SMALL DIAMETER GUIDEWIRES

Abstract: A medical guidewire (10) having a distal tip portion for advancement through a body by application of force to a proximal end portion includes an elongated multi-filar coil structural element (12, 14) and a sheath (32) disposed thereabout and along a substantial portion of the length of the structural element, the sheath formed of material that is non-corrosive within the body. The sheath flexes in unison with the structural element without kinking. The sheath and structural element in combination have a torque response along the joined length approaching 1:1, thereby allowing control of the distal tip at the guidewire within a body by application of rotational force to the proximal end portion outside the body.

Description: SMALL DIAMETER GUIDE IRES Background of the Invention This invention relates to medical guidewires, including medical injection wires. Medical devices consisting of elongated spring coils are employed widely as guidewires, e.g., for negotiating narrow, tortuous passageways of the body to a site to be treated, and then serving as guides for catheters or other larger diameter devices advanced over the guidewires. In order to obtain maximum performance and patient safety, it is important that the guidewire be as small in diameter as possible, particularly in the tip region, but not so small as to create a danger of the tip breaking loose in the body; that the distal tip region be highly flexible to permit negotiation of difficult turns within the body; that the guidewire also be stiff enough axially to be advanced by pressure from the proximal end outside the body; and that the guidewire have good steerability or torque response, i.e., the tip-to-handle turn ratio should be as close to 1:1 as possible, without whipping. Most prior art guidewires offer a compromise of these desired features, e.g., trading tip flexibility for good torque response. Another use of spring coils is in catheter-like medical injection wires or the like which require characteristics similar to those described above. An example of such a device is described in Tate U.S. 3,841,308 as having a spring coil covered with a polyfluoroethylene flexible coating or sheath for delivery of fluid to ports adjacent the distal end. Summary of the Invention According to one aspect of the invention, a medical guidewire having a distal tip portion for advancement through a body by application of force to a proximal end portion comprises an elongated multi-filar coil structural element, and a sheath disposed thereabout and along a substantial portion of the length of the structural element, the sheath formed of material that is non-corrosive within the body, and the sheath being adapted to flex in unison with the structural element without kinking, the sheath and structural element in combination having a torque response along the joined length approaching 1:1, thereby allowing control of the distal tip of the guidewire within a body by application of rotational force to the proximal end portion outside the body. According to one preferred embodiment of this aspect of the invention, a core element formed of elongated metal is disposed within the structural element. According to another preferred embodiment of this aspect of the invention, the distal end of the structural element and the sheath define an orifice for delivery of a fluid through the element to a body.cavity. Preferred embodiments of each of the above may include one or more of the following features. The sheath is disposed along the majority of the element, and has a wall thickness of less than 0.0025 inch (0.064 mm). The material is able to withstand a pressure of at least 300 psi (21.1 kg/cm 2 ) . The material is able to withstand a pressure of at least about 700 psi (50 kg/cm 2 ) and/or the material has a tensile strength of at least 15,000 psi (1,050 kg/cm 2 ) , is not brittle, has a low elongation factor and is dimensionally stable; whereby the material can allow radiopaque fluid to be inserted into a body cavity through the guidewire in sufficient amount to provide good X-ray contrast at the site of insertion. The material is resistant to heat at temperatures suitable for soldering, to allow soldering of material to the structural element. The material has a uniform wall thickness so that the guidewire provides as little trauma to the body cavity as possible as it passes through the body cavity. The material has no pin holes so that fluid does not leak through the material. The sheath has a wall thickness of between 0.00075 inch (0.019 mm) and 0.0015 inch (0.038 mm). The wall