U.S. patent application number 10/288155 was filed with the patent office on 2003-03-27 for high impedance electrode tip.
This patent application is currently assigned to Cardiac Pacemakers, Inc.. Invention is credited to Bartig, Jeffrey T., Cole, Mary Lee, Goebel, Gary W., Heil, Ronald W. JR., Heitkamp, Douglas A., Janke, Aaron W., Peterfeso, Randall M..
Application Number | 20030060868 10/288155 |
Document ID | / |
Family ID | 26819316 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030060868 |
Kind Code |
A1 |
Janke, Aaron W. ; et
al. |
March 27, 2003 |
High impedance electrode tip
Abstract
An implantable lead, being either a fixed or
retractable/extendable lead, having a distal tip electrode is
adapted for implantation on or about the heart and for connection
to a system for monitoring or stimulating cardiac activity. The
electrode includes a mechanical fastener such as a fixation helix
for securing the electrode to cardiac tissue, which may or may not
be electrically active. The implantable electrode with a helical
tip includes an electrode which has a distal end and a proximal
end. A helix is disposed within the electrode, where the helix is
aligned along a radial axis of the electrode. The electrode further
includes one or more of the following features: the helix having a
coating of an insulating material on a surface of the helix, a
porous conductive surface at a base of the helix, or a porous
conductive element at the end of the electrode having an insulating
coating covering from 5-95% of the surface of the porous conductive
element. The electrode may further include an electrode tip having
a porous electrical conductive element, such as a mesh screen,
disposed on a surface at the distal end of the electrode tip, which
can be used as a sensing or pacing interface with the cardiac
tissue.
Inventors: |
Janke, Aaron W.; (St. Paul,
MN) ; Cole, Mary Lee; (St. Paul, MN) ; Heil,
Ronald W. JR.; (Roseville, MN) ; Bartig, Jeffrey
T.; (Maplewood, MN) ; Goebel, Gary W.;
(Vadnais Heights, MN) ; Heitkamp, Douglas A.;
(White Bear Lake, MN) ; Peterfeso, Randall M.;
(St. Paul, MN) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Cardiac Pacemakers, Inc.
|
Family ID: |
26819316 |
Appl. No.: |
10/288155 |
Filed: |
November 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10288155 |
Nov 5, 2002 |
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|
09121288 |
Jul 22, 1998 |
|
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6501994 |
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09121288 |
Jul 22, 1998 |
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08998174 |
Dec 24, 1997 |
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Current U.S.
Class: |
607/123 |
Current CPC
Class: |
A61N 1/0573
20130101 |
Class at
Publication: |
607/123 |
International
Class: |
A61N 001/05 |
Claims
What is claimed:
1. An implantable electrode with a helical tip comprising: an
electrode having a distal end and a proximal end; and a helix
disposed on said electrode, which helix is aligned along a radial
axis of the electrode at said distal end; and said implantable
electrode having at least one feature selected from the group
consisting of: a) said helix having a coating of an insulating
material on 5-95% of its surface, b) said helix having at least
part of its surface beyond said distal end of said electrode and
said distal end of said electrode having a porous conductive
surface, c) a conductive porous surface at said distal end of said
electrode, and d) a porous conductive surface at the distal end of
the electrode having an insulating coating covering from 5-95% of
the surface of said porous conductive surface.
2. The implantable electrode of claim 1, wherein said helix has a
coating of insulating material on it surface which covers from
5-95% of surface area of said helix beyond the distal end of the
electrode.
3. The implantable electrode of claim 1, wherein said helix has a
coating of insulating material on it surface which covers from
10-90% of surface area of said helix beyond the distal end of the
electrode.
4. The implantable electrode of claim 1, wherein said porous
conductive surface at said distal end of said electrode comprises a
mesh, wherein said mesh comprises an electrically conducting
surface.
5. The implantable electrode of claim 4, wherein said mesh is
electrically active.
6. The implantable electrode of claim 1, wherein said helix is
electrically active.
7. The implantable electrode as recited in claim 1, wherein said
helix is electrically inactive.
8. The implantable electrode as recited in claim 7, wherein said
helix is made electrically inactive by forming the helix from a
highly resistant material.
