United States Patent (19)
`Fagan et al.
`
`54) HIGH PERFORMANCE WIRES FOR USE IN
`MEDICAL DEVICES AND ALLOYS
`THEREFOR
`75) Inventors: John R. Fagan. Pepperell, Mass.; Lex
`P. Jansen, Londonderry, N.H.; L. Ven
`Raman, Framingham; John A. Wright,
`Jr., Arlington, both of Mass.
`(73) Assignee: C. R. Bard, Inc., Murray Hill, N.J.
`
`21 Appl. No.: 391,010
`22 Filed:
`Feb. 21, 1995
`Related U.S. Application Data
`63 Continuation-in-part of Ser. No. 149,985, Nov. 10, 1993,
`abandoned.
`int. Cl. ..................... A61B S/00
`(51
`128/772; 604/657; 604/658
`52
`58 Field of Search ............................... 606/198; 604/95;
`128/772; 148/606
`
`56
`
`References Cited
`U.S. PATENT DOCUMENTS
`5/1992 Samson et al..
`Re. 33,911
`2,358,799 9/1944 Franks.
`3,408.178 10/1968 Myers et al..
`4,721,117
`1/1988 Mar et al..
`4,748,986
`6/1988 Morrison et al. .
`4,922,924 5/1990 Gambale et al. .
`4,998,923
`3/1991 Samson et al. .
`5,120,308
`6/1992 Hess.
`5,176,149
`1/1993 Grenouillet.
`5,365,943 11/1994 Jansen ..................................... 128/772
`5,372,144 12/1994 Mortier et al.
`... 128/772
`5,411,613
`5/1995 Rizket al. ...............
`... 148/606
`5,415.170 5/1995 Hammerslag et al. ......
`... 128/657
`5,449,372
`9/1995 Schmaltz et al. ............
`... 606v198
`5,465,733 11/1995 Hinohara et al. ....................... 128/772
`FOREIGN PATENT DOCUMENTS
`O 395 098 10/1990 European Pat. Off..
`
`
`
`III US005720300A
`5,720,300
`Feb. 24, 1998
`
`Patent Number:
`Date of Patent:
`
`11
`45
`
`O 4O7. 965
`0480427
`24497.59
`1124473
`4210422
`1541072
`WO9307303
`WO95/03847
`
`1/1991
`4/1992
`8/1976
`5/989
`7/1992
`2f1979
`4f1993
`2/1995
`
`European Pat. Off. .
`European Pat. Off..
`Germany.
`Japan.
`Japan.
`United Kingdom.
`WIPO :
`WIPO
`
`OTHER PUBLICATIONS
`Szombaltfalvy, "Tempering of High-Strength Steel Wires
`After Patenting and Cold Forming", Chemical Abstracts.
`vol. 83. No. 16, Oct. 20, 1975.
`Assefpour-Dezfully,
`"Strengthening Mechanisms in
`Elgiloy", Journal of Material Science. vol. 6053, No. 17.
`1984.
`Assefpour-Dezfully, "Microplasticity in Elgiloy". Journal of
`Materials Science, vol. 6053, No. 20, 1985.
`
`Primary Examiner-Max Hindenburg
`Assistant Examiner-Pamela L. Wingood
`Attorney, Agent, or Firm-Arthur Z. Bookstein
`57
`ABSTRACT
`An elongate flexible wire-like medical device, such as a
`guidewire for use with a catheter, is formed with a shaft in
`which the difference between the magnitude of the tensile
`yield stress and compressive yield stress of the shaft is
`substantially reduced. The guidewire exhibits superior kink
`resistance without compromising other desirable character
`istics and enables a guidewire to be made in a smaller
`diameter without loss of performance. The guidewire shaft
`may be formed from a precipitation hardenable alloy such as
`an alloy of nickel, cobalt, molybdenum and chromium
`(MP35N and Elgiloy), 455PH stainless steel or stainless
`steel alloy 1RK91. Also disclosed is a process for increasing
`the modulus of elasticity of an alloy of nickel, cobalt
`molybdenum and chromium. Further, the disclosure relates
`to an improved management and manufacturing process for
`constructing the tip of a medical guidewire.