thickness varies less than 0.0002 inch (0.005 mm) along the length of the sheath. The sheath has an inner diameter of at least 0.0075 inch (0.19 mm). The material comprises polyimide. The core element has a distal tapered region, and the core element is fixedly attached within the structural element proximally from the tapered region. The structural element has an inner diameter greater than the outer diameter of the core element by about 0.0005 inch (0.013 mm). The guidewire further comprises an electron dense material, e.g. platinum, in its distal region. The guidewire further comprises a sleeve positioned about the distal tapered region of the core element, the sleeve providing a transition between the core element and the tip of the guidewire. The sleeve comprises polyimide material. The structural element is a cross-wound multi- filar element. The cross-wound multi-filar element comprises an inner coil formed of wire having a flat cross-section. The core element is soldered to the structural element. The sheath is fixed to the structural element, e.g. by glue. The sheath extends along the distal end of the structural element and is fixed at the distal end of the element. The structural element has an inner diameter of greater than 0.022 inch (0.56 mm) and the guidewire has an outer diameter of less than 0.040 inch (1.02 mm). The structural element comprises a wound multi-filar element. The distal end of the sheath is spaced from the distal end of the structural element. According to another aspect of the invention, a method for forming a guidewire comprises the steps of providing an elongated structural element, disposing a sheath thereabout and along a substantial portion of the element, and gluing the sheath to the structural element. Guidewires of this invention can be made to extremely small diameter (less than 0.018 inch) and provide high torque response (e.g., at least approaching 1:1) of proximal to distal ends with high visibility of the tip region. The polyimide sheath acts in conjunction with a wound multi-filar coil to provide this torque. The distal tip of the guidewire is without a sheath to provide a softer tip region. A core provided within a guidewire is fixed to the inner coil of the guidewire but is separated along the majority of its length from that coil by about 0.0005 inch. Thus, the core element only contacts the inner coil constantly when the guidewire is caused to bend, for example, around a curve in a body cavity. At these curves the contact with the core element provides better torque to the guidewire. A polyimide sheath is particularly suited for use in this invention because it provides the features described above, and can be formed into an extremely thin walled material with small inner diameter. Injection wires of this invention provide means by which an extremely small diameter tube can be inserted within a body cavity and still allow a significant amount of fluid to be placed within the cavity at a desired site, since the injection wire has a relatively large lumen and can withstand high fluid pressure. These and other features and advantages of the invention will be seen from the following description of presently preferred embodiments thereof, and from the claims. Description of a Presently Preferred Embodiment We first briefly describe the drawings. Figs. 1 and 2 are sectional views of multi-filar cross-wound spring coil high torque guidewires of the invention; and Figs. 3 and 4 are sectional views, partly in isometric view, of wound multi-filar guidewires formed as injection wires. Referring to Fig. 1, torqueable coronary guidewire 10 has a length of about 145 cm, an outer diameter A, about 0.018 inch (0.46 mm), and is formed of an inner coil 12 and an outer coil 14 joined distally at a ball tip element 16, and joined proximally, e.g., by soldering, at a region 18. Inner coil 12 is bifilar, formed of two flat platinum wires, 20, 22, e.g., about 0.002 inch (0.05 mm) by 0.006 inch (0.15 mm), closely wound at a pitch ratio of about 2:1. Inner coil 12 extends only about 6-8 inches (15 to 20 cm) from ball tip element 16. Outer coil 14 is quadrifilar, formed of four stainless steel circular cross-sectional wires 24, 26, 28, 30 of between 0.002 inch (0.05 mm) and 0.003 inch (0.075 mm) diameter, which are closely wound about inner coil 12, but in a direction opposite to the winding direction of inner coil 12, with a pitch ratio of about 4:1. Outer coil 14 extends the length of guidewire 10. A sheath 32 formed of polyimide of thickness 0.00075 inch (0.019 mm) is provided tightly fitted around outer coil 14. Sheath 32 extends