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1. FIELD OF THE INVENTION
The present invention relates to a catheter guide wire for accessing a
tissue target site via a small-lumen tortuous path within a target tissue.
2. BACKGROUND OF THE INVENTION
Catheters are being used increasingly as a means for delivering diagnostic
or therapeutic agents to internal target sites that can be accessed
through the circulatory system. For example, in angiography, catheters are
designed to deliver a radio-opaque agent to a target site within a blood
vessel, to allow radiographic viewing of the vessel and blood flow
characteristics near the release site. For the treatment of localized
disease, such as solid tumors, catheters allow a therapeutic agent to be
delivered to the target site at a relatively high concentration, with
minimum overall side effects. Methods for producing localized
vaso-occlusion in target tissue regions, by catheter injection of a
vaso-occlusive agent, have also been described (co-owned U.S. patent
application for "Hyperthermic Treatment of Tumors", Ser. No. 751,605,
filed 2 July 1985).
Often the target site which one wishes to access by catheter is buried
within a soft tissue, such as brain or liver, and can be reached only by a
tortuous route through small vessels or ducts--typically less than about 3
mm lumen diameter--in the tissue. The difficulty in accessing such regions
is that the catheter must be quite flexible, in order to follow the
tortuous path into the tissue, and at the same time, stiff enough to allow
the distal end of the catheter to be manipulated from an external access
site, which may be as much as a meter or more from the tissue site.
Heretofore, two general methods for accessing such tortuous-path regions
have been devised. The first method employs a highly flexible catheter
having a dilated or dilatable distal end. A major limitation of this
method is that the catheter will travel in the path of highest blood flow
rate, so many target sites with low blood flow rates cannot be accessed.
In the second prior art method, a torqueable guide wire having a distal
bend is guided, by alternately rotating and advancing the wire, to the
target site. With the wire in place, a thin-walled catheter is then
advanced along the wire until the distal catheter end is positioned at the
target site. Once the catheter is advanced, the guide wire may be
withdrawn to allow fluid delivery or withdrawal through the catheter. An
important advantage of this method is the ability to control the location
of the catheter along a vascular pathway.
Several types of guide wires for use in catheter placement have been
proposed. The simplest type of wire is a preferred diameter of between
about 8-40 mils (thousandths of an inch). The distal end of the wire may
be provided with a bent tip which can be oriented, by means of guide
structure at the proximal end, to guide the wire along a selected vascular
path. Ideally, torque transmission should be controlled, such that a
selected wire rotation at the wire's proximal end produces a corresponding
rotation of the distal end. Because of their greater flexibility, smaller
diameter wires, e.g., having diameters of between about 8-18 mils, may be
required for accessing small-vessel and/or tortuous-path regions. However,
if the wire is too thin along its entire length, it may be difficult to
transmit torque in a controlled manner along the entire wire length.
Further, the wire may buckle with axial movement due to low column
strength.
Constant-diameter guide wires having a wire core encased in a flexible
polymer tubing have also been proposed. The flexible tubing acts to
increase the column strength of the wire core without significantly
reducing overall flexibility. As a result, the problem of wire buckling,
especially in small-diameter wires, is lessened. Biocompatible polymers,
such as TEFLON.RTM., polyolefins, and polyurethane have been suitable.
More recently, guide wires which have multiple variable-thickness steps
along the wire length have been proposed. Wires of this type have the
advantage that the proximal end region, where greater torsional strength
is required, have relatively large diameters--e.g., between about 20-40
mils, and the distal end region, where greater flexibility is required,
have progressively smaller diameters. Typically, a wire of this type will
have different diameter segments extending collectively over an
approximately 25-60 cm distal portion of the wire, and a short (typically
1-3 cm) tapered transition zone across each step. The tapered zones are
typically formed by centerless grinding in which the wire is placed
between two counter-rotating grinding wheels whose confronting grinding
surfaces are angled slightly to produce the desired taper over the width
of the wheels.
If the tapered transition is relatively steep and/or transition occurs in a
region where a sharp vessel bend is encountered, the wire may bend sharply
in the step (transition) zone, due to the differential bending modulus at
the transition zone. If the catheter on the wire has already been advanced
past the point of the bend, the catheter may deform at the wire bend,
making further catheter advance along the wire difficult or impossible.