`
`40 Claims, 7 Drawing Sheets
`
`Page 1
`
`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 1 of 7
`
`5,720,300
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`
`Page 2
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`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 2 of 7
`
`5,720,300
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`
`
`Page 3
`
`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 3 of 7
`
`5,720,300
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`
`
`Page 4
`
`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 4 of 7
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`5,720,300
`
`
`
`(SSBHLS BTISNEL)
`
`
`
`
`
`(SSB HIS BAISSE??dWNOO)
`
`(NOISNBL NI NIVH1S) 3+
`
`(NOISSBBdWOO NI NIWBLS) 3
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`Page 5
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`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet S of 7
`
`5,720,300
`
`(TENSILE
`STRESS)
`--O
`
`
`
`8."
`yC
`-8 (STRAIN IN COMPRESSION) ,
`Cyc -
`
`-- +e (STRAIN INTENSION)
`t-s
`tyt
`eyt
`
`(COMPRESSIVE STRESS)
`
`Fig. 5
`
`Page 6
`
`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 6 of 7
`
`5,720,300
`
`BENDING
`FORCE
`
`
`
`
`
`
`
`
`
`O138 DIAMETER MP35N
`
`O138 DIAMETER STANLESS
`STEEL
`
`s
`
`s 's
`
`*
`
`re
`
`d
`
`s
`
`O.OOO
`10
`
`12
`
`6
`14
`TORTUOSITY RADIUS
`
`18
`
`2.O
`
`Fig. 7
`
`Page 7
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`Medtronic Exhibit 1453
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`

`

`U.S. Patent
`
`Feb. 24, 1998
`
`Sheet 7 of 7
`
`5,720,300
`
`90
`
`
`
`
`
`
`
`
`
`
`at
`| 96-
`
`
`
`98 -
`
`94
`
`
`
`DEFLECTION
`ANGLE u
`
`82
`
`8O
`
`FIG. 8
`
`Page 8
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`Medtronic Exhibit 1453
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`

`

`5,720,300
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`1.
`GH PERFORMANCE WRES FOR USE IN
`MEDICAL DEVICES AND ALLOYS
`THEREFOR
`
`RELATED APPLICATIONS
`This application is a continuation-in-part of U.S. appli
`cation Ser. No. 149,985 filed Nov. 10, 1993 now aban
`donned.
`
`O
`
`5
`
`25
`
`35
`
`2
`arterial anatomy is illustrated in fragmented, somewhat
`diagrammatic, fashion in FIG. 1. The arterial system carries
`blood from the heart 10 through the aorta 12 in a direction
`indicated by the arrows 13. The arterial system leading from
`the heart 10 includes, in a downstream direction, the ascend
`ing portion 14 of the aorta, the aortic arch, indicated gen
`erally at 16, and the remaining (descending) portion 18 of
`the aorta. Numerous arteries branch off the aorta to carry
`blood to the internal organs of the body as well as the limbs
`and extremities. The coronary artery system (suggested
`schematically and in part at 20) through which oxygenated
`blood is directed back to the heart tissue itself includes two
`main arteries, a left main coronary artery 21 and a right
`coronary artery 22, both of which branch off the ascending
`portion 14 of the aorta immediately downstream of the heart.
