U.S. patent application number 09/904466 was filed with the patent office on 2001-11-08 for guidewire with a variable stiffness distal portion.
This patent application is currently assigned to ADVANCED CARDIOVASCULAR SYSTEMS, INC.. Invention is credited to Fariabi, Sepehr.
Application Number | 20010039412 09/904466 |
Document ID | / |
Family ID | 24542841 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010039412 |
Kind Code |
A1 |
Fariabi, Sepehr |
November 8, 2001 |
Guidewire with a variable stiffness distal portion
Abstract
A guidewire having a core section formed of a NiTi alloy which
is in an austenite phase when being manufactured but which is
converted to the martensite phase at operating (body) temperature
(37.degree. C.) and can be transformed to an austenite phase by
heating to a temperature above body temperature but below
50.degree. C. When in the austenite phase, the core section is at a
high strength level which ensures the tracking of a catheter over
the guidewire within a patient's body lumen. In one preferred
embodiment the core section is heated by electrical resistance or
inductance
Inventors: |
Fariabi, Sepehr; (Fremont,
CA) |
Correspondence
Address: |
Edward J. Lynch
HELLER, EHRMAN, WHITE & McAULIFFE LLP
275 Middlefield Road
Menlo Park
CA
94025-3506
US
|
Assignee: |
ADVANCED CARDIOVASCULAR SYSTEMS,
INC.
|
Family ID: |
24542841 |
Appl. No.: |
09/904466 |
Filed: |
July 12, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09904466 |
Jul 12, 2001 |
|
|
|
09287703 |
Apr 6, 1999 |
|
|
|
6287292 |
|
|
|
|
09287703 |
Apr 6, 1999 |
|
|
|
08634208 |
Apr 18, 1996 |
|
|
|
5931819 |
|
|
|
|
Current U.S.
Class: |
604/531 ;
604/170.03 |
Current CPC
Class: |
A61M 2025/09175
20130101; A61M 2025/09141 20130101; A61M 25/0158 20130101; A61M
25/09 20130101 |
Class at
Publication: |
604/531 ;
604/170.03 |
International
Class: |
A61M 005/178; A61M
025/00 |
Claims
What is claimed is:
1. An intravascular guidewire comprising: a) an elongated proximal
core section which has proximal and distal ends; b) an intermediate
core section which has proximal and distal ends, which is formed of
a shape memory alloy with an A.sub.f above 37.degree. but not more
than about 50.degree. C. and which is secured by its proximal end
to the distal end of the proximal core section; c) means to heat
the intermediate core section; and d) a distal core section which
has proximal and distal ends and which is secured by its proximal
end to the distal end of the intermediate core section; and e) a
flexible body disposed about and secured to the distal core
section.
2. The intravascular guidewire of claim 1 including a first
electrical conductor in electrical contact with a proximal
extremity of the intermediate core section and a second electrical
conductor in electrical contact with a distal extremity of the
intermediate core section to facilitate heating the intermediate
core section by induction.
3. The intravascular guidewire of claim 2 wherein the guidewire has
a first electrode on a proximal portion of the proximal core
section which is electrically connected to the first electrical
conductor and a second electrode on the proximal portion of the
proximal core section spaced distal to the first electrode which is
electrically connected to the second electrical conductor.
4. The guidewire of claim 3 wherein the first and second electrical
conductors are layers of electrical conducting material.
5. The guidewire of claim 4 wherein a first layer of insulating
material is disposed on the exterior of the proximal core section
and the layer of conducting material of the first electrical
conductor is disposed on the layer of insulating material.
6. The guidewire of claim 5 wherein a second layer of insulating
material is disposed on the electrical conducting material of the
first electrical conductor and the layer of conducting material of
the second electrical conductor is disposed on the second layer of
insulating material.
7. The guidewire of claim 6 wherein a third layer of insulating
material is disposed on the electrical conducting material of the
second electrical conductor.
8. The guidewire of claim 1 wherein the insulating and electrical
conducting layers encircle a length of the proximal core
section.
9. The guidewire of claim 2 including means to electrically connect
the electrodes on the proximal extremity of the guidewire to a
source of electrical energy to facilitate heating the intermediate
core section by induction.
10. The guidewire of claim 2 wherein the means to electrically
connect the proximal end of the guidewire to a source of electrical
energy has electrical contact means biased against the electrodes
on the proximal end of the proximal core section.
