Stent deployment catheter with collapsible sheath

The present invention provides an improved stent delivery catheter. The stent delivery system comprises a catheter having a stent receiving portion adapted to receive a stent near the distal end of the catheter and a stent concentrically arranged around the catheter within the stent receiving portion. The stent delivery system further comprises a proximal outer sheath, a retractable distal sheath surrounding at least a portion of the stent and containing the stent in its reduced delivery configuration and a pull back means connected to the retractable distal sheath. The system further comprises a collapsible sheath concentrically arranged around the catheter and located between the retractable distal sheath and the proximal outer sheath, whereby when the pull back means is pulled proximally the distal sheath is retracted, causing the collapsible sheath to collapse and freeing the stent for delivery.

FIELD OF THE INVENTION 
This invention relates to a stent delivery catheter system, such as the 
kind used in percutaneous transluminal coronary angioplasty (PTCA) 
procedures. More particularly, it relates to a stent delivery catheter 
employing a collapsible sheath which collapses during the retraction of a 
distal sheath during the release of a self-expanding or balloon expandable 
stent. 
BACKGROUND OF THE INVENTION 
In typical PTCA procedures, a guiding catheter is percutaneously introduced 
into the cardiovascular system of a patient and advanced through the aorta 
until the distal end is in the ostium of the desired coronary artery. 
Using fluoroscopy, a guide wire is then advanced through the guiding 
catheter and across the site to be treated in the coronary artery. An over 
the wire (OTW) balloon catheter is advanced over the guide wire to the 
treatment site. The balloon is then expanded to reopen the artery. The OTW 
catheter may have a guide wire lumen which is as long as the catheter or 
it may be a rapid exchange catheter wherein the guide wire lumen is 
substantially shorter than the catheter. Alternatively, a fixed wire 
balloon catheter could be used. This device features a guide wire which is 
affixed to the catheter and cannot be removed. 
To help prevent arterial closure, repair dissection, or prevent restenosis, 
a physician can implant an intravascular prosthesis, or a stent, for 
maintaining vascular patency inside the artery at the lesion. The stent 
may either be a self-expanding stent or a balloon expandable stent. For 
the latter type, the stent is often delivered on a balloon and the balloon 
is used to the expand the stent. The self-expanding stents may be made of 
shape memory materials such as nitinol or constructed of regular metals 
but of a design which exhibits self expansion characteristics. 
In certain known stent delivery catheters, a stent and an optional balloon 
are positioned at the distal end of the catheter, around a core lumen. The 
stent and balloon are held down and covered by a sheath or sleeve. When 
the distal portion is in its desired location of the targeted vessel the 
sheath or sleeve is retracted to expose the stent. After the sheath is 
removed, the stent is free to self-expand or be expanded with a balloon. 
In a coronary stent deployment system which utilizes a retractable sheath 
one problem which is encountered is the interaction of the sheath and 
guide catheter upon retraction. The traditional way of dealing with this 
is to make the retractable sheath long enough so that it will be contained 
in the guide catheter at all times. This increases system profile, reduces 
flexibility and creates excess friction upon sheath retraction. The 
invention disclosed reduces the sheath length, maintains a reduced system 
profile and provides good flexibility. 
SUMMARY OF THE INVENTION 
The present invention provides an improved stent delivery system. The stent 
delivery system comprises a catheter having a proximal outer, a stent 
receiving portion adapted to receive a stent near the distal end of the 
catheter, a retractable distal sheath concentrically arranged around the 
stent receiving portion and a pull back means connected to the distal 
sheath. The catheter further comprises a collapsible sheath located 
between and adhered to the proximal outer sheath and the retractable 
distal sheath. During retraction of the distal sheath the collapsible 
sheath collapses upon itself, or accordions upon its preformed pleats or 
creases, providing room for the distal sheath to retract unencumbered, 
thereby freeing the loaded stent. The inclusion of the collapsible sheath 
significantly reduces the sheath length, maintains a reduced system 
profile, provides good flexibility and provides a protective covering to 
the wire pull back mechanism. 