`Each of the left and right coronary arteries 21, 22 leads to a
`system of numerous branch arteries, some of which are
`suggested schematically at 20A, 20B.20C, 20D. that spread
`out over and through the wall of the heart muscle thereby
`serving to distribute oxygenated blood and nutrients to the
`entire heart muscle. The object of the PTCA procedure is to
`treat the portion of a coronary artery that has developed a
`stenosis. for example, as suggested at 23, that obstructs
`blood flow through that portion of the artery. In the PTCA
`procedure the region of the stenosis 23 is dilated to enlarge
`the flow area and improve the flow of blood to those portions
`of the heart tissue served by the stenosed artery,
`The PTCA procedure involves initial placement of a
`comparatively large diameter (0.078-0.117 inch outer
`diameter) guide catheter 24 through a percutaneous puncture
`(not shown) in the femoral artery 19. The guide catheter 24
`has a specially formed distal end that facilitates engagement
`of the tip 26 of the guide catheter with the entrance (ostium)
`28 to one or the other of the main coronary arteries 21, 22.
`In a common type of guide catheter (Judkins-left) the
`distal end has primary and secondary curves 30, 32 that may
`have a radius of the order of one-half to one inch as
`compared to the radius of the order of one and one-half to
`two inches for the curve that may be assumed through the
`aortic arch.
`The guide catheter 24, once placed, defines a path through
`and along which an angioplasty catheter (which typically is
`far more flexible than the guide catheter and about 0.040
`inch diameter or less) and its associated guidewire can be
`advanced easily and quickly to the entrance 28 of the
`coronary artery. The procedure for placing the guide catheter
`is well-known to those familiar with the art.
`In a typical procedure, a small diameter (less than about
`0.020 inch and preferably of the order of 0.018 inch or less
`and most commonly about 0.014 inch) steerable guidewire,
`indicated generally at 34 (FIG. 1) is preloaded into the
`receptive guidewire lumen (not shown) in the balloon angio
`plasty catheter, indicated generally at 36. The guidewire is
`longer (e.g., 175 cm) than the catheter (e.g., 145 cm). The
`angioplasty catheter 36 and guidewire 34 are advanced
`together through the previously placed guide catheter 24 to
`the ostium 28. Then, while holding the balloon catheter 36
`in place within the guide catheter 24, the guidewire is
`advanced through the balloon catheter into the coronary
`arteries. The slender guidewire is manipulated from its
`proximal end 35 by the physician while the patient is under
`fluoroscopy so that the distal end of the guidewire can be
`observed fluoroscopically. The physician, by combined rota
`tional and longitudinal movements of the guidewire 34,
`must steer the guidewire 34 through the branches of the
`coronary arterial tree so that the distal end 37 of the
`guidewire passes through the stenosis 23. Once so posi
`
`FIELD OF THE INVENTION
`This invention relates to slender medical devices that
`must be controllably passed through a tortuous path without
`permanent deformation including, for example, guidewires
`used in connection with catheters and, particularly, steerable
`guidewires used in percutaneous transluminal angioplasty,
`including coronary angioplasty (PTCA).
`BACKGROUND OF THE INVENTION
`The invention concerns improvements in medical
`guidewires and other elongate medical devices that incor
`porate stiffening elements and in which the device must be
`controllably passed through a tortuous path without perma
`nent deformation in order that the inserted end of the device
`can be controlled exteriorly of the patient by the physician.
`Such wires are used with catheters that may be inserted into
`a wide variety of blood vessels including, for example,
`peripheral arteries, coronary arteries and cranial vasculature,
`among others. The invention further concerns improvements
`in guidewires adapted for use in coronary angioplasty, in
`which a stenosed region of a coronary artery is dilated to
`increase the blood flow through that artery. Because the
`invention is advantageous with small diameter devices, such
`as guidewires and the like commonly used in PTCA, the
`invention and its background are described in that context.
