Adjustable stylet

[0001] The present invention relates generally to the field of intravascular leads and catheters. More specifically, the present invention relates to an adjustable stylet for use in positioning such leads and catheters.

[0002] Stylets and guidewires are used to control the manner in which intravascular leads and catheters are introduced into the veins or arteries of the body. Although both kinds of devices are often thought of as simply very small wires, the purpose and operation of stylets is significantly different as compared to guidewires.

[0003] Conventional intravascular procedures typically involve an initial step of introducing and routing a guidewire through a patient's vascular system to provide a rail or track along which additional intravascular devices may be introduced. Once a guidewire is in place, a sheath is routed over at least a portion of the guidewire to provide a larger opening into the vein or artery and sometimes to protect the inside walls of the vessels along the route of the guidewire. With the sheath in place, the guidewire may be removed or may remain in place as additional intravascular devices such as intravascular leads and catheters are introduced into the patient's vascular system.

[0004] To better accomplish the purpose of a guidewire of providing a track along the patient's vascular system for other intravascular devices, it is desirable that the guidewire have a region at the tip of the guidewire, referred to as the distal end, that is extremely flexible. Preferably, the guidewire has the ability to vary the flexibility of the distal tip and/or deflect the distal tip so as to aid in routing the guidewire through the patient's vascular system. U.S. Pat. Nos. 4,215,703, 4,456,017, 4,719,924, 4,886,067 and 5,060,660 describe designs for guidewires that use an internal tensioning member or pull wire to alter the characteristics of the non-expandable distal tip and/or to deflect the distal tip. U.S. Pat. Nos. 4,271,845 4,822,345, 5,605,162, 5,762,615, 5,851,203, 5,957,903 and 6,183,420 describe various designs for guidewires with adjustable stiffness by moving a core member axially within the distal region of the guidewire. U.S. Pat. Nos. 5,938,623 and 6,039,743 describe a guidewire with adjustable stiffness that is controlled by running electricity through a memory metal wire tip. U.S. Pat. No. 5,341,817 describes a guidewire extension arrangement in which a smaller inner extension can be pushed out of a larger core segment to extend the distal end of the guidewire. U.S. Pat. Nos. 4,846,174 and 5,338,301 describe guidewires with a core member that can be extended to axially stretch an angioplasty balloon at the distal tip. In a similar manner, U.S. Pat. Nos. 3,841,308 and 4,759,748 describe catheters that utilize a core member to axially stretch a coiled section at the distal end of the catheter for purposes of controlling delivery of a fluid.

[0005] In contrast to the guidewire which serves as a track over which other intravascular devices are routed, a stylet is used within an internal lumen of an intravascular device both to push that device through the vascular system and to steer the device as it is being pushed. Although some intravascular devices are designed to steer themselves using internal pull wires, almost all leads, most catheters and some guidewires have an inner channel or lumen into which a stylet is inserted. In addition to pushing the intravascular device through the vascular system by engaging the distal end of the device, the stylet also serves to deflect the distal end of the intravascular device so as to steer the distal end through the vascular system. Unlike the lead, catheter or guidewire, which has a distal region that is flexible and floppy, the stylet must be stiffer and more rigid so as to enable the stylet to push the lead or catheter through the patient's vascular system. Conventionally, stylets having different bends on the distal end are used at different points of advancing the lead or catheter to a desired location. For straight segments of a vessel a straight stylet is used, whereas a stylet with a curved distal tip is used to navigate the lead or catheter through a curved portion of a vessel. U.S. Pat. No. 2,118,631 shows an early stylet formed of coils of flat wire welded to plugs at both ends that could be bent by the physician into either a straight or curved configuration at its distal end prior to insertion into the lumen of a catheter or the like. In a more recent type of stylet, an operator controls the direction of deflection of the tip of the stylet while it is in place in the lumen, which in turn controls the direction of the cardiac lead or catheter as it is moved along the veins or arteries. An example of a stylet with such a deflecting tip is shown in U.S. Pat. No. 5,824,031. Other examples of steerable stylets can be found in U.S. Pat. No. 5,873,842 and PCT Publ. No. WO 00/22981.

[0006] The more control and flexibility an operator has over an intravascular device, the easier it is to operate that device. In the case of stylets, the physical demands of engaging the distal end of a lumen of an intravascular device so as to push that device through the vascular system impose constraints on the beam strength of the device that are much different than the constraints encountered for a guidewire, catheter or lead. Most guidewires are constructed from a tapered core wire with a coiled round wire wrapped around this tapered core wire in order to achieve the necessary flexibility in the distal region of the guidewire. Stylets, on the other hand, are generally constructed of a solid wire of uniform diameter without any coils around this wire in order to achieve the necessary strength and rigidity required over the entire length of the device so as to function as a stylet. Because of these differences, the techniques for improving control and flexibility that have been utilized for guidewires, catheters and leads are not generally applicable for the design of stylets. It would be desirable to provide for a stylet with improved flexibility and control without the need for changing stylets during a procedure to obtain different orientations of the distal tip of the stylet.