9. The implantable electrode of claim 1 wherein said helix has a
coating of an insulating material on 5-95% of its surface.
10. The implantable electrode of claim 1, wherein said helix has at
least part of its surface beyond said distal end of said electrode
and said distal end of said electrode having a porous conductive
surface.
11. The implantable electrode of claim 1, wherein a conductive
porous surface is at said distal end of said electrode.
12. The implantable electrode of claim 1, wherein a porous
conductive surface at the distal end of the electrode has an
insulating coating covering from 5-95% of the surface of said
porous conductive surface.
13. A distal tip electrode adapted for implantation on or about the
heart and for connection to a system for monitoring or stimulating
cardiac activity, said electrode comprising: an electrode tip; a
porous conductive element disposed at a distal end of the electrode
tip; a surface area at the distal end of the electrode tip, a helix
disposed within said electrode, said helix comprising a conductor
disposed in a helical shape, wherein said helix travels along
radial axis of the electrode through said surface area; and a helix
guiding mechanism for directing movement of the helix during
travel.
14. A distal tip electrode as recited in claim 13, wherein said
porous conductive element comprises a mesh screen.
15. The distal tip electrode as recited in claim 14, wherein said
mesh screen is electrically active.
16. The distal tip electrode as recited in claim 13, wherein said
helix is aligned with a radial axis of the electrode.
17. The distal tip electrode as recited in claim 13, wherein said
helix is electrically active.
18. The distal tip electrode as recited in claim 13, wherein said
helix is electrically inactive.
19. The distal tip electrode as recited in claim 18, wherein said
helix is made electrically inactive by an insulating coating.
20. The distal tip electrode as recited in claim 18, wherein said
helix is made electrically inactive by forming the helix from a
highly resistant material.
21. The distal tip electrode as recited in claim 13, wherein said
helix is seated within said electrode tip.
22. The distal tip electrode as recited in claim 21, wherein said
porous conductive element has a hole therein for guidance of said
helix.
23. The distal tip electrode as recited in claim 13, wherein said
helix guiding mechanism comprises a guiding bar.
24. The distal tip electrode as recited in claim 23, wherein said
guiding bar comprises a cylinder disposed proximate to said
surface.
25. The distal tip electrode as recited in claim 23, wherein said
guiding bar is disposed transverse to said radial axis of said
electrode.
26. The distal tip electrode as recited in claim 13, wherein said
porous conductive element comprises an annular ring, said annular
ring having an open center.
27. A distal tip electrode adapted for implantation on or about the
heart and for connection to a system for monitoring or stimulating
cardiac activity, said electrode comprising: an electrode tip; a
porous conductive element disposed at a distal end of the electrode
tip, said porous conductive element forming a surface; a
protuberance extending from said porous conductive element; a helix
disposed within said electrode, said helix comprises a conductor
disposed in a helical shape, wherein said helix travels along
radial axis of the electrode through said surface; and a helix
guiding mechanism for directing movement of the helix during
travel.
28. The distal tip electrode as recited in claim 27, wherein said
protuberance is disposed along said radial axis.
29. The distal tip electrode as recited in claim 27, wherein said
helix guiding mechanism comprises a groove disposed within said
porous conductive element.
30. The distal tip electrode as recited in claim 27, wherein said
protuberance is positioned such that said helix coils around said
protuberance during travel.
31. The distal tip electrode as recited in claim 27, wherein said
projection has a generally cylindrical cross-section.
32. A distal tip electrode adapted for implantation on or about the
heart and for connection to a system for monitoring or stimulating
cardiac activity, said electrode comprising: an electrode tip; a
mesh screen disposed at a distal end of the electrode tip; a
surface at the distal end of the electrode tip; a fixation device
disposed within said electrode, said fixation device adapted for
travel along radial axis of the electrode through said surface; a
guiding mechanism for directing movement of the fixation device
during travel; and a movement assembly, said movement assembly for
providing movement to said fixation device.
33. The distal tip electrode as recited in claim 32, wherein said
fixation device comprises a helix.
34. The distal tip electrode as recited in claim 32, wherein said
movement assembly comprises a piston.
35. The distal tip electrode as recited in claim 34, wherein the
piston has a slot therein, and the base further comprises a knob,
said slot for mating with said knob.