from proximal end 34 to a distance C, about 2 to 3 cm, from distal end 36. Distal end 38 of sheath 32 is fixed by glue 40 (e.g., cyanoacrylate) to outer coil 14, and along a length of about 3 to 4 cm in the nearby distal region 33. Proximal end 39 of sheath 32 is bonded by cyanoacrylate 50 to the proximal end of outer coil 14. Disposed within inner coil 12 is a core 42 formed of a stainless steel rod of outer base diameter B, about 0.010 inch (0.25 mm), with about a 0.0005 inch (0.013 mm) clearance from inner coil 12. Core 42 and inner coil 12 interact by close fit interference. Core 42 has a distal tapered portion 44 of length about 6 to 8 inches (15 to 20 cm) corresponding generally to the length of inner coil 12, beginning at step 46. Core 42 is fixed to outer coil 14 proxi ally from tapered portion 44 by solder or adhesive 51. Also provided is a polyimide sleeve 52 of length E, e.g. about 2 cm, outer diameter D, 0.0095 inch (0.24 mm), and wall thickness 0.001 inch (0.025 mm), slid onto the distal end of tapered portion 44 to provide a smooth transition from tapered portion 44 to ball tip element 16, and thereby increase torque transmission to ball tip element 16. Sleeve 52 is not fixed to ball tip element 16. Referring to Fig. 2, there is shown another guidewire 60, of diameter H, about 0.018 inch (0.46 mm), having a construction similar to guidewire 10, shown in Fig. 1 and described above. Guidewire 60 is formed with an inner coil 62 formed of a flat wire, and outer coil 64, formed of a circular wire, both extending the length of guidewire 60 and being encased within a polyimide sheath 66 along their length, except for a distance G of 3 to 5 cm at the distal tip. Sheath 66 is bonded by cyanoacrylate (50') to outer coil 64 at its distal end, and inner coil 62 is soldered (51*) at its proximal end to core 68, as described above. Inner core 68, of outer diameter I, about 0.006 inch (0.15 mm), has a tapered tip 69 having a tapered region 70 of length L, about 3 cm, and a flat tip portion 72 of length F, about 2 cm. Proximal end 74 of core 68 has a single filar coil 73 attached to it (e.g., by adhesive) to provide a handle 74. As above, core 68 has a clearance from inner coil 62 of about 0.0005 inch (0.013 mm). Inner coil 62 and outer coil 64 are formed of stainless steel except for a distal region M, of length about 5 cm, formed of platinum and glued or soldered (not shown) to the stainless steel coils. Referring to Figs. 3 and 4, there are shown embodiments of a injection wire formed from a multi-filar coil having a polyimide sheath. As shown in Fig. 3, injection wire 80 has a length of about 100 to 150 cm, and is affixed at its proximal end to fluid delivery device 82, for example, a syringe. Injection wire 80 is formed of a bifilar or quadrifilar coil 84 of wire diameter 0.005 inch (0.13 mm) formed with a lumen of diameter Q, 0.027 inch (0.69 mm), and enveloped by a polyimide sheath of nominal outer diameter P, about 0.038 inch (0.97 mm) . Polyimide sheath 86 and coil 84 are fixed together at the extremities by glue 88 such that polyimide sheath 86 extends a distance N, about 0.5 to 2.0 mm, beyond a tip 89 of coil 84. Referring to Fig. 4, injection wire 90 is formed as described above for injection wire 80, except coils 92 are fixed together by solder 93 to each other and subsequently bonded by cyanoacrylate to polyimide sleeve 94 in distal region 96 such that the tip of coil 92 and the tip of polyimide sheath 94 are adjacent and coextensive. These injection wires are able to withstand high pressure fluid and allow delivery of substantial amounts of fluid to any desired region within a body cavity. These wires may be used in conjunction with a movable and removable core, or a standard 0.025 inch (0.64 mm) guidewire. Other embodiments are within the following claims. What is claimed is:

Claims: 1. A medical guidewire having a distal tip portion for advancement through a body by application of force to a proximal end portion, comprising: an elongated multi-filar coil structural element, and a sheath disposed thereabout and along a substantial portion of the length of said structural element, said sheath formed of material that is non- corrosive within the body, and said sheath being adapted to flex in unison with said structural element without kinking, said sheath and structural element in combination having a torque response along the joined length approaching 1:1, thereby allowing control of said distal tip of said guidewire within a body by application of rotational force to said proximal end portion outside the body. 2. The medical guidewire of claim 1 further comprising a core element formed of an elongated metal and disposed within said structural element. 