11. The guidewire of claim 10 wherein the means to electrically
connect the proximal end of the guidewire to a source of electrical
energy has means to secure the proximal extremity of the proximal
core section to prevent the disengagement thereof.
12. The guidewire of claim 1 wherein the intermediate core section
is formed from an alloy of nickel and titanium and which contains
from about 10 to about 75% martensite phase at body
temperature.
13. The guidewire of claim 1 wherein the intermediate core section
is formed from an alloy of nickel and titanium and which contains
from about 25 to about 50% martensite phase.
14. The guidewire of claim 1 wherein the distal core section is
formed of a superelastic NiTi alloy with an A.sub.f greater than
body temperature.
15. The guidewire of claim 1 wherein a cylindrical connecting
member interconnects the distal core section with the intermediate
core section.
16. The guidewire of claim 15 wherein the cylindrical connecting
member is formed of a superelastic NiTi alloy with an A.sub.f
greater than body temperature.
17. The guidewire of claim 1 wherein a cylindrical connecting
member interconnects the proximal core section with the
intermediate core section.
18. The guidewire of claim 17 wherein the cylindrical connecting
member is formed of a superelastic NiTi alloy with an A.sub.f
greater than body temperature.
19. The guidewire of claim 1 wherein the proximal core section has
a solid proximal portion and a hollow distal portion with an inner
lumen extending therein.
20. The guidewire of claim 19 wherein the first electrical
conductor is an individually insulated electrical wire which
extends through the inner lumen of the hollow distal portion of the
proximal core section and is electrically connected to a proximal
extremity of the intermediate core section.
21. The guidewire of claim 19 wherein the second electrical
conductor is an individually insulated electrical wire which
extends through the inner lumen of the distal portion of the
proximal core section and is electrically connected to a distal
extremity of the intermediate core section.
22. The guidewire of claim 1 wherein the intermediate core section
is formed from an alloy consisting essentially of about 30 to about
52 atomic % titanium and the balance nickel and up to 10 atomic %
of one or more additional alloying elements selected from the group
consisting of up to 3 atomic % each of iron, cobalt, platinum,
palladium and chromium and up to about 10 atomic % copper and
vanadium.
23. A method of performing an intraluminal procedure within a
patient's body lumen comprising: a) providing a guidewire which has
an intermediate core section formed of a NiTi alloy which has a
substantial level of martensite phase at body temperature and which
has a final austenite transformation temperature above body
temperature but below 50.degree. C.; b) positioning the guidewire
at a desirable location within the patient's body lumen; c) heating
the intermediate core section to a temperature above body
temperature to convert at least part of the martensite phase of the
intermediate core section to the austenite phase; and d) advancing
a catheter over the intermediate core section of the guidewire
while the intermediate core section is predominantly in the
austenite phase to a desired location within the patient's body
lumen.
24. The method of claim 23 wherein at least 50% of the martensite
phase in the intermediate core section is converted to the
austenite phase when the intermediate core section is heated within
the body lumen.
25. A method of making an intraluminal guidewire comprising: a)
providing a cold worked, heat treated elongated member formed of a
nickel-titanium alloy having a finish austenite temperature of less
than body temperature; b) further heat treating the elongated
member at a temperature of about 375.degree. to about 450.degree.
C. for at least 15 minutes. c) mechanically working the elongated
member into an intermediate core member of a final desired size and
shape; d) securing a proximal extremity of the intermediate core
member to a distal extremity of a high strength proximal core
member; e) securing a distal extremity of the intermediate core
member to a proximal extremity of a distal core member; and f)
securing a helical coil to at least the distal core member.
26. The method of claim 25 wherein the elongated member is heated
at a temperature between about 375.degree. to about 450.degree. C.
for a period of about 0.5 to about 12 hours.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the field of medical devices, and
more particularly to guiding means such as a guidewire for
advancing a catheter within a body lumen to perform a procedure
such as percutaneous transluminal coronary angioplasty (PTCA).