`The PTCA procedure typically involves advancement of
`a guide catheter through a percutaneous puncture in the
`femoral artery to place the distal end of the guide catheter at
`the entrance (ostium) to one of the two (right or left)
`coronary arteries. The guide catheter remains in place
`throughout the procedure to define a path through which
`other, smaller diameter angioplasty catheters and guidewires
`can be advanced to and withdrawn from the coronary
`arteries. With the guide catheter properly positioned, a
`balloon dilatation catheter and an associated small diameter,
`steerable guidewire then are passed through the guide cath
`eter to an ostium of the coronary arteries. The small diameter
`steerable guidewire is intended to be manipulated into the
`selected arterial branch and through the stenosis that is to be
`dilated. After the guidewire has been manipulated and
`navigated into place through the stenosis, the balloon cath
`eter (in an over-the-wire catheter system) is further
`advanced over and along the guidewire, with the balloon in
`a deflated state to place the balloon within the stenosis. The
`balloon then is inflated under substantial pressure to dilate
`the stenosed region of the artery. The effective placement of
`the guidewire is critical to the success of the procedure. If
`the guidewire cannot be navigated to and through the
`Stenosis, the balloon cannot be guided into the stenosis and
`the stenosis cannot be dilated.
`Numerous difficulties are presented in the design of a
`small diameter steerable guidewire such as that intended for
`use in PTCA. The difficulties may be better appreciated from
`an understanding of the human arterial anatomy from the
`65
`usual point of entry, the femoral artery in the groin region,
`to and including the coronary arteries. The portion of that
`
`45
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`50
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`

`3
`tioned the guidewire 34 is held stationary by the physician
`or an assistant and the balloon catheter 36 then is advanced
`over and along the guidewire 34, thereby guiding the balloon
`40 of the catheter 36 directly to the stenosis 23. With the
`balloon in place. it then is inflated through an inflation lumen
`42, typically with a liquid under high pressure, to forcibly
`dilate the stenosis.
`It should be understood that for ease of illustration, the
`stenosis 23 in FIG. 1 has been shown as in a location in the
`arterial tree that is relatively free of complex tortuousities
`and is relatively close to the coronary ostium. In order for the
`guidewire to effectively serve its function of guiding the
`balloon catheter to the stenosis, the guidewire should be
`capable of being steered and manipulated into any of the
`arterial branches such as suggested schematically at
`20A-20D as well as other branches located at the most distal
`portions of the coronary arterial tree. Frequently the stenosis
`will be located well within a highly tortuous arterial branch
`of the coronary anatomy such as suggested at 23B in branch
`artery 20B. In order to reach and treat a stenosis so located,
`it will be appreciated that the balloon catheter and the
`guidewire must be steered and advanced through the tortu
`ous anatomy along a path suggested in phantom at 34B in
`F.G. 1.
`In order for the guidewire to perform its function
`effectively, it should have a number of characteristics. The
`guidewire should have adequate longitudinal flexibility to
`enable it to conform to the various curves of the patient's
`arteries including the frequently highly tortuous configura
`tion of the coronary arteries. It should have adequate lon
`gitudinal stiffness to have sufficient column strength so that
`it can be pushed, as it is advanced through the arteries,
`withoutbuckling. In order that the guidewire may be steered
`controllably, it should be sufficiently torsionally rigid to be
`able to transmit controllably to its distal end substantially all
`of the rotation applied at the proximal end. Although the
`guidewire must have adequate column strength to be push
`able without buckling, the distal region of the guidewire
`should be soft and flexible to reduce the risk of injury to the
`delicate inner lining of the artery. The guidewire also should
`be kink resistant. Kinking (permanent deformation) in the
`guidewire typically results in aberrant, uncontrolled whip
`ping movement at the distal tip of the guidewire rather than
`the desirable controlled transmission of rotation. The
`guidewire also desirably is highly radiopaque at its distal tip
`in order that its movement and position may be readily
`observed under fluoroscopy. Also important among the
`characteristics of a guidewire is that it have a good tactile
`response in order that the physician may feel, at the proximal
`end of the guidewire, events occurring at the distal end.
`Since the development of the first small diameter steer
`able guidewire (see U.S. Pat. No. 4,545.390 to Leary) a
`primary focus in the continued development of small diam
`eter steerable guidewires has been to reduce the diameter of
`the guidewire without adversely affecting its performance. A
`55
`reduction in guidewire diameter is significant because it
`enables the catheter itself to be made in a smaller diameter.
