U.S. patent application number 11/265999 was filed with the patent office on 2007-05-03 for indirect-release electrolytic implant delivery systems.
This patent application is currently assigned to CardioMind, Inc.. Invention is credited to Frank P. Becking, David Licata, Sudip R. Pandya.
Application Number | 20070100414 11/265999 |
Document ID | / |
Family ID | 37997519 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070100414 |
Kind Code |
A1 |
Licata; David ; et
al. |
May 3, 2007 |
Indirect-release electrolytic implant delivery systems
Abstract
Medical devices and methods for delivery or implantation of
prostheses within hollow body organs and vessels or other luminal
anatomy are disclosed. The subject technologies may be used in the
treatment of atherosclerosis in stenting procedures or be used in
variety of other procedures. The systems may employ a self
expanding stent restrained by one or more members released by an
electrolytically erodable latch. Such release means do not connect
directly to the implant, though one or more portions may contact
it.
Inventors: |
Licata; David; (Menlo Park,
CA) ; Pandya; Sudip R.; (Sunnyvale, CA) ;
Becking; Frank P.; (Palo Alto, CA) |
Correspondence
Address: |
CARDIOMIND, INC.
257 HUMBOLDT COURT
SUNNYVALE
CA
94089
US
|
Assignee: |
CardioMind, Inc.
|
Family ID: |
37997519 |
Appl. No.: |
11/265999 |
Filed: |
November 2, 2005 |
Current U.S.
Class: |
623/1.11 |
Current CPC
Class: |
A61F 2002/9511 20130101;
A61F 2/9522 20200501; A61F 2002/9505 20130101; A61F 2/95 20130101;
A61F 2250/0071 20130101; A61F 2/88 20130101 |
Class at
Publication: |
623/001.11 |
International
Class: |
A61F 2/06 20060101
A61F002/06 |
Claims
1. A power supply for an implant delivery system employing at least
one electrolytically erodable element, the improvement comprising:
adaptation of the power supply to provide an AC voltage profile
with a peak-to-peak configuration of at least about 5V, and a DC
voltage signal of at least about 1V.
2. A method of implant delivery, the method comprising: introducing
an implant delivery system in an electrolytic fluid; and applying
electrical power to an electrolytically erodable member, the power
AC voltage profile with a peak-to-peak configuration of at least
about 5V, and a DC voltage signal of at least about 1V.
3. A method of loading a self-expanding stent onto a delivery
guide, the method comprising: holding the stent compressed to a
reduced diameter configuration in at least one sleeve; engaging the
stent with the delivery guide; and twisting the stent while in the
sleeve.
4. The method of claim 3, further comprising compressing the stent
before loading the stent into the at least one sleeve.
5. The method of claim 3, wherein a plurality of sleeves hold the
stent.
6. The method of claim 5, wherein the stent is twisted by rotating
one sleeve relative to another.
7. The method of claim 3, further comprising removing the at least
one sleeve from the stent.
8. A stent delivery system comprising: a delivery guide body having
a distal portion and at least one elongate member including an
electrolytically erodable section; a stent comprising a near end, a
far end and a structure extending therebetween, at least one of the
near and far end of the stent held in contact with the elongate
body; wherein release of the erodable section initiates stent
release.
9. The system of claim 8, wherein the stent is in a twisted
configuration in contact with the elongate body.
10. The system of claim 8, wherein at least one elongate member
passes through the near or far end of the stent.
11. The system of claim 8, wherein each electrolytically erodable
section is spaced apart from the stent.
12. The system of claim 8, wherein each elongate member defines a
loop of material.
13. The system of claim 8, wherein each end of the stent is
capped.
14. The system of claim 8, further comprising a slidably actuable
tubular restraint over at least a portion of the stent.
15. The system of claim 14, wherein only one of the near and far
ends of the stent is held by an elongate member.
16. The system of claim 8, wherein the delivery guide comprises
near and far seats at the distal portion, and wherein the stent
further comprises at least one of a near and a far mating portion
at the near and far ends, respectively, each seat being adapted to
receive a mating portion.
17. The system of claim 16, wherein at least one elongate member is
wrapped to at least partially cover each mating portion.
18. The system of claim 17, wherein at least some of the mating
portions and seats provide a keyed interface.
19. The system of claim 17, wherein at least some of the mating
portions and seats provide a slide-out interface.
20. The system of claim 16, wherein the stent is in a twisted
configuration in contact with the delivery guide body.
21. The system of 20, wherein each seat receives a mating portion,
and wherein at least one seat is rotatable upon release of an
electrolytically erodible section.
22. The system of claim 8, wherein engagement of the at least one
mating portion on one of the near and far ends of the stent is
released by release of an electrolytically erodable member; and
wherein engagement of the at least one mating portion on the other
end of the stent occurs as a result of release of the same
electrolytically erodable member.
23. The system of claim 22, wherein movement of a floating cap
releases the other end of the stent.
24. The system of claim 22, wherein untwisting of a coil spring
wound around a portion of the elongate body is released to retract
and release the stent upon release of the electrolytically erodable
member.
25. The system of claim 24, wherein the spring retracts the seat
upon release.
26. The system of claim 8, wherein one end of the stent is released
by relative sliding motion between the stent and the delivery guide
body.
27. The stent delivery system of claim 26, wherein the sliding
release occurs as result of release of the
electrolytically-released component.
28. The stent delivery system of claim 26, wherein the sliding
release occurs as result of advancing or withdrawing the delivery
guide by a user.
29. The system of claim 28, further comprising a catheter in which
the delivery guide is received, an end of the catheter adapted to
abut the near end of the stent upon release of the far end of the
stent.
30. The system of claim 8, further comprising a sleeve restraining
the stent in a compressed state, wherein the sleeve is releasably
secured by the erodable section.
31. The system of claim 30, further comprising a spring positioned
to actuate the sleeve.
32. The system of claim 31, wherein the spring is a coil spring
having a compressed, extended state and an expanded, retracted
state.
33. The system of claim 32, wherein retraction of the sleeve frees
the stent to expand from the compressed state.
34. The system of claim 8, wherein the erodable section is spaced
apart from the stent.
35. The system of claim 8, wherein any erodable section releases
the stent directly.
36. The system of claim 8, wherein any erodable section releases
the stent indirectly.
37. The system of claim 8, wherein any elongate member maintains
the stent in a rotationally stable configuration for delivery.
38. The system of claim 37, wherein any elongate member, alone,
maintains the stent in a rotationally stable configuration for
delivery.
Description
BACKGROUND
[0001] Implants such as stents and occlusive coils have been used
in patients for a wide variety of reasons. One of the most common
"stenting" procedures is carried out in connection with the
treatment of atherosclerosis, a disease which results in a
narrowing and stenosis of body lumens, such as the coronary
arteries. At the site of the narrowing (i.e., the site of a lesion)
a balloon is typically dilatated in an angioplasty procedure to
open the vessel. A stent is set in apposition to the interior
surface of the lumen in order to help maintain an open passageway.
This result may be effected by means of a scaffolding support alone
or by virtue of the presence of one or more drugs carried by the
stent to aide in the prevention of restenosis.
[0002] Various stent designs have been developed and used
clinically, but self-expandable and balloon-expandable stent
systems and their related deployment techniques are now
predominant. Examples of self-expandable stents currently in use
are the Magic WALLSTEN.RTM. stents and Radius stents (Boston
Scientific). A commonly used balloon-expandable stent is the
Cypher.RTM. stent (Cordis Corporation). Additional self-expanding
stent background is presented in: "An Overview of Superelastic
Stent Design," Min. Invas Ther & Allied Technol 2002: 9(3/4)
235-246, "A Survey of Stent Designs," Min. Invas Ther & Allied
Technol 2002: 11(4) 137-147, and "Coronary Artery Stents: Design
and Biologic Considerations," Cardiology Special Edition, 2003:
9(2) 9-14, "Clinical and Angiographic Efficacy of a Self-Expanding
Stent" Am Heart J 2003: 145(5) 868-874.
[0003] Because self-expanding prosthetic devices need not be set
over a balloon (as are balloon-expandable designs), self-expanding
stent delivery systems can be designed to a relatively smaller
outer diameter than their balloon-expandable counterparts. As such,
self-expanding stents may be better suited to reach the smallest
vasculature or to achieve access in more difficult cases.
[0004] One consideration pertinent to the delivery of
self-expanding stent designs concerns frictional forces internal to
the subject delivery system. Internal forces can be a significant
issue with respect to system actuation. Testing by the assignee
hereof has clearly demonstrated a loss of motive force available to
actuate a distally located restraint when the delivery system is
subject to conditions of or simulating tortuous anatomy. As such,
systems that require little or no direct user actuation of
components to effect stent release are desirable. Examples of such
systems are presented in a number of patents.
[0005] U.S. Pat. No. 5,873,907 offers a system employing
circumferential bands, each having an electrolytically erodable
section, where the bands hold a stent in a collapsed configuration
until the sections' joints are released. U.S. Pat. No. 5,980,514
discloses a system in which a self-expanding stent is held onto a
wire directly by electrolytically erodable joints. U.S. Pat. No.
6,716,238 describes a system in which one or more tethers are
connected to a stent to releasably restrain it for delivery or to
stabilize its position during delivery. The tethers may work in
conjunction with a sheath to hold a distal end of the stent,
allowing withdrawal of the sheath from the stent to effect release.
When the sheath is withdrawn, the stent expands radially, but is
not fully released until the connections between the tethers and
the stent are mechanically broken, electrolytically eroded or
melted away. In another embodiment described in the '238 patent,
one or more tethers is wrapped around the body of the stent to tie
it down until released.
[0006] Upon closer examination, each of the referenced systems has
serious limitations--either in terms of clinical practicality,
basic mechanical feasibility or both. Issues variously presented by
the referenced stent delivery systems include: [0007] 1) risk of
tissue damage or vulnerable plaque dislodgement by drawing released
tethers or bands past/between an open/opening stent and a vessel
wall; [0008] 2) inability to employ drug elution matrix upon a
stent because of direct connection of an erodable solder joint to
the stent; [0009] 3) unpredictability of joint or release segment
corrosion; [0010] 4) long deployment times as a result of large
amounts of material to erode to effect implant release; and/or
[0011] 5) bulkiness in system design. Other issues may be presented
as well as appreciated by those with skill in the art. Accordingly,
to maximize the potential benefits of electrolytic release for
stents and/or other implants, there exists a need for improved
systems.
SUMMARY
[0012] Variations of the invention hold a radially-expandable,
implantable prosthesis (such as a stent) in a collapsed
configuration for delivery with the assistance of one or more
members including an electrolytically erodable or disintegratable
section. Unlike most electrolytic-based implant delivery systems,
none of those in the subject invention employ a "joint" that joins
or attaches the implant directly to the delivery member. Neither do
the electrolytically erodible sections secure tethers or bands
restraining the central diameter of the implant body.
[0013] Rather, either a twist imparted to the implant or a tubular
sleeve holds the implant in a compressed profile. The sacrificial
electrolytic member maintains the implant or restraining sleeve in
a preloaded configuration until release. Upon release, the implant
is freed to untwist or the sleeve withdrawn therefrom. In each
case, the implant is then able to expand.
[0014] One aspect of the invention offers systems in which one or
more ends of an implant or prosthesis such as a stent are held in a
highly stable manner by a clinically and mechanically robust, yet
compact holding/restraining and releasing means. In these
variations of the invention, one portion of the means comprises
pass-through or male-female interlocking features between an end of
the implant and a delivery guide member body. The engaging features
associated with the delivery member body may comprise as few as two
features; more preferably, three, four or more features arranged
around a ring. Most advantageously, the multiple members are
symmetrically spaced apart.
[0015] The implants employed in connection with the present
invention are often stents. Most typically, the stents employed are
lattice, cage or successive linked ring-type structures. Often they
are cut from tubing or they are mesh-like woven or assembled
bodies. However, other means or modes of manufacture are possible
as well.
[0016] In a number of variations of the invention, the
configuration of the stent or other implant employed is critical to
the operation of the system. In these systems, foreshortening of
the implant (i.e., decreasing length of the body, or at least a
portion thereof, in transitioning from a collapsed to an expanded
state) plays an important roll in stent release. In those examples
of the invention where foreshortening plays a role in implant
release, the implant is often adapted to be twisted and it is this
twisting that assists in holding the stent at a desired
diameter.
[0017] In order to hold such an implant in a radially compressed
and twisted state, the implant (e.g., a stent) optionally includes
one or more extensions or projections from its main body. Such
extensions are adapted to nest or otherwise interface with
complimentary seat features set upon or retained by the guide body
portion of the implant delivery system. The projections may simply
comprise elongate members that offer a laterally stable interface
or comprise hook-shaped forms (e.g., "J", "T", "L", "S", "V" etc.
shapes) that also an axially stable interface. Alternatively, the
implant body or projections therefrom may instead incorporate or
define openings or receptacle features. As such, the prosthesis or
the delivery guide seat features may extend partially to a certain
depth (i.e., forming a pocket). Alternatively, the openings may
extend through the entire member.