[0002] In a typical PTCA procedure a guiding catheter having a
preformed distal tip is percutaneously introduced into the
cardiovascular system of a patient by means of a conventional
Seldinger technique and advanced therein until the distal tip of
the guiding catheter is seated in the ostium of a desired coronary
artery. A guidewire is positioned within an inner lumen of a
dilatation catheter and then both are advanced through the guiding
catheter to the distal end thereof. The guidewire is first advanced
out of the distal end of the guiding catheter into the patient's
coronary vasculature until the distal end of the guidewire crosses
a lesion to be dilated, then the dilatation catheter having an
inflatable balloon on the distal portion thereof is advanced into
the patient's coronary anatomy over the previously introduced
guidewire until the balloon of the dilatation catheter is properly
positioned across the lesion. Once in position across the lesion,
the balloon is inflated one or more times to a predetermined size
with radiopaque liquid at relatively high pressures (e.g., greater
than 4 atmospheres) to compress the arteriosclerotic plaque of the
lesion against the inside of the artery wall and to otherwise
expand the inner lumen of the artery. The balloon is then deflated
so that blood flow resumes through the dilated artery and the
dilatation catheter can be removed therefrom.
[0003] Conventional guidewires for angioplasty and other vascular
procedures usually comprise an elongated core member with the
distal portion of the core member having one or more tapered
sections and a flexible body such as a helical coil disposed about
the distal portion of the core member. A shapable member, which may
be the distal extremity of the core member or a separate shaping
ribbon which is secured to the distal extremity of the core member
extends through the flexible body and is secured to a rounded plug
at the distal end of the flexible body. Torquing means are provided
on the proximal end of the core member to rotate, and thereby
steer, the guidewire while it is being advanced through a patient's
vascular system.
[0004] Further details of guidewires can be found in U.S. Pat. No.
4,516,972 (Samson); U.S. Pat. No. 4,538,622 (Samson, et al.); U.S.
Pat. No. 4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652
(Simpson), U.S. Pat. No. 4,748,986 (Morrison et al.); U.S. Pat. No.
5,135,504 (Abrams); U.S. Pat. No. 5,341,818 (Abrams et al. And U.S.
Pat. No. 5,411,476 (Abrams et al) which are hereby incorporated
herein in their entirety by reference thereto.
[0005] A major requirement for guidewires and other intraluminal
guiding members, whether they be solid wire or tubular members, is
that they have sufficient column strength to be pushed through a
patient's vascular system or other body lumen without kinking.
However, they must also be flexible enough to pass through tortuous
passageways without damaging the blood vessel or other body lumen
through which they are advanced. Efforts have been made to improve
both the strength and flexibility of guidewires in order to make
them more suitable for their intended uses, but these two
properties tend to be diametrically opposed to one another in that
an increase in one usually involves a decrease in the other.
[0006] The prior art makes reference to the use of alloys such as
NITINOL (Ni--Ti alloy) which have shape memory and/or superelastic
or pseudoelastic characteristics in medical devices which are
designed to be inserted into a patient's body. The shape memory
characteristics allow the prior art devices to be deformed while in
the martensite phase to facilitate their insertion into a body
lumen or cavity and then be heated within the body to transform the
metal to the austenite phase so that the device returns to its
remembered shape. Superelastic characteristics on the other hand
generally allow the metal to be deformed and restrained in the
deformed condition to facilitate the insertion of the medical
device containing the metal into a patient's body, with such
deformation causing the phase transformation, e.g. austenite to
martensite. Once within the body lumen the restraint on the
superelastic member can be removed, thereby reducing the stress
therein so that the superelastic member can return to its original
undeformed shape by the transformation back to the original
austenite phase. In other applications, the stress induced
austenite to martensite transformation is utilized to minimize
trauma while advancing a medical device such as a guidewire within
a patient's body lumen.
[0007] Alloys have shape memory/superelastic characteristics
generally have at least two phases, a martensite phase, which has a
relatively low strength and which is stable at relatively low
temperatures, and an austenite phase, which has a relatively high
strength and which is stable at temperatures higher than the
martensite phase.
[0008] Shape memory characteristics are imparted to the alloy by
heating the metal at a temperature above body temperature,
preferably between about 40.degree. to about 60.degree. C. while
the metal is kept in a constrained shape and then cooled to ambient
temperature. The cooling of the alloy to ambient temperature causes
at least part of the austenite phase to transform to the martensite
phase which is more stable at this temperature. The constrained
shape of the metal during this heat treatment is the shape
"remembered" when the alloy is reheated to these temperatures
causing the transformation of the martensite phase to the austenite
phase. The metal in the martensite phase may be plastically
deformed to facilitate the entry thereof into a patient's body. The
metal will remain in the "remembered" shape even when cooled to a
temperature below the transformation temperature back to the
martensite phase, so it must be reformed into a more usable shape,
if necessary. Subsequent heating of the deformed martensite phase
to a temperature above the martensite to austenite transformation
temperature causes the deformed martensite phase to transform to
the austenite phase and during this phase transformation the metal
reverts back to its remembered shape.