Further, torqueability in the wire is reduced at the region of a sharp
bend, since torque tends to be transmitted through the angle of the bend,
rather than along the axis of the wire.
Guide wires having extended sections of continuous taper have also been
disclosed. The long tapered regions have less tendency to undergo
irreversible bending than relatively short tapered wire sections. However,
problems of wire buckling and difficulty in sliding the wire within the
catheter in a tortuous path limit the ability of the wire and catheter to
reach deep tissue sites.
The problems of advancing a catheter along a guide wire in a small-lumen
tortuous tissue pathway are also due to limitations in prior art catheter
construction. If the catheter is relatively rigid, it cannot track over
the final distal portion of the wire in the tortuous path region, because
catheter advancement buckles the wire in a narrow turn, or because
catheter advancement pulls the wire out of the distal vessels. On the
other hand, catheters having more flexible shafts, such as those used in
balloon flow-directed devices, lack the column-strength in the catheter's
proximal section to be advanced over the guide wire without buckling.
3. SUMMARY OF THE INVENTION
It is therefore one general object of the invention to provide a guide wire
designed to overcome the above-discussed limitations in accessing the
tortuous path tissue sites.
A more specific object of the invention is to provide such a guide wire for
accessing soft tissue target sites, such as deep brain sites, which have
heretofore been inaccessible to catheters.
Still another object of the invention is to provide a catheter device for
delivery of an injectable fluid or particle suspension at a tissue site
which can be accessed only by a tortuous vessel path, which may be defined
by arteries, veins, or tissue ducts.
The invention includes, in one aspect, a guide wire designed for use in
guiding a catheter to a target site along a tortuous vessel path which is
at least about 20 cm long and which has sharp-bend vessel junctions. Such
a path requires advancing a distal portion of the wire across the
junction, then sliding the catheter over the advanced portion of the wire.
The wire has three sections with progressively greater flexibility, and
different lubricity or sliding properties. A flexible, torqueable proximal
wire section is between about 50-250 cm in length and is formed of a
proximal wire core segment having an outer diameter of between about 10-40
mils. A more flexible intermediate section has a length between about
20-60 cm and is formed from an intermediate wire-core segment having a
reduced diameter of between about 4-20 mils and between about 10%-50% of
the core's proximal segment, and a flexible tube covering which encases
the intermediate core segment. A most flexible distal end section has a
length between about 1-10 cm and is formed from a distal wire core segment
having a reduced diameter of between about 2-6 mils, and a flexible sleeve
covering the distal end segment and providing column strength thereto. The
intermediate section has a low-friction polymer surface provided by the
covering which makes the section more lubricious than the adjacent distal
end segment.
In a preferred embodiment, the proximal wire core segment is between about
10-20 mils, the intermediate wire core segment has an average diameter of
between about 4-8 mils, and the distal wire core segment has a diameter of
between about 2-5 mils. The intermediate wire core segment has a
substantially constant diameter along its length, and includes a
relatively short region of taper between the constant-diameter portions of
the distal and intermediate wire core segment. The distal wire core
segment has a substantially continuous taper along its length. The guide
wire may have a substantially constant outer diameter along its length, or
a slight reduction in diameter progressing toward the distal end.
Also in a preferred embodiment, the flexible polymer covering in the
intermediate section is a polymer tube which is effective to increase the
column strength of the intermediate section, and which has a low-friction
polymer coating. The sleeve covering is a helical coil formed from a
radio-opaque metal strand material.
In another aspect, the invention includes a catheter device for use in
accessing a target site along a tortuous vessel path. The device includes
a guide wire of the type described above and a catheter designed to be
advanced over the wire, with such advanced to the target site.
In a preferred embodiment, the catheter has a relatively stiff proximal
tube segment dimensioned to track the wire along its proximal end section,
and a relatively flexible distal tube segment constructed and dimensioned
to track the wire along its intermediate and distal end sections. Also in
a preferred embodiment, the catheter and wire have a substantially
constant radial clearance of about 2-5 mils.