[0018] Stated broadly, either the implant and/or the delivery guide
may include male and/or female interlocking features. A grasping
form of interface may be employed to axially tension the implant
and/or provide secure capture at one side of the implant to provide
"bail-out" potential. The delivery guide side of the interface may
be referred to as a "seat" or otherwise. Especially, where the
members hook into one another, they may be regarded as "nesting"
features. "Lock" and "key" terminology may also be used to describe
the features.
[0019] Alternatively, the implant/delivery guide interface may be
adapted for sliding receipt and release. Such configurations enable
various self or automatic release approaches. For these, extension
from the implant or even the crowns of adjacent stent struts may
provide the interface with delivery guide component(s). For these
types of interfaces, "key" and "way" terminology may be most
appropriate. Still, the delivery device side may be regarded as a
"seat" or "seating" region or portion.
[0020] In any of these systems employing a stent that is both
radially compressed and twisted, various approaches to loading the
implant onto or into the delivery guide may be employed. One highly
advantageous method that forms an aspect of the present invention
involves pre-loading the implant into a sleeve. The stent is
compressed by hand, with an automated "crimper" such as produced by
Machine Solutions, Inc., or otherwise, without a substantial twist
and loaded into a tubular body close in diameter to its final size
upon or in the delivery guide. By "close" in diameter, what is
meant is that it is within at least 33%, or more preferably about
25%, or even about 10% of its final diameter. Then, with the stent
so-constrained, it is twisted from either or both ends before or
after partial or full attachment to the delivery guide.
[0021] The sleeve may comprise a plurality of separate pieces or
segments (most conveniently two or three). As such, the individual
segments can be rotated relative to one another to assist in
twisting the stent. In addition, axial manipulation of the relation
of thin individual segments can be employed to allow the implant to
bulge outwardly over one section. The foreshortening caused by this
action may then allow positioning and then axially loading end
interface members by manipulating the segments to collapse the
bulging.
[0022] As for the electrolytically releasable retention members,
one class comprises wire or ribbon passing through at least one
portion of the implant (including any extension or projection
therefrom). A loop of material threaded through a receptacle or
adjacent one or more crown portions of a stent offers a very
strong, yet simple connection to the delivery guide. The loop may
itself be erodable at a section, or an erodable bridging segment
may be incorporated in the loop. An even more elegant connection
employs a pin, post or rivet-like member received through the
implant. The pin or rivet structure may be headed (i.e., have a
bulbous or flattened head or mushroom-like shape) in order to
prevent lift-off of the implant member. Erosion of the head and/or
periphery of the structure will then release the implant.
[0023] Systems employing these pass-through type of securing
features may work alone by holding an implant such as a stent in a
twisted state. Alternatively, they may hold such an implant in a
twisted and/or axially stretched configuration with a retractable
tubular sheath or restraint sleeve over the implant. In this way,
the electrolytically released components can partially restrain the
implant so as to reduce sleeve hold-down and/or withdrawal forces.
The pinned/threaded connections are particularly space-efficient
and, thus, suited for use with supplemental restraining device
components while maintaining small device crossing profiles.
[0024] When employed with a retaining sleeve, as few as one
location on the implant can be secured by the electrolytically
released component(s). For a stent, the location may be proximal or
distal. A distal location may offer improved sleeve withdrawal
characteristics; a proximal location may simplify electrical
conduction and or performance issues. Employing both proximal and
distal electrolytic retainer attachment locations enable axial
and/or torque-based implant diameter reduction techniques to reduce
the force required for restraint withdrawal.
[0025] Another class of retainers or retaining and release means or
releaseable means comprises an overriding means or covering
including at least one electrolytically erodable section that
releasably secures ends of an implant in association with a seating
portion or portions of a delivery guide. In one variation, the
means comprises a wrap or band or plurality of bands. Upon release
of one or more sections, the band opens or wrap loosens. In another
variation, the radial retention member comprises a sleeve or casing
with one or more electrolytically erodable sections that allow (or
upon release, cause) the structure to open. Such a "flower petal"
type design may be soldered or welded together in a pre-stressed
state in order that it self expands upon eroding connecting
webbing, solder, weld point(s), etc.
[0026] When either one of such structures is opened or relaxed, the
captured projections of the implant can release from complimentary
delivery guide side features. When the projection(s) and seat(s)
offer a keyed interface, those on the implant can lift or be pushed
out of plane to release at least one portion of the implant. When
the projection(s) and seat(s) are adapted for sliding receipt and
release, the latter will occur more readily upon release of the
wrap or band and force holding parts together (if only by virtue of
static friction).
[0027] As with the above variation of the invention in which
retention members pass through one or more portions of the implant,
those retention members that overlay one or more portions of the
implant may secure the proximal and/or distal side the implant or
point(s) between. They may be used in complimentary pairs or with
other structures as is convenient. In the latter example, either
one of the wrap-around or openable sleeve retainer may be set at
the distal end of the stent with a mechanical release mechanism
positioned at the proximal side of the stent. Examples of such
mechanically-actuated systems including retractable mini-sheaths
and wire or suture cut-down bands are presented in U.S. patent
application Ser. No. ______, entitled, "Twist-Down Implant Delivery
Technologies" (Atty. Docket No. CRMD-015) filed on even date
herewith, which application is incorporated herein by reference in
its entirety.
[0028] Furthermore, different ones of electrolytically releasable
means may be set at opposite ends (or simply different locations)
of the implant. Certain advantageous pairings are elaborated upon
below, especially for stent release. For the sake of discussion
here, however, one such combination employs the "flower petal"
style means at the proximal side of the device and wrap-around
means at the distal end. After implant delivery, a proximal-side
open "flower petal" device will easily collapse when withdrawn into
a delivery catheter. On the distal side, however, the open
structure could get caught. In contrast, a loose filament released
from a wrap-around means can easily be drawn into the delivery
catheter regardless of location on the delivery guide. Yet, because
the flower petal approach may be more easily slipped over the stent
in a final loading step than a filament wound around the stent and
secured, the former structure may be desired on at least one side
of the system for ease of assembly. Of course, other exemplary
systems employing the various retention and release means are
possible in which the rationale for the combinations may be
apparent upon further review of the subject specification.
[0029] Equally applicable to a mix-and-match approach are
electrolytically releasable means that are specifically adapted to
permit an implant's release by its mating portion(s) sliding out of
a restraining configuration upon some triggering action. In other
words, either one or both sides of a stent delivery system
according to the present invention may employ this type of release
approach.
[0030] As for the various device configurations that enable such
action, a first one is advantageously used to initiate release of
the implant. In one example, the releasable retention means
comprises a covered interface held by an electrolytic latch. Once
released, the interface rotates--allowing the stent to untwist and
expand. The expansion causes the length of the stent to shorten
because of its cell or strut geometry. As it shortens
(foreshortens) the stent draws itself (e.g., end projections) out
of the retaining interface. In one variation, the covering
comprises a band. In another example, it comprises a wrap that
loosens as the stent unwinds. Such a configuration will allow
release of keyed projections, with or without substantial implant
foreshortening.
[0031] In any case, all of the above-described release members are
to be actuated by electrolytic erosion through application of
voltage by user action (or computer programming) with a suitable
power supply. Other variations of the present invention employ a
second implant retaining and release means that is tripped or
actuated by action of the first release means or by the resulting
configuration of the implant. In these variations of the invention,
the second or subsequent means automatically completes implant
release. Such action may be desired as a matter of convenience in
reducing user activity, it may offer improved release speed or
reliability, or it may be desirable for yet one or more other
reasons.
[0032] Of these auto-release systems, a first type is one in which
a floating or non-secured tubular member is set over one end of the
implant. Expansion of the implant--as in the example of a
stent--drives the tube off of the stent in the direction of
expansion. So-displaced, the adjacent captured end of the stent is
released. An interlocking key or slip-type interface may be
freed-up by virtue of moving the outer sleeve. In either example,
the stent may lie upon a core member along its entire length or a
region under the projections may be relieved or undercut. Such
relief allows for steepening of the angle that the end of the
implant can assume without flexing of material. This effect offers
improved mechanical advantage for moving the outer sleeve.
[0033] Another example of an automatically releasable retention
means employs a coil spring attached to or integrally formed with a
sleeve. The sleeve is offered, again, to cap the implant member and
the delivery guide interface features (i.e., the projection and
seat members). Withdrawal of the sleeve permits release. The spring
positively locks the sleeve in place in one state and actively
withdraws it in a second state. In the locked state, the spring is
tightly wound about the system body so that its position is
bound-up by frictional forces. In the second state, the spring is
opened by untwisting so as to be able to retract freely.
[0034] This unwinding of the spring is accomplished by releasing
the pre-twist imparted to the adjoining implant. Until released,
the spring is held twisted by the twisted implant interfacing with
keys or ridge features underlying the sleeve. When the twisted
implant (be it a stent or another medical device) is released, the
spring also untwists and is freed from its cinched-down
configuration--thereby allowing its retraction from a
stretched-out/preloaded state.
[0035] As an alternative to the twist-lock approach described
above, a spring member (in the form of a coil or otherwise
configured) in an axially preloaded state can be secured by an
anchor member. The anchor member may comprise an electrolytic
latch. Alternatively, an "anchor" line in the form of a ribbon,
suture, etc. can be set under the implant and held in place by its
radial compression derived from the twist-down. When the twist to
the implant is released and the body expands, so-too is the
pressure securing the anchor line.
[0036] In another variation of the invention, no active release
means is employed at a second side of the implant. Rather, the
second end of an implant is held by an interface that can be
released by simply withdrawing or advancing the delivery system. An
advantageous configuration in this regard employs a covered
slide-out implant/delivery guide interface at a proximal end of a
stent. After distal release of the stent and expansion into contact
with the body lumen, the delivery system is withdrawn from the
stent, releasing the proximal end. In yet another approach where
the proximal side of the delivery system includes the slide-out
enabled architecture, an end of a catheter in receipt of the
delivery guide is employed to abut the stent proximal/near side.
Then advancement of the catheter or withdrawal of the delivery
guide further into the catheter releases the near side of the
stent.
[0037] In a manner related to the spring-back variations of the
invention for releasing interface features on one side of a
twisted-down implant, the concept can be applied to withdrawal of a
sheath or a restraint covering at least a portion of the body of an
implant. Specifically, an electrolytic latch can be employed for
restraining a stretched-out spring element to withdraw a sheath
from up to the entire length of a stent. In one example, the
releasable trigger member is connected to a spring member that is
only axially stretched. In another variation, the spring member is
both axially stretched and twisted. The twisting in this case would
be for binding-up the spring or at least assisting in its
restraint. Upon release, the restraint untwists and is able to
fully retract. When a twisted spring is employed, the implant to be
delivered will rotate with the restraint as the restraint is
withdrawn. In either of these approaches, end-capture features for
the restraint/sheath may resemble or be identical to features
described above in connection with releasably securing the end of
an implant (i.e., the keyed projection and seat features).
[0038] As stated above, the inventive features may be used to
deliver any of a variety of implants besides lattice or cage-type
stents. Though stents are focused on in this regard, other examples
of implants which may be employed with the subject invention
include coil stents, embolic protection filters and other
"clot-pulling" devices, embolic coils and even application to other
technologies. However, in order to function properly in connection
with certain variation of the invention, the implants must
sometimes be configured such that at least a portion foreshortens
during deployment. Still, other ones of the system variations--such
as spring-back sheath variations discussed directly above--may work
with any sort of deliverable medical device for permanent or
temporary implantation. It is also contemplated that those
improvements described herein pertaining to methodology, power
profiles for electrolytic actuation, insulation and electrical
architectures may be applied in delivery systems for any type of
implant.
[0039] Regarding methodology, the subject methods may include each
of the mechanical activities associated with implant release as
well as electrical activity. As such, methodology implicit to the
use of the devices described forms part of the invention. Such
methodology may include that associated with completing an
angioplasty, bridging an aneurysm, deploying radially-expandable
anchors for pacing leads or an embolic filter, or placement of a
prosthesis within neurovasculature, an organ selected from the
kidney and liver, within reproductive anatomy such as selected
vasdeferens and fallopian tubes or other applications. In some
methods, the various acts of implant release are considered; in
others, the power profiles, monitoring of power and other aspects
of power control are considered.
[0040] More particularly, a number of methods according to the
present invention involve the manner in which the delivery system
operates in releasing an implant. In one such method in which the
implant is restrained at two sides, a first side is released by an
electrolytic latch, followed by automatic release of the second
side, wherein the automatic action is initiated by release of the
first side. In another method, two independently releasable ends
are released one after the other. This action is accomplished not
by the contemporaneous erosion of an electrolytic member on each
side of the implant (with staged release controlled by different
amounts of material to erode as is known, and suitable for certain
variations of the invention disclosed herein) but, rather, by
selecting and eroding material incorporated in separate electrical
circuits. Yet another delivery method is contemplated in which an
electrolytic component is released only on one side of the implant.
Such action may be followed by a mechanical release action such as
withdrawing or tearing a sheath member manually or activating a
"muscle wire" to do the same. Another approach may involve
withdrawing or advancing the delivery guide to effect final implant
release from a second, slidably releasable means holding the other
end of the implant.