[0009] The prior methods of using the shape memory characteristics
of these alloys in medical devices intended to be placed within a
patient's body presented operational difficulties. For example,
with shape memory alloys having a martensite phase which is stable
at a temperature below body temperature, it was frequently
difficult to maintain the temperature of the medical device
containing such an alloy sufficiently below body temperature to
prevent the transformation of the martensite phase to the austenite
phase when the device was being inserted into a patient's body.
With intravascular devices formed of shape memory alloys having
martensite-to-austenite transformation temperatures well above body
temperature, the devices could be introduced into a patient's body
with little or no problem, but they usually had to be heated to the
martensite-to-austenite transformation temperature which was
frequently high enough to cause tissue damage and very high levels
of pain.
[0010] When stress is applied to a specimen of a metal such as
NITINOL exhibiting superelastic characteristics at a temperature at
or above which the transformation of martensite phase to the
austenite phase is complete, the specimen deforms elastically until
it reaches a particular stress level where the alloy then undergoes
a stress-induced phase transformation from the austenite phase to
the martensite phase. As the phase transformation proceeds, the
alloy undergoes significant increases in strain but with little or
no corresponding increases in stress. The strain increases while
the stress remains essentially constant until the transformation of
the austenite phase to the martensite phase is complete.
Thereafter, further increase in stress is necessary to cause
further deformation. The martensitic metal first yields elastically
upon the application of additional stress and then plastically with
permanent residual deformation.
[0011] If the load on the specimen is removed before any permanent
deformation has occurred, the martensitic specimen will elastically
recover and transform back to the austenite phase. The reduction in
stress first causes a decrease in strain. As stress reduction
reaches the level at which the martensite phase transforms back
into the austenite phase, the stress level in the specimen will
remain essentially constant (but substantially less than the
constant stress level at which the austenite transforms to the
martensite) until the transformation back to the austenite phase is
complete, i.e., there is significant recovery in strain with only
negligible corresponding stress reduction. After the transformation
back to austenite is complete, further stress reduction results in
elastic strain reduction. This ability to incur significant strain
at relatively constant stress upon the application of a load and to
recover from the deformation upon the removal of the load is
commonly referred to as superelasticity or pseudoelasticity.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to improve guidewires or
guiding members, wherein a core section which is manufactured in an
austenite phase to facilitate manufacturing such as centerless
grinding or any other desirable shaping or machining and which is
then transformed at least partially into a lower strength
martensite phase to improve its flexibility and to facilitate its
advancement within the patient.
[0013] The guidewire of the invention generally has a high strength
proximal core section, an intermediate core section formed at least
in part of a NiTi alloy which has a significant level of martensite
phase at body temperature (approximately 37.degree. C.) but which
transforms to the higher strength austenite phase at a temperature
above body temperature. A distal core section may have a flexible
body, such as a helical coil, disposed about and secured to at
least part of the distal core section.
[0014] Generally, the intermediate core section should have about
10% to about 75%, preferably about 25% to about 50% martensite at
body temperature. An intermediate core section which is 100%
martensite phase can have inadequate strength to be readily pushed
through body lumens in some instances. Preferably, the temperature
at which the transformation of the martensite to austenite is
complete, i.e. A.sub.f, should not be high enough to cause
significant pain or tissue damage. The conversion to the austenite
phase should be nearly complete, i.e. at least 75%, for best
results. Reference herein to percent metallic phase is to weight
percent unless noted otherwise.
[0015] Means are provided to heat the intermediate core section
while it is disposed within the patient to transform martensite
phase in the NiTi alloy thereof to the austenite phase. Preferably,
the intermediate core section is provided with a straight memory in
the austenite phase, although other shapes may be suitable for many
situations.