These and other objects and features of the invention will become more
fully appreciated when the following detailed description of the invention
is read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows fragmentary portions of a guide wire constructed according to
one embodiment of the present invention;
FIG. 2 shows fragmentary portions of a guide wire constructed according to
another embodiment of the invention;
FIGS. 3 and 4 are enlarged side views of a discrete (FIG. 3) and continuous
(FIG. 4) taper in the tapered region of an embodiment of the guide wire
such as shown in FIG. 1;
FIGS. 5 and 6 are enlarged sectional views of different embodiments of
flexible sleeves suitable for covering the distal end regions of the guide
wires constructed according to the invention;
FIG. 7 shows a catheter device constructed according to the present
invention;
FIG. 8 shows an enlarged section of the catheter device in FIG. 7, taken
along the region indicated at 8--8;
FIG. 9 illustrates a portion of a tortuous path in a soft tissue, and a
catheter and guide wire being advanced along this path;
FIGS. 10 and 11 are enlarged regions of the FIG. 11 path, showing the steps
in advancing the catheter through a sharp-bend junction in the path.
DETAILED DESCRIPTION OF THE INVENTION
I. Guide Wire
FIG. 1 shows a guide wire 20 constructed according to one embodiment of the
invention. The wire is a flexible torqueable wire having an overall length
of between about 70-300 cm between its proximal and distal ends 22, 24,
respectively, and a maximum outer diameter of between about 8-40 mils
(thousandths of an inch). The major portion of the wire is a flexible
proximal section 26 whose overall length ranges from about 40-250 cm. This
section is followed by a more flexible intermediate section 28 having a
length between about 15-60 mils, and a most flexible distal end section 30
wose length is between about 1-10 cm. It will be appreciated that the wire
is shown in greatly exaggerated radial scale, and that a major portion of
the distal end section has been cut away.
A wire core 32 in the guide wire is formed of a flexible, torqueable wire
filament material, such as stainless steel. The diameter of the wire core,
at its maximum, is between about 8-40 mils. The segment of the core
forming the proximal section of the guide wire, indicated at 34, has a
substantially uniform diameter along its length, and corresponds to the
maximum diameter of the core, i.e., between 8-40 mils.
Within the intermediate section of the wire, the core is tapered from the
proximal-section diameter down to a reduced diameter which is preferably
about 4-20 mils and between about 10%-50% of the core's proximal segment
diameter. Thus, for example, where the proximal section core diameter is
18 mils, the core tapers to a minimum of between about 2-9 mils.
In the embodiment shown in FIG. 1, the taper in the core occurs over a
relatively short tapered segment 36 which is followed by a
reduced-diameter segment 38 having a substantially constant diameter along
its length. The length of the tapered segment is typically between about
10%-50% that of the constant-diameter, and the two segments together make
up the length of the intermediate wire section, i.e., about 20-60 cm.
The tapered segment in the FIG. 1 wire embodiment is shown in enlarged view
in FIG. 3. This type of taper may be thought of as a discrete taper, in
that the profile of the tapered section wall is linear, and the segment
intersects the opposed constant-diameter segments at discrete angles at
the annular regions 40a, 40b in the figure. FIG. 4 shows a tapered segment
42 of a wire core 44 formed in accordance with another embodiment of the
invention. Here the slope of the taper is continuously varying, and the
segment has the generally S-shaped wall profile seen. The taper segment
illustrated in FIG. 4 is generally preferred since it minimizes bending
and torque-transmission differentials at ends of the tapered segment.
Methods of forming the two types of tapers will be discussed below.
The two segments making up the core of the intermediate section of the wire
are covered along their length by a flexible polymer covering 46. The
major function of the covering is to provide a lubricious (low-friction)
surface along the intermediate section, and more particularly, a surface
which is more lubricious than the surface of the adjacent distal segment
of the wire and of the wire core. The covering preferably also functions
to provide column support to the reduced-diameter core in the intermediate
section, to reduce the tendency of this section to buckle under axial
compression.
