U.S. patent application number 15/631833 was filed with the patent office on 2017-10-05 for implant delivery system.
This patent application is currently assigned to MicroVention, Inc.. The applicant listed for this patent is MicroVention, Inc.. Invention is credited to Hideo Morita, Helen Nguyen, Tai D. Tieu.
Application Number | 20170281192 15/631833 |
Document ID | / |
Family ID | 42981558 |
Filed Date | 2017-10-05 |
United States Patent
Application |
20170281192 |
Kind Code |
A1 |
Tieu; Tai D. ; et
al. |
October 5, 2017 |
IMPLANT DELIVERY SYSTEM
Abstract
A system and method of delivering and detaching an implant
within a body of a patient is described. A tether connects an
implant with a delivery device. The delivery device includes a
heater coil through which the tether passes. The inner diameter of
the heater coil is about the same size or slightly larger than the
outer diameter of the tether, allowing the tether to more
efficiently break the tether during delivery.
Inventors: |
Tieu; Tai D.; (Fountain
Valley, CA) ; Morita; Hideo; (Irvine, CA) ;
Nguyen; Helen; (Garden Grove, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MicroVention, Inc. |
Tustin |
CA |
US |
|
|
Assignee: |
MicroVention, Inc.
Tustin
CA
|
Family ID: |
42981558 |
Appl. No.: |
15/631833 |
Filed: |
June 23, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12761113 |
Apr 15, 2010 |
9717500 |
|
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15631833 |
|
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61169629 |
Apr 15, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2/01 20130101; A61B
90/39 20160201; A61F 2/011 20200501; A61B 17/12113 20130101; A61B
2017/12068 20130101; A61F 2002/9505 20130101; A61F 2/95 20130101;
A61B 17/12154 20130101; A61F 2002/9511 20130101; A61B 17/12022
20130101; A61F 2250/0071 20130101 |
International
Class: |
A61B 17/12 20060101
A61B017/12; A61F 2/01 20060101 A61F002/01; A61B 90/00 20060101
A61B090/00 |
Claims
1. A delivery system for an implant comprising: an elongated pusher
having a distal end and a proximal end; an implant positioned at
said distal end of said elongated pusher; a resistance heating
element having a first plurality of coils that each have a first
internal diameter and a second plurality of coils that each have a
second internal diameter that is smaller than said first internal
diameter; said resistance heating element increasing in temperature
via application of direct current; a tether member connected to
said elongated pusher, passing through said first plurality of
coils, passing through said second plurality of coils, and being
attached to said implant.
2. The delivery system of claim 1, further comprising a first wire
connected to a distal end of said heating element and a second wire
connected to a proximal end of said heating element; wherein said
first wire and said second wire supply
3. The delivery system of claim 2, further comprising a selectively
actuated power supply that is connectable with said first wire and
said second wire.
4. The delivery system of claim 1, wherein said tether has an
external diameter of about 0.004 inch, said first internal diameter
is about 0.007 inch and said second internal diameter is about
0.005 inch.
5. The delivery system of claim 1, wherein said heating element is
fixed along a side of said elongated pusher.
6. The delivery system of claim 1, wherein said implant is a stent
having a plurality of cells and wherein said tether member is
positioned through at least one of said plurality of cells.
7. The delivery system of claim 6, wherein said tether member
passes through multiple cells of said plurality of cells.
8. The delivery system of claim 1, wherein said implant is an
embolic microcoil.
9. A delivery system for an implant comprising: a pusher having an
elongated shape; a proximal end of said pusher being connectable to
a DC power supply; an implant positioned at a distal end of said
pusher; a heater comprising a lumen formed from a first region and
a second region; said first region have a first internal diameter
and said second region having a second internal diameter that is
smaller than said first internal diameter; a tether connected to
said pusher and extending through said lumen of said first region
and said second region; said tether connecting to said implant and
being breakable by activation of said heater by said DC power
supply.
10. The delivery system of claim 9, wherein said heater has a
tubular shape.
11. The delivery system of claim 9, further comprising a structural
coil having a helical shape and being disposed around said heater
and said tether.
12. The delivery system of claim 9, wherein a distal and proximal
end of said coil are fixed to said pusher, forming a loop engaged
with said implant.
13. The delivery system of claim 9, further comprising a support
mandrel having a distal end fixed to said heater.
14. The delivery system of claim 9, wherein said tether also
extends adjacent to said heater, outside of said lumen.
15. The delivery system of claim 9, wherein said implant is a stent
having a plurality of cells and wherein said tether is located
through at least some of said plurality of cells.
16. The delivery system of claim 15, wherein said tether maintains
said stent in a compressed configuration.
17. An implant delivery system comprising: an elongated pusher
comprising a tubular support structure, a heater fixed within the
support structure, and a tether connected to the elongated pusher
and positioned through an internal passage of said heater; wherein,
said heater comprises a helical coil having a first length formed
to a first diameter and a second length formed to a second diameter
that is smaller than said first diameter.
18. The implant delivery system of claim 17, wherein said second
length is located at a distal end of said heater.
19. The implant delivery system of claim 17, wherein said tether
has an external diameter of about 0.004 inch, said first diameter
is about 0.007 inch, and said second diameter is about 0.005
inch.
20. The implant delivery system of claim 17, wherein an outer
surface of said heater is fixed to a support mandrel.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of and claims priority to
U.S. patent application Ser. No. 12/761,113 filed Apr. 15, 2010
entitled Implant Delivery System, which claims priority to U.S.
Provisional Application No. 61/169,629, filed Apr. 15, 2009
entitled Implant Delivery System, whose contents are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to systems and methods for
delivering implant devices to a target site or location within the
body of a patient. The present invention also relates to a method
of detecting implant detachment within the body of a patient.
BACKGROUND OF THE INVENTION
[0003] Delivery of implantable therapeutic devices by less invasive
means has been demonstrated to be desirable in numerous clinical
situations. For example, vascular embolization has been used to
control vascular bleeding, to occlude the blood supply to tumors,
to occlude fallopian tubes, and to occlude vascular aneurysms,
particularly intracranial aneurysms. In recent years, vascular
embolization for the treatment of aneurysms has received much
attention. Implants used to treat aneurysms are often convoluted or
coiled lengths of wound wire and are referred to as "microcoils."
Microcoils work by filling an aneurysm causing the blood flow
through the aneurysm to slow or stop, thereby inducing thrombosis
within the aneurysm.
[0004] Microcoils are extremely flexible and have very little
structural integrity. In order to make them easier to retrieve and
reposition, recent efforts have been directed to making them
stretch-resistant. For example, a stretch-resistant embolic coil
having a stretch-resistant member passing through the interior
lumen of the coil is described in U.S. Pat. No. 5,582,619 to Ken.
US Patent Publication No. 2004/0034363 to Wilson also discloses an
embolic coil with a stretch resistant member having a distal end
attached near the distal end of the coil and a proximal end of the
member attached to a delivery catheter.
[0005] Several different treatment modalities have been employed in
the prior art for deploying implant devices. For example, numerous
repositionable detachment systems for implant devices have been
described in the prior art including U.S. Pat. No. 5,895,385 to
Guglielmi et al. and 5,108,407 to Geremia et al., the contents of
which are hereby incorporated by reference. Several systems, such
as those disclosed in U.S. Pat. No. 6,500,149 to Gandhi et al. and
U.S. Pat. No. 4,346,712 to Handa et al., the contents of which are
hereby incorporated by reference, describe the use of a heater to
detach and deploy the implant device.
[0006] While implant delivery and detachment systems are known in
the art, they do not provide the user feedback that the implant has
indeed detached from the delivery device. This is especially
important in cases where the detachment relies on the application
of heat or an electrolytic process where an element of time is
involved. These delivery devices leave the user in the position of
wondering whether heat etc., has been applied long enough to cause
detachment. Hence, there exists a need for a method of detecting
whether an implant has properly and effectively detached within the
body of a patient.