[0016] One presently preferred method of heating the intermediate
core member is by resistance or inductive heating. In this case,
one electrical conductor is electrically connected by its distal
end to a location in the proximal extremity of the intermediate
core section and a second electrical conductors is electrically
connected by its distal end to a location in the distal extremity
of the intermediate core section. The proximal ends of the
electrical conductors are electrically connected to a source for
electrical energy by means of a suitable electrical connector. Upon
passage of electrical current through the intermediate core
section, its temperature rises by the resistive or inductive
heating to the desired transformation temperature. The intermediate
core section should be otherwise electrically isolated to avoid
loss of current, to prevent undesirable heating of adjacent
guidewire components and the delivery of electrical current to
adjacent tissue. Preferably, one or more temperature sensor or
other means are provided on or in association with the intermediate
core section to sense the temperature and facilitate the control
thereof by controlling the level of electrical current directed to
the intermediate core section. Conventional control procedures and
systems may be employed to effect this temperature control.
[0017] The intermediate core section with substantial levels of the
martensite phase provides excellent flexibility to the distal part
of the guidewire which allows the guidewire to pass through
tortuous passageways without undergoing plastic deformation or
causing traumatic engagement with the wall of a body lumen through
which the guidewire is passing. The martensite of the intermediate
core section is transformed when the guidewire is in the desired
location within the patient's body lumen and in this condition the
intermediate core section has a higher strength level provided by
the austenite phase so there is little tendency for the distal part
of the guidewire to be displaced from, e.g. pulled out of, a side
branch of a coronary artery when a catheter is advanced over the
guidewire.
[0018] The alloy composition and the thermomechanical processing of
the intermediate core section are selected to provide an austenite
phase during the mechanical working of the intermediate core
section and then the memory inducing heat treatment is selected to
provide a martensite phase at the operating temperature of the
guidewire, i.e body temperature, with a transformation temperature
(to the austenite phase) not greater than about 50.degree. C.,
preferably not greater than about 45.degree. C.
[0019] The intermediate core section is preferably formed from an
alloy consisting essentially of about 30 to about 52% titanium and
the balance nickel and up to 10% of one or more additional alloying
elements. Such other alloying elements may be selected from the
group consisting of up to 3% each of iron, cobalt, platinum,
palladium and chromium and up to about 10% copper and vanadium. As
used herein all references to percent composition are atomic
percent unless otherwise noted. The presently preferred alloy
composition is about 51% nickel with the balance being titanium and
conventional impurities.
[0020] To form the intermediate section of the guiding member,
elongated member of the preferred alloy material is first cold
worked, preferably by drawing, to effect a size reduction of about
30% to about 70% in the transverse cross-section thereof. The
cold-worked material may then be given a memory imparting heat
treatment at a temperature of about 450.degree. to 600.degree. C.
for about 0.5 to about 60 minutes, while maintaining a longitudinal
stress on the elongated portion equal to about 5% to about 50%,
preferably about 10% to about 30%, of the yield stress of the
material (as measured at room temperature). This thermomechanical
processing imparts a straight "memory" to the superelastic portion
and provides a relatively uniform residual stress in the material.
Another method providing similar properties involves mechanically
straightening the wire after the cold work and then heat treating
the wire at temperatures between about 300.degree. and about
450.degree. C., preferably about 330.degree. to about 400.degree.
C. However, this latter treatment provides substantially higher
tensile properties. Finish austenite transformation temperature is
preferably less than body temperature and generally about
-10.degree. C. to about 30.degree. C. For more consistent final
properties, it is preferred to fully anneal the solid rod or
tubular stock prior to cold work so that the material will always
have the same metallurgical structure at the start of the cold
working and so that it will have adequate ductility for subsequent
cold working. It will be appreciated by those skilled in the art
that means of cold working the metal other than drawing, such as
rolling or swaging, can be employed.
[0021] The cold-worked and heat-treated NiTi alloy material is in
the austenite phase at the temperature at which the intermediate
core section is to be mechanically worked, e.g. centerless grinding
to the final diameter or to form tapers therein. Effective grinding
of the intermediate core section is difficult when the alloy has
substantial levels of the martensitic phase, but it is quite easy
when the work piece is in the austenite phase.
[0022] After the final mechanical working of the intermediate core
section, it is subjected to a low temperature aging treatment at
about 375.degree. to about 450.degree. C. for at least 15 minutes,
preferably about 0.5 to about 12 hours to ensure a martensite phase
at body temperature with a finish austenite phase transformation
temperature above body temperature but less than 50.degree. C. For
an alloy comprising about 51 atomic % nickel and the balance
titanium, a low temperature aging treatment of 400.degree. C. for
two hours provides an austenite start temperature of 30.degree. C.,
a austenite peak temperature of 38.degree. C. and an austenite
finish temperature of 44.degree. C., and a martensite start
temperature of 38.degree. C. a martensite peak temperature of
34.degree. C. and a martensite finish temperature of 25.degree.