[0041] Another aspect of the invention provides methods involving
power profiles for electrolytic element erosion and
hardware/systems and software to control the methods. While
electrocoagulation (e.g., by thrombus formation in blood by blood
cell attraction to a positive charge) can be a positive factor in
embolic coil delivery, it has been appreciated that such action can
severely hamper or interfere delivery of other types of implants.
Rather than isolating the member to be eroded, however, an aspect
of the present invention involves use of power profiles to
ameliorate or eliminate any problems with electrocoagulation.
Specifically, an AC signal is employed. Not to be bound by the
theory, but it is believed that the negative charge of the cycle
repulses blood cells. However, to effect the desired erosion, a net
positive charge is required. Thus, a positive DC offset is applied
to the AC voltage. The positive offset and amplitude of the AC
signal yields higher peak voltages to drive electrolytic corrosion.
Irrespective of electrocoagulation, these higher peak energies may
result in increased erosion and consequent implant deployment.
Numerous potential power profiles according to this general
principle are detailed below. Furthermore, experimental results are
provided which illustrate the effectiveness of such an
approach.
[0042] Another approach according to the present invention involves
system insulation in order to focus erosion, or at least maximize
current density at the point of erosion. Generally, it is known
that "fast acting" detachable systems can be produced by insulating
or electrically isolating everything but that portion of the system
where electrolytic erosion is desired. The present invention
improves upon this concept in certain variations by producing
system components with high-strength titanium or titanium alloy. In
addition, they can be anodized to form an oxide layer insulative to
DC voltage. The components are typically pre-anodized. Yet, when
using higher voltages, the systems are "self-healing" such that any
scratches, etc. exposing material to unintended corrosion/erosion
will skin-over and maintain their integrity. Such a system is
highly advantageous as it eliminates the need for polymeric
insulation; further, such a system need not rely on the use of
noble (or high Mendelev number) metal material selection to protect
components that can be costly or cumbersome to apply, or cause
failures if disturbed.
[0043] Yet another aspect of the invention concerns the electrical
architecture or design of the subject systems. In order to minimize
or eliminate any potential risk associated with the electrical
signal carried by the system, certain variations of the invention
are configured such that the release member(s) are positively
charged at the point where erosion is desired and the section(s)
are directly adjacent (i.e., within about 1 cm, preferably less) to
a negatively charged element. In one variation of the invention,
the subject retention and release means is located at a distal end
of the delivery system. It is electrically connected to the (net)
positive side of a power source via wiring running within a
delivery guide body made from hypotubing.
[0044] In all, the implant retention member configurations,
electrical connectivity and conductivity as well as the manner in
which they are employed can vary in a number of ways according to
the present invention. Furthermore, some variations of the
invention are adapted to release an implant or prosthesis such as a
stent without the use of any mechanically actuated components. In
other variations of the invention, systems may include
manually-actuated or activated components. However, it is
envisioned that the former class of purely electrically-actuated
systems may offer particular flexibility as subcomponents for
systems requiring off-axis implant delivery.
[0045] Used as a subcomponent, a discrete electrically-actuated
system as described in detail below could be attached in a
non-axial or "V" shaped configuration to allow treating a crossing
vessel in a "T" shaped site such as at or near the basilar artery
junction. In which case, a tether underlying the implant or a
distal sheath may be provided to re-constrain an open "V"
configuration to allow its recapture and withdrawal into a catheter
body. Alternatively, an electrically-actuated system could be
provided at a distal end of a system that includes a drawstring or
wire to force a dramatic prolapse in the system in order to treat
such a vessel configuration as described above. Unless such
features are provided, however, the subject systems typically
comprise flexible linear or unidirectional delivery guide members
without extensions, arms or fittings at the far end of the delivery
guide body.
[0046] The delivery systems described herein offer a number of
advantages in their efficient construction and ability to deliver
implants with or without coatings in highly challenging
applications. Those with skill in the art may appreciate further
benefits or advantages of the subject inventive variations.
DEFINITIONS
[0047] The term "stent" as used herein includes any stent, such as
coronary artery stents, other vascular prosthesis, or other
radially expanding or expandable prosthesis or scaffold-type
implant suitable for the noted treatments or otherwise. Exemplary
structures include wire mesh or lattice patterns and coils, though
others may be employed in certain variations of the present
invention. A "self-expanding" stent as used herein is a
scaffold-type structure (serving any of a number of purposes) that
expands from a reduced-diameter (be it circular or otherwise)
configuration to an increased-diameter configuration. The mechanism
for shape recover may be elastic or pseudoelastic. While it is
generally desirable to employ an alloy (such as nickel-titanium, or
Nitinol alloy) set for use as a superelastic alloy, it may
alternatively employ thermal shape memory properties to drive
expansion upon release.
[0048] A "wire" as used herein generally comprises a common
metallic member such as made of stainless steel or another
material. The wire may be at least partially coated or covered by a
polymeric material (e.g., with an insulating polymer such as
Polyamide, or a lubricious material such as TEFLON.RTM., i.e.,
PolyTetraFluoroEthelyne or PTFE). Still further, the "wire" may be
a hybrid structure with metal and a polymeric material (e.g.,
Vectran.TM., Spectra.TM., Nylon, etc.) or composite material (e.g.,
carbon fiber in a polymer matrix). The wire may be in the form of a
filament, bundle of filaments, cable, ribbon or in some other form.
It is generally not hollow. The wire may comprise different
segments of material along an overall length.
[0049] A "hypotube" or "hypotubing" as referred to herein means
small diameter tubing in the size range discussed below, generally
with a thin wall. The hypotube may specifically be hypodermic
needle tubing. Alternatively, it maybe wound or braided cable
tubing, such as provided by Asahi Intec Co., Ltd. or otherwise. As
with the "wire" discussed above, the material defining the hypotube
may be metallic, polymeric or a hybrid of metallic and polymeric or
composite material.
[0050] An "atraumatic tip" may comprise a plurality of spring coils
attached to a tapered wire section. At a distal end of the coils
typically terminate with a bulb or ball that is often made of
solder. In such a construction, the coils and/or solder are often
platinum alloy or another radiopaque material. The coils may also
be platinum, or be of another material. In the present invention,
the wire section to which the coils are attached may be tapered,
but need not be tapered. In addition, alternate structures are
possible. In one example, the atraumatic tip may comprise a molded
tantalum-loaded 35 durometer Pebax.TM. tip. However constructed,
the atraumatic tip may be straight or curved, the latter
configuration possibly assisting in directing or steering the
delivery guide to a desired intravascular location.
[0051] To "connect" or to have or make a "connection" between parts
refers to fusing, bonding, welding (by resistance, by pressure,
laser, chemically, ultrasonically, etc.), gluing, pinning,
crimping, clamping or otherwise mechanically or physically joining,
attaching or holding components together (permanently or
temporarily). To "electrically connect" or to have or make an
"electrical connection" between parts refers to providing a
low-resistance path for current to flow upon the application of a
voltage (AC and/or DC). The connection may be in the form of a
wire, a trace of material such as cladding or plating overlying a
selected area, conductive fill material (such as silver-loaded
epoxy resin), adhesive, solder, etc.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0052] The figures provided herein are not necessarily drawn to
scale, with some components and features being exaggerated for
clarity. Each of the figures diagrammatically illustrates aspects
of the invention. Of these:
[0053] FIG. 1 shows a heart in which its vessels may be the subject
of one or more angioplasty and stenting procedures;
[0054] FIGS. 2A and 2B show a first expanded stent cut pattern and
an expanded view of a section of the same, respectively;
[0055] FIGS. 3A and 3B show a second expanded stent cut pattern and
an expanded view of a section of the same, respectively;
[0056] FIGS. 4A-4L show stent deployment hardware and methodology
for carrying out an angioplasty and stenting procedure;
[0057] FIG. 5 shows an overview of a delivery system according to
the present invention;
[0058] FIGS. 6A-6F illustrate hardware and methodology for loading
a delivery guide with a stent in a twisted configuration;
[0059] FIGS. 7A and 7B show wrap-through restraint delivery guide
variations;
[0060] FIGS. 8A-8D show stent end variations that may be used in
conjunction with the delivery guides of FIGS. 7A and 7B;
[0061] FIG. 9 shows a delivery guide variation in which the ends of
a stent are capped by an erodable member;
[0062] FIGS. 10A-10C, show a stent twisted-down and held in a
compressed configuration;
[0063] FIGS. 11A-11F show stent end variations that may be used in
conjunction with delivery guide in FIG. 8 and those that
follow;
[0064] FIG. 12A shows an end sectional view of a manner in which to
construct a wrap-over electrolytically releasable ember to cover an
end of an implant to restrain it for delivery; FIG. 12B shows the
wrap-over variation of FIG. 12A upon a delivery guide in which the
stent is absent for the sake of clarity in illustrating features;
FIG. 12C show a variations of a near side of such a delivery guide
as shown in FIG. 12B, illustrating a different electrical
connection approach;
[0065] FIG. 13A shows an alternate stent end cover variation
including electrolytically separable segments; FIG. 13B shows a
related construction in which wire segments are provided to hold
and release the cover segments;
[0066] FIG. 14 shows a portion of a delivery guide with a slidable
cover releasing the ends of an implant;
[0067] FIG. 15 shows a portion of a delivery guide with a tear-down
cover for holding and releasing the ends of an implant;
[0068] FIG. 16 shows a portion of a delivery guide with a rotatable
covered member for holding and releasing the ends of an
implant;
[0069] FIGS. 17A and 17B show a portion of a delivery guide with a
rotatable and expandable ribbon cover for holding and releasing the
ends of an implant, respectively;
[0070] FIG. 18 shows a distal portion of a delivery guide variation
employing features as shown in FIGS. 16 and 17A and 17B, with a
stent loaded thereon and a distal atraumatic tip;
[0071] FIG. 19 shows a distal portion of a delivery guide variation
with features as shown in FIGS. 13A and 16, minus an implant and
distal tip;
[0072] FIG. 20 shows a distal portion of yet another delivery guide
variation employing features as shown in FIG. 16 for implant
release at a distal end and a basic slotted interface at a proximal
side, together with a catheter body as may be used to assist
proximal implant release;
[0073] FIGS. 21A and 21B show two states of a distal portion of a
delivery guide in which features shown in FIG. 16 provide for
distal implant release and a self locking/auto-releasing member
provides for proximal implant release;
[0074] FIGS. 22A and 22B show two states of a distal portion of a
delivery system resembling that in FIGS. 21A and 21B, where the
auto-releasing member effects withdrawal of a restraint covering at
least a portion of a body of an implant;
[0075] FIG. 23 shows a delivery guide variation employing a tubular
restraint for releasing a stent secured by distal keyed and covered
electrolytically releasable implant/delivery guide interface;
[0076] FIGS. 24A and 24B shown preloaded spring-back restraint
systems secured in position by an electrolytic latch and joint,
respectively, until release;
[0077] FIG. 25 illustrates principles behind an e-safe electrolytic
corrosion based delivery system;
[0078] FIG. 26 shows an exemplary power profile for driving
indirect-release electrolytic implant delivery systems according
the present invention or other systems as may be employed by a
medical practitioner.
Variation of the invention from the embodiments pictured is, of
course, contemplated.
DETAILED DESCRIPTION OF THE INVENTION
[0079] Various exemplary embodiments of the invention are described
below. Reference is made to these examples in a non-limiting sense.
They are provided to illustrate more broadly applicable aspects of
the present invention. Various changes may be made to the invention
described and equivalents may be substituted without departing from
the true spirit and scope of the invention. In addition, many
modifications may be made to adapt a particular situation,
material, composition of matter, process, process act(s) or step(s)
to the objective(s), spirit or scope of the present invention. All
such modifications are intended to be within the scope of the
claims made herein.
Self-Expanding Stent Designs and Opportunities
[0080] In light of this framework, FIG. 1 shows a heart 2 in which
its vessels may be the subject of one or more angioplasty and/or
stenting procedures. To date, however, significant difficulty or
impossibility is confronted in reaching smaller coronary arteries
4. If a stent and a delivery system could be provided for accessing
such small vessels and other difficult anatomy, an additional 20 to
25% of percutaneous coronary procedures could be performed with
such a system. Such potential offers opportunity for huge gains in
human healthcare and a concomitant market opportunity--with the
further benefit of avoiding loss of income and productivity of
those treated.
[0081] Features of the present invention are uniquely suited for a
system able to reach small vessels (though use of the subject
systems s not limited to such a setting.) By "small" coronary
vessels, it is meant vessels having an inside diameter from between
about 1.5 to 2 mm and up to about 3 mm in diameter. These vessels
include, but are not limited to, the Posterior Descending Artery
(PDA), Obtuse Marginal (OM) and small diagonals. Conditions such as
diffuse stenosis and diabetes produce situations that represent
other access and delivery challenges that can be addressed with a
delivery system according to the present invention. Other extended
treatment areas addressable with the subject systems include vessel
bifurcations, chronic total occlusions (CTOs), and prevention
procedures (such as in stenting of vulnerable plaque).
[0082] It may be preferred to use a drug eluting stent (DES) in
such an application to aid in preventing restenosis. A review of
suitable drug coatings and available vendors is presented in "DES
Overview: Agents, release mechanism, and stent platform" a
presentation by Campbell Rogers, MD incorporated by reference in
its entirety. However, bare-metal stents may be employed in the
present invention.