`That, in turn, enables the catheter to be advanced into tighter
`stenoses and smaller diameter arteries. Efforts to improve
`small diameter steerable guidewires, either by reducing the
`diameter or otherwise, have involved trade-offs and com
`promises among the desirable characteristics described
`above.
`Some guidewires have been formed from a superelastic
`alloy such as a nitinol (nickel-titanium) alloy. The super
`elastic characteristic of the material provides for excellent
`kink resistance and a desirably soft, flexible distal tip.
`
`35
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`Representative of such guidewires are those described in
`U.S. Pat. No. 4.925.445 (Sakamoto). The advantages of such
`superellastic guidewires have been achieved, however, at the
`expense of other desirable characteristics, particularly in
`small diameter guidewires of the type now commonly used
`in PTCA, of the order of 0.014 inch. Although the perfor
`mance of superellastic guidewires may be less problematic in
`larger sizes, the performance may become marginal when
`the diameter is as small as 0.014 inch and poor in smaller
`sizes. Performance becomes marginal to poor, particularly
`with respect to the column strength of the guidewire and its
`ability to be pushed without buckling. Similarly, superellastic
`guidewires of the order of 0.014 inch diameter and smaller,
`adapted for use in PTCA tend to display marginal to poor
`steerability characteristics. These disadvantages also com
`promise the tactile response of the wire.
`In order to achieve improved column strength, it has been
`proposed to make guidewires from tungsten or a tungsten
`alloy. Although such a guidewire results in improved column
`strength (sometimes referred to as "pushability") it does so
`at the expense of flexibility and kink resistance.
`To date, the most commonly used material for small
`diameter steerable guidewires, has been type 302 or 304
`stainless steel because it appears to have been the most
`acceptable compromise. Among the compromised features
`in a stainless steel guidewire is its diameter. Typically,
`guidewires that have been made in diameter less than 0.014
`have exhibited marginal to poor performance and have
`found considerably less use.
`It would be desirable to provide a small diameter steerable
`guidewire in which the foregoing desirable characteristics
`are maximized, with a minimum amount of compromise of
`one characteristic for another. It also would be desirable to
`provide a small diameter steerable guidewire in still smaller
`diameters than those presently in use without sacrificing
`performance. It is among the objects of the invention to
`provide such a guidewire.
`SUMMARY OF THE INVENTION
`The present invention is based, in part, on a recognition as
`to the manner in which a medical guidewire becomes kinked
`and in the construction of the guidewire to avoid such
`kinking. In particular, a guidewire in accordance with the
`invention is formed from an alloy having a modulus of
`elasticity that is at least about that of stainless steel and has
`been worked and treated to have a more balanced stress/
`strain curve, that is, a stress/strain curve in which the
`magnitude of the compressive yield strength is substantially
`closer to that of the tensile yield strength than has been the
`case with prior guidewires. Ideally, the guidewire shaft is
`formed from wire of an alloy in which the compressive and
`tensile yield stresses are approximately equal during bend
`ing. Desirable materials for practising the invention may
`include a number of specially treated precipitation hardened
`alloys including, for example, alloys commercially available
`under the trade designations MP35N. Elgiloy, 455PH and
`Sandvik 1RK91.
`More specifically, it has been determined that when a
`guidewire becomes permanently deformed in use, it gener
`ally fails in compression, not in tension. When a guidewire
`is advanced through a right bend or tortuous arterial
`anatomy, the radially inward side of the guidewire shaft at
`the region of the bend is compressed while the radially
`outward side is in tension. If the radius of the bend is so
`small as to stress the material beyond its elastic limit, the
`wire will deform permanently, forming a permanent kink
`
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`

`5
`that will impair the subsequent functioning of the guidewire.