36. The distal tip electrode as recited in claim 34, wherein the
slot is mated with said knob to form a stop mechanism for said
fixation device.
37. The distal tip electrode as recited in claim 32, wherein the
mesh screen has a groove guide disposed therein.
38. The distal tip electrode as recited in claim 34, wherein said
distal tip electrode further comprises a seal, said seal disposed
between said piston and said base.
39. An electrode adapted for implantation on or about the heart and
for connection to a system for monitoring or stimulating cardiac
activity, said electrode comprising: a lead body having a first end
and a second end; an electrode disposed proximate the first end of
the lead body; connector terminal disposed at said second end of
the lead body, said connector terminal for connecting with a pulse
generating unit; an electrode tip disposed proximate one end of the
electrode; a surface at the distal end of the electrode tip, said
surface further comprising an electrical conducting surface wherein
said surface is comprised of a porous conductive element; a helix
disposed within said electrode, said helix comprising a conductor
disposed in a helical shape, wherein said helix travels along
radial axis of the electrode through said surface thereby placing
said helix in extension and retraction; and a helix guiding groove
for directing movement of the helix during extension and retraction
of said helix.
40. A system for delivering signals to the heart, said system
comprising: an electronics system including a cardiac activity
sensor and a signal generator for producing signals to stimulate
the heart; and a lead adapted for implantation heart, said lead
comprising: an electrode tip; a porous conductive element disposed
at a distal end of the electrode tip; a surface at the distal end
of the electrode tip, a helix disposed within said electrode, said
helix comprises a conductor disposed in a helical shape, wherein
said helix travels along radial axis of the electrode through said
surface; and a helix guiding mechanism for directing movement of
the helix during travel.
41. A tip electrode, comprising: a fixation helix having a surface
with an electrically insulating coating thereon which electrically
insulating coating covers less than all of the surface of said
fixation helix.
42. The tip electrode of claim 41, wherein the surface of said
fixation helix with an insulating coating thereon comprises 5-95%
of said which is coated with an aqueous insoluble insulating layer
so that 95-5% of said surface is electrically conductive.
43. The tip electrode of claim 41, further comprising a
circumferential steroid eluting matrix.
44. The tip electrode of claim 43, wherein the circumferential
steroid eluting matrix is tapered.
45. The tip electrode of claim 43, further comprising a cylindrical
polymeric tubing.
46. The tip electrode of claim 42, wherein the electrically
insulating coating comprises PARYLENE.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This patent application is a division of U.S. patent
application Ser. No. 09/121,288, filed on Jul. 22, 1998, which is a
continuation-in-part of U.S. patent application Ser. No.
08/998,174, filed on Dec. 24, 1997, entitled "RETRACTABLE LEAD WITH
MESH SCREEN", (now abandoned), the specifications of which are
incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention relates generally to leads for
conducting electrical signals to and from the heart. More
particularly, it pertains to electrode tips for delivering
electrical charges to the heart, and to tips which tend to reduce
power consumption from cells without reducing the effective level
of each pace.
BACKGROUND OF THE INVENTION
[0003] Leads implanted in the body for electrical cardioversion or
pacing of the heart are generally known in the art. In particular,
electrically transmissive leads may be implanted in or about the
heart to reverse (i.e., defibrillate or cardiovert) certain life
threatening arrhythmias or to stimulate contraction (pacing) of the
heart. Electrical energy is applied to the heart via the leads to
return the heart to normal rhythm. Leads have also been used to
sense conditions, materials or events (generally referred to as
"sense" or "sensing") in the body, such as in the atrium or
ventricle of the heart and to deliver pacing pulses to the atrium
or ventricle. Tachy leads generally can at least sense, pace, and
deliver defibrillation shocks. Brady leads can at least perform the
combination functions of pacing and sensing the heart. One of the
available functions of the pacemaker or the automatic implantable
cardioverter defibrillator (AICD) is to receive signals from a lead
and interpret signals. In response to these signals, the pacemaker
can decide to pace or not pace. The AICD can decide to pace or not
pace, and shock or not shock. In response to a sensed bradycardia
or tachycardia condition, a pulse generator produces pacing or
defibrillation pulses to correct the condition. The same lead used
to sense the condition is sometimes also used in the process of
delivering a corrective pulse or signal from the pulse generator of
the pacemaker.
