U.S. patent application number 12/487191 was filed with the patent office on 2009-10-08 for delivery system for medical device.
This patent application is currently assigned to Cook Incorporated. Invention is credited to Palle Hansen, Nathaniel A. Irwin, Fred T. Parker.
Application Number | 20090254168 12/487191 |
Document ID | / |
Family ID | 40799386 |
Filed Date | 2009-10-08 |
United States Patent
Application |
20090254168 |
Kind Code |
A1 |
Parker; Fred T. ; et
al. |
October 8, 2009 |
DELIVERY SYSTEM FOR MEDICAL DEVICE
Abstract
A system for delivery of a medical device to a target site
within the body of a patient includes an introducer sheath, and a
delivery assembly receivable within a passageway of the sheath. The
delivery assembly comprises an inner tubular and an outer tubular
member. At least a distal portion of the inner tubular member has a
diameter such that the medical device is receivable thereover. The
outer tubular member is generally coaxial with the inner tubular
member, and has a length such that the outer tubular member distal
end terminates proximal to the inner tubular member distal portion.
The outer tubular member has a first outer diameter at the proximal
end and extends for a length of the outer tubular member to a first
diameter boundary point. The outer tubular member has a gradual
inward taper in the distal direction from the boundary point to a
second outer diameter, and has an abrupt outward taper in the
distal direction from the second diameter to the first
diameter.
Inventors: |
Parker; Fred T.;
(Unionville, IN) ; Hansen; Palle; (Bjaeverskov,
DK) ; Irwin; Nathaniel A.; (Bloomington, IN) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE/INDY/COOK;BRINKS HOFER GILSON & LIONE
CAPITAL CENTER, SUITE 1100, 201 NORTH ILLINOIS STREET
INDIANAPOLIS
IN
46204-4220
US
|
Assignee: |
Cook Incorporated
Bloomington
IN
William Cook Europe ApS
Bjaeverskov
|
Family ID: |
40799386 |
Appl. No.: |
12/487191 |
Filed: |
June 18, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11965210 |
Dec 27, 2007 |
7566342 |
|
|
12487191 |
|
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|
Current U.S.
Class: |
623/1.11 |
Current CPC
Class: |
A61F 2/95 20130101; A61F
2002/9665 20130101; A61M 2025/0004 20130101; A61M 2025/0681
20130101 |
Class at
Publication: |
623/1.11 |
International
Class: |
A61F 2/84 20060101
A61F002/84 |
Claims
1-15. (canceled)
16. A delivery assembly for use in delivering a medical device to a
target site within the body of a patient, comprising: an inner
tubular member having a proximal end and a distal end, at least a
distal portion of said inner tubular member having a diameter such
that said medical device is receivable thereover in a compressed
condition; an outer tubular member having a proximal end and a
distal end, said outer tubular member generally coaxial with the
inner tubular member and having a length such that said outer
tubular member distal end terminates proximal to said inner tubular
member distal portion, said outer tubular member having a first
outer diameter at said proximal end and having a gradual inwardly
tapered portion in a distal direction to a second outer diameter;
and a holder band having a proximal end and a distal end, at least
a portion of said holder band disposed over said outer tubular
member second diameter, said holder band sized and arranged to
maintain a position of said medical device on said inner tubular
member.
17. The delivery assembly of claim 16, wherein said first outer
diameter extends for a major length of said outer tubular member to
a first diameter boundary point, said outer tubular member having
said gradual inward taper in the distal direction from said
boundary point to said second outer diameter.
18. The delivery assembly of claim 17, wherein said holder band has
an outward taper from said distal end to said proximal end, at
least a portion of said outward taper corresponding to said outer
tubular portion inward taper.
19. The delivery assembly of claim 16, wherein the distal end of
said holder band comprises a shoulder for inhibiting proximal
movement of said medical device.