`The present invention is based, in part, on a recognition that
`the wires that have been used for forming guidewire shafts
`typically are weaker in compression than in tension.
`Generally, the yield stress (the point at which permanent
`deformation results) in compression for such wires typically
`has been substantially less than that of the yield stress in
`tension. The magnitude of the compressive yield stress (and
`corresponding strain at the yield point) may be of the order
`of 60% that of the tensile yield stress and corresponding
`strain. When the guidewire is bent, as when passing through
`curved anatomy, the stresses on the outside and the inside of
`the curve increase equally as the degree of bend increases.
`The guidewire fails prematurely in compression because the
`compressive yield stress, on the inside of the bend, is
`reached before the tensile yield stress, on the outside of the
`bend, is reached.
`An important aspect of the invention concerns the provi
`sion of a guidewire in which the guidewire shaft is formed
`so that its tensile yield stress (and corresponding strain at
`yield) and compressive yield stress (and corresponding
`strain at yield) are substantially less disproportionate. Thus,
`when the guidewire is bent, it will remain elastic through a
`greater range of stresses than with prior guidewires in which
`the compressive stress prematurely reaches the point of
`failure. With the present invention, compressive failure is
`delayed enabling the wire to be bent in a sharper curve
`without permanent deformation.
`Among the exemplary alloys that may be used in the
`practice of the invention is a precipitation hardenable alloy
`of nickel, cobalt, molybdenum and chromium commercially
`designated as MP35N. The wire that is to form the shaft of
`the guidewire is cold worked, by drawing through dies, to an
`extent sufficient to raise its tensile strength to a desired level.
`The wire then is cut to a desired length and is straightened
`using conventional wire straightening techniques. In this
`state, the wire can be heat treated at selected temperatures
`for a time period sufficient to cause the alloy to become
`precipitation hardened to the extent desired. The manufac
`ture of the guidewire shaft can be controlled such that the
`precipitation hardened alloy exhibits a more balanced stress/
`strain curve in which the magnitudes of the compressive and
`tensile yield points are substantially closer to each other than
`had been the case with prior guidewire shaft materials.
`Consequently, the magnitudes of the compressive and ten
`sile yield stresses are closer. The magnitude of the compres
`sive yield stress may be of the order of 85% of the tensile
`yield stress. Similarly, the more balanced nature of the stress
`strain curve may be demonstrated by a comparison of the
`compressive and tensile strains at yield, With the present
`invention, the magnitude of those strains is substantially
`closer than with the prior art.
`The heat treatment for each of the above alloys serves not
`only to precipitation harden the alloy, to make it stronger, but
`also serves to partially relieve internal stresses in the alloy
`that were developed during the cold working of the metal.
`By relieving some of the internal stress, the wire is less
`likely to become seriously deformed during subsequent
`manufacturing steps, such as centerless grinding.
`Additional exemplary alloys that can be treated to a state
`where they are precipitation hardened sufficiently to define
`less disproportionate yield points include an alloy composed
`of nickel, cobalt, molybdenum and chromium having a small
`amount of iron, such alloy being commercially available
`under the trade designation Egiloy from Elgilloy,
`Incorporated, Elgin, Ill. Still another exemplary alloy is that
`commercially available under the designation 455PH from
`
`45
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`65
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`Carpenter Steel Co. of Reading, Pa. That alloy is a single
`stage martensitic precipitation hardenable stainless steel.
`modified by changing the proportions of chromium and
`nickel and further modified by adding copper and titanium.
`Still another exemplary precipitation hardenable alloy is that
`commercially available from Sandvik Steel of Scranton, Pa.
`under the trade designation Sandvik steel lRK91 (believed
`to be described in PCT patent application No. PCT/SE92/
`O0688, Int'l, Publication No. WO 93/07303).
`Another aspect of the invention relates to the discovery
`that for MP35N. and possibly for Elgiloy, the heat treatment
`surprisingly increases its modulus of elasticity.