Other objects, features, embodiments and characteristics of the present 
invention, as well as the methods of operation and functions of the 
related elements of the structure, and the combination of parts and 
economics of manufacture, will become more apparent upon consideration of 
the following description with reference to the accompanying drawings, all 
of which form a part of this specification.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows a cross-section of the distal portion of a specific embodiment 
of the stent delivery catheter, generally designated as 5, that is the 
subject of the present invention. The device generally comprises a 
proximal outer 10 which covers the majority of the catheter 5 excluding a 
portion of the distal end of the catheter 5. This outer 10 is 
characterized by a flexible tube which contains a pull wire lumen and a 
guide wire lumen. Preferably the outer 10 is comprised of a high density 
polyethylene (HDPE) or SURLYN material. The proximal outer 10 encloses an 
optional guide wire lumen 15 which extends through and terminates with the 
distal tip 25 of the catheter 5. Preferably the guide wire lumen 15 
encloses a guide wire 20 which aids in the navigation of the catheter 5 
through the appropriate vessel. The guide wire lumen 15 is made of 
flexible, but incompressible construction such as a polymer encapsulated 
braid or coil. The flexibility of the braid/coil allows the catheter 5 to 
navigate through body lumens and the incompressibility of the braid/coil 
aids in maintaining the integrity of the catheter and aids in deployment 
accuracy when the sheath is being retracted during stent release. The 
braid/coil may be comprised of stainless steel or nitinol, but preferably 
stainless steel encased in a polymer such as a polyimide, HDPE, teflon or 
urethane, but preferably polyimide or teflon. 
Situated just proximal to the distal tip 25 is the portion 30 of catheter 5 
around which the stent is concentrically carried. The stent 35 surrounds 
the guide wire lumen 25. The stent 35 is preferably a Nitinol.TM. or mesh 
self-expanding stent, but may also be a balloon expandable stent carried 
by an expansion balloon. Self-expanding and balloon expandable stents are 
well known in the art and require no further instruction. 
The present invention further comprises a retractable distal sheath 40 
which covers and contains the loaded stent 35. The retractable distal 
sheath 40 will hold a self-expanding stent in its reduced delivery 
configuration. The retractable distal sheath will merely contain a balloon 
expandable stent which was positioned over an expansion balloon. The 
distal sheath 40 is connected to a retracting member 45, or pull wire, 
which allows a physician to retract the distal sheath 40 from the proximal 
end of the catheter 5, thus releasing the stent 35 in the targeted area of 
the vessel. The retractable sheath 40 may be flexible or rigid, and is 
generally used to retain the stent 35 and protect the vessel wall. The 
distal sheath is preferably formed of a material which provides tensile 
strength, but is flexible, such as a braid, coil, a super elastic alloy, 
polymer, stainless steel or other similar composites. The retracting 
member 45 may be a rod, a cable, a tube which may also be used to 
transport fluids, a pull back wire, guide wire or the like, but is 
preferably a wire. In addition, the retracting member 45 may be tapered 
along its length to impart varying flexibility. Those skilled in the art 
will recognize other suitable materials and constructions may be employed 
to serve substantially the same function. The figures show two pull wires, 
but one is preferred. It should be understood that any desired number of 
pull wires could be utilized. The retracting member 45 extends 
longitudinally within the proximal outer 10, optionally through a 
retracting member lumen (not shown), such as a HDPE, nylon, or polyether 
block amide (PEBAX) tube. In one embodiment, the retracting member lumen 
extends longitudinally under the proximal outer 10, and houses the pull 
back wire 45. The retracting member lumen that houses the pull back wire 
45 may also carry fluid for purging air from the catheter 5. 