20. The delivery assembly of claim 16, wherein said holder band has
a greater flexibility than a flexibility of said outer and inner
tubular members.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a delivery system for
transporting a medical interventional device to a target site
within the body of a patient. More particularly, the invention
relates to a system of coaxial tubular members for delivering a
medical device, such as a stent, into a designated lumen in the
body of a patient to establish, or maintain, patency of the
lumen.
[0003] 2. Background Information
[0004] In modern medicine, interventional devices are often
percutaneously introduced into the body of a patient via a suitable
delivery apparatus, and delivered to a target site within the body
for a medical purpose. One common example of a medical
interventional device introduced in this manner is a stent. A stent
is typically inserted into the lumen of a vessel or other bodily
passageway to reinforce, repair, or otherwise provide support to
establish or maintain the patency of the lumen. For example, when a
patient suffers from atherosclerosis (hardening of the arteries), a
stent may be placed in a coronary or a peripheral artery at a
location where the artery is weakened, damaged or otherwise
susceptible to collapse. The stent, once in place, reinforces that
portion of the artery, thereby restoring normal blood flow through
the vessel.
[0005] One form of stent which is particularly desirable for
implantation in arteries and other body lumens is a cylindrical
stent which is radially expandable upon implantation from a smaller
first diameter to a larger second diameter. Radially expandable
stents are typically loaded onto, or into, a delivery catheter, and
fed internally through the arterial pathways of the patient until
the unexpanded stent reaches the target site. Radially expandable
stents are normally of two general types. One type, generally
referred to as a "balloon-expandable" stent, is fitted in a
compressed state over an uninflated balloon at the distal end
portion of the delivery catheter. Once the catheter reaches the
target site, the balloon is inflated by transmitting an inflation
fluid through a lumen in the delivery catheter to the interior of
the balloon. Upon inflation, the balloon exerts a radial pressure
on the stent, thereby causing the compressed stent to radially
expand to a larger diameter. Following expansion, the stent
exhibits sufficient radial rigidity to remain in the expanded
condition after the balloon has been deflated and the catheter has
been removed.
[0006] The other type of radially expandable stent, generally
referred to as a "self-expanding" stent, is formed from a resilient
or shape memory material which is capable of self-expanding from a
compressed state to an expanded state without the application of a
radial outwardly-exerted force on the stent. Typically, a
self-expanding stent is loaded into a delivery device that
restrains the stent in the compressed state. Once the delivery
device is directed to the target site, an ejection mechanism, such
as a pusher, is employed to eject the stent from the distal end of
the delivery device. Alternatively, an outer sheath of the delivery
device is withdrawn such that it no longer covers the stent. In
either event, once the stent is freed from the restraints of the
device, it self-expands to the desired diameter.
[0007] The use of radially expandable stents advantageously allows
the physician to insert relatively smaller diameter medical devices
to prop up, reinforce or otherwise support relatively larger
diameter vessels. However, the delivery of such stents to the
target site has at times proven to be problematic. For example, the
structure of a conventional delivery catheter may cause the
catheter shaft to be subject to stress risers as it traverses the
vessel. Stress risers comprise weakened or high stress segments of
the catheter which may cause the catheter shaft to undesirably bend
or otherwise fail during passage through the vessel. In a delivery
system for a self-expanding stent that includes coaxial catheters,
such high stress segments may occur, for example, at the point
where the inner catheter meets the outer catheter. This typically
occurs when the delivery system traverses a tortuous pathway in the
body of the patient. In some cases, such as the bifurcation into
the iliacs, the catheter is required to go around a high angle
bend. In these instances, kinking and decreased trackability are
prone to occur due to the high stress in the system as it attempts
to traverse the high angle bend.
[0008] It is desired to provide a delivery system for a stent or
other interventional medical device that avoids the problems of
prior art devices.