`By constructing a guidewire shaft in accordance with the
`invention, the guidewire shaft can be made in a smaller
`diameter without loss of desirable performance characteris
`tics including resistance to kinking, stiffness (column
`strength) and torque transmission, among others. That, in
`turn, allows the use of smaller diameter catheters.
`Alternately, if the shaft diameter is not reduced, a guidewire
`made in accordance with the invention can be expected to
`exhibit improved operating characteristics as compared to an
`identical guidewire constructed of conventional stainless
`steel wire.
`In another aspect the invention, an improved. It is among
`the general objects of the invention to provide a guidewire
`construction by which the guidewire can be made in a
`smaller diameter without significant loss of performance.
`Another object of the invention is to provide a guidewire
`having an ideal combination of characteristics without
`adversely compromising certain of the desirable guidewire
`characteristics in favor of others.
`A further object of the invention is to provide a guidewire
`having a superior combination of pushability, rotational
`transmission and kink resistance.
`Still another object of the invention is to provide a
`guidewire shaft having a more balanced stress/strain curve
`than guidewires of the prior art.
`A further object of the invention is to provide a technique
`in which the modulus of elasticity of selected alloys may be
`increased by selective heat treatment.
`DESCRIPTION OF THE DRAWINGS
`The foregoing and other objects and advantages of the
`invention will be appreciated more fully from the following
`further description thereof, with reference to the accompa
`nying drawings wherein:
`FIG. 1 is a fragmented, somewhat diagrammatic, illustra
`tion of the human arterial and coronary anatomy with an
`angioplasty apparatus of a guide catheter, a balloon angio
`plasty catheter and a guidewire in place to perform an
`angioplasty;
`FIG. 2 is a fragmented, partly sectioned illustration of a
`common form of guidewire with which the invention may be
`used;
`FIG. 2A is a fragmented, greatly enlarged illustration of a
`guidewire shaft having a reduced diameter (step tapered)
`distal shaft segment;
`FIG. 3 is a somewhat diagrammatic illustration of a
`portion of a guidewire shaft that has been subjected to a
`sharp bend with the guidewire having failed in compression
`on the inside of the radius of the bend;
`FIG. 4 is a diagrammatic illustration of the stress/strain
`curve of a typical prior art guidewire having a shaft formed
`from cold drawn stainless steel;
`FIG. 5 is a diagrammatic illustration of a balanced stress/
`strain curve in accordance with the invention and illustrating
`
`Page 11
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`Medtronic Exhibit 1453
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`5,720,300
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`10
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`15
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`20
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`25
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`30
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`35
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`7
`further, in phantom, the additional strength that may be
`obtained in the practice of the invention;
`FIG. 6 is an illustration of a test fixture that may be used
`for comparative testing of the guidewires of the present
`invention with those of the prior art;
`FIG. 7 is a graph diagrammatically illustrating the
`extended range of operation of guidewires made in accor
`dance with the invention;
`FIG. 8 is an elevation of a test apparatus for use in
`comparing the present invention with guidewires of the prior
`art;
`FIG. 9 is a plan view of the test apparatus as shown in
`FIG. 8; and
`FIG. 10 is an illustration of the distal portion of a
`guidewire in which the core wire is attached to the distal tip
`of the coil at a tip weld.
`DESCRIPTION OF THE ILLUSTRATIVE
`EMBODIMENTS
`Guidewires embodying the invention may include a wide
`range of guidewire constructions. A typical guidewire
`construction, illustrated generally in FIG. 2, includes an
`elongate, flexible, torsionally rigid shaft 50 in which a distal
`segment 52 of the shaft is of reduced diameter to increase its
`longitudinal flexibility. The reduced diameter distal segment
`of the shaft typically may be contained within a flexible
`helical coil 54 or other covering. Representative of such
`guidewire constructions are those disclosed in U.S. Pat. Nos.