3. The medical guidewire of claim 1 wherein the distal end of said structural element and said sheath define an orifice for delivery of a fluid through said element to a body cavity. 4. The guidewire of claim 1, 2 or 3 wherein said sheath is disposed along the majority of said element, and has a wall thickness of less than 0.0025 inch (0.064 mm) . 5. The guidewire of claim 1, 2 or 3, wherein said material is able to withstand a pressure of at least 300 psi (21.1 kg/cm 2 ) . 6. The guidewire of claim 5 wherein said material is able to withstand a pressure of at least about 700 psi (50 kg/cm 2 ) ; whereby said material can allow radiopaque fluid to be inserted into a body cavity through said guidewire in sufficient amount to provide good X-ray contrast at the site of insertion. 7. The guidewire of claim 1, 2 or 3 wherein said material has a tensile strength of at least 15,000 psi (1,050 kg/cm 2 ) , is not brittle, has a low elongation factor and is dimensionally stable; whereby said material can allow radiopaque fluid to be inserted into a body cavity through said guidewire in sufficient amount to provide good X-ray contrast at the site of insertion. 8. The guidewire of claim 1, 2 or 3 wherein said material is resistant to heat at temperatures suitable for soldering, to allow soldering of material to said structural element. 9. The guidewire of claim 1, 2 or 3 wherein said material has a uniform wall thickness so that said guidewire provides as little trauma to said body cavity as possible as it passes through said body cavity. 10. The guidewire of claim 1, 2 or 3 wherein said material has no pin holes so that fluid does not leak through said material. 11. The guidewire of claim 1, 2 or 3 wherein said sheath has a wall thickness of between 0.00075 inch (0.019 mm) and 0.0015 inch (0.038 mm). 12. The guidewire of claim 1, 2 or 3 wherein said wall thickness varies less than 0.0002 inch (0.005 mm) along the length of said sheath. 13. The guidewire of claim 1, 2 or 3 wherein said sheath has an inner diameter of at least 0.0075 inch (0.19 mm) . 14. The guidewire of claim 1, 2 or 3 wherein said material comprises polyimide. 15. The guidewire of claim 2 wherein said core element has a distal tapered region, and said core element is fixedly attached within said structural element proximally from said tapered region. 16. The guidewire of claim 2 wherein said structural element has an inner diameter greater than the outer diameter of said core element by about 0.0005 inch (0.013 mm) . 17. The guidewire of claim 2 further comprising an electron dense material in its distal region. 18. The guidewire of claim 17 wherein said electron dense material comprises platinum. 19. The guidewire of claim 2 further comprising a sleeve positioned about said distal tapered region of said core element, said sleeve providing a transition between said core element and the tip of said guidewire. 20. The guidewire of claim 19 wherein said sleeve comprises polyimide material. 21. The guidewire of claim 2 wherein said structural element is a cross-wound multi-filar element. 22. The guidewire of claim 21 wherein said cross- wound multi-filar element comprises an inner coil formed of wire having a flat cross-section. 23. The guidewire of claim 15 wherein said core element is soldered to said structural element. 24. The guidewire of claim 1, 2 or 3 wherein said sheath is fixed to said structural element. 25. The guidewire of claim 24 wherein said sheath is fixed by glue to said structural element. 26. The guidewire of claim 1, 2 or 3 wherein said sheath extends along the distal end of said structural element and is fixed at the distal end of said element. 27. The guidewire of claim 3 wherein said structural element has an inner diameter of greater than 0.022 inch (0.56 mm) and said guidewire has an outer diameter of less than 0.040 inch (1.02 mm). 28. The guidewire of claim 26 wherein said structural element comprises a wound multi-filar element. 29. The guidewire of claim 26 wherein the distal end of said sheath is spaced from the distal end of said structural element. 30. A method for forming a guidewire comprising the steps of providing an elongated structural element. disposing a sheath thereabout and along a substantial portion of said element, and gluing said sheath to said structural element.

Inventors: ALVAREZ DE TOLEDO FERNANDO, ALVAREZ DE TOLEDO, FERNANDO
Applicants: BOSTON SCIENT CORP, BOSTON SCIENTIFIC CORPORATION
Application year: 1989
Main classification: A61B6
IPC codes: A61B6