SUMMARY OF THE INVENTION
[0007] The present invention is an implant delivery and detachment
system used to position and deploy implantable devices such as
coils, stents, filters, and the like within a body cavity
including, but not limited to, blood vessels, fallopian tubes,
malformations such as fistula and aneurysms, heart defects (e.g.
left atrial appendages and sepal openings), and other luminal
organs.
[0008] The system comprises an implant, a delivery catheter
(generically referred to as the pusher or delivery pusher), a
detachable joint for coupling the implant to the pusher, a heat
generating apparatus (generically referred to as the heater), and a
power source to apply energy to the heater.
[0009] The present invention also includes a method for detecting
detachment of an implant. In particular, detachment of an implant
is detected by measuring the change in the electrical resistance of
the delivery system.
[0010] The present invention may also be used in conjunction with
the delivery mechanism disclosed in U.S. patent application Ser.
No. 11/212,830 filed Aug. 25, 2005 entitled "Thermal detachment
system for implanting devices," which is incorporated by reference
herein in its entirety.
[0011] In one aspect of the present invention, the implant is
coupled to the pusher using a tether, string, thread, wire,
filament, fiber, or the like. Generically this is referred to as
the tether. The tether may be in the form of a monofilament, rod,
ribbon, hollow tube, or the like. Many materials can be used to
detachably join the implant to the pusher. One class of materials
is polymers such as polyolefin, polyolefin elastomer such as those
made by Dow marketed under the trade name Engage or Exxon marketed
under the trade name Affinity, polyethylene, polyester (PET),
polyamide (Nylon), polyurethane, polypropylene, block copolymer
such as PEBAX or Hytrel, and ethylene vinyl alcohol (EVA); or
rubbery materials such as silicone, latex, and Kraton. In some
cases, the polymer may also be cross-linked with radiation to
manipulate its tensile strength and melt temperature. Another class
of materials is metals such as nickel titanium alloy (Nitinol),
gold, and steel. The selection of the material depends on the
capacity of the material to store potential energy, the melting or
softening temperature, the power used for detachment, and the body
treatment site. The tether may be joined to the implant and/or the
pusher by welding, knot tying, soldering, adhesive bonding, or
other means known in the art. In one embodiment where the implant
is a coil, the tether may run through the inside lumen of the coil
and be attached to the distal end of the coil. This design not only
joins the implant to the pusher, but also imparts stretch
resistance to the coil without the use of a secondary stretch
resistant member. In other embodiments where the implant is a coil,
stent, or filter; the tether is attached to the proximal end of the
implant.
[0012] In another aspect of the present invention, the tether
detachably coupling the implant to the pusher acts as a reservoir
of stored (i.e. potential) energy that is released during
detachment. This advantageously lowers the time and energy required
to detach the implant because it allows the tether to be severed by
application of heat without necessarily fully melting the material.
The stored energy also may exert a force on the implant that pushes
it away from the delivery catheter. This separation tends to make
the system more reliable because it may prevent the tether from
re-solidifying and holding the implant after detachment. Stored
energy may be imparted in several ways. In one embodiment, a spring
is disposed between the implant and pusher. The spring is
compressed when the implant is attached to the pusher by joining
one end of the tether to one of either the pusher or implant,
pulling the free end of the tether until the spring is at least
partially compressed, then affixing the free end of the tether to
the other of the implant or the pusher. Since both ends of the
tether are restrained, potential energy in the form of tension on
the tether (or compression in the spring) is stored within the
system. In another embodiment, one end of the tether is fixed as in
the previous embodiment, and then the tether is placed in tension
by pulling on the free end of the tether with a pre-determined
force or displacement. When the free end of the tether is then
affixed, the elongation (i.e. elastic deformation) of the tether
material itself stores energy.
[0013] In another aspect of the present invention, a heater is
disposed on or within the pusher, typically, but not necessarily,
near the distal end of the pusher. The heater may be attached to
the pusher by, for example, soldering, welding, adhesive bonding,
mechanical boding, or other techniques known in the art. The heater
may be in the form of a wound coil, heat pipe, hollow tube, band,
hypotube, solid bar, toroid, or similar shape. The heater may be
made from a variety of materials such as steel, chromium cobalt
alloy, platinum, silver, gold, tantalum, tungsten, mangalin,
chromium nickel alloy available from California Fine Wire Company
under the trade name Stable Ohm, conductive polymer, or the like.
The tether is disposed in proximity to the heater. The tether may
pass through the lumen of a hollow or coil-type heater or may be
wrapped around the heater. Although the tether may be disposed in
direct contact with the heater, this is not necessary. For ease of
assembly, the tether may be disposed be in proximity to, but not
actually touching, the heater.
[0014] The delivery catheter or pusher is an elongate member with
distal and proximal ends adapted to allow the implant to be
maneuvered to the treatment site. The pusher comprises a core
mandrel and one or more electrical leads to supply power to the
heater. The pusher may taper in dimension and/or stiffness along
the length, with the distal end usually being more flexible than
the proximal end. In one embodiment, the pusher is adapted to be
telescopically disposed within a delivery conduit such as a guide
catheter or microcatheter. In another embodiment, the pusher
contains an inner lumen allowing it to be maneuvered over a guide
wire. In still another embodiment, the pusher can be maneuvered
directly to the treatment site without a secondary device. The
pusher may have a radiopaque marking system visible with
fluoroscopy that allows it to be used in conjunction with
radiopaque markings on the microcatheter or other adjunctive
devices.
[0015] In another aspect of the present invention, the core mandrel
is in the form of a solid or hollow shaft, wire, tube, hypotube,
coil, ribbon, or combination thereof. The core mandrel may be made
from plastic materials such as PEEK, acrylic, polyamide, polyimide,
Teflon, acrylic, polyester, block copolymer such as PEBAX, or the
like. The plastic member(s) may be selectively stiffened along the
length with reinforcing fibers or wires made from metal, glass,
carbon fiber, braid, coils, or the like. Alternatively, or in
combination with plastic components, metallic materials such as
stainless steel, tungsten, chromium cobalt alloy, silver, copper,
gold, platinum, titanium, nickel titanium alloy (Nitinol), and the
like may be used to form the core mandrel. Alternatively, or in
combination with plastic and/or metallic components, ceramic
components such as glass, optical fiber, zirconium, or the like may
be used to form the core mandrel. The core mandrel may also be a
composite of materials. In one embodiment, the core mandrel
comprises an inner core of radiopaque material such as platinum or
tantalum and an outer covering of kink-resistant material such as
steel or chromium cobalt. By selectively varying the thickness of
the inner core, radiopaque identifiers can be provided on the
pusher without using secondary markers. In another embodiment, a
core material, for example stainless steel, with desirable material
properties such as kink resistance and/or compressive strength is
selectively covered (by, for example, plating, drawing, or similar
methods known in the art) with a low electrical resistance material
such as copper, aluminum, gold, or silver to enhance its electrical
conductivity, thus allowing the core mandrel to be used as an
electrical conductor. In another embodiment, a core material, for
example, glass or optical fiber, with desirable properties such as
compatibility with Magnetic Resonance Imaging (MRI), is covered
with a plastic material such as PEBAX or polyimide to prevent the
glass from fracturing or kinking.
[0016] In another aspect of the present invention, the heater is
attached to the pusher, and then one or more electrical conductors
are attached to the heater. In one embodiment a pair of conductive
wires run substantially the length of the pusher and are coupled to
the heater near the distal end of the pusher and to electrical
connectors near the proximal end of the pusher. In another
embodiment, one conductive wire runs the substantially the length
of the pusher and the core mandrel itself is made from a conductive
material or coated with a conductive material to act as a second
electrical lead. The wire and the mandrel are coupled to the heater
near the distal end and to one or more connectors near the proximal
end of the pusher. In another embodiment, a bipolar conductor is
coupled to the heater and is used in conjunction with
radiofrequency (RF) energy to power the heater. In any of the
embodiments, the conductor(s) may run in parallel to the core
mandrel or may pass through the inner lumen of a substantially
hollow core mandrel (for example, a hypotube).
