Abstract:
A medical guidewire including a tapered corewire formed from a superelastic material and a hypotube extending around the outer surface over a portion of the corewire resulting in improved torque characteristics for the guidewire.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a flexible elongated guidewire which may be used to position a catheter within a patient or may be used in a therapeutic procedure, such as to remove an occlusion within a vessel.  
         [0003]     2. Description of the Prior Art  
         [0004]     Percutaneous coronary angioplasty (PTA) is a therapeutic medical procedure used to increase blood flow through the coronary artery and can often be used as an alternative to coronary by-pass surgery. An elongated catheter having a deflated balloon at its distal end is guided through a patient&#39;s cardiovascular system to the coronary artery of the heart. The balloon is inflated to compress or crack deposits that have accumulated along the inner walls of the coronary artery to widen the artery lumen and increase blood flow.  
         [0005]     One prior art technique for positioning the balloon catheter uses an elongated guidewire that is inserted into the patient and passed through the cardiovascular system as guidewire progress is viewed on an x-ray imaging screen. The path the guidewire follows as it is inserted is tortuous. The distal tip is flexible to avoid damaging inner walls of the blood vessels that the guidewire tip contacts along the tortuous path. The distal tip is often pre-bent to a desired configuration so that the guidewire can be inserted into the branching blood vessels along the path. When the tip is pre-bent the physician must be able to orient the tip so it can be pushed into these branching blood vessels.  
         [0006]     Representative prior art patents that disclose flexible, elongated guidewires are U.S. Pat. No. 4,545,390 to Leary; U.S. Pat. No. 4,538,622 to Samson, et al., and U.S. Pat. No. 3,906,938 to Fleischhacker. The Leary &#39;390 patent discloses a narrow flexible guidewire having a distal portion which tapers and includes a flexible coiled spring at its distal end.  
         [0007]     In order to increase the flexibility of guidewires, some guidewires have been formed from a superelastic material, such as Nitinol, which exhibits the property of being extremely flexible, particularly when the Nitinol material becomes warmed as a result of passage through the vasculature of the human body. Representative prior art patents that disclose guidewires formed from a super elastic alloy, such as Nitinol, is U.S. Pat. No. 5,069,226 to Yamauchi, et al. One disadvantage of guidewires formed from Nitinol is that such guidewires have reduced so-called “torqueability,” or the ability to rotate or orient the distal tip of the guidewire by rotating the proximal end of the guidewire.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention relates to an elongated flexible guidewire designed for insertion into blood vessels to aid in positioning a catheter within the vessel or alternatively, to aid in a therapeutic procedure such as the removal of an obstruction in a vessel.  
         [0009]     In accordance with the invention, an elongated flexible guidewire is constructed from a flexible corewire having a first constant diameter that extends over a major portion of the guidewire from a proximal end to a distal region of the guidewire. At this distal region, the core tapers uniformly along a first tapered portion to a second lesser constant diameter portion that is shorter than the first constant diameter portion. The corewire then tapers along a second tapered portion in a uniform manner to a final flattened distal portion of the corewire. A flexible coiled wire spring is attached to the corewire along the length of the lesser constant diameter portion and extends distally and separates from the corewire as the corewire tapers along the second tapered portion. At the extreme distal tip of the guidewire, the coiled wire spring is attached to the distal tip of the flattened distal portion of the corewire by, for example brazing, to form the tip of the guidewire. The corewire is preferably formed of a superelastic material, such as Nitinol, which extends for the entire length of the guidewire. In order to increase the “torqueability,” or the ability of the distal tip to be oriented by twisting the proximal end of the guidewire, the proximal portion of the Nitinol corewire is ground down to a reduced diameter and a stainless steel hypotube is placed over this portion of the core.  
         [0010]     This guidewire construction results in a flexible distal guidewire portion which can be pre-bent into a desired orientation and easily oriented by the physician while inserting the guidewire into a vessel of the body.  
         [0011]     In accordance with another aspect of the present invention there is provided an elongated flexible guidewire which includes a flexible corewire formed from a superelastic material, such as Nitinol, having a first constant diameter portion that tapers distally along a first tapered portion to a second lesser constant diameter portion shorter than the first diameter portion and that again tapers distally along a second tapered portion to a flattened distal portion of the guidewire. The first constant diameter portion includes a proximal section having a reduced diameter section. A hypotube extends over the reduced diameter section of the first constant diameter section and is bonded to the reduced diameter section. In addition, a flexible coil surrounds the corewire and is attached to the corewire along a length of the second lesser constant diameter portion of the corewire and is also attached to a distal end of the flattened distal portion of the corewire. Preferably, a polymer coating is applied to the outer surface of the guidewire and extends over a major portion of the guidewire.  
         [0012]     In accordance with still a further aspect of the present invention, there is provided an elongated flexible guidewire including a flexible corewire formed from a superelastic material and having a first constant diameter portion that tapers distally along a first tapered portion. A proximal section of the first constant diameter portion has a reduced diameter from that of the first diameter portion. A hypotube extends over the proximal section of the first constant diameter portion and is bonded to the proximal section. In addition, a flexible coil surrounds a portion of the corewire and is attached to the distal tip of the first tapered portion, and a polymer coating covers an outer surface of the guidewire and extends over a major portion of the length of the guidewire.  
