Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02517702 2008-02-20
STENT FOR IMPLANTATION
TECHNICAL FIELD
[0002] The technical field of the invention is implantable medical devices,
and
in particular a stent useful for urinary drainage.
BACKGROUND
[0003] Minimally-invasive surgery has evolved to a point where procedures
that were unimaginable a few years ago are now routinely performed on a daily
basis. Even in these procedures, however, there is room for improvement. One
example is the removal of stones and calculi from kidneys and ureters, to the
great
relief of many suffering patients.
[0004] To treat this condition, several individual steps are involved. In one
procedure, these steps include placing a relatively narrow guidewire through a
urethra and a bladder, and then through the ureter and into the kidney. After
the
guidewire is placed, a catheter is run along the guidewire, dilating the body
passages (the urethra and the ureter) as it moves down the guidewire. In the
next
sequence for this procedure, a ureteral access sheath is guided along and down
the
guidewire and the catheter. The access sheath also dilates the body passages
as it
moves from outside the body, through the urethra, and into the ureter, down to
the
desired location, and into or very near the kidney.
[0005] The physician may then remove calculi and stones through the access
sheath, using a grasper, a retrieval basket or other device. The access sheath
protects the ureter from repeated passage of the retrieval device while the
stones or
calculi are removed. After the stones are removed, a ureteral stent may be
placed
into the ureter through the access sheath, using the catheter or a pushing
tube to
position the stent. The stent is used to retain patency of the ureteral lumen
and to
continue normal urinary drainage.
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[0006] One problem with this procedure is that the guidewire may need to be
very long in order for the physician to control passage first of the catheter
and then
of the access sheath to the desired location within the patient's body. Very
long
guidewires are not standard, and it may require two people to handle such a
guide
wire so that it does not drape onto the floor. The surgeon may decide he or
she
needs a guidewire with a stiffness different from the one provided with the
particular kit in order to negotiate the pathway. A substitute stiffer
guidewire may
not be readily available in non-standard lengths.
[0007] Using this procedure for sequential placement of first a catheter and
then an access sheath, the guidewire needs to be as long as the combination of
both the catheter and the access sheath. A long guidewire leads to two
problems,
including a greater tendency to kink, and a need for greater skill on the part
of the
physician to maneuver the guidewire while placing the guidewire itself, the
catheter, and the sheath.
[0008] Another problem that is encountered with ureteral stents occurs in
cancer patients, where a growth may apply radial compression to a ureter. Such
compression can make fluid flow difficult. In these cases, a typical
polymeric,
relatively soft pig-tail stent may not have sufficient radial strength to
resist
compression by a cancerous or other growth. In these cases, a stronger,
sturdier
ureteral stent is needed to resist radial compression and allow for continued
drainage from the kidney to the bladder. In some cases, a urethral stent or
catheter
may also be helpful to ensure drainage from the bladder. What is needed is a
better way to dilate the body passages in order to place the access sheaths
and
stents.
BRIEF SUMMARY
[0009] This need is met by embodiments of the present invention. One
embodiment of the present invention is a kit for placing a stent. The kit
includes a
wire guide, a catheter securable to an access sheath, the catheter further
comprising a connector at a proximal end of the catheter, and a stent for
placing in
a body passage of a patient through the access sheath. The stent comprises a
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hollow coiled wire with an internal lumen, the internal lumen communicating
outside the coiled wire through small spaces between adjacent coils, and
wherein
the stent further comprises a distal end with a distal pigtail portion and a
proximal
end with a proximal pigtail portion, each pigtail portion comprising an end-
cap,
the end caps secured to the wire and joined to an internal rod.
100101 Another embodiment is a stent. The stent includes a hollow coiled wire
having an intental lumen, the internal lumen communicating outside the coiled
wire through small spaces between adjacent coils, the coiled wire further
comprising a distal pigtail portion and a proximal pigtail portion. The stent
also
includes a distal cap on a distal end and a proximal cap on a proximal end of
the
coiled wire, the caps secured to the wire and also secured with a rod between
the
caps.
[0011] Another embodiment is a method of preparing a stent suitable for
implantation. The method includes steps of winding a wire coil, inserting a
rod
into the wound coil, attaching at least one end cap to the coil and/or to the
rod,
and electropolishing the stent. The wire coil may be wound such that small
spaces exist between adjacent coils. 7'here are many embodinients of the kit
and
stcnts according to the present invention, of which only a few are described
herein. The accompanying drawings and descriptions are meant to be
illustrative rather than limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Fig. I is an illustration of a present technique for ureteral stent
placement;
100131 Fig. 2 is an illustration of a technique for dual dilatation;
100141 Fig. 3 is a cross-sectional view of a first embodiment of a kit
according
to the present invention;
[00151 Figs. 3a and 3b depict a catheter and a sheath useful in kit
enlbodiments;
[0016] Fig. 4 depicts a pigtail ureteral stent;
100171 Figs. 5, 5a and 5b depict a ureteral stent usefiil in kit embodiments;
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[0018] Fig. 5c depicts a second embodiment of a stent; and
[0019] Fig. 6 depicts a stricture in a body lumen.