Covering 46 is preferably formed of a polymer, such as TEFLON.TM.,
polyolefin, or polyurethane which can be bonded or otherwise tightly
affixed to the core wire, and which itself has a low-friction surface, as
is the case for TEFLON.TM., or whose surface can be coated with a
low-friction surface. Other suitable coverings include a tube formed from
virtually any polymer having exposed hydrogens, such as polyester,
polyolefins, polycarbonate, polyvinylchloride, latex or silicon rubber,
polystyrene, and polyacrylics, and a surface coating formed of a highly
hydrophilic, low-friction polymer, such as polyvinylpyrrolidone (PVP),
polyethyleneoxide, or polyhydroxyethylmethacrylate (polyHEMA) or
copolymers thereof.
In the embodiment shown in FIG. 1, covering 46 is formed of a relatively
thick-walled tubing 48 and a surface coating 50 of a low-friction polymer.
The inner diameter of the tubing is such as to form a tight fit of the
tubing on the wire core, and the outer diameter is substantially the same
as that of the core wire proximal section. Thus the proximal and
intermediate wire sections have substantially the same outer diameters,
e.g., between about 8-40 mils. The segment of the tubing encasing tapered
section 36 preferably has a complementary taper, as seen best in FIG. 3.
The low-friction polymer coating may also cover an adjacent portion of the
wire's proximal section, as shown in FIG. 1. Typically, the coating will
be applied to the 20-50 cm of the distal section core adjacent the
intermediate section. Alternatively, the proximal section core may be
coated with a less lubricious protective coating material, such as
silicone coating or the like.
With continued reference to FIG. 1, distal section 30 of the wire has a
length between about 1-10 cm and preferably has still greater flexibility
than the intermediate wire section. The wire core in the distal section,
referred to a segment 54, has a diameter which is substantially no greater
than that of the intermediate section core, and preferably is tapered to a
reduced diameter of between about 2-6 mils. In the embodiment shown in
FIG. 1, the core has a linear taper over its entire length. Alternatively,
the core may contain one or more discrete tapers.
The distal section portion of the core is fully or partially encased in a
flexible sleeve. The sleeve shown in FIG. 1 is a soft, flexible helical
coil 56 which is formed conventionally, e.g., as a winding of radio-opaque
wire strand, such as platinum, gold, or tungsten strand. As shown, the
coil extends from covering 46 to the distal end of the wire core. The coil
preferably has a fixed-dimension inner diameter, as shown, or may be
tapered, e.g., to match the taper in the core. Attachment of the coil to
the core is preferably by two or three solder or weld joints, including a
proximal joint 60 and a rounded distal joint 62. An intermediate joint
(not shown) serves to transmit torque in the wire to the coil, to cause
the end region of the guide wire to bend slightly at this solder joint, to
allow the wire to be guided in a selected direction in a vessel network,
by torqueing the proximal end of the wire. The core and coil can be
irreversibly shaped, prior to use, to include wire bend useful in guiding
the wire.
In addition to providing a mechanism for wire bending near the wire tip,
the coil also gives the distal section of the wire increased column
strength (in the axial direction), and reduces the chance of buckling in
this section with axial compression. At the same time, the combined
flexibility of the reduced diameter core and the coil are compatible with
a series of sharp bends, as the wire is moved through a tortuous pathway
in the target tissue. The rounded joint at the end of the wire acts to
shield vessel walls from the sharp end of the wire core.
According to an important feature of the invention, the distal section of
the wire, including the sleeve encasing the wire core in this section, is
less lubricious, i.e., has a higher frictional coefficient, than that of
the adjacent intermediate section. The higher-friction surface in this
section functions specifically, during a catheter placement operation, to
help anchor the distal section against a vessel wall at a vessel junction,
as will be seen below. The higher friction can be achieved in a number of
ways. Where the sleeve is a coil, the coiled surface inherently has a
higher surface coefficient than a low-friction polymer coating.
FIG. 5 is an enlarged sectional view of a distal section of a wire such as
shown in FIG. 1. The coil in the section, here indicated at 64, is formed
as a helical winding of a radio-opaque strand 66 which has been precoated
by a polymer cover 67. The polymer can be selected for low- or
high-friction surface properties, to selectively vary the frictional
properties of the sleeve. Alternatively, a coil formed from a bare strand
may be coated, after attachment to the wire core, with a suitable
protective polymer, such as silicon or the like.