`4.545,390 (Leary); 4,763.647 (Gambale); 4,922,924
`(Gambale et al.) and 5,063,935 (Gambale), the disclosures
`of which are incorporated herein by reference.
`In a guidewire used for percutaneous transluminal coro
`nary angioplasty, a typical length for the guidewire is of the
`order of 175 centimeters. That is sufficiently longer than the
`catheter with which the guidewire is to be used so that the
`distal end of the guidewire can extend distally beyond the
`distal end of the catheter while the proximal end of the
`guidewire can be grasped and manipulated by the physician.
`The guidewire shaft may be considered as having a sub
`stantially uniform diameter proximal segment 56, that may
`range from about 0.010 inch to about 0.018 inch in diameter.
`The reduced diameter distal segment 52 may terminate at its
`end 62 in a diameter of the order of a few thousandths of an
`inch. The coil 54 typically is attached at its end regions to the
`shaft 50. The distal segment 52 may terminate short of the
`distal end of the coil and may be connected to the distal end
`of the coil by one or more slender safety ribbons 61. The
`safety ribbon 61 is attached at one end to the distal segment
`and at its other end to the tip weld 63 formed at the distal tip
`of the coil 54. The length of the distal segment and helical
`coil may vary from about 15 centimeters to about 40
`centimeters long. The distal segment 52 is intended to be
`more flexible, longitudinally, than the proximal segment in
`order that the distal segment can accommodate the bends
`that must be traversed through the aortic arch, the primary
`and secondary curves 30, 32 of the guide catheter and the
`sometimes tortuous anatomy of the coronary arteries, as
`illustrated somewhat diagrammatically in FIG. 1.
`FIG. 2A illustrates a typical guidewire shaft geometry.
`The shaft is formed from wire having a diameter of between
`0.010 to 0.018 inch, most commonly 0.014 inch. The distal
`segment 52 of the shaft is reduced in diameter, typically by
`centerless grinding. The distal segment 52 of the shaft may
`be formed in a continuous taper or in a step tapered
`arrangement, as illustrated in FIG. 2A. For example, the
`distal segment of the shaft may be centerless ground to form
`
`8
`a series of progressively reduced diameter barrel segments
`58. 60, 62 alternated with tapered segments 64, 66, 68. The
`number of barrel and taper segments, as well as their
`respective lengths, may be varied to provide different flex
`ibility and torsional characteristics for the distal segment 52
`of the guidewire as may be desired.
`It should be appreciated that the guidewire may include a
`construction in which the flexibility of the distal segment
`increases in a distal direction in order to enable that portion
`of the guidewire to more readily flex to accommodate
`tortuous arterial anatomy that can be expected to be encoun
`tered within the coronary arteries. Typically, the length for
`the distal segment is selected so that the most flexible
`portions of the guidewire can be inserted deeply into the
`coronary arteries should that be desired. Among the diffi
`culties presented by increasing the flexibility at the distal
`portion of the guidewire is that in so doing, the ability for the
`guidewire to transmit rotation from its proximal end to its
`distal end may be compromised. Also, among the significant
`difficulties encountered in the use of such guidewires is that
`if any portion of the guidewire becomes kinked, and espe
`cially if a kink develops in the distal region, the ability for
`the wire to controllably transmit rotation from the proximal
`to the distal end is destroyed and the guidewire loses its
`steerability. Steerability is essential if the guidewire is to be
`successfully navigated through the coronary arterial tree to
`the location of the stenosis to be treated. It is not uncommon
`to encounter a tortuous anatomy having small radius curves
`or bends such that when it is attempted to advance the
`guidewire through the bends, the guidewire is stressed
`beyond its elastic limit, resulting in plastic deformation of
`the guidewire shaft and a resulting kink. When that occurs,
`the controllability of the guidewire is lost and it may be
`necessary to remove the guidewire and replace it with one
`that is undamaged.
`Prior art guidewires have been propo