DETAILED DESCRIPTION OF THE DRAWINGS AND THE
PRESENTLY PREFERRED EMBODIMENTS
[0020] Figs. 1 and 2 illustrate the differences in technique between a present
method for ureteral stent placement and a new method of coaxial dual
dilatation.
In both figures, a physician desires to perform a procedure upon a kidney 10.
In
Fig. 1, a guidewire 14 is advanced through a urethra 13, a bladder 12, and a
ureter
11 to the kidney on which the procedure is to be performed. In order to
accomplish this, the wire guide is placed, and a ureteral stent 15 is guided
along
the guidewire, extending as far as desired, typically into the kidney by means
of a
pushing tube 18 that is also placed along the guidewire as shown. The
physician
places the stent by passing first the guidewire, and then passing the ureteral
stent
and the pushing tube over the guidewire. The urethra may be dilated separately
to
accommodate an instrument such as a cystoscope to aid the surgeon.
[0021] The guidewire is typically between 0.0 18 to 0.038 inches in diameter
(about 0.46 mm to 0.97 mm). The catheter may be 4-8 Fr. The ureteral stent may
be used for patency of the ureteral lumen. In order to achieve this
dilatation,
however, a very long wire guide was needed to extend the length of the both
the
catheter and the access sheath, where the access sheath is capable of
extending to
the ureteropelvic junction. This may lead to kinking and may also lead to
difficulty in the physician controlling the wire guide as he or she must
control the
entire length of the wire guide while sequentially running the catheter and
the
access sheath down the wire guide.
100221 An improved method is illustrated in Fig. 2. In this method, a
physician
places a wire guide 17 through a urethra 13, a bladder 12, and a ureter 11
into a
kidney 10. After the wire guide is placed, a catheter 19 secured to an access
sheath 16 is guided along the wire guide, the catheter and access sheath
combination coaxially "dual dilating" at least the proximal portion of the
ureter.
This coaxial dilatation procedure enables the physician to use a shorter wire
guide,
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e.g., using a 145 or 150 cm wire guide rather than a wire guide that may have
to be
220 cm or even longer, perhaps 250-260 cm. This may also shorten the time
required to position the access sheath, and thus shorten the actual time spent
in the
therapeutic procedure and reduce the number of personnel required. The access
sheath and the catheter are advanced to the desired location, e.g., into the
calices
of a kidney. The catheter may then be removed and replaced by a stent. The
stent
is then implanted by a surgeon pushing on a stent positioner, such as a
catheter or
other pushing device of appropriate diameter and length. The sheath is then
retracted while the positioner or other device is used to keep the stent in
place.
[00231 In addition to the method shown in Fig. 2, there are other ways to
practice the invention. For instance, rather than accessing the ureter through
the
urethra and bladder, a physician may use a nephrostomy method, in which the
access sheath and catheter are advanced through a person's skin to reach the
calices of the kidney directly. If a path to a bile duct is needed, the
physician may
access the bile duct through an endoscope via the mouth, esophagus, stomach
and
intestines, or via laparoscopic methods directly through the skin
(percutaneous). If
vascular access is desired, a physician may access the blood vessel through an
opening, such as an opening manufactured in the femoral artery.
[0024] An embodiment of a kit useful in the above procedure is depicted in
Figs. 3, 3a and 3b. The kit includes a wire guide 31, which may be shorter
than a
wire guide used for a sequential procedure as described above. A wire guide
with
a length of about 145-150 cm is preferred, but other lengths may be used. A
catheter 32 is included, the catheter preferably having a proximal end 32a
with a
flared tip 32b, and a soft rounded/tapered non-traumatic tip 32c for
protection of
the patient. Materials for the catheter are typically plastic or elastomeric
materials,
e.g., PVC, PTFE, polyurethane, silicone, and urethane, but any medically
acceptable materials may be used. Catheters suitable for this use are
preferably
about 50-85 cm long. The tip is flared for ease in securing to connectors and
in
sealing with connectors so that the catheter may deliver a fluid, such as a
radiopaque fluid for diagnostic procedures or for visualization purposes. The
catheter may have a hydrophilic coating 32d on at least part of its outer
surface.