[0017] In another aspect of the present invention, an electrical
and/or thermally insulating cover or sleeve may be placed over the
heater. The sleeve may be made from insulating materials such as
polyester (PET), Teflon, block copolymer, silicone, polyimide,
polyamide, and the like.
[0018] In another aspect of the present invention, electrical
connector(s) are disposed near the proximal end of the pusher so
that the heater can be electrically connected to a power source
through the conductors. In one embodiment, the connectors are in
the form of a plug with one or more male or female pins. In another
embodiment, the connector(s) are tubes, pins, or foil that can be
connected with clip-type connectors. In another embodiment, the
connector(s) are tubes, pins, or foil that are adapted to mate with
an external power supply.
[0019] In another aspect of the present invention, the pusher
connects to an external power source so that the heater is
electrically coupled to the power source. The power source may be
from battery(s) or connected to the electrical grid by a wall
outlet. The power source supplies current in the form of direct
current (DC), alternating current (AC), modulated direct current,
or radiofrequency (RF) at either high or low frequency. The power
source may be a control box that operates outside of the sterile
field or may be a hand-held device adapted to operate within a
sterile field. The power source may be disposable, rechargeable, or
may be reusable with disposable or rechargeable battery(s).
[0020] In another aspect of the present invention, the power source
may comprise an electronic circuit that assists the user with
detachment. In one embodiment, the circuit detects detachment of
the implant and provides a signal to the user when detachment has
occurred. In another embodiment, the circuit comprises a timer that
provides a signal to the user when a pre-set length of time has
elapsed. In another embodiment, the circuit monitors the number of
detachments and provides a signal or performs an operation such as
locking the system off when a pre-set number of detachments have
been performed. In another embodiment, the circuit comprises a
feedback loop that monitors the number of attachment attempts and
increases the current, voltage, and/or detachment time in order to
increase the likelihood of a successful detachment.
[0021] In another aspect of the present invention, the construction
of the system allows for extremely short detachment time. In one
embodiment the detachment time is less than 1 second.
[0022] In another aspect of the present invention, the construction
of the system minimizes the surface temperature of the device
during detachment. In one embodiment, the surface temperature at
the heater during detachment is under 50.degree. C. In another
embodiment, the surface temperature at the heater during detachment
is under 42.degree. C.
[0023] In another aspect of the present invention, detachment of
the implant is detected by measuring a change in the electrical
resistance of the delivery system, specifically the heater zone, to
detect implant detachment.
[0024] These and other aspects and features of the present
invention will be appreciated upon consideration of the following
drawings and detailed descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 illustrates a cross-sectional side view of a first
embodiment of a detachment system according to the present
invention;
[0026] FIG. 2 illustrates a cross-sectional side view of a second
embodiment of a detachment system according to the present
invention;
[0027] FIG. 3A illustrates example direct signaling current
according to the present invention;
[0028] FIG. 3B illustrates example alternating signaling current
according to the present invention;
[0029] FIG. 4 illustrates a cross-sectional side view of a third
embodiment of a detachment system according to the present
invention;
[0030] FIG. 5 illustrates example temperature data of the surface
of a detachment system according to the present invention;
[0031] FIG. 6 illustrates a cross-sectional side view of an
electrical connector of a detachment system according to the
present invention;
[0032] FIG. 7 illustrates a cross-sectional side view of radiopaque
layers of a detachment system according to the present invention;
and
[0033] FIG. 8 illustrates a cross-sectional side view of a
detachment system including a stent according to the present
invention;
[0034] FIG. 9 illustrates a side view of a implant device according
to the present invention;
[0035] FIG. 10 illustrates a perspective view of a coil and spacer
of the delivery system of FIG. 9;
[0036] FIG. 11 illustrates a side view of a pusher of the delivery
system of according to the present invention;
[0037] FIG. 12 illustrates a side view of the pusher of the
delivery system of FIG. 11;
[0038] FIG. 13 illustrates a perspective view of a delivery system
according to the present invention;
[0039] FIG. 14 illustrates a side view of the delivery system of
FIG. 13;
[0040] FIG. 15 illustrates a perspective view of the delivery
system of FIG. 13;
[0041] FIG. 16 illustrates a side view of the tether and implant
device of FIG. 13;
[0042] FIG. 17 illustrates a side view of the delivery system of
FIG. 13; and
[0043] FIG. 18 illustrates a side view of an alternate tether
arrangement for the delivery system of FIG. 13.
DETAILED DESCRIPTION OF THE INVENTION
[0044] Turning to FIG. 1, a detachment system 100 of the present
invention, and specifically the distal portion of the detachment
system 100, is illustrated. The detachment system 100 includes a
pusher 102 that is preferably flexible. The pusher 102 is
configured for use in advancing an implant device 112 into and
within the body of a patient and, specifically, into a target
cavity site for implantation and delivery of the implant device
112. Potential target cavity sites include but are not limited to
blood vessels and vascular sites (e.g., aneurysms and fistula),
heart openings and defects (e.g., the left atrial appendage), and
other luminal organs (e.g., fallopian tubes).
[0045] A stretch-resistant tether 104 detachably couples the
implant 112 to the pusher 102. In this example, the tether 104 is a
plastic tube that is bonded to the pusher 102. A substantially
solid cylinder could also be a design choice for the tether 104.
The stretch resistant tether 104 extends at least partially through
the interior lumen of an implant device 112.
[0046] Near the distal end of the pusher 102, a heater 106 is
disposed in proximity to the stretch resistant tether 104. The
heater 106 may be wrapped around the stretch resistant tether 104
such that the heater 106 is exposed to or otherwise in direct
contact with the blood or the environment, or alternatively may be
insulated by a sleeve, jacket, epoxy, adhesive, or the like. The
pusher 102 comprises a pair of electrical wires, positive
electrical wire 108 and negative electrical wire 110. The wires 108
and 110 are coupled to the heater 106 by any suitable means, such
as, e.g., by welding or soldering.
[0047] The electrical wires 108, 110 are capable of being coupled
to a source of electrical power (not shown). As illustrated the
negative electrical wire 110 is coupled to the distal end of the
heater 106 and the positive electrical wire 108 is coupled to the
proximal end of the heater 106. In another embodiment, this
configuration may be reversed, i.e., the negative electrical wire
110 is coupled to the proximal end of the heater 106 while the
positive electrical wire 108 is coupled to the distal end of the
heater 106.
[0048] Energy is applied to the heater 106 from the electrical
wires 108, 110 in order to sever the portion of the tether 104 in
the proximity of the heater 106. It is not necessary for the heater
106 to be in direct contact with the tether 104. The heater 106
merely should be in sufficient proximity to the tether 104 so that
heat generated by the heater 106 causes the tether 104 to sever. As
a result of activating the heater 106, the section of the stretch
resistant tether 104 that is approximately distal from the heater
106 and within the lumen of an implant device 112 is released from
the pusher 102 along with the implant device 112.
[0049] As illustrated, the implant device 112 is an embolic coil.
An embolic coil suitable for use as the implant device 112 may
comprise a suitable length of wire formed into a helical microcoil.
The coil may be formed from a biocompatible material including
platinum, rhodium, palladium, rhenium, tungsten, gold, silver,
tantalum, and various alloys of these metals, as well as various
surgical grade stainless steels. Specific materials include the
platinum/tungsten alloy known as Platinum 479 (92% Pt, 8% W,
available from Sigmund Cohn, of Mount Vernon, N.Y.) and
nickel/titanium alloys (such as the nickel/titanium alloy known as
Nitinol).