C.
[0023] In one presently preferred embodiment, the intermediate core
section and the distal core section are initially formed from the
same starting NiTi workpiece. After the workpiece has been cold
worked and heat treated to the austenite phase in the prescribed
manner and then further mechanically formed to the final desired
shape, e.g. by centerless grinding, the intermediate and distal
core sections are separated by suitable cutting means. The
intermediate core section is subjected to the low temperature aging
treatment to generate the martensite phase which is stable at body
temperature. The separated distal core section, which is used in
the austentite phase, is assembled without further processing into
the guidewire. The proximal and distal core sections are preferably
connected to proximal and distal ends of the intermediate section
respectively, by means of a cylindrical shaped tubular connector
element which is formed of essentially the same NiTi alloy with
superelastic properties to provide a smooth transition between the
proximal and intermediate core sections and the intermediate and
distal core sections.
[0024] These and other advantages of the invention will become more
apparent from the following detailed description thereof when taken
in conjunction with the following exemplary drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is an elevational view, partially in section, of a
guidewire having features of the invention.
[0026] FIG. 2 is a transverse cross-sectional view of the guidewire
shown in FIG. 1 taken along the lines 2-2.
[0027] FIG. 3 is a transverse cross-sectional view of the guidewire
shown in FIG. 1 taken along the lines 3-3.
[0028] FIG. 4 is a transverse cross-sectional view of the guidewire
shown in FIG. 1 taken along the lines 4-4.
[0029] FIG. 5 is a longitudinal cross-sectional view of an
electrical connector system which has inserted therein the proximal
end of a guidewire such as that shown in FIG. 1 to provide
electrical connection between the electrodes on the proximal end of
the guidewire and an electrical source (not shown)
[0030] FIG. 6 is a top view, partially in section, of the connector
shown in FIG. 5.
[0031] FIG. 7 is a longitudinal view, partially in section of an
alternative embodiment of the invention.
[0032] FIG. 8 is a transverse cross-sectional view of the guidewire
shown in FIG. 7 taken along the lines 8-8.
[0033] FIG. 9 is a transverse cross-sectional view of the guidewire
shown in FIG. 7 taken along the lines 9-9.
[0034] FIG. 10 is a partial elevational view, partially in section,
of an alternative embodiment of the invention.
[0035] FIG. 11 is a partial elevational view, partially in section,
of another alternative embodiment of the invention.
[0036] FIG. 12 is a transverse cross-sectional view of the
guidewire shown in FIG. 11 taken along the lines 12-12.
[0037] FIG. 13 is a transverse cross-sectional view of the
guidewire shown in FIG. 11 taken along the lines 13-13.
DETAILED DESCRIPTION OF THE INVENTION
[0038] FIGS. 1-4 illustrate a guidewire 10 which embodies features
of the invention. Generally, the guidewire 10 includes a elongated
shaft 11 with a proximal core section 12, an intermediate core
section 13 and a distal core section 14. A helical coil 15 is
disposed about the distal core section 14 and is secured by solder
or adhesive at locations 16 and 17. A shaping ribbon 18 is secured
by its proximal end to the distal core section 14 at location 17
and by its distal end to the distal end of the helical coil 15 by
welding or brazing forming the rounded end 19 in a conventional
"floppy" construction.
[0039] A first cylindrical connector member 20 interconnects the
distal end of the proximal core section 12 and the proximal end of
the intermediate core section 13. A second cylindrical connector
member 21 interconnects the distal end of the intermediate core
section 13 and the proximal end of the distal core section 14. The
first and second cylindrical connector members 20 and 21 may be
secured to the respective core sections by a suitable adhesive or
by solder. The intermediate and distal core sections 13 and 14 and
the connector members 20 ans 21 are formed of a NiTi alloy which
generates a titanium oxide surface making the soldering difficult.
However, these members can be effectively soldered by removing the
oxide layer and pre-tinning the nascent surface with a gold-tin
solder as described in U.S. Pat. No. 5,341,818 (Abrams et al.)
which is incorporated herein by reference.