The invention additionally comprises a collapsible sheath 50 situated 
between the proximal outer 10 and the distal sheath 40. The collapsible 
sheath 50 covers the exposed area between the proximal outer 10 and the 
distal sheath 40, serving to protect the guide wire lumen 15 and the 
retracting member 45 in this area. The collapsible sheath 50 is adhered to 
the proximal end of the distal sheath 40 at point 42 and the distal end of 
the proximal outer 10 at point 48. These connections between components 
are preferably made using adhesives such as urethane or cyanoacrylate, and 
other suitable adhesives that are well known in the art. Connections 
between polymer components can also be made using other bonding techniques 
such as thermal welding, ultrasonic welding and the like. 
The collapsible sheath 50 is manufactured to induce collapsibility by 
winding a coil around the collapsible sheath material, such as a tube of 
SURLYN. The coil winder controls the pitch or distance between adjacent 
wraps of wire. After the tube is wound, the tube is pressurized, causing 
the material to expand between the gaps in the wire and creating the 
pleats or creases which allow it to collapse. The coil is then removed 
producing the collapsible sheath 50 behind. 
As the distal sheath 40 is retracted, the collapsible sheath 50 is forced 
back, collapsing upon itself into an accordion type configuration to give 
the distal sheath 40 room to retract. The collapsible sheath 50 is longer 
than the distal sheath 40 and is made from a highly flexible material such 
as SURLYN, PEBAX, or LDPE, but preferably SURLYN. The distal sheath 40 and 
the collapsible sheath 50 may be two separate sheaths adhered to one 
another, or they may form one continuous sheath. 
In the preferred embodiment, the distal sheath 40 is connected via a collar 
comprised of a short section of hypotube 55, configured as an annular 
ring, to the pull back wire 45. The proximal end of the distal sheath 40 
is attached by adhesive or heat bond to the annular ring 55 and the distal 
end of the pull back wire 45 is connected, preferably brazed, to the 
inside of the annular ring 55. Although one pull back wire 45 is 
preferred, a plurality of pull back wires may be connected to the collar 
55. The illustrative figures enclosed herein utilize one pull back wire. 
Proximal to the stent 35 is a stopper 60. The stopper 60 is preferably HDPE 
and is attached to the guide wire lumen 15, or whatever may comprise the 
rigid inner core, and is used to prevent the stent 35 from moving 
proximally when the distal sheath 40 is retracted. 
Preferably, the catheter 5 further comprises an optional neck portion 62 
located just proximal to the collar 55. This portion 62 is a slight 
reduction in diameter of the catheter 5 just behind the collar 55. The 
neck portion 62 aids in containing the collar 55 and supplies added 
leverage to the collar 55 as it retracts the distal sheath 40. It 
additionally aids in compressing the collapsible sheath 50 by providing an 
added brace for the collar 55 as the collar pushes back collapsing the 
collapsible sheath 50. 
In an alternative embodiment a stiffening wire 60, preferably stainless 
steel but optionally nitinol may also be incorporated longitudinally along 
the axis of the catheter 5 for extra stability and control. 
In a fixed wire embodiment the guide wire lumen 15 may be replaced with 
just a guide wire, wherein the distal portion of the guide wire 20 is 
bonded to the distal tip 25. 
The proximal portion of the catheter 5, as shown in FIGS. 1-3, comprises of 
a manifold system, generally designated 100, which includes a sliding 
member 110 slidably integrated between the distal and proximal end of the 
manifold. By retracting the sliding member 110 of the manifold 100, distal 
to proximal, the distal sheath 40 is retracted exposing the stent 35. The 
manifold 100 may further comprise a hydrating luer 130, which is 
preferably located on the distal end of the manifold 100 and is used to 
purge air from the catheter. 
To prepare the stent delivery catheter 5 the stent 35 is compressed and 
loaded into the stent receiving portion 30 and covered by protective 
distal sheath 40. The distal sheath 40 remains covering the underlying 
stent 35 during the placement of the stent 35 by the delivery catheter 5 
through the patient's vasculature. During the placement of the stent 35, 
protective distal sheath 40 protects the patient's vasculature from the 
stent 35. 