[0050] Another material that may be advantageous for forming the
coil is a bimetallic wire comprising a highly elastic metal with a
highly radiopaque metal. Such a bimetallic wire would also be
resistant to permanent deformation. An example of such a bimetallic
wire is a product comprising a Nitinol outer layer and an inner
core of pure reference grade platinum, available from Sigmund Cohn,
of Mount Vernon, N.Y., and Anomet Products, of Shrewsbury,
Mass.
[0051] Commonly-assigned U.S. Pat. No. 6,605,101 provides a further
description of embolic coils suitable for use as the implant device
112, including coils with primary and secondary configurations
wherein the secondary configuration minimizes the degree of
undesired compaction of the coil after deployment. The disclosure
of U.S. Pat. No. 6,605,101 is fully incorporated herein by
reference. Furthermore, the implant device 112 may optionally be
coated or covered with a hydrogel or a bioactive coating known in
the art.
[0052] The coil-type implant device 112 resists unwinding because
the stretch resistant tether 104 that extends through the lumen of
the implant device 112 requires substantially more force to
plastically deform than the implant device 112 itself. The stretch
resistant tether 104 therefore assists in preventing the implant
device 112 from unwinding in situations in which the implant device
112 would otherwise unwind.
[0053] During assembly, potential energy may be stored within the
device to facilitate detachment. In one embodiment, an optional
spring 116 is placed between the heater 106 and the implant device
112. The spring is compressed during assembly and the distal end of
the tether 104 may be tied or coupled to the distal end of the
implant device 112, or may be melted or otherwise formed into an
atraumatic distal end 114.
[0054] In one embodiment, the stretch resistant tether 104 is made
from a material such as a polyolefin elastomer, polyethylene, or
polypropylene. One end of the tether 104 is attached to the pusher
102 and the free end of the tether 104 is pulled through the
implant 112 with the proximal end of the implant 112 flush to
either the heater 106 (if no spring 116 is present) or to the
compressed spring 116. A pre-set force or displacement is used to
pre-tension the tether 104, thus storing energy in an axial
orientation (i.e. co-linear or parallel to the long axis of the
pusher 102) within the tether 104. The force or displacement
depends on the tether material properties, the length of the tether
104 (which itself depends on the tether's attachment point on the
pusher and the length of the implant). Generally, the force is
below the elastic limit of the tether material, but sufficient to
cause the tether to sever quickly when heat is applied. In one
preferred embodiment wherein the implant to be deployed is a
cerebral coil, the tether has a diameter within the range of
approximately 0.001 to 0.007 inches. Of course the size of the
tether can be changed to accommodate different types and sizes of
other implants as necessary.
[0055] Turning to FIG. 2, another embodiment of a detachment system
of the present invention, detachment system 200, is illustrated.
Detachment system 200 shares several common elements with
detachment system 100. For example, the same devices usable as the
implant device 112 with detachment system 100 are also usable as
the implant device 112 with detachment system 200. These include,
e.g., various embolic microcoils and coils. The implant device 112
has been previously described with respect to detachment system
100. As with the implant device 112, the same identification
numbers are used to identify other elements/components of
detachment system 100 that may correspond to elements/components of
detachment system 200. Reference is made to the description of
these elements in the description of detachment system 100 as that
description also applies to these common elements in detachment
system 200.
[0056] With detachment system 200, an interior heating element 206
is used to separate a section of a stretch resistant tube 104 and
an associated implant device 112 from the detachment system 200.
Detachment system 200 includes a delivery pusher 202 that
incorporates a core mandrel 218. The detachment system 200 further
includes a positive electrical wire 208 and a negative electrical
wire 210 that extend through the lumen of the delivery pusher
202.
[0057] To form the internal heating element 206, the positive
electrical wire 208 and the negative electrical wire 210 may be
coupled to the core mandrel 218 of the delivery pusher 202.
Preferably, the electrical wires 208, 210 are coupled to a distal
portion of the core mandrel 218.
[0058] In one embodiment, the positive electrical wire 208 is
coupled to a first distal location on the core wire 218, and the
negative electrical wire 210 is coupled to a second distal location
on the core wire 218, with the second distal location being
proximal to the first distal location. In another embodiment, the
configuration is reversed, i.e., the positive electrical wire 208
is coupled to the second distal location and the negative
electrical wire 210 is coupled to the first distal location on the
core wire 218. When the positive electrical wire 208 and the
negative electrical wire 210 are coupled to the distal portion of
the core mandrel 218, the distal portion of the core mandrel 218
along with the electrical wires 208, 210 forms a circuit that is
the interior heating element 206.
[0059] The heater 206 increases in temperature when a current is
applied from a power source (not shown) that is coupled to the
positive electrical wire 208 and the negative electrical wire 210.
If a greater increase in temperature/higher degree of heat is
required or desired, a relatively high resistance material such as
platinum or tungsten may be coupled to the distal end of the core
mandrel 218 to increase the resistance of the core mandrel 218. As
a result, higher temperature increases are produced when a current
is applied to the heater 206 than would be produced with a lower
resistance material. The additional relatively high resistance
material coupled to the distal end of the core mandrel 218 may take
any suitable form, such as, e.g., a solid wire, a coil, or any
other shape or material as described above.
[0060] Because the heater 206 is located within the lumen of the
tube-shaped tether 104, the heater 206 is insulated from the body
of the patient. As a result, the possibility of inadvertent damage
to the surrounding body tissue due to the heating of the heater 206
may be reduced.
[0061] When a current is applied to the heater 206 formed by the
core mandrel 218, the positive electrical wire 208, and the
negative electrical wire 210, the heater 206 increases in
temperature. As a result, the portion of the stretch resistant
tether 104 in proximity to the heater 206 severs and is detached,
along with the implant device 112 that is coupled to the tether
104, from the detachment system 200.
[0062] In one embodiment of the detachment system 200, the proximal
end of the stretch resistant tether 104 (or the distal end of a
larger tube (not shown) coupled to the proximal end of the stretch
resistant tether 104) may be flared in order to address size
constraints and facilitate the assembly of the detachment system
200.
[0063] In a similar manner as with detachment system 100, energy
may be stored within the system with, for example, an optional
compressive spring 116 or by pre-tensioning the tether 104 during
assembly as previously described. When present, the release of
potential energy stored in the system operates to apply additional
pressure to separate the implant device 112, and the portion of the
stretch resistant tether 104 to which the implant device 112 is
coupled, away from the heater 206 when the implant device 112 is
deployed. This advantageously lowers the required detachment time
and temperature by causing the tether 104 to sever and break.
[0064] As with detachment system 100, the distal end of the stretch
resistant tether 104 of detachment system 200 may be tied or
coupled to the distal end of the implant device 112, or may be
melted or otherwise formed into an atraumatic distal end 114.
[0065] FIG. 4 illustrates another preferred embodiment of a
detachment system 300. In many respects, the detachment system 300
is similar to the detachment system 200 shown in FIG. 2 and
detachment system 100 shown in FIG. 1. For example, the detachment
system 300 includes a delivery pusher 301 containing a heater 306
that detaches an implant device 302. Detachment system 300 also
utilizes a tether 310 to couple the implant device 302 to the
delivery pusher 301.
[0066] In the cross-sectional view of FIG. 4, a distal end of the
delivery pusher 301 is seen to have a coil-shaped heater 306 that
is electrically coupled to electrical wires 308 and 309. These
wires 308, 309 are disposed within the delivery pusher 301, exiting
at a proximal end of the delivery pusher 301 and coupling to a
power supply (not shown). The tether 310 is disposed in proximity
to the heater 306, having a proximal end fixed within the delivery
pusher 301 and a distal end coupled to the implant device 302. As
current is applied through wires 308 and 309, the heater 306
increases in temperature until the tether 310 breaks, releasing the
implant device 302.