CA 02517702 2005-08-31
The proximal portion may also have one or more marking bands 32e to assist the
physician in deploying the stent.
[0025] Catheter 32 may interface with one or more connectors 36 for mating
with syringe adapter 37 (such as a female Luer lock adapter) so that a syringe
(not
shown) can inject the radiopaque fluid. Connector 36 may include a male Luer
lock fitting 36a on a distal end of connector 36 and internal threads 36b on
its
proximal end. Male Luer lock connection 36a may be used to connect first
connector 36 to second connector 35. Threads 36b may interface with matching
external threads 37a of syringe adapter 37 for delivery of a fluid through
lumen
37b. Flared end 32b of the catheter helps to seal the connection between
connector 36, catheter 32, and syringe 37. While the Luer lock and threaded
connections depicted and described are preferred, other connectors may be used
instead. For example, quick-release connectors could be used to secure the
catheter or sheath to their proximal fittings. When connectors 36 and 37 are
joined with flared end 32b, a leak-tight connection is formed, and the
catheter may
reliably deliver fluid without undesirable leakage.
[0026] Access sheath 33 includes a proximal portion 33a and an end portion
with a flared tip 33b. The access sheath also includes a distal end 33c,
preferably
atraumatic, soft and rounded or tapered for ease of introduction into the
patient.
Distal end 33c of the access sheath is also preferably more highly radiopaque
than
the remainder of the access sheath, so that the end may be observed with x-ray
or
fluoroscopic detection means during the implantation procedure. Flared tip 33b
helps to seal an interface between access sheath 32 and connector 34. Access
sheaths are preferably are made from low friction polymers (e.g. PTFE, FEP
etc.)
with reasonable radial compressive strength - wire reinforcement can be added
to
the sheath for extra radial strength. Suitable access sheaths sold under the
name of
Check-Flo II Introducer sheaths sold by Cook Incorporated, Indiana may be
used. Also Flexor sheaths available from Cook Urological Incorporated of
Spencer, Indiana may be used. In this application the sheath is typically 70cm
long so to extend from the urethral meatus to the ureteropelvic junction. The
access sheath is generally just slightly larger in inner diameter than the
outer
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diameter of the catheter, e.g. 0.5Fr. If catheter 32, as shown in Fig. 3 and
preferably with a blunt distal tip, is the same size diameter as the stent,
the catheter
may be used as a stent positioner, with the physician simply butting the
distal end
of the catheter against the proximal end of the stent so that the positioner
can be
used to push the stent into position.
[0027) Connector 34 may include internal threads 34a for connecting to Luer
lock connector 35 having female Luer lock connection 35b. While Luer lock
connections and connectors are preferred, other connectors and other types of
medically-acceptable connectors may be used. At least a distal portion of
sheath
33 may also include a hydrophilic coating 38.
[0028) The fittings described above may be used to connect access sheath 32
with catheter 33. To help insure that access sheath 32 seals securely,
connector 34
may be temporarily joined to connector 35 with an adhesive. Other methods may
also be used, such as securely tightening connectors 34, 35 together. Joining
the
female Luer lock connection 35b to male Luer lock connection 36a reliably
secures access sheath 32 to catheter 33 for insertion or for removal. By
breaking
the connection between connectors 35, 36 after insertion, catheter 32 may be
removed and the access sheath may be used for other purposes. These other
purposes may include diagnostic purposes, such as insertion of an endoscope,
or
therapeutic procedures, such as breaking up stones or calculi, using a holmium
laser or other type of lithotripter. A grasper or basket may then be inserted
into
the working channel of the endoscope to remove the fragments. In the same
manner, connectors 36, 37 may also be temporarily joined with an adhesive to
prevent easily breaking the connection. By adhering connector pairs 34, 35 and
36, 37, it is easier for the surgeon to make and break the Luer lock
connection
between connectors 35, 36.
[0029] In the assembled view of Fig. 3, note that the catheter may be longer
than the access sheath, and may extend slightly further distally than the
access
sheath. Nevertheless, the sheath and the catheter are substantially coaxial,
i.e.,
catheter 32 runs the entire length of access sheath 33. Substantially coaxial
means
that substantially the length of one of the sheath and the catheter is coaxial
with
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the other of the sheath and the catheter during the procedure for implanting a
stent
or other device into a human or mammalian body.