SUMMARY
[0009] The problems of the prior art are addressed by the inventive
delivery system. In one form thereof, the invention comprises an
assembly for use in the delivery of a medical device to a target
site within the body of a patient. The assembly comprises an inner
tubular member having a distal portion sized to receive the medical
device thereover. An outer tubular member is coaxial with the inner
tubular member, and has a length such that the distal end of the
outer tubular member distal end terminates proximal to the inner
tubular member distal portion. The outer tubular member has a first
outer diameter at its proximal end, and a gradual inwardly tapered
portion in a distal direction to a second outer diameter. The outer
tubular member then has an abrupt outward taper in the distal
direction from the second diameter.
[0010] In another form thereof, the invention comprises a system
for delivery of a medical device to a target site within the body
of a patient. The delivery system includes an introducer sheath
having a proximal end, a distal end, and a passageway extending
therebetween. The introducer sheath has a length sufficient for
insertion through a pathway in the body of the patient from an
entry site to the target site. A delivery assembly is receivable
within the sheath passageway for carrying the medical device. The
delivery assembly comprises an inner tubular member having a
proximal end and a distal end, at least a distal portion of the
inner tubular member having a diameter such that the medical device
is receivable thereover, and an outer tubular member having a
proximal end and a distal end. The outer tubular member is
generally coaxial with the inner tubular member and has a length
such that the outer tubular member distal end terminates proximal
to the inner tubular member distal portion. The outer tubular
member has a first outer diameter at the proximal end and extends
for a length of the outer tubular member to a first diameter
boundary point. The outer tubular member has a gradual inward taper
in the distal direction from the boundary point to a second outer
diameter, and has an abrupt outward taper in the distal direction
from the second diameter.
[0011] In still another form thereof, the invention comprises a
delivery assembly for use in delivering a medical device to a
target site within the body of a patient. The delivery assembly
comprises an inner tubular member and an outer tubular member. At
least a distal portion of the inner tubular member has a diameter
such that the medical device is receivable thereover in a
compressed condition. The outer tubular member is generally coaxial
with the inner tubular member, and has a length such that the
distal end of the outer tubular member terminates proximal to the
inner tubular member distal portion. The outer tubular member has a
first outer diameter at its proximal end, and has a gradual
inwardly tapered portion in a distal direction to a second outer
diameter. A holder band is disposed over the outer tubular member
second diameter. The holder band is sized and arranged to maintain
a position of the medical device on the inner tubular member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a longitudinal sectional view of a delivery system
according to one embodiment of the present invention;
[0013] FIG. 2 is an enlarged view of a portion of FIG. 1;
[0014] FIG. 3 is a longitudinal sectional view of the inner
delivery assembly of the delivery system of FIG. 1;
[0015] FIG. 4 is an enlarged view of the distal end portion of the
outer tube of the inner delivery assembly;
[0016] FIG. 5 is a longitudinal sectional view of an alternative
embodiment of an inner delivery assembly for use in a delivery
system; and
[0017] FIG. 6 is an enlarged view of a portion of the inner
delivery assembly of FIG. 5.
DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED
EMBODIMENTS
[0018] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiments illustrated in the drawings, and specific language will
be used to describe the same. It should nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, such alterations and further modifications in the
illustrated device, and such further applications of the principles
of the invention as illustrated therein being contemplated as would
normally occur to one skilled in the art to which the invention
relates.
[0019] In the following discussion, the terms "proximal" and
"distal" will be used to describe the opposing axial ends of the
delivery system, as well as the axial ends of various component
features. The term "proximal" is used in its conventional sense to
refer to the end of the system (or component thereof) that is
closest to the operator during use of the system. The term "distal"
is used in its conventional sense to refer to the end of the system
(or component thereof) that is initially inserted into the patient,
or that is closest to the patient during use.
[0020] FIG. 1 is a longitudinal sectional view of a delivery system
10 according to one embodiment of the present invention. FIG. 2 is
an enlarged view of a portion of the delivery system of FIG. 1. As
illustrated, delivery system 10 comprises an introducer sheath 12,
and an inner delivery assembly 14. In the embodiment shown, inner
delivery assembly 14 comprises coaxial outer 16 and inner 18
tubular members. The figures also illustrate the presence of a
medical interventional device, such as stent 20, that is loaded
into the delivery system at a distal end of inner delivery assembly
14. A conventional handle (not shown) may be provided at the
proximal end of the system.