[0067] To reduce the transfer of heat from the heater 306 to the
surrounding tissue of the patient and to provide electrical
insulation, an insulating cover 304 is included around at least the
distal end of the outer surface of the delivery pusher 301. As the
thickness of the cover 304 increases, the thermal insulating
properties also increase. However, increased thickness also brings
increased stiffness and a greater diameter to the delivery pusher
301 that could increase the difficulty of performing a delivery
procedure. Thus, the cover 304 is designed with a thickness that
provides sufficient thermal insulating properties without overly
increasing its stiffness.
[0068] To enhance attachment of the tether 310 to the implant
device 302, the implant device 302 may include a collar member 322
welded to the implant device 302 at weld 318 and sized to fit
within the outer reinforced circumference 312 of the delivery
pusher 301. The tether 310 ties around the proximal end of the
implant device 302 to form knot 316. Further reinforcement is
provided by an adhesive 314 that is disposed around the knot 316 to
prevent untying or otherwise unwanted decoupling.
[0069] In a similar manner as with detachment systems 100 and 200,
energy may be stored within the system with, for example, an
optional compressive spring (similar to compressive spring 116 in
FIG. 1 but not shown in FIG. 4) or by axially pre-tensioning the
tether 104 during assembly. In this embodiment, one end of the
tether 310 is attached near the proximal end of the implant device
302 as previously described. The free end of the tether 310 is
threaded through a distal portion of the delivery pusher 301 until
it reaches an exit point (not shown) of the delivery pusher 301.
Tension is applied to the tether 310 in order to store energy in
the form of elastic deformation within the tether material by, for
example, placing a pre-determined force on the free end of the
tether 310 or moving the taut tether 310 a pre-determined
displacement. The free end of the tether 310 is then joined to the
delivery pusher 301 by, for example, tying a knot, applying
adhesive, or similar methods known in the art.
[0070] When present, the release of potential energy stored in the
system operates to apply additional pressure to separate the
implant device 302, and the portion of the tether 310 to which the
implant device 302 is coupled, away from the heater 306 when the
implant device 302 is deployed. This advantageously lowers the
required detachment time and temperature by causing the tether 310
to sever and break.
[0071] The present invention also provides for methods of using
detachment systems such as detachment systems 100, 200, or 300. The
following example relates to the use of detachment system 100, 200,
or 300 for occluding cerebral aneurysms. It will, however, be
appreciated that modifying the dimensions of the detachment system
100, 200, or 300 and the component parts thereof and/or modifying
the implant device 112, 302 configuration will allow the detachment
system 100, 200, or 300 to be used to treat a variety of other
malformations within a body.
[0072] With this particular example, the delivery pusher 102, 202,
or 301 of the detachment system 100, 200, or 300 may be
approximately 0.010 inches to 0.030 inches in diameter. The tether
104, 310 that is coupled near the distal end of the delivery pusher
102, 202, or 301 and is coupled to the implant device 112, 302 may
be 0.0002 inches to 0.020 inches in diameter. The implant device
112, 302; which may be a coil, may be approximately 0.005 inches to
0.020 inches in diameter and may be wound from 0.0005 inch to 0.005
inch wire.
[0073] If potential energy is stored within the detachment system
100, 200, or 300, the force used to separate the implant device
112, 302 typically ranges up to 250 grams.
[0074] The delivery pusher 102, 202, or 301 may comprise a core
mandrel 218 and at least one electrically conductive wire 108, 110,
208, 210, 308, or 309. The core mandrel 218 may be used as an
electrical conductor, or a pair of conductive wires may be used, or
a bipolar wire may be used as previously described.
[0075] Although the detachment systems 100, 200, and 300 have been
illustrated as delivering a coil, other implant devices are
contemplated in the present invention. For example, FIG. 8
illustrates the detachment system 300 as previously described in
FIG. 4 having an implant that is a stent 390. This stent 390 could
similarly be detached by a similar method as previously described
in regards to the detachment systems 100, 200, and 300. In a
further example, the detachment systems 100, 200, or 300 may be
used to deliver a filter, mesh, scaffolding or other medical
implant suitable for delivery within a patient.
[0076] FIG. 7 presents an embodiment of a delivery pusher 350,
which could be used in any of the embodiments as delivery pusher
102, 202, or 301, which includes radiopaque materials to
communicate the position of the delivery pusher 350 to the user.
Specifically, the radiopaque marker material is integrated into the
delivery pusher 350 and varied in thickness at a desired location,
facilitating easier and more precise manufacturing of the final
delivery pusher 350.
[0077] Prior delivery pusher designs, such as those seen in U.S.
Pat. No. 5,895,385 to Guglielmi, rely on high-density material such
as gold, tantalum, tungsten, or platinum in the form of an annular
band or coil. The radiopaque marker is then bonded to other, less
dense materials, such as stainless steel, to differentiate the
radiopaque section. Since the radiopaque marker is a separate
element placed at a specified distance (often about 3 cm) from the
tip of the delivery pusher, the placement must be exact or the
distal tip of the delivery pusher 350 can result in damage to the
aneurysm or other complications. For example, the delivery pusher
350 may be overextended from the microcatheter to puncture an
aneurysm. Additionally, the manufacturing process to make a prior
delivery pusher can be difficult and expensive, especially when
bonding dissimilar materials.
[0078] The radiopaque system of the present invention overcomes
these disadvantages by integrating a first radiopaque material into
most of the delivery pusher 350 while varying the thickness of a
second radiopaque material, thus eliminating the need to bond
multiple sections together. As seen in FIG. 7, the delivery pusher
350 comprises a core mandrel 354 (i.e. the first radiopaque
material), preferably made from radiopaque material such as
tungsten, tantalum, platinum, or gold (as opposed to the mostly
radiolucent materials of the prior art designs such as steel,
Nitinol, and Elgiloy).
[0079] The delivery pusher 350 also includes a second, outer layer
352, having a different radiopaque level. Preferably, outer layer
352 is composed of a material having a lower radiopaque value than
the core mandrel 354, such as Elgiloy, Nitinol, or stainless steel
(commercially available from Fort Wayne Metals under the trade name
DFT). In this respect, both the core mandrel 354 and the outer
layer 352 are visible and distinguishable from each other under
fluoroscopy. The outer layer 352 varies in thickness along the
length of the delivery pusher 350 to provide increased flexibility
and differentiation in radio-density. Thus the thicker regions of
the outer layer 352 are more apparent to the user than the thinner
regions under fluoroscopy.
[0080] The transitions in thickness of the outer layer 352 can be
precisely created at desired locations with automated processes
such as grinding, drawing, or forging. Such automated processes
eliminate the need for hand measuring and placement of markers and
further eliminates the need to bond a separate marker element to
other radiolucent sections, thus reducing the manufacturing cost
and complexity of the system.
[0081] In the present embodiment, the delivery pusher 350 includes
three main indicator regions of the outer layer 352. A proximal
region 356 is the longest of the three at 137 cm, while a middle
region 358 is 10 cm and a distal region 360 is 3 cm. The length of
each region can be determined based on the use of the delivery
pusher 350. For example, the 3 cm distal region 360 may be used
during a coil implant procedure, as known in the art, allowing the
user to align the proximal edge of the distal region 360 with a
radiopaque marker on the microcatheter within which the delivery
pusher 350 is positioned. The diameter of each of the regions
depends on the application and size of the implant. For a typical
cerebral aneurysm application for example, the proximal region 356
may typically measure 0.005-0.015 inches, the middle region 358 may
typically measure 0.001-0.008 inches, while the distal region 360
may typically measure 0.0005-0.010 inches. The core mandrel 354
will typically comprise between about 10-80% of the total diameter
of the delivery pusher 350 at any point.