         [0013]     In accordance with another aspect of the present invention, the hypotube is formed of a flexible material but a material which has excellent torque characteristics, such as stainless steel. The hypotube preferably extends over the corewire from the proximal end of the corewire for a length of at least about half the length of the corewire in order to in part improve torque characteristic to the corewire which is formed of a superelastic material, such as Nitinol.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a diagrammatic view showing a blood vessel that has been occluded with deposits along an inner wall and illustrating the positioning of a flexible guidewire within a blood vessel;  
         [0015]      FIG. 2  is partially sectioned, elevation segmented view of a flexible guidewire constructed in accordance with the invention; and  
         [0016]      FIG. 3  is an enlarged sectioned view as seen from the plane defined by the lines  3 - 3  in  FIG. 2 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Turning now to the drawings,  FIG. 1  illustrates a distal portion of a flexible, small diameter guidewire  10  that can be guided through a patient&#39;s vascular system. A distal end of the guidewire is approaching a region in a blood vessel  12  having an occlusion  14  which has restricted blood flow through the blood vessel  12 . The guidewire  10  is long enough to be routed from an entry point of the patient through the vessels of the patient to the obstructed blood vessel region. As the guidewire  10  is inserted along the tortuous path to the obstructed blood vessel region, an attending physician conducting the procedure monitors progress of the guidewire  10  on a fluorographic viewing screen.  
         [0018]     The  FIG. 1  depiction illustrates use of a guidewire for routing a balloon catheter  20  to the vicinity of the occlusion  14 . The balloon catheter  20  includes a first passageway or lumen which extends from a proximal location outside the patient&#39;s body to a distally located balloon  22 . A distal tip portion  24  of the catheter  20  includes a marker band  26  to aid the attending physician in monitoring balloon catheter progress as it is positioned within the patient. A second, center passageway or lumen in the catheter  20  has a diameter sufficient to accommodate the guidewire  10  so that once the guidewire is properly positioned the catheter  20  can be slid over the guidewire to a desired location.  
         [0019]     The distal tip portion of the guidewire  10  is flexible and can be bent to a predetermined configuration to facilitate routing the guidewire  10  along the vascular system. The pre-bent tip can be oriented by the physician. Torque applied to the proximal end of the guidewire is transmitted along the length of the guidewire to orient or rotate the distal tip of the guidewire in order to direct the distal tip in a desired direction.  
         [0020]     In use, a distal end of the guidewire  10  is routed through a narrow passageway in the occlusion  14  and the balloon catheter  20  slipped over the guidewire until the balloon  22  bridges the occlusion  14  within the blood vessel  12 . The balloon  22  is then pressurized from a pressure source and as the balloon outer surface contacts the occlusion  14 , inner walls of the obstruction are compressed and a wider lumen or passageway is created in the blood vessel  12 .  
         [0021]     Although the  FIG. 1  depiction has been used to illustrate one use of the guidewire, it should be appreciated that a guidewire constructed in accordance with the invention has utility with angiographic catheters or any application requiring the routing of a tubular device within a patient, or alternatively, may be used with certain therapeutic procedures, such as the removal of an obstruction within a vessel.  
         [0022]     Turning now to  FIG. 2 , the guidewire  10  includes a corewire  40  formed from a superelastic material, such as Nitinol, having a first uniform diameter proximal portion  42  extending well over half the length of the guidewire. To increase the “torqueability,” or torque characteristics of the guidewire  10 , the proximal portion  42   a  of the uniform diameter portion  42  is ground down to a reduced diameter and a stainless steel hypotube  43   a  is placed over the reduced diameter portion of the proximal portion  42   a  and is bonded to the proximal portion  42   a  by use of an adhesive, such as epoxy. The proximal portion  42   a  of the uniform diameter portion of the corewire  40  extends for a length “V” which is preferably about 120 cm.  
         [0023]     Preferably, the total length of the guidewire  10  is approximately 150 centimeters. The outer surface of a most proximal segment  45   a  of the guidewire having a length indicated as “U” is not covered with a lubricious coating, but the remaining length “T” of the guidewire  10  up to a distal tip portion  44   a  is covered with a thin Teflon coating  44 . The exposed segment  45   a  may be more easily grasped by the attending physician in order to rotate the proximal end of the guidewire  10 .  
         [0024]     The Teflon coating which is applied to the guidewire  10  preferably has a thickness of approximately 0.00065 inch and is applied by a hot dipping process. The corewire  40  tapers along a portion  50  in a uniform manner to a second reduced constant diameter portion  52 . The reduced constant diameter portion  52  is bounded by a coiled wire spring  60 . The proximal portion  60   a  of the spring  60  is comprised of coil turns having a rectangular cross-section and the distal portion  60   b  of the spring  60  is comprised of coil turns having a circular cross-section.  
         [0025]     The spring  60  separates from the corewire  40  where the core begins to taper in a uniform manner along a portion  62 . A distal portion  64  of the corewire  40  is flattened and surrounded by the less tightly coiled portion of the spring  60 . This distal portion of the guidewire  10  may be pre-bent to a particular configuration by the attending physician to facilitate insertion of the guidewire within the vessels of a patient.  
         [0026]     At the extreme distal tip portion of the guidewire  10 , braze material  70  is used to attach the distal portion of the spring  60  to the flattened portion  64  of the corewire  40 . A preferred braze material is a gold alloy which upon being applied defines a hemispherical bead which covers several coils and is polished to a smooth shape so that it does not damage the inner lining of the blood vessels as the tip comes in contact with those linings.  
         [0027]     The dimensions shown are for a preferred embodiment in the invention for use in small diameter blood vessels. These dimensions are representative of this use and are not intended to limit the invention, but rather define a small diameter guidewire whose characteristics are particularly advantageous. It is the intent, however, that the invention include all modifications and/or alterations from the disclosed dimensions and design falling within the spirit or scope of the appended claims.