[0021] Introducer sheaths are well known in the medical arts.
Optimally, an introducer sheath should be capable of traversing
tortuous pathways in the body of the patient without kinking. This
generally necessitates that the sheath have sufficient flexibility
to negotiate high angle bends, such as the bifurcation into the
iliacs. At the same time, the sheath should have sufficient
trackability to enable it to enter, and pass into, the target
area.
[0022] A preferred introducer sheath for use in the inventive
system is the FLEXOR.RTM. introducer sheath, available from Cook
Incorporated, of Bloomington, Ind. The FLEXOR.RTM. sheath includes
an inner lubricious liner, an outer polymeric jacket, and a coil
reinforcement between the inner and outer layers. Typically, the
sheath comprises one or more longitudinal segments of decreasing
durometer in the distal direction. This sheath provides very
favorable flexibility without kinking or compression. One or more
radiopaque bands or markers may be incorporated within the sheath
material to allow precise location of the sheath's distal tip for
positioning accuracy. Those skilled in the art will appreciate that
other known introducer sheaths may also be suitable for a
particular purpose. The length of the introducer sheath will
typically be between about 80 and 150 cm. Preferably, the length of
the introducer sheath will be between about 110 and 130 cm, and
more preferably, about 125 cm. Those skilled in the art will
appreciate, however, that all dimensions provided herein are
intended as examples only, and that sheaths and inner delivery
assemblies of different dimensions may be substituted for a
particular use.
[0023] FIG. 3 is a longitudinal sectional view of the inner
delivery assembly 14 of delivery system 10. For illustrative
purposes, a stent 20 has been loaded onto the distal end of
assembly 14. Coaxial outer and inner tubes 16, 18 are preferably
immovable relative to each other, or at most, only minimally
movable such that the relative positioning of the tubes as shown in
the figures is substantially maintained during use of delivery
system 10. Outer and inner tubes 16, 18 can be rendered
substantially immovable, for example, by utilizing an adhesive or
other attachment mechanism that connects the tubes at their
respective proximal ends. Alternatively, the adhesive or other
attachment mechanism can be applied anywhere along the length of
the outer and inner tubes in a manner sufficient for maintaining
the respective relative positions substantially as shown in the
figure.
[0024] Inner tube 18 may have a length the same as, or
substantially similar to, the length of the introducer sheath.
Inner tube 18 includes a passageway 22 extending therethrough
having a diameter sufficient to accommodate a wire guide (not
shown). A distal seat portion 24 of inner tube 18 is sized for
seating stent 20 on an outer surface thereof. Typically, a soft
polymeric tip 19 is positioned at the distal end of inner tube 18
to ease entry into the body.
[0025] Outer tube 16 of inner delivery assembly 14 has a length
less than the length of inner tube 18. Thus, for example, when a
125 cm introducer sheath is used, the length of inner tube 18 may
also be about 125 cm, and the length of outer tube 16 may be about
117 cm. The difference in length between inner tube 18 (125 cm) and
outer tube 16 (117 cm) represents the length of seat portion 24 for
stent 20. In this case, seat portion 24 and stent 20 each have a
length of about 8 cm. The components of delivery system 10 can, of
course, be formed to have other lengths so that stents or other
medical interventional devices having lengths other than 8 cm can
also be delivered via the inventive delivery system 10.
[0026] Beginning at proximal end 17 and extending in the distal
direction for the major part of its length, outer tube 16 of inner
delivery assembly 14 preferably has a generally uniform outer
diameter, referred to herein as the "nominal" diameter of tube 16.
As described herein, a "major" part of the length of outer tube 16
refers to a length that exceeds one-half of the overall length of
outer tube 16. Preferably, the "major" length of outer tube 16
refers to a length of at least about 75% of the length of the tube.