In another embodiment, the sleeve in the distal segment may be a polymer
tubing which is both flexible and capable of providing column strength to
the distal-section wire core. The tubing, if formed to have a smooth wall,
can be made from a variety of polymers, such as polyethylene, latex or the
like, which have relatively high frictional coefficients. Alternatively,
the sleeve may be formed with surface features which increase the
frictional coefficient substantially. One such sleeve is shown in enlarged
view in FIG. 6, showing a portion of a distal section similar to FIG. 5.
Here the distal segment of the wire core, indicated at 70, is encased in a
polymer tube 72 having a series of annular grooves, such as grooves 74
formed in its surface. It can be appreciated that these grooves provide
increased tube flexibility as well as greater frictional coefficient. At
the same time, the added column strength contributed by the tube is
substantially preserved since axial compression on the tube acts to press
the grooved regions against one another. The polymer sleeve is preferably
provided with a radio-opaque band (not shown).
FIG. 2 shows a guide wire 80 constructed according to a second general
embodiment of the invention. The wire has proximal, intermediate, and
distal sections 82, 84, 86, respectively, and a wire core with
corresponding core segments 88, 90, 92, respectively. The wire differs
from that shown in FIG. 1 in that the wire core has a continuous, linear
(or, alternatively, a continuous S-shaped curve) through the intermediate
and distal sections rather than a shorter tapered segment and a longer
reduced-diameter segment. The other features of the wire, including a
polymer surface coating 94 which provides a low-friction surface over the
intermediate section and an adjacent portion of the distal section, are
substantially identical to those described above with reference to FIG. 1.
In forming the guide wire of the invention, the wire core is typically
constructed by grinding a conventional, constant-diameter guide wire, such
as is commercially available stainless steel wires. Step grinding can be
used to form relatively short tapered segments, such as in forming the
core used in the FIG. 1 wire. Methods of forming relatively long,
continuously tapered cores (FIG. 2) and non-linear tapered regions (FIG.
4) have been described in co-owned PCT patent application for "Catheter
and Tissue Accessing Method", W087/07493, filed Dec. 17, 1987, and
incorporated herein by reference.
The flexible polymer tube covering the intermediate core is segment(s) can
be applied to the core by conventional polymer spraying or dipping
methods, or by attaching a preformed polymer tube to the core segment(s).
The latter can be accomplished by attaching the tube to the core under
heat shrinking conditions, or by securing the tube to the wire by a
suitable wire/polymer bonding agent. As indicated above, the lubricious
surface coating may be formed by the surface of the covering, or
preferably, by applying a lubricious polymer surface coating. Such a
surface coating, which preferably covers a portion of the distal section,
can be applied by spraying or dipping, according to known methods.
II. Catheter Device
FIG. 7 shows a catheter device 100 constructed according to one aspect of
the invention. The device includes a catheter 102 which will be described
below, and a guide wire, here indicated at 104, of the type described
above. The device is designed for accessing a target site which can be
reached only along a small-lumen tortuous path within a target tissue, as
will be described with reference to FIGS. 9-11 below.
With reference to FIG. 7, catheter 102 is formed of a flexible tube 110
which is dimensioned to receive the guide wire therethrough, as shown. In
a preferred embodiment of the invention, the catheter has a relatively
stiff proximal segment 116 which makes up between about 70%-95% of the
total tube length, and a relatively flexible distal segment 118 which
makes up the remaining approximately 5%-30% of the tube length. The
construction of a catheter of this type has been detailed in
above-mentioned PCT patent application for "Catheter and Tissue Accessing
Method". Briefly, and with reference to FIG. 8, the relatively stiff
section of the tube is composed of inner and outer coaxial tubes 120, 122
which are tight-fitting with respect to each other. The stiffness in the
proximal segment is provided predominantly by tube 120. The inner, stiffer
tube is preferably polypropylene or high-density polyethylene tubing
having a final wall thickness (in the assembled catheter) of between about
2-4 mils. The outer, more flexible tube is preferably low-density
polyethylene or silicone tubing, also having a preferred wall thickness of
between about 2-4 mils.