[0082] Alternately, the delivery pusher 350 may include any number
of different regions greater than or less than the three shown in
FIG. 7. Additionally, the radiopaque material of the core mandrel
354 may only extend partially through the delivery pusher 350. For
example, the radiopaque material could extend from the proximal end
of the core mandrel 354 to three centimeters from the distal end of
the delivery pusher 350, providing yet another predetermined
position marker visible under fluoroscopy.
[0083] In this respect, the regions 356, 358, and 360 of delivery
pusher 350 provide a more precise radiopaque marking system that is
easily manufactured, yet is readily apparent under fluoroscopy.
Further, the increased precision of the markers may decrease
complications relating to improper positioning of the delivery
pusher during a procedure.
[0084] In operation, the microcatheter is positioned within a
patient so that a distal end of the microcatheter is near a target
area or lumen. The delivery pusher 350 is inserted into the
proximal end of the microcatheter and the core mandrel 354 and
outer layer 352 are viewed under fluoroscopy. The user aligns a
radiopaque marker on the microcatheter with the beginning of the
distal region 360, which communicates the location of the implant
112, 302 relative to the tip of the microcatheter.
[0085] In some situations, for example, small aneurysms where there
may be an elevated risk of vessel damage from the stiffness of the
delivery pusher 350, the user may position the proximal end of the
implant slightly within the distal end of the microcatheter during
detachment. The user then may push the proximal end of the implant
112, 302 out of the microcatheter with the next coil, an adjunctive
device such as guidewire, or the delivery pusher 102, 202, 301, or
350. In another embodiment, the user may use the radiopaque marking
system to locate the distal end of the delivery pusher outside the
distal end of the microcatheter.
[0086] Once the implant device 112, 302 of the detachment system
100, 200, or 300 is placed in or around the target site, the
operator may repeatedly reposition the implant device 112, 302 as
necessary or desired.
[0087] When detachment of the implant device 112, 302 at the target
site is desired, the operator applies energy to the heater 106,
206, or 306 by way of the electrical wires 108, 110, 208, 210, 308,
or 309. The electrical power source for the energy may be any
suitable source, such as, e.g., a wall outlet, a capacitor, a
battery, and the like. For one aspect of this method, electricity
with a potential of approximately 1 volt to 100 volts is used to
generate a current of 1 milliamp to 5000 milliamps, depending on
the resistance of the detachment system 100, 200, or 300.
[0088] One embodiment of a connector system 400 that can be used to
electrically couple the detachment system 100, 200, or 300 to the
power source is shown in FIG. 6. The connector system 400 includes
an electrically conductive core mandrel 412 having a proximal end
surrounded by an insulating layer 404. Preferably the insulating
layer 404 is an insulating sleeve such as a plastic shrink tube of
polyolefin, PET, Nylon, PEEK, Teflon, or polyimide. The insulating
layer 404 may also be a coating such as polyurethane, silicone,
Teflon, paralyene. An electrically conductive band 406 is disposed
on top of the insulating layer 404 and secured in place by molding
bands 414, adhesive, or epoxy. Thus, the core mandrel 412 and the
conductive band 406 are electrically insulated from each other. The
conductive band 406 is preferably composed of any electrically
conductive material, such as silver, gold, platinum, steel, copper,
conductive polymer, conductive adhesive, or similar materials, and
can be a band, coil, or foil. Gold is especially preferred as the
conductive material of the conductive band 406 because of the
ability of gold to be drawn into a thin wall and its ready
availability. The core mandrel 412 has been previously described
and may be plated with, for example, gold, silver, copper, or
aluminum to enhance its electrical conductivity.
[0089] The connector system 400 also includes two electrical wires
408 and 410 which connect to the conductive band 406 and core
member 412, respectively, and to a heating element at the distal
end of a delivery system such as those described in FIGS. 1, 2, and
4 (not shown in FIG. 6). These wires 408 and 410 are preferably
connected by soldering, brazing, welding, laser bonding, or
conductive adhesive, or similar techniques.
[0090] Once the user is ready to release the implant 112, 302
within the patient, a first electrical clip or connector from a
power source is connected to a non-insulated section 402 of the
core mandrel 412 and a second electrical clip or connector from the
power source is connected to the conductive band 406. Electrical
power is applied to the first and second electrical clips, forming
an electrical circuit within the detachment system 100, 200, or
300, causing the heater 106, 206, or 306 to increase in temperature
and sever the tether 104, 310.
[0091] Once the detachment system 100, 200, or 300 is connected to
the power source the user may apply a voltage or current as
previously described. This causes the heater 106, 206, or 306 to
increase in temperature. When heated, the pre-tensioned tether 104,
310 will tend to recover to its unstressed (shorter) length due to
heat-induced creep. In this respect, when the tether 104, 310 is
heated by the heater 106, 206, or 306; its overall size shrinks.
However, since each end of the tether 104, 310 is fixed in place as
previously described, the tether 104, 310 is unable to shorten in
length, ultimately breaking to release the implant device 112,
302.
[0092] Because there is tension already within the system in the
form of a spring 116 or deformation of the tether material 104,
310; the amount of shrinkage required to break the tether 104, 310
is less than that of a system without a pre-tensioned tether. Thus,
the temperature and time required to free the implant device 112,
302 is lower.
[0093] FIG. 5 is a graph showing the temperatures at the surface of
the PET cover 304 of the detachment system 300. As can be seen, the
surface temperature of the detachment system 300 during detachment
does not vary linearly with time. Specifically, it only takes just
under 1 second for the heat generated by the heating coil 306 to
penetrate the insulating cover 304. After 1 second, the surface
temperature of the insulating cover 304 dramatically increases.
Although different outer insulating material may slightly increase
or decrease this 1-second surface temperature window, the
necessarily small diameter of the detachment system 100, 200, or
300 prevents providing a thick insulating layer that may more
significantly delay a surface temperature increase.
[0094] It should be understood that the embodiments of the
detachment system 100, 200, or 300 include a variety of possible
constructions. For example, the insulating cover 304 may be
composed of Teflon, PET, polyamide, polyimide, silicone,
polyurethane, PEEK, or materials with similar characteristics. In
the embodiments 100, 200, or 300 the typical thickness of the
insulating cover is 0.0001-0.040 inches. This thickness will tend
to increase when the device is adapted for use in, for example,
proximal malformations, and decrease when the device is adapted for
use in more distal, tortuous locations such as, for example,
cerebral aneurysms.
[0095] In order to minimize the damage and possible complications
caused by such a surface temperature increase, the present
invention detaches the implant device 112, 302 before the surface
temperature begins to significantly increase. Preferably, the
implant device 112, 302 is detached in less than a second, and more
preferably, in less than 0.75 seconds. This prevents the surface
temperature from exceeding 50.degree. C. (122.degree. F.), and more
preferably, from exceeding 42.degree. C. (107.degree. F.).
[0096] Once the user attempts to detach the implant device 112,
302, it is often necessary to confirm that the detachment has been
successful. The circuitry integrated into the power source may be
used to determine whether or not the detachment has been
successful. In one embodiment of the present invention an initial
signaling current is provided prior to applying a detachment
current (i.e. current to activate the heater 106, 206, or 306 to
detach an implant 112, 302). The signaling current is used to
determine the inductance in the system before the user attempts to
detach the implant and therefore has a lower value than the
detachment current, so as not to cause premature detachment. After
an attempted detachment, a similar signaling current is used to
determine a second inductance value that is compared to the initial
inductance value. A substantial difference between the initial
inductance and the second inductance value indicates that the
implant 112, 302 has successfully been detached, while the absence
of such a difference indicates unsuccessful detachment. In this
respect, the user can easily determine if the implant 112, 302 has
been detached, even for delivery systems that utilize nonconductive
temperature sensitive polymers to attach an implant, such as those
seen in FIGS. 1, 2, and 4.