[0083] Examples of various therapeutic agents that may be used in
or on the subject prosthesis include, but are not limited to,
antibiotics, anticoagulants, antifungal agents, anti-inflammatory
agents, antineoplastic agents, antithrombotic agents,
endothelialization promoting agents, free radical scavengers,
immunosuppressive agents, antiproliferative agents, thrombolytic
agents, and any combination thereof. The therapeutic agent may be
coated onto the implant, mixed with a biodegradable polymer or
other suitable temporary carrier and then coated onto the implant,
or, when the implant is made from a polymeric material dispersed
throughout the polymer. The agent can be directly applied to the
stent surface(s), or introduced into pockets or an appropriate
matrix set over at least an outer portion of the stent.
[0084] While some might argue that the particular role and optimal
usage of self expanding stents has yet to be defined, they offer an
inherent advantage over balloon expandable stents. The latter type
of devices produce "skid mark" trauma (at least when delivered
uncovered upon a balloon) and are associated with a higher risk of
end dissection or barotraumas caused at least in part by high
balloon pressures and related forces when deforming a
balloon-expandable stent for deployment to account for recoil upon
balloon deflation.
[0085] Yet, with an appropriate deployment system, self-expanding
stents may offer one or more of the following advantages over
balloon-expandable models: 1) greater accessibility to distal,
tortuous and small vessel anatomy--by virtue of decreasing crossing
diameter and increasing compliance relative to a system requiring a
deployment balloon, 2) sequentially controlled or "gentle" device
deployment, 3) use with low pressure balloon pre-dilatation (if
desirable) to reduce barotraumas, 4) strut thickness reduction in
some cases reducing the amount of "foreign body" material in a
vessel or other body conduit, 5) opportunity to treat
neurovasculature--due to smaller crossing diameters and/or gentle
delivery options, 6) the ability to easily scale-up a successful
treatment system to treat larger vessels or vice versa, 7) a
decrease in system complexity, offering potential advantages both
in terms of reliability and system cost, 8) reducing intimal
hyperplasia, and 9) conforming to tapering anatomy--without
imparting complimentary geometry to the stent (though this option
exists as well).
[0086] At least some of these noted advantages may be realized
using a stent 10 as shown in FIG. 2A. The stent pattern pictured is
well suited for use in small vessels. It may be collapsed to an
outer diameter of about 0.018 inch (0.46 mm), or even smaller to
about 0.014 inch (0.36 mm)--including the restraint/joint used to
hold it down--and expanded to a size (fully unrestrained) between
about 1.5 mm (0.059 inch) or 2 mm (0.079 inch) or 3 mm (0.12 inch)
and about 3.5 mm (0.14 inch).
[0087] In use, the stent will be sized so that it is not fully
expanded when fully deployed against the wall of a vessel in order
to provide a measure of radial force thereto (i.e., the stent will
be "oversized" as discussed above). The force will secure the stent
and offer potential benefits in reducing intimal hyperplasia and
vessel collapse or even pinning dissected tissue in apposition.
[0088] Stent 10 preferably comprises NiTi that is superelastic at
or below room temperature (i.e., as in having an Af as low as 15
degrees C. or even 0 degrees C.). Also, the stent is preferably
electropolished to improve biocompatibility and corrosion and
fatigue resistance. The stent may be a DES unit as referenced
above. The stent may be coated with gold and/or platinum to provide
improved radiopacity for viewing under medical imaging. It may be
biodegradable.
[0089] For a stent able to collapse to an outer diameter of about
0.012 inches and expand to about 3.5 mm, the thickness of the NiTi
is about 0.0025 inch (0.64 mm). Such a stent is designed for use in
a 3 mm vessel or other body conduit, thereby providing the desired
radial force in the manner noted above. Further information
regarding radial force parameters in coronary stents may be noted
in the article, "Radial Force of Coronary Stents: A Comparative
Analysis," Catheterization and Cardiovascular Interventions 46:
380-391 (1999), incorporated by reference herein in its
entirety.
[0090] In one manner of production, the stent in FIG. 2A is laser
or EDM cut from round NiTi tubing, with the flattened-out pattern
shown wrapping around the tube as indicated by dashed lines. In
such a procedure, the stent is preferably cut in its fully-expanded
shape. By initially producing the stent to full size, the approach
allows cutting finer details in comparison to simply cutting a
smaller tube with slits and then heat-expanding/annealing it into
its final (working) diameter. Avoiding post-cutting heat forming
also reduces production cost as well as the above-reference
effects.
[0091] Regarding the finer details of the subject stent, as readily
observed in the detail view provided in FIG. 2B, necked down bridge
sections 12 are provided between axially/horizontally adjacent
struts or arms/legs 14, wherein the struts define a lattice of
closed cells 16. Such a closed cell designs facilitate twist-down
of the stent where applicable because the otherwise free ends of an
open ended cell (or successive ring) design have a tendency to
radially lift-off in a radial direction due to complex stress
distributions.
[0092] In certain variations of the invention, however, the bridge
sections can be strategically separated or opened as indicated by
the broken lines in FIG. 2A. Doing so disrupts the closed cell
pattern discussed above, but may increase stent conformability to
tortuous anatomy. One situation in which such modification may be
useful is in those variations of the invention employing a sleeve
or sheath overlying the stent. In any case, to facilitate such
tuning of the stent, the bridge sections are preferably
sufficiently long so that fully rounded ends may be formed
internally to the lattice just as shown at terminal ends or crowns
18 of the cells not carrying stent/delivery system interface
features.
[0093] As for the optional double-concave profile of each strut
bridge 12 shown, this form is advantageous in that it reduces
material width (relative to what would otherwise be presented by a
parallel side profile) to improve flexibility and thus trackability
and conformability of the stent within the subject anatomy while
still maintaining the option for separating/breaking the cells
apart. Whether cut to provide rounded end portions or adjoined by a
bridge section 12, strut junction sections 28 connect
circumferentially or vertically adjacent struts (as illustrated).
Where no bridge sections are provided, the junction sections can be
unified between horizontally adjacent stent struts as indicated in
region 30.
[0094] Further optional features of stent 10 are employed in the
strut junction sections 28 of the design. Specifically, strut ends
20 increase in width relative to medial strut portions 22. Such a
configuration distributes bending (during collapse of the stent)
preferentially toward the mid region of the struts. For a given
stent diameter and deflection, longer struts allow for lower
stresses within the stent (and, hence, a possibility of higher
compression ratios). Shorter struts allow for greater radial force
(and concomitant resistance to a radially applied load) upon
deployment.
[0095] In order to increase stent compliance so that it compresses
as much as possible, accommodation is made for the stiffer strut
ends 20 provided in the design shown in FIG. 2A. Namely, the gap 24
between the strut ends 22 is set at a smaller angle as if the stent
were already partially collapsed in that area. Thus, the smaller
amount of angular deflection that occurs at ends 20 can bring the
sections parallel (or nearly so) when the strut medial portions 22
are so-arranged. In the variation of the invention in FIG. 2A,
radiused or curved sections 26 provide a transition from a medial
strut angle .alpha. (ranging from about 85 degrees to about 60
degrees) to an end strut angle .beta. (ranging from about 30 to
about 0 degrees) at the strut junctions 28 and/or extensions
therefrom.
[0096] In addition, it is noted that gap 24 an angle .beta. may
actually be configured to completely close prior to fully
collapsing angle .alpha.. The stent shown is not so-configured.
Still, the value of doing so would be to limit the strains (and
hence, stresses) at the strut ends 22 and cell end regions 18 by
providing a physical stop to prevent further strain.
[0097] In the detail view of FIG. 2B, angle .beta. is set at 0
degrees. The gap 24 defined thereby by virtue of the noticeably
thicker end sections 20 at the junction result in very little
flexure along those lever arms. The strut medial portions are
especially intended to accommodate bending. In addition, a hinging
effect at the corner or turn 32 of junction section 28 may allow
the strut to swing around angle .alpha. to provide the primary mode
for compression of the stent.
[0098] Additional features of interest in the stent design include
near and far delivery system interface mating portions 92 and 94,
respectively. These elements are formed within projections 90 that
may be integral to the prosthesis (e.g., when the prosthesis is
constructed from a single tube of material, or when a number of
wire-type elements are woven to form the body where the ends of the
elements form the prosthesis). Alternatively, the projections may
be affixed or connected to the stent (e.g., via welding, adhesive
bonding, fastening, etc.). In another variation of the invention,
the projections may comprise polymeric material that is coated onto
the prosthesis 82. Other modes of construction are possible as
well. Further details of the projections and respective mating
portions are discussed in detail below. Suffice it to say, the
elements are sufficiently "floppy" and/or rounded to offer an
atraumatic interface with opposing tissue.
[0099] The stent pattern 40 shown in FIG. 3A and detailed in FIG.
3B offers certain similarities as well as some major differences
from the stent pattern presented in FIGS. 2A and 2B. As in the
variation above, the pattern includes necked down bridge sections
42 provided between adjacent struts or arms/legs 44, wherein the
struts define a lattice of closed cells 46. In addition, terminal
ends or crowns 48 of the cells are preferably rounded-off so as to
be atraumatic, as may be projections 90 and associated delivery
guide mating portions 92, 94.
[0100] Furthermore, the bridge sections 42 of stent 82 can be
separated for compliance purposes. In addition, they may be
otherwise modified (e.g., as described above) or even eliminated.
Also, in each design, the overall dimensions of the cells and
indeed the number of cells provided to define axial length and/or
diameter may be varied (as indicated by the vertical and horizontal
section lines in FIG. 3A).
[0101] Like the previous stent design, strut ends 50 may offer some
increase in width relative to medial strut portions 52. However, as
shown in FIG. 3B, as compared to FIG. 2B, the angle .beta. is
relatively larger. Such a configuration is not concerned with
developing a hinge section and a relatively stiffer outer strut
section. Instead, angle .beta. in the FIG. 3A/3B design is meant to
collapse and the strut ends are meant to bend in concert with the
medial strut portions so as to essentially straighten-out upon
collapsing the stent, generally forming tear-drop spaces between
adjacent struts. This approach offers a stress-reducing radius of
curvature where struts join, and maximum stent compression.
[0102] The "S" curves defined by the struts are produced in a stent
cut to a final or near final size (as shown in FIGS. 3A and 3B).
The curves are preferably determined by virtue of their origination
in a physical or computer model that is expanded from a desired
compressed shape to the final expanded shape. So derived, the stent
can be compressed or collapsed under force to provide an outer
surface profile that is as solid or smooth and/or cylindrical as
possible or feasible. Such action is enabled by distribution of the
stresses associated with compression to generate stains to produce
the intended compressed and expanded shapes. This effect is
accomplished in a design unaffected by one or more expansion and
heat setting cycles that otherwise deteriorate the quality of the
superelastic NiTi stent material. Further details regarding the "S"
stent design and alternative stent constructions as may be used in
the present invention are disclosed in U.S. patent application Ser.
No. 11/238,646 entitled, "Small Vessel Stent Designs", filed Sep.
28, 2005 and incorporated herein by reference in its entirety.
[0103] For use in the present invention when employing a stent that
is twisted down upon the delivery guide in order to reduce its
diameter, it has been discovered that the design in FIGS. 3A and 3B
not only compresses to a closely cylindrical profile, but that it
maintains such a shape when twisted. Not to be bound by a
particular theory, but it is believed that this device excels in
the twisting mode because of the extremely even stress distribution
it offers when simply compressed. As such, while each of the stent
types shown in FIGS. 2A-3B may be employed in any of the systems
described herein, the latter design may be preferred. Furthermore,
the manner in which the "S" curves have been generated (as
described in the incorporated patent filing) may be extended such
that the analysis used to generate the as-cut (or near to as-cut)
structures specifically accounts for the twist the design will be
subject to in certain variations of the invention. Specifically,
physical or computational models may be employed in expanding a
stent from an idealized compressed state to generate the desired
uncompressed stent geometry.
[0104] However derived, in order that the stent pack cleanly when
twisted, it may be desired to pre-curve its shape. That is to say,
the stent may be configured so that when it is twisted, its members
go from a pre-twisted shape to a straightened configuration as
shown. The amount of shaping to account for hold-down twist may be
in the form of a simple bias or helix, S-curves or other
shape(s).
[0105] Since each of the above stent designs account for
problematic strain (and in the latter case actually uses the same
to provide an improved compressed profile), very high compression
ratios of the stent may be achieved from about 5.times. to about
10.times. or above. Moreover, they can be twisted a number of times
to maintain a compressed delivery profile. The number of twists
required for such action will vary depending on stent diameter and
length. For a 28 mm stent sized to treat 3.0 mm vessels, between
three and four twists may be desired. Similar diameter, shorter
stents will require proportionally fewer rotations, as will
generally smaller diameter stents.
[0106] Regardless of the design selected, it is noted that each of
them exhibit a degree of foreshortening when expanding from a
compressed profile. Essentially, the angle change of the struts
relative to the central axis of the tubular body accounts for
change in length. The amount of foreshortening experienced will,
thus, depend on a combination of factors: strut length and angle as
well as the number of repeating units within the design. The manner
in which the resultant foreshortening is put to use in the present
invention is elaborated upon below.