The outer profile of a distal portion A (FIG. 3) of outer tube 16
is modified when compared to the nominal diameter of its major
length. For the delivery system having the dimensions provided
hereinabove, the distal most portion A having the modified profile
represents approximately the distal most 16 cm of the outer tube
16. Beginning at the proximal boundary 40 of portion A (which has
the nominal outer diameter), and extending in a distal direction
therefrom, the outer diameter of outer tube 16 has a gradual inward
taper for a distance of between about 10 and 20 cm, preferably
about 15 cm, to a minimum diameter point 42. This inwardly tapering
portion is designated in FIG. 3 as portion B. There is then a
short, or abrupt, outward taper back (over a distance of
approximately 0.2 cm) to the nominal diameter. The nominal diameter
thereafter extends substantially in the distal direction the
remainder (approximately 0.8 cm) of portion C until it terminates
in outward flared portion 44. As described herein, a "gradual
inward taper" is one that extends from a larger diameter over a
relatively large length to a smaller diameter. An "abrupt outward
taper" is one that extends from a smaller diameter over a
relatively short length, typically not more than about 1 cm, to a
larger diameter.
[0027] Although it is preferred that outer tube 16 maintains the
nominal diameter for the major part of its length prior to the
gradual inward taper, this is not necessary in all instances. If
desired, a more gradual inward taper of tube 16 that commences from
a point proximal to that of boundary 40 up to proximal end 17 maybe
substituted. Similarly, although it is preferred that the abrupt
outward taper occur over a relatively short length (such as 0.2 cm
in the example provided), this is not necessary in all instances,
and a somewhat less abrupt outward taper may be substituted.
Preferably, however, the respective "gradual" and "abrupt" tapers
will be in general proportion to those of the inward and outward
tapers recited in the example provided.
[0028] Outer tube 16 is configured such that it includes a shoulder
28 at its distal end. Preferably, the distal most extension of
portion C is also provided with the slight outward flare 44. This
is best shown in FIG. 4. As a result, when inner delivery assembly
14 is received in introducer sheath 12 as shown in FIG. 1, the
radial extension of flared portion 44 substantially butts against
the inner surface of the introducer sheath. In this manner,
shoulder 28 and flare 44 act in the nature of a holding, or
restraining, band to prevent proximal movement or drifting of stent
20 as introducer sheath 12 is withdrawn in the proximal direction
during deployment of the stent.
[0029] Typically in a coaxial catheter assembly utilized in a
delivery system, a high stress point is created where the inner
tube meets the outer tube. This is particularly true in the
vicinity of the distal portion of the outer tube. This is due, in
part, to the stiffness of the combined tubes being greater than the
stiffness of the single inner tube, and, in part, to the stiffness
of the medical interventional device, such as stent 20, seated on
the inner tube. As stated, when the catheter assembly is required
to go around a high angle bend, such as the aforementioned
bifurcation into the iliacs, kinking and decreased trackability are
prone to occur due to the high stress point described above, as
well as any other stress risers that may form or otherwise be
present. In the embodiment of the inventive arrangement described,
the stress at the high stress point is reduced by providing the
gradual inward taper of the outer tube diameter to the smaller
diameter in the vicinity of the distal end of the inner delivery
assembly, and then providing the abrupt outward taper in the
inverse direction. This arrangement will distribute the stress more
evenly, and improve trackability.
[0030] Tapered portion B may be formed in outer tube 16 by any
conventional means. Preferably, tube 16 is ground to the desired
tapered configuration, such as with use of a conventional grinder
that can be programmed to grind different profiles, a process often
referred to as centerless grinding. Alternatively, other known
means for forming a tapered catheter, such as extrusion, may be
employed. The distal flare 44 of tube 16 may be formed by
conventional means, such as by heating the portion to be flared
(e.g., via a conventional flare gun) and forming the desired flare
on the heated portion. The flare need not have any specific
configuration, as long as the configuration is suitable for acting
as a pusher or holder against the stent, such that proximal drift
of the stent is inhibited upon withdrawal of the introducer sheath.