[0097] In the following description and examples, the terms
"current" and "electrical current" are used in the most general
sense and are understood to encompass alternating current (AC),
direct current (DC), and radiofrequency current (RF) unless
otherwise noted. The term "changing" is defined as any change in
current with a frequency above zero, including both high frequency
and low frequency. When a value is measured, calculated and/or
saved, it is understood that this may be done either manually or by
any known electronic method including, but not limited to, an
electronic circuit, semiconductor, EPROM, computer chip, computer
memory such as RAM, ROM, or flash; and the like. Finally, wire
windings and toroid shapes carry a broad meaning and include a
variety of geometries such as circular, elliptical, spherical,
quadrilateral, triangular, and trapezoidal shapes.
[0098] When a changing current passes through such objects as wire
windings or a toroid, it sets up a magnetic field. As the current
increases or decreases, the magnetic field strength increase or
decreases in the same way. This fluctuation of the magnetic field
causes an effect known as inductance, which tends to oppose any
further change in current. Inductance (L) in a coil wound around a
core is dependant on the number of turns (N), the cross-sectional
area of the core (A), the magnetic permeability of the core (.mu.),
and length of the coil (I) according to equation 1 below:
L = .4 .pi. N 2 A .mu. I Equation 1 ##EQU00001##
[0099] The heater 106 or 306 is formed from a wound coil with
proximal and distal electrically conductive wires 108, 110, 308, or
309 attached to a power source. The tether 104, 310 has a magnetic
permeability .mu.1 and is positioned through the center of the
resistive heater, having a length l, cross sectional area A, and N
winds, forming a core as described in the previous equation. Prior
to detachment, a changing signaling current i1, such as the
waveforms shown in FIGS. 3A and 3B, with frequency f1, is sent
through the coil windings. This signaling current is generally
insufficient to detach the implant. Based on the signaling current,
the inductive resistance XL (i.e. the electrical resistance due to
the inductance within the system) is measured by an electronic
circuit such as an ohmmeter. The initial inductance of the system
L1 is then calculated according to the formula:
L 1 = X L 2 .pi. f 1 Equation 2 ##EQU00002##
[0100] This initial value of the inductance L1 depends on the
magnetic permeability .mu.1 of the core of the tether 104, 310
according to Equation 1, and is saved for reference. When
detachment is desired, a higher current and/or a current with a
different frequency than the signaling current is applied through
the resistive heater coil, causing the tether 104, 310 to release
the implant 112, 302 as previously described. If detachment is
successful, the tether 104, 310 will no longer be present within
the heater 106, 306 and the inside of the heater 106, 306 will fill
with another material such as the patient's blood, contrast media,
saline solution, or air. This material now within the heater core
will have a magnetic permeability .mu.2 that is different than the
tether core magnetic permeability .mu.1.
[0101] A second signaling current and frequency f2 is sent through
the heater 106, 306 and is preferably the same as the first
signaling current and frequency, although one or both may be
different without affecting the operation of the system. Based on
the second signaling current, a second inductance L2 is calculated.
If the detachment was successful, the second inductance L2 will be
different (higher or lower) than the first inductance L1 due to the
difference in the core magnetic permeabilities .mu.1 and .mu.2. If
the detachment was unsuccessful, the inductance values should
remain relatively similar (with some tolerance for measurement
error). Once detachment has been confirmed by comparing the
difference between the two inductances, an alarm or signal can be
activated to communicate successful detachment to the user. For
example, the alarm might include a beep or an indicator light.
[0102] Preferably, the delivery system 100, 300 used according to
this invention connects to a device that automatically measures
inductance at desired times, performs required calculations, and
signals to the user when the implant device has detached from the
delivery catheter. However, it should be understood that part or
all of these steps can be manually performed to achieve the same
result.
[0103] The inductance between the attached and detached states can
also preferably be determined without directly calculating the
inductance. For example, the inductive resistance XL can be
measured and compared before and after detachment. In another
example, the detachment can be determined by measuring and
comparing the time constant of the system, which is the time
required for the current to reach a predetermined percentage of its
nominal value. Since the time constant depends on the inductance, a
change in the time constant would similarly indicate a change in
inductance.
[0104] The present invention may also include a feedback algorithm
that is used in conjunction with the detachment detection described
above. For example, the algorithm automatically increases the
detachment voltage or current automatically after the prior attempt
fails to detach the implant device. This cycle of measurement,
attempted detachment, measurement, and increased detachment
voltage/current continues until detachment is detected or a
predetermined current or voltage limit is attained. In this
respect, a low power detachment could be first attempted, followed
automatically by increased power or time until detachment has
occurred. Thus, battery life for a mechanism providing the
detachment power is increased while the average coil detachment
time is greatly reduced.
[0105] Referring now to FIGS. 9 and 10, there is shown an
embodiment of a delivery system 500 for use with the present
invention that includes a detachment detection capability. The
delivery system 500 operates under the principle that electrical
current passing through a coil held in an expanded, open gap
configuration will encounter more resistance than electrical
current passing through a coil in a contracted, closed gap
configuration. In the expanded configuration, the electrical
current must follow the entire length of the coiled wire. In the
contracted configuration, the electrical current can bridge the
coils and travel in a longitudinal direction.
[0106] The delivery system 500 is generally similar to the
previously described detachment system 300 of the present invention
seen in FIG. 4, including a delivery pusher 301, containing a
heater coil 306 that detaches an implant device 302. The detachment
system 500 similarly utilizes a tether 310 to coupled the implant
device 302 to the delivery pusher 301.
[0107] The heater coil 306 is preferably a resistance-type heater
having a plurality of loops 306A as seen in FIG. 10, that connects
to a voltage source through a connector system at the proximal end
of the delivery pusher 301, such as the connector system 400
described in FIG. 6.
[0108] The delivery system 500 also includes a heater coil expander
502 that serves two functions. First, it expands the heater coil
306 such that the heater coil 306 maintains a friction-fit
attachment to the inside of the insulating cover 309, thereby
connecting the two. Second, the heater coil expander 502 expands
the heater coil 306 in such a manner that electricity is forced to
flow around each individual loop 306A of the coil 306 in order to
maximize the resistance of the coil 306.
[0109] Maximizing the coil resistance not only serves to heat the
coil 306 when voltage is passed through, it also sets an initial
value (or "normal" value) for the resistance provided by the coil
306, which can be used to compare a changed resistance state,
indicating detachment of the implant 302. Hence, the heater coil
expander 502 must also be capable of undergoing change when
subjected to heat. In this regard, the heater coil expander 502 may
be made of any suitable sturdy material capable of holding the
heater coil 306 in an expanded, biased state while also being
capable of melting or being otherwise reduced by the heat of the
heater coil 306 in order to yield to the bias of the heater coil
306 to return to an unbiased state. Examples of acceptable
materials include, but are not limited to, polymers and
monofilament.
[0110] The heater coil expander 502 shown in FIGS. 9 and 10
operates by longitudinally, or radially and longitudinally,
expanding a heater coil 306 which is normally a closed gap coil in
a relaxed state. In other words, the individual loops 306A contact
each other when the heater coil 306 is not stretched or radially
expanded. Preferably, the heater coil expander 502 may have a
coiled shape, similar to the heater coil 306 and as seen in FIG.
10. Alternately, the heater coil expander may have a continuous,
tubular shape with helical ridges similar to the individual coil
shapes of the expander 502 in FIG. 10. It should be understood that
a variety of different expander shapes that expand the loops or
coils 306A of the heater coil 306 from each other.
[0111] Preferably the power source (previously described in this
embodiment and connected to the connector system 400) also includes
a measuring instrument for measuring the resistance of the heater
coil 306. In this respect, the power source (preferably located in
a hand-sized unit) includes an indicator that communicates when a
change in resistance has occurred and therefore when detachment of
the implant has occurred.