FIGS. 1-3 illustrate three stages of the deployment of a self-expanding 
stent 35 using the preferred embodiment of the catheter of the present 
invention. FIG. 1 represents a loaded deployment catheter 5, with the 
stent 35 covered by the distal sheath 40 and the collapsible sheath 50 in 
its extended state. FIG. 2 shows the stent 35 partially deployed, with the 
distal sheath retracted to cause the collapsible sheath to partially 
collapse. In the preferred embodiment the pull wire is attached to sliding 
member 110, which is used to retract sheath 40. As the sliding member 110 
is pulled back the distal sheath 40 begins to retract. The stent is 
prevented from moving proximally with the sheath by the stopper and 
therefore, the stent 35 begins to release and expand while the collapsible 
sheath 50 begins to collapse upon itself in an accordion fashion. Since 
the distal sheath 40 does not slide back over the proximal sheath, but 
rather the collapsible sheath 50 collapses in place, the profile of the 
catheter 5 remains nearly the same. FIG. 3 shows the stent fully released. 
At this point the distal sheath 40 is fully retracted and the collapsible 
sheath 50 is compressed releasing the stent 35 to allow it to self-expand 
against the vessel wall 65. After the stent 35 is expanded and in place, 
the catheter 5 is withdrawn. It should be understood that a balloon 
expandable stent could also be utilized by arranging the stent around an 
optional placement balloon (not shown). Once the sheath 40 is fully 
retracted the placement balloon would be inflated through its inflation 
lumen (not shown) to deploy the stent. 
Preferably the stent 35 is self expanding, such as a Nitinol.TM. stent, or 
it may be expanded by means of an internal balloon positioned under the 
stent 35 on the distal end of the inner core 40. Those skilled in the art 
will recognize other suitable materials and constructions which may be 
employed to serve substantially the same function. 
The collapsible sheath is formed such that upon retraction of the distal 
sheath 40 the collapsible sheath 50 is compressed to a state approximately 
1/5 of its longitudinally expanded state. The collapsible sheath 50 
provides covering of the wire mechanism, eliminates the relative motion of 
the proximal edge of the distal sheath 40 and reduces the friction 
involved in retraction of the distal sheath 40. Unlike known retractable 
systems, the distal sheath does not retract over or under the proximal 
outer, which results in an increase in the profile of the catheter, an 
increase in friction as the distal sheath resists being pulled back over 
the proximal outer and a higher likelihood of hang ups due to the faulty 
engagement between the proximal end of the distal sheath and the guide 
catheter or vessel. In the present invention the collapsible sheath 50 
compresses thereby providing space for the distal sheath 40 to retract 
without any encumbrances. 
FIGS. 4 and 5 illustrate an alternative embodiment of the present 
invention. In this case the proximal outer 70 extends distally over the 
catheter, generally designated 90, up to a position in close proximity 
with the stopper 60 and the collapsible sheath 75 performs as the distal 
sheath. The distal end of the proximal outer 70 is adhered to the proximal 
end of the collapsible sheath 75 at point 80. In this embodiment the 
collar 55 is connected to collapsible sheath 75 at the distal end at point 
85. As the pull back wire 45 is drawn proximally, the collapsible sheath 
75 is retracted, collapsing upon itself, and begins to release. As 
discussed earlier, stopper 60 prevents the stent from moving proximally 
with the retracting sheath 75. FIG. 5 illustrates the fully retracted 
collapsible sheath 75 and the release of the stem 35 to its fully expanded 
position urging against the inner wall of the vessel 65. 