In general, it is preferred to shield as much of the proximal end
of the stent area as possible with the flare.
[0031] The dimensions of the introducer sheath 12 and the outer and
inner tubes 16, 18 will, of course, depend upon the intended use of
the delivery system 10. The following non-limiting example is
provided to illustrate the relative dimensions of the various
component features for a representative use. In this example, the
length of the introducer sheath is 125 cm. The outer diameter (OD)
of the sheath will, of course, be dependent upon the vessel to be
traversed. In most cases the OD of the introducer sheath will be
between about 0.069 and 0.10 inch (1.75 and 2.54 mm), and in the
example provided herein, about 0.092 inch (2.34 mm). The inner
diameter (ID) of the sheath will, in most cases, be between about
0.0535 and 0.090 inch (1.36 and 2.29 mm), and in the example
described herein, about 0.076 inch (1.93 mm). As stated, these
dimensions are merely exemplary of possible dimensions for a
particular use. Those skilled in the art can readily select
appropriate dimensions for a specific use.
[0032] With reference to the components of the inner delivery
system 14, the ID of the inner tube 18 may be about 0.040 inch
(1.02 mm), or large enough such that a wire guide can be
accommodated therethrough. The 0.040 inch ID is large enough to
accommodate a standard wire guide of about 0.035 inch (0.89 mm)
diameter. The OD of the inner tube may be about 0.051 inch (1.30
mm). The nominal OD of outer tube 16 may be about 0.071 inch (1.80
mm), and the ID of the tube may be about 0.058 inch (1.47 mm). The
minimum OD of the outer tube at point 42 of maximum taper may be
about 0.064 inch (1.63 mm). The maximum OD at flared portion 44 may
be about 0.075 inch (1.91 mm), or in other words, only slightly
less than the 0.076 inch (1.93 mm) ID of the introducer sheath.
Once again, those skilled in the art will appreciate that these
dimensions are merely exemplary of possible dimensions for a
particular use, and that appropriate dimensions can be readily
selected for a specific intended use.
[0033] One specific example of a taper of outer tube 16 has been
provided above. In that non-limiting example, the outer diameter of
outer tube 16 has a gradual inward taper (portion "B") for a
distance of about 15 cm, to a minimum diameter point 42. There is
then a short outward taper of approximately 0.2 cm to the nominal
diameter, which thereafter extends substantially in the distal
direction the remainder (approximately 0.8 cm) of portion C. Those
skilled in the art will appreciate that these dimensions are also
merely exemplary of possible dimensions for a particular use, and
that appropriate dimensions can be readily selected for a specific
intended use. Typically, virtually any taper into the nominal
diameter of the outer tube will provide at least some enhanced
flexibility to the tube, and serve to distribute the stress more
evenly than before. A skilled artisan may utilize routine
experimentation to determine an optimal taper for a particular use,
which taper may include a more, or less, gradual inward taper than
described in the example above, and a more, or less, gradual
outward taper. Such a taper will, in many instances, be dependent
upon the respective compositions of the sheath and inner delivery
assembly, as well as the anticipated degree of bend of the sheath
and assembly as they pass through one or more bends in a tortuous
body passageway.
[0034] Outer and inner tubes 16, 18 of inner delivery assembly 14
are preferably formed of a composition having sufficient strength,
flexibility, and resistance to compression to traverse tortuous
areas of the anatomy. One particularly preferred composition is
PEEK (polyetheretherketone). PEEK is a particularly favored
composition for medical use based upon the properties recited
above, as well as its biocompatibility and resistance to
degradation under extreme conditions. Those skilled in the art will
appreciate, however, that other compositions may also be suitable
for a particular application. Non-limiting examples of other
suitable catheter compositions include nylon (polyamide), polyether
block amides, and PET (polyethylene terephthalate).
[0035] FIGS. 5 and 6 illustrate an alternative inner delivery
assembly 114 for use in the inventive delivery catheter 10.
