MEDICAL INSTRUMENT WITH CONTROLLED TORQUE TRANSMISSION

Abstract

A medical instrument such as a guidewire that is designed to have controlled torque transmission along its length. Specially treated areas are placed in selected and equal areas along the entire length of the elongated shaft of the medical instrument, and are separated from one another by untreated areas. This process ensures that any torque is transmitted distally, in a smooth manner, regardless of the guidewire position, thus resulting in a substantial reduction in whipping. In one embodiment, a stainless steel guidewire is utilized, and is subjected to annealing heat treatment in selected areas. This annealing process creates a mandrel that has repeated temper properties along its length. Torque applied at one end of this mandrel is transmitted to the opposite end in an even and controlled manner, even when the mandrel is formed into a loop.

Claims

1. An elongated medical instrument that is subject to torque when in use, comprising: a first plurality of sections that have been subjected to a selected treatment process; a second plurality of sections located between each of the sections of the first plurality of sections, the second plurality of sections not having been subjected to the selected treatment process; and wherein the first plurality of sections and the second plurality of sections have different torque transmission characteristics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0015] FIG. 1 is a side view of a prior art polymer medical guidewire;

[0016] FIG. 2 is a schematic of the prior art guidewire of FIG. 1, as being delivered into a patient;

[0017] FIGS. 3A and 3B are expanded views of the prior art guidewire of FIG. 2 illustrating torquing of the proximal end and rotation of the distal end; and

[0018] FIG. 4 is a side view of a guidewire that has been subjected to heat treatments in selected areas in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019] Low carbon alloy steel, such as stainless steel, has strength and hardness imparted through drawing or extrusion. This hardness is an ideal quality for guidewires as they can be torqued effectively over a long length. A guidewire made from this material is very cost effective as compared to a wire made from elastic alloys such as nitinol. An important factor is the ability of the wire to track and thus create a mechanical pathway through a portion of the human anatomy in order to allow a physician to direct other devices such as catheters to a precise location.

[0020] The ability to track is related to a combination of both pushing and rotating the guidewire. Often placed in a tortuous path, a guidewire cannot effectively transmit torque from the proximal to the distal end in a 1:1 ratio. As the proximal end is rotated, the torsion is stored as energy in the end of the guidewire proximal to the tortuous path. When the threshold is reached where the stored energy overcomes the resistance of the tortuous path, whipping of the distal tip of the guidewire will occur. As a result, accurate placement of the guidewire is difficult.

[0021] FIG. 4 is a side view of a guidewire 100 that is formed in accordance with the present invention. The guidewire 100 has been subjected to selective area annealing. More specifically, localized sections 112a, 114a, 116a, and 118a have been subjected to selected area annealing. The sections 112b, 114b, 116b, and 118b are untreated (normally tempered) sections.

[0022] As noted above, the use of stainless steel as the material is a cost-effective choice for the guidewire 100. In one embodiment, the guidewire 100 comprises an elongated stainless steel element with a length of 220 cm and an outer diameter of 0.018 inches. The stainless steel guidewire 100 is provided with a tapered distal tip. The taper, as in most guidewires, increases the flexibility at the distal end. To improve the ability to push the guidewire 100, the middle and proximal sections are greater in diameter than the distal end. As described above, the middle section may be severely turned as it passes through the aortic arch into the carotid arteries. A curve in the guidewire 100 would be an area where effective torque transmission could be hampered, and which could cause the distal tip to whip upon attempted rotation of the guidewire 100. In this instance, a more ductile middle section that is formed in accordance with the present invention will aid in torque transmission without whipping.

[0023] As an example embodiment, in an experiment a guidewire 100 was formed by creating a repeating pattern of 1 cm heat treated (annealed) sections (e.g., 112a, 114a, 116a, 118a) followed by 2 cm untreated (normally tempered) sections (e.g., 112b, 114b, 116b, 118b). These sections were produced working 20 cm from the proximal end of a 150 cm long, 0.16 diameter stainless steel shaft guidewire 100. In the experiment, to form the guidewire 100 a hydrogen gas generator was fitted with a torch tip that produced a flame 0.030 in diameter and approximately 0.200 long. The annealing temperature for stainless steel is approximately 1200 degrees Fahrenheit. In the experiment, the stainless steel was heated with the hydrogen gas torch until it just changed from a dark red color to a bright red color. In order to create very localized sections, a short annealing time was applied to the 1 cm sections (e.g., 112a, 114a, 116a, 118a). The short annealing time comprised raising each of the sections from room temperature to above 1,280 degrees Fahrenheit over approximately 10 seconds. Heat sinks were used to protect the untreated sections (e.g., 112b, 114b, 116b, 118b). Time as well as heat is important for proper annealing so the heat was allowed to rise above the 1280 degree Fahrenheit mark briefly to compensate for time. The process was followed by a quick quench. Once the guidewire 100 was formed according to this process, it was tested in a looped environment and there was a substantial reduction in whipping for the guidewire 100 as compared with an untreated guidewire of the same material. In other words, upon rotation at the proximal end, a substantial reduction in whipping at the distal end was apparent for the guidewire 100 as compared to an untreated guidewire of the same material.

[0024] In actual production, in one embodiment a guidewire 100 may be produced by utilizing RF generation and induction coil heating to achieve selective annealing. Induction heating at precise local areas and for a specific time restores ductility to the heat-treated areas while the hardness of the untreated areas is not compromised. An automated system may be used to control atmosphere, movement, temperature, duration and post process actions such as quenching.

[0025] While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention. For example, the guidewire may be further coated with materials such as silicone or hydrophilic coatings. In addition, a coiled platinum spring may be provided at the distal end to aid in the flexibility. The guidewire may comprise either a tapered wire from the proximal end to the distal tip, or a straight wire from the proximal end to the distal tip, or any combination thereof. Furthermore, a stainless steel wire base tensile strength can be varied to fit applications where more or less flexibility is required. In addition, a guidewire torque device may be provided to assist with the rotation of the guidewire. Many types of guidewires may benefit from the disclosed method of production, such as neuro/coronary/peripheral vascular guidewires. Other applications include devices such as catheters and driveshafts, as well as other instruments that use shafts which require rotation, such as retrieval baskets and snares. The selective annealing procedure may also aid in the flexibility of devices such as stents, where variable stiffness could aid placement in tortuous anatomy. Various types of metals and materials may be utilized, being either round or non-round, that can be subjected to annealing or tempering.