[0040] The proximal core section 12 is provided with a pair of
electrodes 22 and 23 which are in electrical contact with
conducting layers 24 and 25 respectively. Insulating layer 26,
which is disposed on the surface of the proximal core section 12,
electrically isolates the proximal core section from the electrode
22, and, as shown is FIG. 1, extends to the proximal end of the
intermediate core section 13. The conducting layer 24 extends to
location 27 on the proximal end of the intermediate core section 13
just beyond the end of the insulating layer 26 where it is in
electrical contact with the surface of the intermediate core
section at the said location.
[0041] An intermediate insulating layer 28 is provided on the
surface of the conducting layer 25 which extends from the distal
end of electrode 22 to the distal portion of the intermediate core
section 13 and electrically isolates the electrode 23 from the
conducting layer 24. The conducting layer 25 extends distally on
top of the intermediate insulating layer 28 to a location 30
immediately beyond the distal end of the insulating layer 28 where
it is in electrical contact with the surface of the intermediate
core section. A third insulating layer 31 is disposed on the
surface of the conducting layer 25 and extends from the distal end
of the electrode 23 to beyond the location 30 to ensure complete
insulation of the conducting layer 25. An insulating tubular member
32, formed of suitable material such as polyimide, is disposed on
the inner surface of the cylindrical connecting member 21 to ensure
that no electrical current can pass from the intermediate core
section 13 to the distal core section 14. Both the insulating and
conducting layers may be applied by dip coating, spraying or other
suitable methods known to those skilled in the art. Interfitting
tubular members of insulating and conducting materials may likewise
be used.
[0042] FIGS. 5-6 schematically illustrate an electrical connector
40 for connecting the electrodes 22 and 23 on the proximal end of
the guidewire 10 to a source of high frequency electrical energy
(not shown). The connector 40 has an elongated passageway 41
extending inwardly from an exterior port 42 which is configured to
slidably receive the proximal end of the guidewire 10. The
connector 40 has a pair of electrical contacts 43 and 44 which are
spaced along passageway 41 so as to be aligned with the electrodes
22 and 23 when the proximal end of the guidewire 10 is properly
positioned within the passageway. The electrical contacts 43 and 44
are ball bearings which are urged into contact with the electrodes
22 and 23 by the biasing action of springs 45 and 46 disposed
within the passageways 47 and 48 perpendicular with the passageway
41. Set screws 50 and 51 are threadably disposed within the upper
threaded portions of the passageways 47 and 48 to engage the
springs 45 and 46 to effect the biasing against the electrical
contacts 43 and 44. A screw clamp 52 is threadably disposed within
the threaded channel 53 to be tightened against the proximal end of
the guidewire 10 to hold the guidewire in place and prevent its
removal. Electrical conductors 53 and 54 are electrically connected
by their distal ends to set screws 50 and 51 and by their proximal
ends to a high frequency (e.g. RF) electrical energy source (not
shown). The electrical power requirements for the system will vary
depending upon the nature of the current transmission to the
intermediate core section and the mass of the intermediate section.
Generally, however, the power requirements will be within the range
of about 3 to about 15 watts, usually about 6 to about 10
watts.
[0043] An alternate embodiment of the invention is depicted in
FIGS. 9. The proximal core section 12 of this embodiment has a
solid core portion 55 and a tubular portion 56. Individually
insulated electrical wire 57 is electrically connected by it
proximal end at location 58 to the solid core portion 55 to which
electrode 22 is electrically connected. Insulated electrical
conducting wire 59 is electrically connected by its proximal end to
electrode 23 at location 60. Insulating sheath 61 is disposed
between the electrode 23 and the solid core portion 55. An
insulating sheath 62 is disposed between the proximal end of the
tubular portion 56 and the solid core portion 55 and insulating
sheath 63 is disposed between the tubular portion 56 and the
intermediate core section 13 to electrically isolate the tubular
portion. Polyimide is a suitable material for the sheaths 61, 62
and 63. The conductor wire 57 is electrically connected by its
distal end to the proximal end of the intermediate core section 13
at location 64 and electrical conducting wire 59 is electrically
connected by its distal end to the distal portion of the
intermediate section 13 at location 65. A polymer sleeve 66 is
disposed over the junction between the solid core portion 55 and
the tubular portion 56. The distal end of the guidewire 10 has
essentially the same structure as that shown in FIG. 1 and is
numbered accordingly.