[0030] The access sheath may also be used to place a ureteral stent when the
above diagnostic or therapeutic procedures are completed. No matter how gentle
the procedures described above, there is a chance of some amount of trauma to
the
ureter during the procedures. Accordingly, it may be prudent to place a stent
into
the ureter to maintain patency of the ureteral lumen. Ureteral stents may be
of the
"double pigtail" variety, such as those available from Cook Urological
Incorporated, Spencer, Indiana. Fig. 4 depicts one such stent 40. These
ureteral
stents are typically available in sizes of 4 Fr to 8 Fr and may be placed into
a
ureter using a wire guide and the procedure described above.
[0031] The procedure described above for dual, coaxial dilatation may be
especially useful when there is a stricture or narrowing of a ureter for any
reason.
Fig. 6 depicts one such case. In Fig. 6, ureter 70 is constrained from its
normal
width 73 into a narrower path 71 along part of its length by a constricting
body
mass 72. An example would be a cancerous growth near the ureter that would
cause compression on the ureter, e.g., colon cancer, bladder cancer, ovarian
cancer, endometrial cancer, cervical cancer, and the like. In such cases, a
stent
with greater radial strength may be needed in order to maintain its lumen and
allow drainage of urine through the ureter. Instead of elastomeric or plastic
stents,
a stent made from material that is more resistant to deformation may be
needed.
In addition, the stent must be removable without significant deformation or
resistance.
100321 Such a stent is depicted in Figs. 5, 5a, and 5b. Stent 50 is made from
coiled wire along its length 51 and at both distal and proximal ends 52, 53,
which
may be substantially the same or may be different. The coils should be closely
spaced so that they touch, but still allow fluid, such as urine or bile, to
flow
through the coils. The coils should also be spaced closely enough so that no
tissue
ingrowth occurs. Materials used in these stents are preferably biocompatible
and
corrosion-resistant. The wire is preferably made from alloys with minimal or
low
magnetic properties to avoid interference with diagnostic equipment, such as
MRI
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machines. Alloys such as MP35N, MP 159, Astroloy M, Inconel 625, 316
stainless steel, 35N LT, Biodur 108, pure titanium, and Hastelloy S are
preferred.
[0033] An inner wire 57 extends throughout the length of the stent and is
secured to both ends 52, 53, such as by welding, brazing or swaging to a tip
54 on
each end. The tips and the wire are preferably made from the same metallic
alloy
as the coil. The tips may be formed into a molten domed mass from the coiled
wire and the inner wire during the joining process. It is important that both
ends
be atraumatic to the patient. The coils 55 have small gaps 56 between them so
that
urine may soak or leak into the stent in the kidney area or anywhere along the
ureter and may leak out of the coils in the ureter or bladder area. The
internal wire
is helpful in preventing unraveling or extension of the coils, especially when
the
stent is being removed. The portion of the stent between the pigtails is
preferably
about 20 cm to about 32 cm long. Other lengths may be used.
[0034] In order to present a surface highly resistant to encrustation during
long-term implantation, stent embodiments should be highly polished,
preferably
electro-polished. In electro-polishing, the article to be polished is placed
into an
electrolytic bath, but instead of being plated, the current is reversed.
Asperities,
tiny projections of metal on the surface of the stent coils, are vulnerable to
this
process, and are removed without changing the dimensions or temper of the
stent.
This highly polished surface is believed to be resistant to the bacteria
responsible
for encrustation because there are fewer sites of surface roughness suitable
for
adherence.
100351 The wire 55 used for the outer coils is preferably coated, such as with
a
fluoropolymer or other protective, lubricious coating 58 before it is wound
into a
coil. It is preferred that the entire coil length be coated, while preserving
the small
gaps between the coil-turns of the stent for functioning of the stent drainage
mechanism. In addition, a layer 59 of a preventive or other medication may be
applied over coating 58, such as a layer containing heparin or other drug.
Heparin
tends to resist encrustation with long-term implantation of urinary tract
medical
devices. Heparin or other drug-containing coatings are preferably applied
after the
coil is wound. Fluoropolymers such as PTFE help to enable the bonding of
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certain drugs, such as heparin, to the surface of the coils and are therefore
desirable in stents intended for long-term implantation. Other drugs useful
for
discouraging encrustation include heparin, covalent heparin, dexamethazone,
dexamethasone sodium phosphate, dexamethasone acetate and other
dexamethasone derivatives, triclosan, silver nitrate, ofloxacin, ciproflaxin,
phosphorylcholine and triemethoprim.
100361 In one preferred embodiment, the wire for coiling is coated, as by
extrusion, with a fluoropolymer or other lubricious polymer or plastic
material,
and is then wound into a coiled stent, complete with end caps and a coated
internal
wire. The stent is then immersed into a solution of heparin, and a partial
vacuum
is applied to the vessel containing the solution. Preferred is a vacuum of 10
Torr
or less for a time period of about one minute to one hour, depending on the
amount of coating desired. The stents are then rinsed in distilled water and
dried
before being packaged.