[0107] Before this discussion, however, it is noted that systems
according to the present invention are advantageously sized to
correspond to existing guidewire sizes. For example, the system may
have about a 0.014 (0.36 mm), 0.018 (0.46 mm), 0.022 (0.56 mm),
0.025 (0.64 mm), 0.035 (0.89 mm) inch crossing profile. Of course,
intermediate sizes may be employed as well, especially for
full-custom systems. Still further, it is contemplated that the
system sizing may be set to correspond to French (FR) sizing. In
that case, system sizes contemplated range at least from about 1 to
about 2 FR, whereas the smallest known balloon-expandable stent
delivery systems are in the size range of about 3 to about 4 FR. In
instances where the overall device crossing profile matches a known
guidewire size, they may be used with off-the-shelf components such
as balloon and microcatheters.
[0108] At least when produced in the smallest sizes (whether in an
even/standard guidewire or FR size, or otherwise), the system
enables a substantially new mode of stent deployment in which
delivery is achieved through an angioplasty balloon catheter or
small microcatheter lumen. Further discussion and details of
"through the lumen" delivery is presented in U.S. patent
application Ser. No. 10/746,455 "Balloon Catheter Lumen Based Stent
Delivery Systems" filed on December 24, 823 and its PCT counterpart
US824/008909 filed on March 23, 824, each incorporated by reference
in its entirety.
[0109] In larger sizes (i.e., up to about 0.035 inch crossing
profile or more), the system is most applicable to peripheral
vessel applications as elaborated upon below. Yet, even in "small
vessel" cases or applications (where the vessel to be treated has a
diameter up to about 3.0 mm), it may also be advantageous to employ
a stent delivery system sized at between about 0.022 to about 0.025
inch in diameter. Such a system can be used with catheters
compatible with 0.022 and/or 0.025 inch diameter guidewires.
[0110] While such a system may not be suitable for reaching the
very smallest vessels, this variation of the invention is quite
advantageous in comparison to known systems in reaching the larger
of the small vessels (i.e., those having a diameter of about 2.5 mm
or larger). By way of comparison, among the smallest known
over-the-guidewire delivery systems are the Micro-Driver.TM. by
Medtronic and Pixel.TM. systems by Guidant. These are adapted to
treat vessels between 2 and 2.75 mm, the latter system having a
crossing profile of 0.036 inches (0.91 mm). A system described in
U.S. Patent Publication No. 2002/0147491 for treating small vessels
is supposedly capable of downsizing to 0.026 inch (0.66 mm) in
diameter. Furthermore, because certain of the subject devices can
be used as a guidewire (in one fashion or another) after stent
delivery, the present invention offers further advantages in use as
elaborated upon below.
[0111] Still, as referenced above, it may be desired to design a
variation of the subject system for use in deploying stents in
larger, peripheral vessels, biliary ducts or other hollow body
organs. Such applications involve a stent being emplaced in a
region having a diameter from about 3.5 to 13 mm (0.5 inch). In
which case, a 0.035 to 0.039 inch (3 FR) diameter crossing profile
system is advantageously provided in which the stent expands
(unconstrained) to a size between about roughly 0.5 mm and about
1.0 mm greater than the vessel or hollow body organ to be treated.
Sufficient stent expansion is easily achieved with the exemplary
stent patterns shown in FIGS. 2A/2B or 3A/3B.
[0112] Again, as a matter of comparison, the smallest delivery
systems known to applicants for stent delivery in treating such
larger-diameter vessels or biliary ducts is a 6 FR system (nominal
0.084 inch outer diameter), which is suited for use in an 8 FR
guiding catheter. Thus, even in the larger sizes, the present
invention affords opportunities not heretofore possible in
achieving delivery systems in the size range of a commonly used
guidewire, with the concomitant advantages discussed herein.
Angioplasty Balloon Lumen Based Stent Delivery
[0113] As for the manner of using the inventive system as
optionally configured for "through the lumen use", FIGS. 4A-4L
illustrate an exemplary angioplasty procedure. Still, the delivery
systems and stents or implants described herein may be used
otherwise--especially as specifically referenced herein.
[0114] Turning to FIG. 4A, it shows a coronary artery 60 that is
partially or totally occluded by plaque at a treatment site/lesion
62. Into this vessel, a guidewire 70 is passed distal to the
treatment site. In FIG. 4B, a balloon catheter 72 with a balloon
tip 74 is passed over the guidewire, aligning the balloon portion
with the lesion (the balloon catheter shaft proximal to the balloon
is shown in cross section with guidewire 70 therein).
[0115] As illustrated in FIG. 4C, balloon 74 is expanded (dilatated
or dialated) in performing an angioplasty procedure, opening the
vessel in the region of lesion 62. The balloon expansion may be
regarded as "predilatation" in the sense that it will be followed
by stent placement (and optionally) a "postdilatation" balloon
expansion procedure.
[0116] Next, for compatible systems (i.e., systems able to pass
through a balloon catheter lumen) the balloon is at least partially
deflated and passed forward, beyond the dilate segment 62' as shown
in FIG. 4D. At this point, guidewire 70 is removed as illustrated
in FIG. 4E. It is exchanged for a delivery guide member 80 carrying
stent 82 as further described below. This exchange is illustrated
in FIGS. 4E and 4F.
[0117] However, it should be appreciated that such an exchange need
not occur. Rather, the original guidewire device inside the balloon
catheter (or any other catheter used) may be that of item 80,
instead of the standard guidewire 70 shown in FIG. 4A. Thus, the
steps depicted in FIGS. 4E and 4F (hence, the figures also) may be
omitted.
[0118] Alternatively, the exchange of the guidewire for the
delivery system may be made before the dilatation step. Yet another
option is to exchange the balloon catheter used for predilatation
for a fresh one to effect postdilatation.
[0119] In addition, there may be no use in performing the step in
FIG. 4D of advancing the balloon catheter past the lesion, since
such placement is merely for the purpose of avoiding disturbing the
site of the lesion by moving a guidewire past the same. FIG. 4G
illustrates the next act in either case. Particularly, the balloon
catheter is withdrawn so that its distal end 76 clears the lesion.
Preferably, delivery guide 80 is held stationary, in a stable
position. After the balloon is pulled back, so is delivery device
80, positioning stent 82 where desired. Note, however, that
simultaneous retraction may be undertaken, combining the acts
depicted in FIGS. 4G and 4H. Whatever the case, it should also be
appreciated that the coordinated movement will typically be
achieved by virtue of skilled manipulation by a doctor viewing one
or more radiopaque features associated with the stent or delivery
system under medical imaging.
[0120] Once placement of the stent across from dilated segment 62'
is accomplished, stent deployment commences. The manner of
deployment is elaborated upon below. Upon deployment, stent 82
assumes an at least partially expanded shape in apposition to the
compressed plaque as shown in FIG. 41. Next, the aforementioned
postdilatation may be effected as shown in FIG. 4J by positioning
balloon 74 within stent 82 and expanding both. This procedure may
further expand the stent, pushing it into adjacent plaque--helping
to secure each.
[0121] Naturally, the balloon need not be reintroduced for
postdilatation, but it may be preferred. Regardless, once the
delivery device 80 and balloon catheter 72 are withdrawn as in FIG.
4K, the angioplasty and stenting procedure at the lesion in vessel
60 is complete. FIG. 4L shows a detailed view of the emplaced stent
and the desired resultant product in the form of a supported, open
vessel.
[0122] Furthermore, it is to be recognized that the subject
invention may be practiced to perform "direct stenting." That is, a
stent may be delivered alone to maintain a body conduit, without
preceding balloon angioplasty. Likewise, once one or more stents
are delivered with the subject system (either by a single system,
or by using multiple systems) the post-dilatation procedure(s)
discussed above are merely optional. In addition, other endpoints
may be desired such as implanting an anchoring stent in a hollow
tubular body organ, closing off an aneurysm, delivering a plurality
of stents, etc. In performing any of a variety of these or other
procedures, suitable modification will be made in the subject
methodology. The procedure shown is depicted merely because it
illustrates a preferred mode of practicing the subject invention,
despite its potential for broader applicability.
Stent and Delivery System Overview
[0123] Returning to FIG. 4L, the stent 82 employed in the subject
delivery systems comprise a near or proximal end 84, a far or
distal end 86 and a main body or support structure 88 extending
therebetween. The stent 82 may further comprise projections 90. The
projections 90 comprise a near mating portion 92 and a far mating
portion 94 that permit retention of the prosthesis 82 on a delivery
system. In one mode of operation, such retention is through
twisting the stent down into a reduced profile when the ends are
rotated relative to one another. In some variations of the
invention, no projections need be provided; in others, they are
only required on one side of the stent body 88.
[0124] A given implant may have a number of projections 90, each
having various shapes rather than having a single configuration.
For twist-down applications, at least two projections 90 will be
provided on each side of the stent. When not every stent crown is
capped by a projection, the projections are advantageously spaced
substantially equally about the perimeter of the stent to evenly
distribute loads upon the stent. In which case, the projections may
be aligned with one another along the axis of the stent as shown in
FIG. 4L or staggered about the circumference of the ends of the
stent. More typically, each crown will terminate with a projection
and mating features. In this manner, the stent can be fully
constrained without members tending to lift-off the delivery guide
in a pure twisting mode of diameter reduction for delivery. Still
further, it is contemplated that the number of crowns may be
reduced by taking out adjacent arm sections to turn what was a
four-crown design on each end into a two-crown design. In this way,
fewer projections can be used, while still providing one for every
full cell at each end of the stent.
[0125] The projections may vary in length, especially depending on
the form of interface or mating portion it carries or forms. The
projections advantageously have a length that allow for efficiently
transition or transfer twisting load to the stent while occupying
minimal space. Though not necessarily excluded from the invention,
projections longer than about one cell's length may have a tendency
to wrap or twist about the delivery device body in attempted
use.
[0126] Now that stents as optionally used in the subject delivery
systems have been described, an overview of an implant delivery
system according to the invention is presented in FIG. 5. Here an
implant delivery system 100 is shown as including a delivery guide
102 with a handle 104, an elongate body 106 with a distal implant
carrying section 108 and terminating in an atraumatic coil tip 110.
The handle may incorporate a circuit board 112 and one or more
batteries (e.g., lithium ion "coin" cells) to provide power to the
system's electrolytic features.
[0127] Alternatively, a power supply 116 connected by or to the
delivery guide 102 by a cord 118 including one or more leads may be
employed. In which case, the power supply is preferably also
battery powered in that such an approach offers safety in control
of current without resort to sophisticated electronics.
[0128] Irrespective of the approach employed, the electronics will
be hard-wired or suitably programmed to operate to delivery a
suitable power profile. Certain optional profiles as discussed
below. As such, the subject power source may include such standard
features as overrides and shutoffs as recognized by one with skill
in the art as prudent. Further, the systems may be adapted to
deliver power on one or more channels. In other words, where two
electrolytic components are employed, it will be possible to power
one component and corrode its member until deployment, check or
monitor such deployment as evidenced by a drop-off in current, and
then power another electrolytically erodable member in a staged or
sequential fashion. Alternatively, every one or a selected number
of electrolytic members may be powered simultaneously. However, a
number of advantages as presented below are available as a result
of staged deployment.
[0129] Still further, (in a configuration not shown) the handle may
include one or more of a lever, slider, trigger, knob, wheel, etc.
for release of any mechanical features as may be employed in a
hybrid mechanical/electrical approach as referenced above.
Furthermore, a removable interface member 120 may be provided to
facilitate taking the handle off of the delivery system near or
proximal end 122. The interface may be lockable with respect to the
body and preferably includes internal features for disengaging the
handle from the delivery guide. Once accomplished, it will be
possible to attach or "dock" a secondary length of wire 124 on the
delivery guide proximal end, allowing the combination to serve as
an "exchange length" guidewire, thereby facilitating changing-out
the balloon catheter or performing another procedure.
Alternatively, a core member within the system may serve as an
exchange-length (i.e., 300 cm) wire.
[0130] Irrespective of such options, common to the delivery guide
systems is the inclusion of an electrolytically erodable release
latch that releases at least one side of the implant carried by the
delivery guide. A number of examples are provided below. Sections
of systems are shown that can be mixed-and-matched with others
(both in configurations shown and others as may be apparent to one
with skill in the art).
[0131] Before describing these systems, however, it is noted that
FIG. 5 also shows packaging 150 containing at least one coiled-up
delivery guide 102. Packaging may include one or more of an outer
box 152 and one or more inner trays 154, 156 with peel-away
coverings as is customary in medical device product packaging.
Naturally, instructions for use 158 may also be provided. Such
instructions may be printed product included within packaging 150
or be provided in connection with another readable (including
computer-readable) medium. The instructions may include provision
for basic operation of the subject devices and associated
methodology. In cases where computer-readable media is provided, it
may even include programming for a power supply for use in
connection with a general purpose computer or more customized
hardware to set and/or run the desired approach to powering
activity of the delivery guide.
[0132] In support of implant delivery, it is to be understood that
various radiopaque markers or features may be employed in the
system to 1) locate stent position and length, 2) indicate device
actuation and stent delivery and/or 3) locate the distal end of the
delivery guide. As such, platinum (or other radiopaque material)
bands, use of such material in constructing various elements of the
subject systems, and/or markers (such as tantalum plugs) may be
incorporated into the system.