With continued reference to FIG. 8, the inner diameter of the proximal
segment is dimensioned, with respect to the guide wire, to provide
sufficient wire clearance to allow the catheter to be moved easily over
the wire in an axial direction, during catheter placement at the target
site. The guide wire itself must have a relatively small diameter, to
permit its guided movement along a tortuous path in a target tissue. In a
preferred embodiment of the invention, the inner diameter of the catheter
and the outer diameter of the guide wire are substantially constant along
their lengths, and the clearance between the two is between about 2-5
mils. Thus, for example, a catheter designed for use with
constant-diameter guide wire whose outer diameter is 18 mils has a
preferred inner diameter of 20-25 mils, and more preferably 21-22 mils.
The preferred clearance between the wire and inner wall of the segment
reduces the tendency of the segment to buckle under compressional strain,
since the wire provides column support against tube bending and crimping.
The optimal length of the proximal segment will vary according to the
distance between the tissue region which is to be accessed by the catheter
and the external body site at which the catheter is introduced. In a
preferred embodiment, the total length of the catheter distal section is
about the same length as that of the intermediate and distal wire sections
combined.
Completing the description of the catheter, and with reference to FIG. 7,
the free end of the proximal segment is attached to a fitting 124, such as
a standard syringe fitting, for use in connecting a syringe to the
catheter for fluid injection and withdrawal. At the distal end of the
catheter, a radio-opaque band 125 (FIG. 9), such as a gold or platinum
band, serves as a marker for following the position of the catheter
radiographically.
III. Operation
The method of inserting the catheter into a tissue region which is reached
by a tortuous path will be described now with reference to FIG. 9. The
figure shows a region of soft tissue 140, such as brain tissue, containing
a target site 142. Initially the guide wire, indicated at 104, is fed from
a vascular access region adjacent the target tissue into a tissue-supply
vessel 144 which extends into the tissue. In the present example, the
tortuous path to the target site involves vessel 144, a vessel 146 which
branches off vessel 144 at more than a right angle, and branch vessels 148
and 150 which each branch off the preceding vessel as shown. The path
shown involves (a) a number of bends, some of which may be 90 degrees or
more, (b) small vessels, typically with lumen diameters of less than about
3 mm, and (c) a total path length within the target tissue of at least
about 10-20 cm.
In operation, the catheter device is threaded as a unit from an external
access site through the vasculature to a region adjacent, but not into the
tortuous path region of the target tissue. This is done, in the usual case
where the catheter must pass through the cardiac aorta, by first placing a
relatively large diameter guiding catheter (e.g., about 40 mils inner
diameter) from the access site through the aorta and toward the target
site. The present catheter device is then threaded through the guiding
catheter past the aorta, where large vessel diameters and high blood flow
volumes make it difficult to control the movement and position of the
catheter. Once beyond the guiding catheter, the catheter device can be
advanced as a unit toward the target site. In general, the path from the
access site to the region adjacent the tissue is easily accessible, in
that sharp bends, small-lumen vessels, and/or soft tissue structure are
not encountered.
Typically, when the tortuous path tissue region is reached, and
particularly where sharp bends in the path are encountered, the wire is
advanced ahead of the catheter. This is done by advancing the wire axially
within the catheter and at the same time torqueing the wire to orient the
bent tip of the wire in the direction of desired wire movement. After the
wire has been so advanced, the catheter is then advanced over the wire
until the catheter end is close to the wire end. This procedure is
repeated until the wire and catheter have been fully advanced through the
small-diameter tissue vessel region to the target tissue site.
The features of the present invention which contribute to its ability to
reach target sites along tortuous, soft-tissue paths can be appreciated
from FIGS. 10 and 11, which show an enlarged portion of the region 140
indicated at dash-dot line 151 in FIG. 9. FIG. 10 shows the configuration
of the catheter just after the distal section of the guide wire, indicated
at 152, has been advanced ahead of the catheter into branch vessel 148
from vessel 146. The wire advance is achieved by first torquing the wire
to orient the wire bend toward vessel 148, then moving the wire axially
until the wire end moves into the branch vessel.