Introducer sheath 12 has been omitted from these figures to better
illustrate the features of the inner delivery assembly. FIG. 5 is a
longitudinal sectional view of the inner delivery assembly 114.
FIG. 6 is an enlarged view of a portion of FIG. 5. In this
embodiment, inner delivery assembly 114 comprises coaxial outer 116
and inner 118 tubes. The figures also illustrate the presence of a
stent 20 that is loaded into the delivery system at a distal end of
inner delivery assembly 114.
[0036] Inner tube 118 includes a passageway 122 extending
therethrough having a diameter sufficient to accommodate a wire
guide (not shown). A distal portion 124 of inner tube 118 is sized
for seating stent 20 on an outer surface thereof. Outer tube 116 of
inner delivery assembly 114 has a length less than the length of
inner tube 118, which difference in length represents the length of
distal seat portion 124 for stent 20. The components of inner
delivery assembly 114 not specifically described are generally the
same as or similar to corresponding components in the
previously-described inner delivery assembly 14.
[0037] In the preferred embodiment shown, outer tube 116 extends in
the distal direction from proximal end 117 at a generally uniform
"nominal" diameter for the major part of its length. The outer
profile of a distal portion X of outer tube 116 (FIG. 5) is
modified when compared to the nominal diameter of its major length.
In this embodiment, the distal most portion X begins at point 140,
and exhibits a gradual inward taper to a minimum diameter at the
distal end 142 of outer tube 116. Alternatively, the taper may
commence at a point proximal to point 140 if an even more gradual
taper is desired.
[0038] A holder band 150 for the medical device, such as stent 20,
is fitted over the distal portion of outer tube 116. In the
preferred embodiment shown in FIG. 6, holder band 150 has an inner
diameter that increases from a smaller ID at the distal end 152 to
a larger ID at proximal end 154. Preferably, at least a portion of
the distal length of holder band 150 extends distal of outer tube
distal end 142. In a preferred embodiment, at least a portion of
the interior surface of holder band 150 has an outward taper that
substantially corresponds to the inward taper of outer tube 116.
When fitted onto inner delivery assembly 114 as shown, the outer
diameter of holder band 150 will preferably be substantially the
same as the nominal outer diameter of outer tube 116. The
respective outer diameters of the outer tube and the holder band
will preferably be similar to, but slightly smaller than, the inner
diameter of the introducer sheath (not shown). As a result, the
outer diameter of the holder band will be as close to the inner
diameter of the introducer sheath as possible, without causing
interference or friction upon relative movement with the introducer
sheath.
[0039] Holder band 150 terminates in the distal direction in a
shoulder 156. Shoulder 156 is preferably sized and configured to
inhibit stent 20 from protruding or otherwise drifting in the
proximal direction beyond shoulder 156 upon withdrawal of the
introducer sheath during deployment of the stent, in the same
manner as shoulder 28 in the previous embodiment. The holder band
need not be formed to have the identical configuration described
herein, as long as the selected configuration provides enhanced
flexibility to the overall assembly, and will suffice to maintain,
or hold, the position of the stent as described. Use of a separate
element, such as the holder band, may provide enhanced flexibility
in a particular case when compared to the use of an integral tube
as described in the previous embodiments. Utilizing a separate
element also provides the ability to use different materials for
this portion of the assembly, such as a more flexible composition,
if desired.
[0040] Holder band 150 is preferably formed of a flexible polymeric
material such as nylon. Other known materials, such as polymers and
non-ferrous metals, having favorable compression strength and
flexibility may be substituted. The tapered portion may be formed
in outer tube 116 in the same manner in which the taper is formed
in outer tube 16. A flare may be formed at the distal end of the
holding band in the same manner as the flare in outer tube 16.
[0041] While these features have been disclosed in connection with
the illustrated preferred embodiments, other embodiments of the
invention will be apparent to those skilled in the art that come
within the spirit of the invention as defined in the following
claims.
* * * * *