Stent Loading
[0133] In certain variations of the invention, the stent is loaded
upon the delivery guide in a twisted configuration. Essentially, a
cage or lattice/mesh type stent assumes a decreased diameter
through twisting by pulling each portion of the body of the stent
across its diameter inwardly compressing the body. When the stent
and delivery system offer an interlocking or keyed interface,
loading of the stent is easily accomplished by engaging the
interface and then pulling (thereby causing the stent to "neck"
down) and/or twisting the stent into a compressed profile by
rotating the seat member in receipt of the mating portions of the
stent about a core member of the delivery guide.
[0134] Another approach according to the present invention is
suitable for use both in instanced in which a keyed or a slide-out
stent and delivery guide interface is provided. In this method, the
stent is compressed by hand, with an automated "crimper" such as
produced by Machine Solutions, Inc., or otherwise, without a
substantial twist imparted thereto. The stent may be compressed by
virtue of the act of loading it into a tube, or loaded into a tube
after being compressed by a machine. In any case, the tube or
sleeve that it is loaded into will generally be close in diameter
to its final size when secured upon or the delivery guide. By
"close" in diameter, what is meant is that it is within at least
about 33%, or more preferably within about 25% to about 10%, or
even within about 5% or substantially at its final diameter. Then,
with the stent so-constrained, it is twisted from either one or
both ends before of after partial or full attachment to the
delivery guide.
[0135] The sleeve may comprise a plurality of separate pieces or
segments (most conveniently two or three). As such, the individual
segments can be rotated relative to one another to assist in
twisting the stent. In addition, axial manipulation of the relation
of thin individual segments can be employed to allow the implant to
bulge outwardly over one section. The foreshortening caused by this
action may then allow positioning and then axially loading end
interface members by manipulating the segments to collapse the
bulging.
[0136] FIGS. 6A-6F illustrate a process of loading a delivery guide
using only a single restraint sleeve. To carry out the additional
acts above, or to reduce the degree to which the stent must twist
inside a single sleeve, sleeve 160 may be broken into a number of
segments (before or after loading a compressed stent therein) as
indicated by broken line.
[0137] As for the specific example of loading, FIG. 6A shows stent
82 captured within a temporary restraint 160 and set over a
delivery guide distal section 108. Its placement therein causes the
stent to lengthen to about its full extent. The stent 82 includes
projections serving as near and far mating portions 92, 94
interfacing with proximal seat and distal seat features 200, 202,
respectively. Further details of the seat features and associated
features are discussed below. Suffice it to say, here, that each of
the seats may--at first--be free to rotate.
[0138] FIG. 6B shows a first glue or solder joint laid-down to
secure one of the seats from rotating. While the near seat 200 is
the one secured, either one them may be. The approach shown here is
merely intended to be illustrative.
[0139] Then, as shown in FIG. 6C, clamp member 164 and 166 grasp
portions of the delivery guide. The near clamp 164 grasps the body
168 of the delivery guide (though the proximal-side attachment
shown in FIG. 6B could have been performed later, and the claim
attached to structure associated with the near seat 200) and the
far clamp 166 holds structure associated with the far seat 202.
[0140] The clamps may comprise part of a simple twist fixture
supporting chucks aligned on bearings, etc. In any case, in FIG.
6D, the clamps are rotated relative to one another (in the example
illustrated, only the distal clamp is rotated because the proximal
one is held stationary). As indicated by the change in the
illustrated structure, the twisted stent form 82' now lays
underneath restraint tube 160.
[0141] Following the twisting of the stent within the tube, the
distal seat 202 is secured from counter rotation by a glue or
solder joint 170. Finally, clamps or chucks 164 and 166 are
released and restraint 160 is cut or slid off of the delivery guide
body to ready the system for stent deployment as shown in FIG.
6F.
[0142] Note, however, that the act of restraint 160 removal may
take place even in the operating room as a final step prior to
delivery guide use. Otherwise, it may occur as some step along the
manufacturing process. When employed in the former manner, sleeve
160 will then do double duty as a loading and a storage sleeve.
Delivery Guide Implant Retention and Release Features
[0143] While FIG. 5 illustrates a full-size delivery system, a
number of the following figures illustrate detail views of the far
or distal end 108 of such a system. The delivery guide distal
portions shown depict a number of approaches for releasably
securing a stent or other implant for delivery according to the
present invention. The device features are typically incorporated
into complete systems and may be used in the manner described, as
well as others as may be apparent to those with skill in the
art.
[0144] Accordingly, FIG. 7A illustrates the stent bearing region
108 of a delivery system end including a prosthesis (e.g., a stent)
82 placed about an elongate body 180 of the delivery guide
underlying in the stent. As referenced above, prosthesis 82
comprises a proximal/near end 84, a distal/far end 86 and a support
structure 88 extending therebetween.
[0145] The delivery guide further comprises a number of wires or
ribbons 182 passing through at least a portion of the implant 82 to
secure it to the delivery guide. These members may form loops of
material as shown. In any case, an erodible section 184 (indicated
by the circled portion on each elongate member) serves as a
releasable latch. When corroded away, the wire passing through
receptacle portions at or adjacent the stent crowns is released,
allowing the implant to expand.
[0146] The wire including the sacrificial material latch section
may be steel or stainless steel wire. To define the sacrificial
region, polyimide insulation or a protective layer of noble (or
more noble) metal such as platinum or gold covered other portions
of the material is stripped off (or never laid-down in the first
place via a masking process) that section. The wire may be about
0.001 inch in diameter, with insulation or protective metal removed
from about a 0.005 inch long section of the wire to provide the
erodible section. Stainless steel wire will generally be selected
for its strength and because it offers corrosion resistance "on the
shelf" while being erodable in an electrolytic solution under
power. Other material selection and construction options are
discussed below.
[0147] As for configuration, the latch members may comprise
portions of a loop of wire, as shown in FIG. 7A, which are wrapped
around and secured to a delivery guide body or are passed through
apertures in the delivery guide body. Solder or glue (e.g.,
standard medical-use epoxy or UV cure) is used to secure the ends
of the material as indicated in the figure. The delivery guide body
may comprise hypotube to carry one or more electrical leads 186 to
the distal end of the system. In the case shown, the lead reaching
to the distal connection passes through the tube then wraps back
over body 180 connecting to wire 182. The lead to the proximal
wires may simply ride upon the body as shown or also be received
within the lumen of the hypotube.
[0148] However situated, leads 186 may be employed for connection
to discrete channels or circuits of a power supply to provide
individual control over corrosion of the wires. Such a setup may be
desired in order to first release the distal side of the implant
and then release the proximal side.
[0149] Otherwise, leads 186 may be omitted and body 180 will itself
serve as the electrical conductor, in which case it will likely be
covered with an insulation layer 188 or be constructed of titanium
as discussed below. When the body serves as the conductor, it will
be connected to the live or "hot"/positive side of a power supply.
Then a hypotube outer body member or separate catheter (such as the
catheter described in U.S. Pat. No. 6,059,779 to Mills) in receipt
of the delivery guide can will offer the ground or negative side of
the circuit. Still further, an external ground pad could be applied
to the patient as known in the art. See, e.g., U.S. Pat. No.
6,620,152 to Guglielmi. When the near and far erodable sections are
not electrically isolated from one another, their release may still
be staged by virtue of difference in the volume or type of material
to be eroded as well as by proximity of such material to
"ground".
[0150] In another delivery guide configuration, the elongate
body/wire may be solid and/or comprise a number of pieces 182/182'
as shown in FIG. 7B. These may be soldered together and, rather
than eroding an uninsulated or unprotected or less noble section of
wire inserted between more noble (i.e. higher Mendelev number)
sections, the solder can be electrolytically corroded to release
the implant. Still, any of the options may be employed, depending
on the circumstances.
[0151] For use in such a system, various stent end receptacle 190
configurations are shown in FIGS. 8A-8C. In FIGS. 8A and 8B, the
receptacle is integrated with the cell structure of the stent. In
FIG. 8B, the struts include an additional relieved section to
relieve stress from the end of the crown. In FIGS. 8C and 8D, a
separate aperture 194 is provided adjacent the strut ends to
receive the elongate member that passes therethrough. While the
implant may not be as compact (overall) if produced in such a
manner, addition benefits in term of design flexibility or
performance may be realized by such an approach. An example of
which may be presented in FIG. 8D which combines the features shown
in FIGS. 8B and 8C.
[0152] Overall, the system shown in FIGS. 7A-8D may offer excellent
advantages in terms of space-saving designs. However, there are
occasions (as in when using stronger or larger stents) where it may
be desirable to offer more robust hold-down features. FIG. 9
illustrates the first of a series of such structures.
[0153] The delivery guide portion 108 shown in FIG. 9 employs a
stent 82 including projections 90 that are adapted for an
interlocking interface with near and far seat features 204 as
illustrated in the cutaway expanded view of the same figure. Here,
one can observe the manner in which a wire or ribbon 206 overrides
or covers the keyed interface. A proximal end of the ribbon may be
secured to the delivery guide by glue, solder, etc away from the
stent as illustrated. At the ribbon/seat interface, the materials
are preferably laser-welded together to best accommodate the
potential delicacy of the parts.
[0154] As in the previous examples, the ribbon includes an erodible
section 184. It is not connected to the stent, but it may overlay
the same. Upon release of the ribbon by erosion of the erodible
section (exposed to corrode by stripped insulation, etc.) the
ribbon at least partially unwinds or unravels to allow projections
90 to release and the stent body to untwist and expand.
[0155] The coil, ribbon or segment that cover or overlays the
interlocking feature(s) of the stent and delivery guide seat(s)
serve to secure the interlocking features in engagement such that
those associated with the stent cannot lift out (or be driven out)
of their mates. The wrap may subtend only a small arc across the
body of the delivery system or it may wrap around several times. In
those several wraps, the same member may cross over the engagement
features multiple times. Still, only a portion of the wrap need
overlay the engaged features. Conversely, sections of more than one
capture member may wrap over one or more sets of engagement
features.
[0156] By including a wrap over the interlocking or interfitting
features, their orientation is stabilized relative to opposing
surfaces. This characteristic is of particular value when the
implant secured has a torsional load or preload upon it. Even where
torsional load bearing characteristics are not required, the
configuration offers potential for very low-profile assembly.
Strong flat ribbon can be utilized as the capture member(s).
Alternatively, multiple strands of wire wound in parallel can offer
the requisite strength while maintaining a low profile.
[0157] Further, note that the system overview in FIG. 9 shows a
stent twisted in the manner depicted in FIGS. 6D-6F. Photographs of
a stent so-loaded on a delivery system are shown in FIGS. 10A-10C.
FIG. 10A shows a proximal end 84 of a stent 82. It is held in a
keyed interface by a tubular restraint 208. The stress upon the
members is apparent in view of their flex. An advantage offered by
the present variation of the invention is the strength offered by
the cover in so-restraining the members.
[0158] While in this variation of the invention at least one of the
ends of the stent will be held by an electrolytically releasable
latch, one side may be mechanically released. In the case shown in
FIG. 10A, such release may be effected by withdrawal of the sleeve
like a sheath. Further examples are provided below, in the
above-referenced "Twist-Down Implant Delivery Technologies" case
incorporated herein by reference. In any case, FIG. 10B shows the
manner in which the body of the stent assumes an essentially
cylindrical profile with no external confinement by virtue of the
twist imparted thereto. FIG. 10 C shows the far end of the stent
with ribbon 206 neatly securing the keyed interface.
[0159] FIG. 11A provides an enlarged view of the type of mating
portion employed in the delivery system just described. As
partially illustrated in FIGS. 11B-11D, the mating portions may
alternatively comprise shapes including, but not limited to an "L"
shape, "T" shape, "V" shape, circular, oval, oblong, rectangular,
square, polygonal, diamond, triangular shapes. Generally, the
delivery guide seat features will offer complimentary geometry as
illustrated variously throughout this disclosure. Also shown are
elongate projections 90 in FIGS. 11E and 11F. These too may be
employed in a delivery system such as illustrated in FIG. 9. They
will not offer a locking interface of the type previously
described. Yet, because they will not be axially constrained in the
manner of the other mating projections, they may be used in other
ways as detailed further below.
[0160] In any case, one side of the implant may include features of
one type and the other side another. There may even be instances in
which a mix of different projection types may be desired on a
single side of the implant.
[0161] As for special features that the projections may possess,
certain ones may incorporate a tantalum or platinum plug 210 for
radiopacity (such as the variation in FIG. 11D), or be shaped (such
as the curved variation in FIG. 11F) to account for the stresses
the members will be subject to. Alternatively, a member as shown in
FIG. 11D could leave aperture 194 open for use of such a projection
in a wrap-through variation of the invention--such as illustrated
in FIGS. 7A and 7B.