[0037] Another embodiment of a stent with greater radial strength is depicted
in Fig. 5c. In this embodiment, which is similar to the embodiment of Fig. 5a,
a
narrow hollow cannula 64 extends between the distal and proximal ends of the
stent 60. Stent 60 includes metallic ends 61 which include an orifice 63 to
accommodate cannula 64. The stent includes a hollow outer coil 62 for greater
radial strength. Cannula lumen 65 may be used to enable placement by a wire
guide, and also may act as a lumen for drainage of body fluids, such as urine
or
bile. Fluid connector 66 may be attached to a proximal end of the cannula for
connection for fluid drainage or for infusion of diagnostic or therapeutic
fluids.
The fluid connector may be attached by threads, by soldering or brazing, by or
by
any convenient method.
[0038] In addition, one or more additional medications or drugs may be placed
on the surface of the stent in order to assist in patient care and comfort.
For
instance, an antimicrobial drug, such as a combination of rifampin and
minocycline, may help to reduce inflammation and microbial activity in the
vicinity of the stent. Antimicrobial coatings applied to the stent may include
the
following drugs, or their salts or derivatives: rifampin, minocycline, a
mixture of
CA 02517702 2005-08-31
rifampin and minocycline, a non-steroidal anti-inflammatory agent, a
penicillin, a
cephalosporin, a carbepenem, a beta-lactam, an antibiotic, an aminoglycoside,
a
macrolide, a lincosamide, a glycopeptide, a tetracyline, a chloramphenicol, a
quinolone, a fucidin, a sulfonamide, a trimethoprim, a rifamycin, an oxaline,
a
streptogramin, a lipopeptide, a ketolide, a polyene, an azole, an
echinocandin,
alpha-terpineol, methylisothiazolone, cetylpyridinium chloride,
chloroxyleneol,
hexachlorophene, chlorhexidine and other cationic biguanides, methylene
chloride, iodine and iodophores, triclosan, taurinamides, nitrofurantoin,
methenamine, aldehydes, azylic acid, rifampycin, silver, benzyl peroxide,
alcohols, and carboxylic acids and salts, and silver sulfadiazine. Also useful
as
antimicrobials are anthracyclines, such as doxorubicin or mitoxantrone,
fluoropyrimidines such as 5-fluoroacil, and also podophylotoxins, such as
etoposide. The salts and the derivatives of all of these are meant to be
included as
examples of antimicrobial drugs.
[0039] Analgesics, such as aspirin or other non-steroidal anti-inflammatory
drugs, may also be applied to the surface to reduce pain and swelling upon
implantation of the stent. These drugs or their salts or derivatives may
include
aspirin and non-steroidal anti-inflammatory drugs, including naproxen,
choline,
diflunisal, salsalate, fenoprofen, flurbiprofen, ketoprofen, ibuprofen,
oxaprozin,
diclofenac, indomethacin, sulindac, acetoaminophen, tolmetin, meloxicam,
piroxicam, meclofenamate, mefanimic acid, nabumetone, etodelac, keterolac,
celecoxib, valdecoxib and rofecoxib, mixtures thereof, and derivatives
thereof.
[0040] Other analgesics or anesthetics that may be coated onto the surface of
the stent include opioids, synthetic drugs with narcotic properties, and local
anesthetics to include at least paracetamol, bupivacaine, ropivacaine,
lidocaine,
and novacaine.alfentanil, buprenorphine, carfentanil, codeine, codeinone,
dextropropoxyphene, dihydrocodeine, endorphin, fentanyl, hydrocodone,
hydromorphone, methadone, morphine, morphinone, oxycodone, oxymorphone,
pethidine, remifantanil, sulfentanil, thebaine, and tramadol, mixtures
thereof, and
derivatives thereof.
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[0041] Any of these drugs and coatings are preferably applied in a time-
release
manner so that the beneficial effect of the drug is sustained over a period of
at
least several weeks or months. This may be especially helpful in the case
where a
stent or catheter will remain in place for a considerable length of time.
[0042] While the present stent is highly useful for drainage of the kidneys,
similar stents may be used in other hollow parts of the body. These may
include
biliary or gall bladder stents, stents for use in percutaneous nephrostomy
procedures, hepatic drainage, gastro-intestinal drainage, and so on, for
drainage of
other body cavities. It is intended that the foregoing detailed description be
regarded as illustrative rather than limiting, and that it be understood that
it is the
following claims, including all equivalents, that are intended to define the
spirit
and scope of this invention.
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