[0044] FIG. 10 depicts another alternate embodiment of the
invention wherein the guidewire 10 has the proximal electrode 22
electrically connected to the proximal core section 12, and an
individually insulated conductor wire 70 is electrically connected
to the distal electrode 23. Electrical connection between the
distal end of the proximal core section 12 and the proximal end of
the intermediate core section 13 is made by the cylindrical
connector member 20. A first insulating layer 71 covers the
exterior of the proximal core section 12 to insulate the latter
from the electrode 23. Cylindrical connector 20 mechanically and
electrically connects the distal end of the proximal core section
12 with the proximal end of the intermediate core section 13. The
conductor wire 70 electrically interconnects the distal electrode
23 with the distal end of the intermediate section 13 at location
72. An insulating sleeve 73 is disposed about the distal end of the
intermediate section and the proximal end of the distal core
section 14 within the cylindrical connector member 21 to
electrically isolate the distal core section from the intermediate
core section. An outer polymer jacket 74 is provided over a
substantial part of the guidewire shaft 11 distal to the electrode
23.
[0045] Yet another embodiment of the invention is illustrated in
FIGS. 11-13 which is similar to both of the prior alternate
embodiments. In this embodiment the proximal core section has a
proximal solid core portion 80 with a distal tubular portion 81
which is electrically and mechanically connected to the solid core
portion. Electrode 22 of the guidewire 10 is electrically connected
directly to the solid core portion 80. Distal electrode 23 is
electrically connected to the proximal end of individually
insulated electrical conductor wire 82 which has its distal end
connected to the distal end of the intermediate core section 13 at
location 83. Insulating layer 84 is disposed about the distal end
of the intermediate core section and the proximal end of the distal
core section and is disposed between these ends and the cylindrical
connector member 21. Insulating layer 85 is disposed between the
solid core portion 80 and the electrode 23. An outer jacket 86 is
provided about the exterior of the guidewire distal to the
electrode 23. The distal portion of the guidewire 10 is essentially
the same as in the prior embodiments.
[0046] The overall dimensions of the guidewire are generally about
140 to about 190 cm in length, typically about 175 cm, and about
0.008 to about 0.035 inch (0.89 mm) in diameter. The transverse
dimensions of the intermediate and distal core sections may be
substantially smaller than the transverse dimensions of the
proximal core section. The intermediate core sections has a length
of about 15 to about 40 cm, preferably about 20 to about 30 cm, and
the distal core section is about 3 to about 15 cm, preferably about
4 to about 7 cm. The distal core section may have one or more
tapers and the most distal part is preferably flattened, e.g.
0.002.times.0.003 inch (0.05-0.075 mm) and 0.001.times.0.003 inch
(0.025-0.075 mm). To the extent not otherwise described,
conventional construction techniques and materials may be
utilized.
[0047] The intermediate core section is formed of a shape memory
NiTi alloy as previously described and at operating temperature
(37.degree. C.) is in the martensite phase. The preferred alloy
composition is about 51% (atomic) nickel and the balance titanium
and conventional impurities. The distal core section 14 is
preferably formed from the same alloy but in the austenite phase at
operating temperature.
[0048] The guidewire of the invention is utilized in essentially
the same fashion as conventional guidewires, except that after
placement of the guidewire at a desirable location within the
patient's body lumen, but before a catheter is advanced over the
distal portion of the guidewire, the intermediate core section is
heated to a temperature which transforms a substantial portion,
preferably all, of the martensite phase to the austenite phase.
While it is usually desirable to convert all of the martensite
phase of the intermediate core section to the austenite phase,
total conversion is not necessary to obtain the advantages of the
invention. However, usually at least 50% of the martensite phase
must be converted to provide the strength desirable to facilitate
effective tracking of a catheter over the in-place guidewire. The
guidewire must be long enough for its distal end to extend out the
distal end of the catheter to be advanced over the guidewire and it
proximal end with the electrodes to enable the electrodes thereon
to be electrically connected to a high frequency electrical energy
source.
[0049] A variety of modifications and improvements may be made to
the present invention without departing from the scope thereof.
Although individual features of embodiments of the invention may be
shown in some of the drawings and not in others, those skilled in
the art will recognize that individual features of one embodiment
of the invention can be combined with any or all the features of
another embodiment.
* * * * *