[0162] It is understood that the shape and configuration of the
projection may vary for any number of factors (e.g., the particular
application, the size of the stent, the tortuousity of the
vasculature, etc.). As a result, the projections may comprise any
hook, prong, opening, socket, key, grasper, tooth, bar or slot
shaped configuration (whether the shape is nearly planar or the
shape significantly extends in three dimensions) in addition to
those shapes discussed herein. In accordance with the above, it
follows that the corresponding seating features will be selected to
receive or accommodate the shape of the respective projection. In
any case, the shapes of the projections will be selected so as not
to create undue risk of injury to the patient. For example, for
vascular applications, the shape of the projections must be chosen
so as not to create undue trauma to the vessel wall. On the other
hand, non-vascular applications may not present the same risks.
Accordingly, the design of the projections may be more aggressive
for stents or other implants intended for such applications.
[0163] In all, the various implant/delivery guide interface
features shown include captured types (via hook-in type or keyed
interfaces or those that accommodate a member passing into or
through an interior space) and slide-out types. The captured types
offer an axial retention component at minimum. To a varying degree,
they also offer lateral or radial support, where the interlocking
interfaces excel in such regard. Elongate members adapted to slide
out of an interface when desired are designed (together with their
respective seat features) primarily to offer lateral or radial
support--especially for twist-down type applications as follow.
[0164] As for more specific features pertaining to the construction
of the wrapping covers to secure such relevant features, FIG. 12A
shows an end sectional view of one manner of construction.
Pertinent here is the manner in which ribbon 206 is fed through
open regions of the seat member 200/202. This construction provides
a stable interface for a weld point or well "W" to receive glue or
solder (without increasing the system outer diameter) and/or a
pass-through "P" allowing a full or partial wrap of ribbon 206
directly upon body core or mandrel 180 so as to take advantage of
frictional forces at their interface to reduce the force that the
connection point would otherwise bear.
[0165] FIG. 12B shows a distal end of a delivery system employing
seats with the features shown in FIG. 12A. Here, the system is
configured such that core member 180 serves as the positive
electrode in the system. The seats and ribbon are all in electrical
contact with this member. A hypotube body, 210 then serves as the
negative or ground pole. An insulation layer 212 (e.g., in the form
of a coating or tube of material) is interposed between the core
member and the hypotube to prevent the system from
shorting-out.
[0166] As with the variations above, where the latch members are
not isolated in discrete circuits, other parameters (e.g., ribbon
thickness or width at the erodable section, etc.) may be varied to
manipulate release timing. And, again, because more of the system
is positively charged (as opposed to the releasable members, alone)
the system may require insulation to focus erosion and/or avoid
current leak resulting in higher power requirements, etc.
[0167] FIG. 12C shows a variation of a near side of such a delivery
guide as shown in FIG. 12B, but illustrates a different electrical
connection approach (also applicable to the far side
retention/release means). In FIG. 12C, the ribbon 206 is powered by
a separate electrical lead 212. When the lead is insulated itself
or separated from other members by insulation, and the ribbon can
be completely insulated expect for its erodable section 184, then
only the sacrificial material will be "hot". However, because
small-size ribbon is difficult to insulate on its sides, in some
cases a gold or platinum coating over the material will be employed
to ensure erosion at the desired location. Then, seat 200 would
also be in electrical contact with the positive side of the system.
Under such conditions, seat 200 should likewise receive a
protective coating (i.e., polymeric insulation or noble metal) or
be made of a self-passivating material such as titanium to avoid
corrosion.
[0168] To electrically isolate seat 200, ribbon 206 and any
uninsulated stent loaded onto the delivery guide from core member
180 and/or hypotube 210, insulation material 210 is employed. As
shown, the insulation material may comprise a plurality of tube or
sleeve segments "A, B, C" in order to facilitate twisting the stent
in-situ into a minimal diameter. Regardless of the manner in which
it is electrically isolated, the core member and/or hypotube can
then be employed as "ground" or negative component in the delivery
system.
[0169] Just as any of a variety of electrical architectures can be
adopted, so too are there different approaches to constructing the
cover over the interface of the mating portions of the stent. FIG.
13A shows an alternate stent end cover variation 220 including
electrolytically separable regions 222 joining adjacent "flower
petal" sections until release. FIG. 13B shows a related
construction in which wire segments 226, each with an erodible
segment 184 restrain sections 224 until release.
[0170] As referenced above, the invention also contemplates systems
with electrolytic release on one side of a stent and some other
form of release on the other. One example is shown in FIG. 14 where
a "floating" or unsecured band 230 can be driven off the seat
section 200 by expansion of the stent 82 propagating from the
opposite side of the stent bearing region 108 of the device. To
assist this action which is driven by an increasing angle .theta.
of the stent end the delivery guide core member 180 upon which the
stent rides may be undercut or a construction provided such as
shown where a band 232 provides a raised fulcrum with open space
"O" behind it. Since distal-to-proximal stent deployment is often
favored, it will generally be preferred that it is near seat 200
overlaid by such an automatically releasable or self-releasing
cover.
[0171] FIG. 15 shows the proximal side of a distal portion 108 of a
delivery guide with a tear-down cover 234 for holding and releasing
the proximal end of an implant. A wire, suture or another type of
rip line 236 may be situated to tear-down cover 234. The cover may
include a notch 238 to assist in such action. The line may connect
to a core wire 242 housed within a hypotube body 244 of the
delivery guide in order to confine the mechanical action within the
body of the delivery guide. Similarly, while the restraint-based
capture discussed above in connection with FIG. 10A may occur by
actuation of a simple sheath, it may instead be effected by an
internal core wire crossing into a body tube in a manner similar to
that shown in FIG. 15 or as described in U.S. patent application
Ser. No. 10/991,721 entitled, "Corewire Actuated Delivery System
with Fixed Distal Stent-Carrying Extension," filed Nov. 18, 2004
and incorporated herein by reference in its entirety.
[0172] While hybrid mechanical systems may certainly be employed in
certain variations of the invention, another class advantageously
employs two electrolytically released assemblies at the near and
far end of the implant to be delivered. FIG. 16 illustrates
architecture for retention and release of a first side of the
implant. Other complementary structures release the second side of
the implant. Since the first side of stent release is
advantageously at the distal side, FIG. 16 shows the release
members so-situated.
[0173] Here, a distal seat 202 is situated over a hypotube core
member 250. An electrical lead wire 252 passes through the core
member from a proximal end of the delivery guide to emerge to meet
or define wrap section 254. Wire 252 may be a small gauge copper
conductor and wrap section will comprise stainless steel with an
insulative coating except at the erodible sacrificial section 184.
Alternatively the same piece of stainless steel wire may serve as
the electrical lead and length including the sacrificial section.
The number of turns of wire 254 around the delivery guide body may
vary from as few as a fraction of a turn to many (as shown). Still,
at least one turn around the body may be desirable to direct force
along the axis of the wire and/or take advantage of friction
between the wire and delivery guide to hold position of the
wire
[0174] Regardless, one end of the wire may be connected to an
insulative layer 256 between core member 250 and band 260. In this
manner, erodible section 184 is isolated from the delivery guide
body, which in operation of this variation of the invention serves
as "ground" or "negative" to the extent applicable in view of the
power profile selected. Band 260 is secured to seat 202 by sleeve
262. The members may be metallic and laser-welded together as
indicated or otherwise connected. A blocker 264 under sleeve
prevents axial movement of untwisting assembly 266.
[0175] To release the stent received within seat 202, sacrificial
latch section 184 is eroded thereby untwisting assembly 266
rotates. The rotation causes the associated stent to untwist and
expand. The expansion results in foreshortening that pulls the
stent's distal projections out of capped slot 268.
[0176] Untwisting assembly 266 is advantageous, among other
reasons, because it requires no translation to operate; the
assembly simply rotates to effect release. As such, it offers an
extremely robust operation in even the most tortuous anatomy.
[0177] Still, a pair of sleeve sections 262 and 262' may be
provided as indicated by broken line. The near section 262' would
then be set to slide back for stent release in a manner similar to
the approach taught in connection with FIG. 14 with sleeve 230. The
other would still be used to connect band 260 and seat 202.
[0178] FIGS. 17A and 17B illustrate another retention and release
approach employing an unwinding assembly 270--typically for use at
a proximal end of a delivery guide. Here, a ribbon 206 is connected
to a band 256 and a seat 200 secured against rotation by a wire
252/254. Upon release of a sacrificial section 184 of the wire, the
band and seat can rotate relative to one another, to the extent
that the ribbon expands. So configured, the ribbon is able to open
some amount to aid in releasing the near projections from the
stent. Different states of the ribbon 206, the erodible wire
252/254 and proximal seat 200 are illustrated in each of FIGS. 17A
and 17B showing restraining and release states, respectively.
[0179] A blocker (like blocker 264) can be set within gap "G" to
stabilize band 256 and allow seat 200 to travel in a distal
direction to reduce the ribbon diameter upon withdrawal. Another
blocker can be set distal to seat 200 to limit such travel as
indicated in phantom line. However, it may be desirable to allow
the member to "float" so that, upon withdrawal of the system, the
distal movement of seat 200 pulls ribbon 206 into a reduced
diameter.
[0180] FIG. 18 shows a distal portion of a stent delivery guide,
together with a stent 82 employing a proximal unwinding assembly
270 and distal untwisting assembly 266 for stent retention and
release. Of course, other delivery guide combinations of
retention/release assemblies may alternatively be provided.
[0181] FIG. 19 shows a system employing an untwisting assembly 266
and a covered key interface like that illustrated in FIGS. 13A and
13B. This system may be desirable from the perspective of
maintaining a positive lock on the implant until proximal release
is desired. Therefore, the system can be withdrawn (with the stent
attached thereto) most easily in case emergency withdrawal is
required.
[0182] FIG. 20 shows another advantageous system. It employs an
untwisting assembly 266 at a far end of the stent-bearing region
108, and a simplified proximal seat interface 272 on the near side.
Seat 200 is merely covered by a sleeve 274. To effect final stent
delivery, with the stent distal side 86 seated against the vessel
wall, the delivery guide is simply withdrawn so that the near stent
projections slide out. Of course, if the retention/release
components were reversed, then advancing the delivery guide would
finalize delivery. Yet, (as shown) the system may advantageously
employ the leading edge 276 of a catheter body 278 to help urge the
stent from the slotted interface 268.
[0183] Yet another class of delivery systems according to the
present invention employing an untwisting assembly 266 is shown in
FIGS. 21A and 21B. These figures illustrate two states of a distal
portion of a delivery guide that employ a
self-locking/auto-releasing proximal spring-spring back assembly
280.
[0184] Spring-back assembly 280 includes a coil spring 282 or a
similar member that is wound-down upon the delivery guide body
portion 284 when the stent is fully twisted. As wound, the position
of the spring is locked. However, when untwisting assembly 266
allows the stent to unwind, spring 282 follows, and its coils
expand. As the coils expand, the spring withdraws seat 200. As
such, it pulls seat 200 off of the stent some distance "D". One or
more blocker members can be provided to maintain the proximal
position of the stent for this withdrawal. Alternatively, the
spring may withdraw sleeve 262 alone such that the seat is left
uncovered by action of the spring.
[0185] FIGS. 22A and 22B show a somewhat related system to that in
FIGS. 21A and 21B. It also employs an untwisting assembly 266
unlocking a coil spring 282 for retracting a member. FIGS. 22A and
22B show two states of the delivery guide. In the first, a
restraint covers the stent-bearing region 108. Upon unlocking the
spring as a result of releasing assembly 266, the restraint is
withdrawn, releasing the stent that is at least partially abutted
by stop or blocker member 286.
[0186] As indicated by the broken line, the restraint 284 may cover
the whole stent or only some portion thereof. Where only a partial
restraint sleeve is used, the stent will be twisted down in
diameter distal to the edge of the restraint. It may also lie
twisted under the restraint. When a restraint covering the entirety
of the stent is employed, the stent may or may not be
twisted--though at least the restraint and coil assembly will be
twisted relative to the delivery guide body and assembly 266 to
effect the lock/unlock approach described.
[0187] FIG. 23 shows another delivery guide variation employing a
tubular sleeve. As above, sleeve 290 may be in the form of a pull
wire actuated restraint or a full sheath. In this variation of the
invention, the stent 82 is generally not twisted, but rather only
compressed within the sleeve. A blocker may optionally be provided,
but is not necessary in that a far end 86 of the stent is held by
an electrolytically releasable band covering a keyed interface.
This approach stabilizes the end of the stent for delivery.
[0188] An advantage of such a system is to reduce the force by
which the stent pushes against the sleeve, thereby lowering (at
least initial) sleeve withdrawal forces. After initial movement of
the sleeve, the far end of the stent may be released so that the
expansion of the stent helps drive the sleeve off the body 88 of
the stent. In which case, blocker 286 will be necessary to
stabilize the near end 84 of the stent in completing sleeve 290
withdrawal. In another approach, the ribbon is not electrolytically
released until after complete sleeve withdrawal.
[0189] FIGS. 24A and 24B show preloaded spring-back restraint
systems. In each, a coil spring, elastomeric tube, or relived metal
(e.g., NITINOL) tube (as shown) serves as a spring 292 to withdraw
a sleeve 294 restraining a stent in a compressed profile. The
spring is preloaded under tension to offer a return stroke upon
release. In the variation shown in FIG. 24A, a wire latch 296 with
a sacrificial erodible section 184 is provided to hold the
structure in its preloaded condition until release. The sleeve 294
will generally comprise a polymeric tube. Therefore, a reinforcing
band 298 to receive the latch wire may be desired so as to insure
the system does not inadvertently release. The system in FIG. 24B
resembles that in FIG. 24A, except in that an erodible solder
connection 300 between the delivery guide core 250 and at least a
portion of the spring acts to pin the system in a preloaded
configuration until erosion of the material and release upon
applying power. Further, it is to be understood that other
approaches may be utilized to restrain and then release a
spring-loaded sleeve for stent delivery.