FIG. 6 discloses an alternative embodimemt of the present invention. In 
this case the stent delivery system is generally designated 145 and the 
catheter 155 is comprised of a guide wire lumen 15 and a pull back lumen 
150. The pull back lumen is axially connected to the guide wire lumen, 
travelling along the length of the guide wire lumen 15 up to the distal 
tip 25 at point 153, as the guide wire lumen continues through the distal 
tip 25. FIG. 7 illustrates the configuration of the catheter 155 from a 
cross-section perspective along lines 7--7 in FIG. 6. A stent 35 may be 
concentrically arranged around the catheter 15 near the distal end on the 
stent receiving portion 30. The device further comprises a retractable 
distal sheath 40 surrounding at least a portion of the stent 35. FIG. 6 
shows the retractable distal sheath 40 partly retracted. The proximal end 
of the retractable distal sheath 40 is attached to the collapsible sheath 
50 at point 143. The collapsible sheath 50 is concentrically arranged 
around the catheter 155 and is shown in FIG. 6 as partially collapsed. The 
proximal end of the collapsible sheath 50 is connected, preferably 
adhered, to a fixed anchoring device 140, preferably an annular collar, 
which is affixed to the catheter 155 at point 160. The fixed anchoring 
device 140 stabilizes the proximal end of the collapsible sheath 50 
allowing it to collapse upon itself during retraction of the distal sheath 
40. The pull back wire 45 travels, proximal to distal, through the pull 
back lumen 150 and exits through an axial slit (not shown) in the surface 
of the pull back lumen 150. The distal end of the pull back wire is 
attached to annular ring 55, which is in turn attached to the retractable 
distal sheath 40. During the application of the device the pull back wire 
45 is retracted, sliding proximally through the axial slit in the pull 
back lumen, proximally retracting the distal sheath 40 causing the 
collapsible sheath 50 to collapse and freeing the stent 35 for delivery. 
The stopper 60 prevents the stent from moving proximally with the 
retracting sheath 75. 
FIG. 8 illustrates a rapid exchange embodiment of the invention. The distal 
end of the catheter is structured and functions in the same fashion as 
that of the device shown in FIG. 1. The overall length of the catheter is 
approximately 135 cm, while the length of the guide wire lumen 15 is 
between approximately 5 cm to 35 cm from the distal tip 25 to a point 
where the guide wire lumen 15 and the guide wire 20 exit the catheter. 
It should be understand that other mechanical methods of retracting the 
pull back wire, besides the manifold apparatus disclosed herein, may be 
employed. 
It should also be understood that the retractable distal sheath 40 and the 
collapsible sheath 50 may comprise one continuous sheath, wherein the 
preform creases or pleats are incorporated only into the intended 
collapsible portion. 
The design disclosed herein also aids in flushing the catheter. Since the 
catheter essentially is sealed to the distal tip 25 and has only one 
opening in the distal segment, that being the end portion of the guide 
wire lumen 15 at the distal tip 25, flushing is made easier and more 
efficient. 
The present invention may be incorporated into both of the two basic types 
of catheters used in combination with a guide wire, commonly referred to 
as over-the-wire (OTW) catheters and rapid-exchange (RX) catheters. The 
construction and use of both over-the-wire and rapid-exchange catheters 
are well known in the art. The usable length of the delivery catheter is 
approximately 135 cm. For a rapid exchange catheter the distance from 
where the guide wire accesses the guide wire lumen to the distal tip will 
be approximately 5 cm to 35 cm. 
The key features of the longitudinally collapsible sheath include, without 
limitation: low profile both proximally and distally when extended, 
relatively thin walls for low profile and large interior lumens, efficient 
packing upon collapse, flexible, pushable and trackable. 
The above disclosure is intended to be illustrative and not exhaustive. 
These examples and description will suggest many variations and 
alternatives to one of ordinary skill in this art. All these alternatives 
and variations are intended to be included within the scope of the 
attached claims. Those familiar with the art may recognize other 
equivalents to the specific embodiments described herein which equivalents 
are also intended to be encompassed by the claims attached hereto.