[0007] The present invention is an adjustable stylet. The stylet includes a core wire having a portion surrounded by a compression member preferably comprised of a flat wire spring. Depending upon the configuration, compression or relaxation of the compression member in response to forces at the tip or handle of the stylet results in adjustments to the characteristics of the stylet. In a first embodiment, the stiffness of the stylet is adjustable. In a second embodiment, the length of the stylet is adjustable. In a third embodiment, both the stiffness and the length of the stylet are adjustable.

[0008] Unlike most guidewires that are so flexible the guidewire will fall over when grasped only by the ends, the stylet in accordance with the present invention requires a much greater rigidity such that the stylet forms an arc that generally stands up and does not fall over when the stylet is grasped only by the ends. The present invention utilizes a core wire that has a relatively uniform beam strength over its axial length so as to provide the necessary rigidity and strength required for a stylet. The compression member augments the characteristics of the core wire in a manner that is adjustable so as to also be able to more closely emulate the desired characteristics of an adjustable guidewire.

[0009] FIG. 1 is a side view of an adjustable stiffness stylet in a relaxed state.

[0010] FIG. 2 is a side view of the adjustable stiffness stylet of FIG. 1 in a compressed state.

[0011] FIG. 3 is a side view of an alternative embodiment of the adjustable stiffness stylet.

[0012] FIG. 4 is a partial side view of an adjustable length stylet.

[0013] FIG. 5 is a cutaway partial side view of the adjustable length stylet of FIG. 4.

[0014] FIGS. 6a, 6b and 6c are side views of the component pieces of the adjustable length stylet of FIG. 4.

[0015] FIGS. 7 and 8 show cutaway partial sides views of alternate embodiments of the handle for the adjustable stiffness stylet of FIG. 1.

[0016] Referring to FIG. 1, an adjustable stiffness stylet 10 comprises a stylet core wire 12, a space wound flat wire spring or compression member 14, a sliding handle 16 located at a proximal end 18 of the core wire 12 and a tip 20 of the core wire 12. Preferably, the compression member 14 is welded, crimped or otherwise secured to the core wire 12 near the tip 20. Preferably, the space wound compression member 14 has an inner diameter (I.D.) that is just slightly larger than the outer diameter (O.D) of the core wire 12. Optionally, a cover tube (not shown) may be secured over the exterior so long as the tube does not interfere with the movement of compression member 14.

[0017] As the sliding handle 16 is pushed toward the tip 20, the handle 16 makes contact with the proximal end of compression member 14 but does not slide over compression member 14. Compression member 14 is compressed in response and the overall flexibility of the stylet 10 begins to stiffen. As more force is applied to the handle 16, the open windings of compression member 14 close and the stiffness of stylet 10 is increased as shown in FIG. 2. When the desired stiffness is achieved, the operator may advance stylet 10 without altering the stiffness by applying force to the proximal end 18 of the core wire 12 without displacing the position of handle 16 relative to the compression member 14. Alternatively, handle 16 may be provided with locking mechanisms to lock the handle 16 in a given position relative to core wire 12, or proximal end 18 of the core wire 12 may be equipped with a separate handle. Handle 16 preferably is slide operated along the longitudinal axis of core wire 12, although it will be understood that handle 16 also could operate in a screw manner (as shown in FIG. 7) or ratchet manner (as shown in FIG. 8) along the longitudinal axis of core wire 12.

[0018] FIG. 3 shows an alternate embodiment of an adjustable stylet 22 in which a rigid tube 24 is located between the handle 16 and the compression member 14. In this case, compression member 14 is secured to the tip 20 of the core wire 12 and the resulting stylet has a flexible tip portion corresponding to the length of the core wire 12 surrounded by compression member 14. As the handle 16 is pushed toward the tip 20, the tube 24 is pushed into the proximal end of the compression member 14 and the space wound coils of compression member 14 are compressed, thereby increasing the stiffness of the stylet 22.

[0019] Referring now to FIG. 4, a second embodiment of an adjustable stylet 30 comprises a proximal core wire 32, a compression member 34 (FIG. 5), a distal core wire 36 and a cover tube 38. The cover tube 38 is welded to the proximal core wire 32, but not to the distal core wire 36. The compression member 34 is preferably a space wound flat wire spring that is welded, crimped or otherwise secured to the adjacent ends of the proximal core wire 32 and the distal core wire 36. As shown in FIGS. 6b and 6c, the stylet core wire is preferably centerless ground at the adjacent ends of the proximal core wire 32 and distal core wire 36 to all several turns of the compression member 34 to be centered on each core wire 32, 36.