Erosion Control
[0190] In describing the various systems above, some discussion was
offered as to which elements are insulated from one another or
shielded from corrosion by noble metal. Certain details regarding
the same are readily understood by those with skill in the art.
Generally speaking, however, numerous ones of the above systems
illustrate separate lead wires to actuate the electrolytically
erodible release means. Likewise, many of the systems include
separate lead wires to actuate the proximal electrolytically
erodible release means. By providing separate circuits, especially
in instances in which the body of the device serves as a return
path, the latches can be actuated individually. Their action can be
monitored. When current no longer flows on a given circuit,
positive indication is offered that the subject latch has been
released. Furthermore, the latches can be released individually
without unintended early release of one relative to the other as is
possible in systems which simply rely on the volume of material to
be eroded. Another beneficial factor is that by eroding one latch
at a time, current is limited relative to a system in which
multiple sections of material would be eroded at once.
[0191] In certain variations of the invention, isolation of one
member from another in order to isolate their respective polarities
is accomplished through the use of interposed polymer tubing or
coatings. However, one aspect of the invention contemplates systems
in which little insulation is employed, and rather system
components intended to be protected from corrosion are made from
titanium. Those members which are to be set for erosion are to be
made of stainless steel or another suitable material. The
sacrificial material may be a section of material connected to or
interposed between one or more titanium sections of material by
laser welding, resistance welding, soldering, etc. Otherwise, some
portion of the system may comprise titanium, while the ribbon, wire
or other member including a sacrificial section consist
substantially of one material (such as stainless steel) and the
rest is covered by insulation or a noble metal protective
coating.
[0192] Other components not to be eroded are made of anodized
titanium. With the anodized layer, the material is far less
susceptible to erosion. What is more, upon application of voltage,
small nicks or scratches in the titanium will passivate (become
anodized) given a voltage applied of about 3V or more. Some current
drain will be experienced, but the major site for ion transfer will
be at the section intentionally left bare.
Electrical Safety Architecture
[0193] In yet another aspect of the invention bi-polar systems are
provided in which the referenced "hot" and ground sections are in
close proximity to one another. By limiting the distance over which
ion travel must occur to transfer charge/pass current, the spread
of electrical lines of flux are minimized. The graphic of FIG. 25
illustrates this effect. Generally, one aspect of the invention
involves minimizing the separation between an electrolytically
erodible section 184 and return path 302. The separation "S" is
desirably within 1 cm distance. More preferably, it is within 5 mm
to 1 mm distance or less. In this manner, the amount of potential
electrical penetration in a 2 to 3 mm vessel is minimized.
Electrical Performance
[0194] Electrolytic erosion of a section of metal on a delivery
system element to release an implant is driven by applying voltage
to develop a positive charge on the element resulting in a strong
motive force to cause current to flow to a negatively charged body.
The mechanism by which current flows is ion transfer from the
section to be eroded. Further discussion of this process is
described and/or relates to the mode of release in various patents
including U.S. Pat. No. 5,122,136 to Guglielmi; U.S. Pat. No.
6,716,238 to Elliot; U.S. Pat. No. 6,168,592 to Kupiecki, et al.;
U.S. Pat. No. 5,873,907 to Frantzen and the multiplicity of
continuation, continuations-in-part and divisional applications
related to these patents.
[0195] In the present invention, a DC voltage component is likewise
applied to effect corrosion/erosion of the implant release means.
And while adding an AC voltage component for sensing purposes is
known (e.g., as described U.S. Pat. No. 5,569,245 to Guglielmi, et
al.; U.S. Pat. No. 5,643,254 to Scheldrup, et al.) the invention
hereof does so and uses the AC voltage in a very different
manner.
[0196] Specifically, it has been appreciated that use of
significant AC component offset by a DC signal can dramatically
improve the process of implant delivery through electrolytic
corrosion. Not to be bound by a particular theory, but it is
thought that efficiency gains are related to controlling blood
electrocoagulation and to having periods of higher peak voltage
during the upsweep of the AC signal.
[0197] This AC component is especially beneficial in coronary
therapy because high frequency (e.g., 10 kHz to 100 kHz or greater)
AC power does not effect heart rhythm unless the waveform becomes
unstable. Controlling electrocoagulation is very important for
safety reasons (in avoiding emboli formation that could lead to
stroke or other complications) and also to increase the speed of
corrosion.
[0198] Generally speaking, while corroding a positively charged
section of metal, the positive charge attracts negatively charged
blood cells which coagulate on the surface of the metal. The
coagulated blood cells cover the corroding metal and slow the
deployment process. Higher DC levels can be employed to push past
this effect, but for safety considerations (especially in the
vicinity of the heart) it is desirable to use lower DC
voltages.
[0199] Instead, when an AC signal is employed that drops the trough
of the waveform into the negative regime, an opportunity exists to
repel the negatively charged blood cells. The resulting decrease or
lack of electrocoagulation offers an efficiency increase so that DC
voltage can be dropped while maintaining deployment times that are
subjectively acceptable to a medical practitioner (e.g., less than
about 1 minute or about 30 seconds).
[0200] Power is preferably delivered to the subject systems
employing a custom battery-powered power supply. Still, various
function generators may be employed for experimental purposes. A
Fluke model PM 5139 Function Generator proved adequate in
practicing the subject invention. A square wave function is most
advantageously employed to maximize the time spent at peak and
minimum voltage levels, but sinusoidal, saw-tooth, and other
variations of these forms may be employed. Still further, frequency
modulated waveforms in which more or less time is spent in the
positive or negative regimes may be employed.
[0201] Regardless of how it is generated, FIG. 26 shows an
exemplary power profile as may be used with the current invention.
The Figure shows a square wave at about 100 kHz with a 10V peak to
peak (10Vpp) AC component that is offset by a 2.2V DC signal." This
results in a square wave with a 7.2V peak and -3.8V trough. Through
testing is has been appreciated that such a power profile erodes
sacrificial material in an electrolytic solution much faster than
would DC signal alone. Indeed, testing has shown that using DC
voltage alone at steady state voltages below 2.5V results in very
long erosion times (i.e., upwards of 2 minutes to erode 0.003 inch
diameter wire) and providing power at 2V will often not erode
stainless steel wire at all. With the addition of an AC profile of
at least 4Vpp, however, the DC component could drop to as low as
about 1V to about 1.5V giving a resulting waveform with a peak from
3 to 3.5V and a trough from -1 to -0.5V and still offer an
acceptable rate of corrosion.
[0202] In porcine blood, it was determined that a peak waveform
voltage of above 8V begins to cause electrocoagulation, even with
trough voltages of -6 to -7V. The level of electrocoagulation
varies with the level of the DC component and the size of the piece
of metal to be eroded, but usually the peak voltage should remain
below 9V and most often below 8V to avoid appreciable
electrocoagulation.
[0203] In view of the above, and further for safety
reasons--especially in the vicinity of the heart--it may be
desirable to maintain the DC component of the power applied between
about 1 and about 5V, and more preferably between about 1.75 and
about 3V, and possibly most preferably between about 2 and about
3V. The AC waveform employed will generally then be selected to
generate a peak below about 9V and usually below about 8V, with
7-7.5V being typical per the above. Accordingly, the resultant
power profile may have a peak or maximum between about 4 and about
9V, and a minimum of about -0.5 to about -5V. Within this range
(and in certain circumstances, outside the range, given situations
where some amount of electrocoagulation is acceptable), more
effective combinations exist as detailed herein and as may be
apparent to those with skill in the art in review of the present
disclosure.
EXAMPLE 1
[0204] The impact of AC voltage on actual erosion/corrosion rates
during bench tests of tensioned 0.002'' stainless steel wire was
conducted. Setups were provided in which an insulated wire was
equally tensioned and exposed along a 0.020 inch long section. The
wires were placed in 38.degree. porcine blood and power was
applied. When applying 2V DC, it took 3-4 minutes to break the
wire. When applying 2V DC and 10Vpp AC, time to separation ranged
from 20-30 seconds. The setups tested under DC-only conditions were
observed to generate roughly 0.040 inch balls of electrocoagulation
on the ends of the wire opposite the eroded section. In marked
contrast, the AC/DC power driven setups showed no visible
electrocoagulation.
EXAMPLE 2
[0205] The same test piece setup described in Example 1 was used
with a lower DC voltage. With only 1V DC the wire would not break
even after 15 minutes of applied power. When a 10Vpp AC signal was
added to the 1V DC signal, the sample test section broke in roughly
1 minute.
EXAMPLE 3
[0206] Tests were conducted to determine the improvement offered
over the power supply provided by Target Therapeutics for
detatching GDC.RTM. coils. First a comparative model was developed.
The electrolytic "joint" in a GDC system was determined to be about
a 0.005 inch long, 0.003 inch diameter stainless steel wire. In
38.degree. porcine blood, with the Target Therapeutics power supply
set at a 1 mA currently delivery setting, voltage metered by the
power supply initially showed at 3V, rose to 6.5V for the majority
of the deployment time, and then rose to 8V. Over a deployment time
measured at 40 seconds, the average voltage observed was about
6.5V. In addition, a ball of electrocoagulation having about a 1/32
inch diameter was observed.
[0207] A "test joint" model was developed to compare a number of
samples in performance. It employed a roughly identically sized
exposed wire extension as described above, but no occlusive coil
attached thereto. In eroding the wire extension with the Target
Therapeutics power supply set at a constant 1 mA current,
significant variability about the above referenced GDC test results
was observed. Voltage varied over a greater range from 1.9V to 9V.
Time to complete erosion ranged from 40-50 seconds irrespective of
such variance. Average voltage was about 4V. Electrocoaguation was
observed on all samples. In instances where voltage climbed to
about 6V, similarly large 1/32 inch diameter balls of
electrocoagulation were observed. When applying a 2.5V DC with
10Vpp AC signal to test joint systems, current floated between 0.5
and 0.75 ma. Deployment times were consistently about 50 seconds.
No electrocoagulation was visible upon inspection.
Variations
[0208] The invention includes methods that may be performed using
the subject devices or by other means. The methods may all comprise
the act of providing a suitable device. Such provision may be
performed by the end user. In other words, the "providing" (e.g., a
delivery system) merely requires the end user obtain, access,
approach, position, set-up, activate, power-up or otherwise act to
provide the requisite device in the subject method. Methods recited
herein may be carried out in any order of the recited events which
is logically possible, as well as in the recited order of
events.
[0209] Exemplary aspects of the invention, together with details
regarding material selection and manufacture have been set forth
above. As for other details of the present invention, these may be
appreciated in connection with the above-referenced patents and
publications as well as generally know or appreciated by those with
skill in the art. For example, one with skill in the art will
appreciate that a lubricious coating (e.g., hydrophilic polymers
such as polyvinylpyrrolidone-based compositions, fluoropolymers
such as tetrafluoroethylene, hydrophilic gel or silicones) may be
placed on the core member of the device, if desired to facilitate
low friction manipulation. The same may hold true with respect to
method-based aspects of the invention in terms of additional acts
as commonly or logically employed.
[0210] In addition, though the invention has been described in
reference to several examples, optionally incorporating various
features, the invention is not to be limited to that which is
described or indicated as contemplated with respect to each
variation of the invention. Various changes may be made to the
invention described and equivalents (whether recited herein or not
included for the sake of some brevity) may be substituted without
departing from the true spirit and scope of the invention. In
addition, where a range of values is provided, it is understood
that every intervening value, between the upper and lower limit of
that range and any other stated or intervening value in that stated
range is encompassed within the invention.
[0211] Also, it is contemplated that any optional feature of the
inventive variations described may be set forth and claimed
independently, or in combination with any one or more of the
features described herein. Reference to a singular item, includes
the possibility that there are plural of the same items present.
More specifically, as used herein and in the appended claims, the
singular forms "a," "an," "said," and "the" include plural
referents unless the specifically stated otherwise. In other words,
use of the articles allow for "at least one" of the subject item in
the description above as well as the claims below. It is further
noted that the claims may be drafted to exclude any optional
element. As such, this statement is intended to serve as antecedent
basis for use of such exclusive terminology as "solely," "only" and
the like in connection with the recitation of claim elements, or
use of a "negative" limitation.
[0212] Without the use of such exclusive terminology, the term
"comprising" in the claims shall allow for the inclusion of any
additional element--irrespective of whether a given number of
elements are enumerated in the claim, or the addition of a feature
could be regarded as transforming the nature of an element set
forth in the claims. Except as specifically defined herein, all
technical and scientific terms used herein are to be given as broad
a commonly understood meaning as possible while maintaining claim
validity.
[0213] The breadth of the present invention is not to be limited to
the examples provided and/or the subject specification, but rather
only by the scope of the claim language. That being said, we
claim:
* * * * *