[0112] An alternative embodiment of the heater coil expander 512 is
shown in FIGS. 10 and 11. The heater coil expander 512 operates in
conjunction with the heater coil 306 so that the heater loops are
in an open gap state (FIG. 10), and a pusher 350, as previously
described in FIG. 7, that conducts electricity. The heater coil 306
is sized to snugly fit around the pusher 350 in a contracted state.
The heater coil expander 512 operates to separate the heater coil
306 from the pusher 350, electrically isolating the heater coil 306
therefrom. As the heat from the heater coil 306 melts or otherwise
reduces or degrades the heater coil expander 512, the heater coil
306 resumes a contracted state (i.e., reduced diameter
configuration), making electrical, if not physical, contact with
the pusher 350 (FIG. 11). In this respect the individual loops are
shortened, significantly reducing the resistance of the circuit and
thereby indicating detachment has occurred.
[0113] Another alternative embodiment of the present invention, the
heater coil expander 502 may be sized to expand the heater coil 306
against the conductive reinforcement circumference 312 (shown in
FIG. 9). Hence, when the coil 306 is in its initial expanded
position, the electrically conductive reinforcement circumference
312 maintains a low initial resistance that is registered by the
controller for the circuit (i.e., the measurement device of the
power source).
[0114] When the heater coil 306 is energized, the initial
resistance is noted and the heater coil expander 306 melts,
degrades or otherwise reduces. The heater coil 306 then contracts,
releasing the attachment tube (and the rest of the implant 510) and
the heater coil 306 is no longer shorted out by the reinforcement
circumference 312. Thus, the circuit experiences a change in
resistance as the electrical current must travel through each of
the individual loops. This increase in resistance signifies the
implant 302 is detached.
[0115] FIGS. 13-16 illustrate another preferred embodiment of a
delivery system 600 according to the present invention. For
illustrative purposes, it should be noted that the outer body of
the system 600 is not shown. The delivery system 600 is generally
similar to some of the previously described embodiments, in that it
includes a tether 606 that secures an implantable device 612 to the
delivery system 600 and a heater coil 604 that causes the tether
606 to break, thereby releasing the implantable device 612.
[0116] However, as seen in these Figures, the heater coil 604 is
sized with a diameter that is much smaller than previous
embodiments. More specifically, the heater coil 604 preferably has
an internal passage that is only slightly larger in diameter than
the outer diameter of the tether 606. In other words, the internal
diameter of the heater coil 604 is substantially the same as the
outer diameter of the tether 604.
[0117] According to one embodiment, the internal passage of the
heating coil 604 solely contains the tether 606. According to
another embodiment, the diameter of the internal passage may be
large enough for only the tether 606 to pass through. In another
embodiment, the diameter may be large enough for only the tether
and other components, such as support mandrel 611 or electrical
wires 608 and 610. In either case, at least a portion of the
internal diameter of the heater coil 604 maintains a close
proximity to the tether 606, allowing the tether 606 to pass
through once.
[0118] Additionally, the heater coil 604 preferably includes a
smaller diameter region 604A which is positioned closer to the
tether 606 than the remaining portions of the coil 604. In this
respect, the region 604A can more efficiently transfer heat to the
tether 606 and therefore break the tether with an otherwise lower
temperature than without the region 604A. Providing a lower
temperature reduces the risk of damaging the patient's tissue
surrounding the system 600. In a specific example, the heater coil
604 has an internal diameter of about .007 inch and an internal
diameter of about .005 inch at region 604A while the tether 606 has
an external diameter of about .004 inch.
[0119] As in previously described embodiments, the heater coil 604
may be composed of a coiled heating element wire. However, it
should be understood that other heater configurations are possible,
such as a solid, conducting tube or a wire arranged in a non-coiled
shape, such as a wave or undulating pattern that forms an overall
tubular shape (that may not completely surround the tether
606).
[0120] Both ends of the tether 606 are preferably secured to an
outer structural coil 602 of the delivery device 600. For example,
the ends of the tether 606 can be tied, glued (e.g., with U.V.
cured adhesive), welded or clamped. It should be understood that
the ends of the tether 606 can be secured at almost any location
along the length of the structural coil 602, as long as those
locations allow at least a portion of the tether 606 to pass
through the heater coil 604. For example, both ends of the tether
606 can be secured proximal to the heater coil 604. In another
example, one end of the tether can be secured proximal to heater
coil 604 and another end can be secured distal to the heater coil
604.
[0121] As seen in FIGS. 13, 16, and 17, the tether 606 preferably
passes through openings, cells, loops or other structures of the
implantable device 612. For example, the tether 606 may pass
through cells of a stent. As seen in FIG. 16, the tether 606 can
pass through multiple cells of the device 612 and is maintained
under tension as seen in FIGS. 13 and 17. The tension of the tether
606 keeps the device 612 in a compressed state (i.e., compressed in
diameter) and abutted to the distal end of the system 600 (e.g.,
the distal end of the outer body member 609). In this respect, when
the tether 606 is broken by the heater coil 604, the tether 606
unwraps from the device 612 and stays with the delivery system 600,
not the device 612. Hence, the tether 606 does not remain in the
patient to potentially cause unwanted complications.
[0122] As with previously described embodiments, the delivery
system 600 is connectable to a selectively actuated power supply
(e.g., via a button on a handle of the delivery device 600). Wires
608 and 610 deliver electric current to the heater coil 604 at a
desired time, causing the coil 604 to heat and thereby break the
tether 606.
[0123] Preferably, the heater coil 604 is supported within the
delivery system 600 by a support mandrel 611 (best seen in FIG. 15)
that extends along a length of the system 600. Preferably, the
support mandrel 611 is secured to the heater coil 604 by welding,
adhesive or a mechanical interlocking arrangement (not shown). The
proximal end of the support mandrel 611 is preferably attached to a
core wire or delivery pusher (e.g., pusher 350 described in other
embodiments in this specification).
[0124] The outer coil 602 provides support to the delivery system
and can be positioned on the inside of a lumen of the delivery
system body 609 (see FIG. 17). Alternately, this coil 602 can be
positioned between material layers of the delivery system body 609
(not shown) or otherwise embedded in the material of the delivery
system body 609.
[0125] In operation, a distal end of the delivery system 600 is
positioned at a target location within a patient. When the
implantable device 612 (e.g., catheter, valve or microcoil) has
achieved a desired position, the user provides electric current to
the heater coil 604 (e.g., via a button on the delivery device
600). The heater coil 604, including section 604A, increases in
temperature, causing the tether 606 to break. The tether 606,
previously under tension, passes through the cells or attachment
points of the implantable device 612 releasing the device 612 from
the delivery system 600. The delivery system 600 can then be
removed from the patient, along with the attached tether 606.
[0126] It should be understood that other tether arrangements are
possible according to the present invention. For example, FIG. 18
illustrates the use of three tethers 614A, 614B and 614C which
attach to different locations on the device 612. Preferably, these
tethers 614A, 614B and 614C have a smaller diameter than the
previously described tether 606. In the present preferred
embodiment, the tethers 614A, 614B and 614C are tied to the device
612 at knots 616. However, adhesives, clamps and other attachment
arrangements are also possible. While not shown in the Figures,
each tether 614A, 614B and 614C can be looped through a portion of
the device 612, similar to the single tether of previously
described embodiments and attached to a location in the delivery
system 600.
[0127] Although the invention has been described in terms of
particular embodiments and applications, one of ordinary skill in
the art, in light of this teaching, can generate additional
embodiments and modifications without departing from the spirit of
or exceeding the scope of the claimed invention. For example, the
heater coil or heater coil expander could be constructed to
activate a switch that provides a user indication of detachment in
some manner. Additionally, a visual indicator may be associated
with the change in resistance to provide easy indication of
detachment. Accordingly, it is to be understood that the drawings
and descriptions herein are proffered by way of example to
facilitate comprehension of the invention and should not be
construed to limit the scope thereof.
* * * * *