With the wire now held in its advanced position, the catheter is moved
axially over the wire, in the direction of the vessel branch. It can be
appreciated from FIG. 10 that movement of the catheter over the wire bend
indicated at 156 causes this region of the wire to straighten, with the
effect of increasing the force of the catheter distal section against the
side of vessel 148. If the frictional force between the wire end region
and the vessel is quite low, the end region of the wire within vessel 148
will now tend to slip out of the vessel, since the wire in this region is
very flexible and easily capable of forming the type of rolling loop
needed to excricate itself from vessel 148. For this reason, it is
important that the surface of the distal region of the wire be a
relatively high-friction surface.
It is also seen in FIG. 10 that the intermediate section of the wire, here
indicated at 160, is contained largely within the catheter as the distal
section of the wire is advanced through the vessel branch junction. At
each bend in the catheter, the wire is pressed against the adjacent wall
section of the catheter, as shown at bend 162. This pressure, it can be
seen, increases the frictional resistance encountered in moving the wire
axially within the catheter. In particular, it has been found with prior
art wires that two or more such sharp bends in the catheter can make it
impossible either to advance the guide wire relative to the catheter,
during catheter placement, or to remove the wire after placement.
According to an important feature of the invention, this problem is solved
substantially by the low-friction surface on the intermediate wire
section.
To illustrate, as the catheter in FIG. 10 is advanced over the distal
section of the wire to the position shown in FIG. 11, only the most distal
bend will involve a higher-friction portion of the wire, although the
low-friction intermediate section may engage the catheter at several
bands. Even along the distal wire section, the force needed to overcome
the frictional resistance between the wire and distal catheter section is
reduced by high flexibility of this segment. Similarly, the relatively
high flexibility of the wire's intermediate section cooperates with the
low-friction surface to facilitate axial movement of the wire in the
catheter in a tortuous path.
Summarizing the important features of the invention, the greater
flexibility in the distal and intermediate sections of the guide wire,
related to the reduced-diameter feature of the wire core, allows the wire
to be guided along a tortuous small-vessel path in a soft tissue, for
accessing deep-tissue sites. The high flexibility in these sections also
reduces frictional forces set up between the wire and catheter in bend
regions along the access path.
The relatively high friction surface of the distal section is required in
anchoring the distal section of the wire within a branch vessel, as the
catheter is advanced across the junction. By contrast, the low-friction
surface of the intermediate section acts to minimize the frictional
resistance to axial wire movement through the catheter at regions of sharp
bending in the catheter. This allows the wire to slide (and rotate) within
the catheter with greater ease and reduces the liklihood that the wire
will become immobilized within the catheter during a placement operation.
In a preferred embodiment of the invention, a portion of the proximal wire
section adjacent the intermediate section is also provided with a
low-friction surface, i.e., substantially lower than that of the wire
core, to further reduce frictional resistance to wire movement. The more
proximal portion of this section which will be handled by the user in
guiding the wire from a body-access site to the target site preferably has
a higher friction surface, to allow the wire to be manipulated without
slippage.
Also in a preferred embodiment, the low-friction covering in the
intermediate section is formed of a flexible tube which gives column
support to the wire core. The greater column strength allows higher axial
force to be applied to the wire in a catheter placement operation, without
wire buckling. Where the guide wire and catheter each have constant
diameters along their lengths, and a clearance of 2-5 mils between the
two, the catheter also serves to resist wire buckling.
Additional advantages, in terms of target-site accessibility, are gained
when the guide wire is used with the gradient-flexibility catheter
described above. The greater flexibility in the distal region of the
catheter allows the catheter to follow or track a wire bend with less
axial force, since catheter deformation is reduced. Further, because the
catheter end region flexes more easily, it exerts less force on the distal
section of the wire when being advanced through a branch vessel junction,
so the wire stays anchored in the branch vessel with less frictional
resistance between the wire and vessel wall.
Preliminary clinical studies with the present invention indicate that the
guide wire/catheter can be guided to deep brain sites which have been
inaccessible previously. These sites typically involve catheter guidance
along a 15-25 cm brain vessel pathway which has 2 to 6 vessel junctions
where sharp turns are encountered, and spacing between adjacent turns of
between about 1 to 5 cm.
While the invention has been described with respect to particular
embodiments and uses, it will be appreciated that various changes and
modifications can be made without departing from the scope of the
invention.
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