformly spaced about the circumference of the shaft.

3. An intravascular catheter as inclaim 2, wherein four axial members are uniformly spaced apart by 90° about the circumference of the shaft.

4. An intravascular catheter as inclaim 2, wherein eight axial members are uniformly spaced apart by 45° about the circumference of the shaft.

5. An intravascular catheter as inclaim 2, wherein the elongate shaft includes a proximal portion and a distal portion, and wherein the distal shaft portion has fewer axial members than the proximal shaft portion.

6. An intravascular catheter as inclaim 5, wherein the proximal shaft portion has the plurality of axial members and the distal shaft portion has one axial member selected from the plurality of axial members.

7. An intravascular catheter as inclaim 1, wherein the axial members are movable relative to the inner and outer layers.

8. An intravascular catheter as inclaim 1, wherein the inner and outer layers have respective inner and outer surfaces free of protrusions caused by the axial members.

9. An intravascular catheter as inclaim 1, wherein the first and second helical members each comprise polymeric material.

10. An intravascular catheter as inclaim 9, wherein the first and second helical members each comprise a plurality of monofilaments.

11. An intravascular catheter as inclaim 1, wherein the axial members each comprise a polymeric material.

12. An intravascular catheter as inclaim 11, wherein the axial members each comprise a plurality of polymeric monofilaments.

13. An intravascular catheter as inclaim 12, wherein the monofilaments are held together statically.

14. An intravascular catheter as inclaim 13, wherein the monofilaments comprise LCP.

15. An intravascular catheter as inclaim 14, wherein the monofilaments are arranged side-by-side to collectively define a flat ribbon.

16. An intravascular catheter comprising an elongate shaft having a reinforcement layer comprising a tubular braid having a first helical member interwoven with a second helical member and a plurality of axial members disposed between the first helical member and the second helical member.

17. An intravascular catheter as inclaim 16, wherein the axial members are uniformly spaced about the circumference of the shaft.

18. An intravascular catheter as inclaim 17, wherein four axial members are uniformly spaced apart by 90° about the circumference of the shaft.

19. An intravascular catheter as inclaim 17, wherein eight axial members are uniformly spaced apart by 45° about the circumference of the shaft.

20. An intravascular catheter as inclaim 16, wherein the elongate shaft includes a proximal portion and a distal portion, and wherein the distal shaft portion has fewer axial members than the proximal shaft portion.

21. An intravascular catheter as inclaim 20, wherein the proximal shaft portion has the plurality of axial members and the distal shaft portion has one axial member selected from the plurality of axial members.

22. An intravascular catheter as inclaim 16, wherein the first and second helical members each comprise polymeric material.

23. An intravascular catheter as inclaim 22, wherein the first and second helical members each comprise a plurality of monofilaments.

24. An intravascular catheter as inclaim 16, wherein the axial members each comprise a polymeric material.

25. An intravascular catheter as inclaim 24, wherein the axial members each comprise a plurality of polymeric monofilaments.

26. An intravascular catheter as inclaim 25, wherein the monofilaments are held together statically.

27. An intravascular catheter as inclaim 26, wherein the monofilaments comprise LCP.

28. An intravascular catheter as inclaim 27, wherein the monofilaments are arranged side-by-side to collectively define a flat ribbon.

29. A method of making a portion of a shaft of an intravascular catheter, the method comprising the steps of:

braiding a first helical member and a second helical member about a carrier such that a plurality of axial members are disposed between the first and second helical members.

30. A method of making a portion of a shaft of an intravascular catheter as inclaim 29, wherein the axial members are uniformly spaced about the circumference of the shaft.

31. A method of making a portion of a shaft of an intravascular catheter as inclaim 30, wherein four axial members are uniformly spaced apart by 90° about the circumference of the shaft.

32. A method of making a portion of a shaft of an intravascular catheter as inclaim 30, wherein eight axial members are uniformly spaced apart by 45° about the circumference of the shaft.

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