[0020] Preferably, the distal core wire segment 36 is relatively short in comparison to the proximal core wire 32, although the lengths of the core wire segments 32 and 36 may be various lengths. In this embodiment, the compression member 34 is compressed and the overall effective length of the stylet 30 is shortened in response to a compressive force exerted at the distal end of the distal core wire 36. The ability of the stylet 30 to adjust in length reduces the need for stocking and maintaining a variety of different length stylets.

[0021] In a third embodiment, the stylet 30 is used as the core wire 12 of the stylet 10 to combine both of the adjustable qualities of the present invention in a single embodiment.

[0022] FIGS. 7 and 8 show alternate embodiments for the handle of the adjustable stiffness stylet of FIG. 1 in partial cross-sectional views. In FIG. 7, the proximal end of the stylet core wire 39 is threaded to accept a threaded handle 40. The stiffness of the stylet 10 is increased by compressing the compressive member 14 through turning of the threaded handle 40 clockwise to move the handle 40 away from the threaded proximal end of the stylet core wire 39. Similarly, the stiffness of the stylet 10 may be decreased by decompressing the compressive member 14 through turning the threaded handle 40 counterclockwise toward the threaded proximal end of the stylet core wire 39.

[0023] Referring now to FIG. 8, the proximal end 18 of the core wire 12 of the adjustable stiffness stylet 10 is welded or otherwise secured to the bottom part 41 of a multi-piece handle 42 that has a tongue 43. The tongue 42 engages slots 44 of the top part 45 of a multi-piece handle 42, which has an aperture 46 whose inside diameter is slightly larger than the outside diameter of the stylet core wire 12 to allow the stylet core wire 12 to freely slide through the top part 45 of the multi-piece handle 42. The stiffness of the stylet 10 is accomplished through compression of the compressive member 14 by pulling the bottom part 41 of the multi-piece handle 42 toward the proximal end of the core wire 18 in relation to the top part 45 of the multi-piece handle 42. Correspondingly, the stiffness of the stylet 10 can be decreased through relieving compression of the compressive member 14 by pushing the bottom part 41 of the multi-piece handle 42 away from the proximal end of the core wire 18 in relation to the top part 45 of the multi-piece handle 42. Once the desired stiffness of the stylet 10 has be accomplished by placement of the top part 45 and bottom part 41 of the multi-piece handle 42, the tongue 43 on the bottom part 41 engages a slot 44 on the top part 45 of the multi-piece handle 42 to maintain the chosen stiffness.

[0024] The core wire 12 is preferably a stainless steel wire having an outer diameter of less than 0.020 inches and preferably in a range between 0.005 and 0.018 inches and in the preferred embodiment approximately 0.014 inches. Above this range, the diameter of the core wire is generally too large to effectively serve as a stylet for insertion in the lumens of most intravascular devices. The physical characteristics of core wire 12 must be suitable for use as a stylet, as opposed to use as a guidewire. Most importantly, the core wire 12 should have a relatively uniform beam strength over its axial length so as to provide the necessary rigidity and strength required for a stylet. By relatively uniform it is understood that manufacturing tolerances or even minor variations in beam strength of less than about /10% would be considered relatively uniform in terms of the beam strength of the core wire. The tensile strength of the wire should be at least 150K psi and preferably in a range between 200K psi and 400K psi. Alternative wires suitable for core wire 12 include MP35N, AC10 tungsten, or Nintonal. With existing technologies for wound wire or braided wire, it is not possible to utilize such wires for the core wire 12 in accordance with the present invention because these wires do no exhibit the desired characteristics. As such, the core wire 12 is preferably a solid round wire having a relatively uniform cross-sectional diameter over its axial length.

[0025] The compression member 14 is preferably a flat or ribbon wire made of stainless steel or a similar material. The compression member preferably has an aspect ratio of at least 2:1. While the wider cross-sectional dimension of the flat wire can vary anywhere above the lower range of the aspect ratio, preferably the narrow cross-sectional dimension of the flat wire is less than 0.003 inches.

[0026] In the embodiment of the adjustable length stylet 30, the principle advantage of this feature is its use in those situations where the length of stylet must be held to very tight tolerances. Typically, the stylet 30 is inserted into an intravascular device within a sterile field prior to insertion in the patient's vascular system with the proximal ends of the stylet 30 and intravascular device locked together with a Luer lock or the like. In some applications, such as neurological applications, the tolerances for the match between the length of the lumen of the intravascular device and the length of the stylet 30 must be within less than 0.010 inches. The ability to adjust the length of the stylet 30 reduces the need for tight tolerance matches between these lengths, thereby affording more interchangeability between stylets and intravascular devices.