[0004] Sick sinus syndrome and symptomatic AV (atrial-ventricular)
block constitute two of the major reasons for insertion of cardiac
pacemakers today. Cardiac pacing may be performed by the
transvenous method or by leads implanted directly onto the
ventricular epicardium. Most commonly, permanent transvenous pacing
is performed using a lead positioned within one or more chambers of
the heart. A lead, sometimes referred to as a catheter, may be
positioned in the right ventricle or in the right atrium through a
subclavian vein or other vascular port, and lead terminal pins are
attached to a pacemaker which is implanted subcutaneously. The lead
may also be positioned in both chambers, depending on the lead, as
when a lead passes through the atrium to the ventricle. Sense
electrodes may be positioned within the atrium or the ventricle of
the heart as appropriate for the particular condition or the choice
of the medical practitioner.
[0005] Pacemaker leads represent the electrical link between the
pulse generator and the heart tissue which is to be excited. These
pacemaker leads include single or multiconductor coils of insulated
wire having an insulating sheath. The coils provide a cylindrical
envelope or tube, many times referred to as a lumen, which provides
a space into which a stiffening stylet can be inserted. The
conductive coil is connected to an electrode in an electrode
assembly at a distal end of a pacing lead. Typically, a terminal
member is molded within a flexure sleeve at the proximal end of the
pacing lead and connected to the proximal end of the conductive
coil.
[0006] After the electrode assembly is positioned at a desired
location within the heart, it is desirable to provide some method
for securing the electrode assembly at that location. Mechanical
fixation devices are used to firmly anchor the electrodes in the
heart. One type of mechanical fixation device used is a corkscrew,
or a helix electrode connector. During placement of the lead, the
tip of the lead travels intravenously through veins and the heart.
While traveling through the veins, the helix electrode connector at
the tip of the lead may snag or attach to the side wall of the
vein. Since this is highly undesirable as it may cause damage or
other complications to a patient, retractable helixes are one of
the optional constructions which have been provided for leads. In
addition, temporary caps over the helix (such as an aqueous soluble
cap, particularly a water soluble, innocuous organic material such
as a sugar, starch or other biologically inert, or digestible
material such as sugars, starches and the like (e.g., mannitol,
sorbitol)) may be formed over the helix or tip. Preferably these
materials are at least soluble or dispersible and preferably are
inert or even digestible.
[0007] When using a retractable helix, the helix is extended and
screwed into the heart muscle by applying a torque to the other end
of the conductor without use of any further auxiliary device or
with a special fixation stylet. A fixed or non-retractable helix
electrode connector needs only to be positioned and secured to the
heart muscle by the application of torque. If a soluble/dispersible
cap is present on the helix, the cap must be given sufficient time
to dissolve or disperse before complete securement of the helix
electrode connector is attempted. A lead must be capable of being
firmly secured into the wall of the cardiac tissue to prevent
dislodgement therefrom, while avoiding perforation of the electrode
completely through the cardiac tissue.
[0008] The pulse generator circuitry and power supply work in
concert with the electrodes as a system which provides electrical
pulses to the heart tissue. A low impedance electrode design may
increase power delivery to the heart tissue, but at the same time,
this higher energy usage results in shorter battery life. Shorter
battery life is undesirable, since it increases the average number
of surgical procedures to perform battery replacement for a
patient.
[0009] There is a need for a body-implantable lead that has a helix
for fixation to the wall of the atrium or ventricle of the heart. A
separate desirable feature in body-implantable leads is for a lead
having an electrode for positioning within the atrium or ventricle
that allows for tissue ingrowth. Tissue ingrowth further enhances
the electrical performance of the lead. The lead and electrode are
further stabilized within the heart as a result of tissue ingrowth.
Furthermore, there is a need for a relatively high pacing impedance
electrode design which offers reasonable average voltage threshold
with sufficient signal amplitude so that the pacing function would
be effectively provided with reduced energy utilization and
consequently extend battery life.
SUMMARY OF THE INVENTION
[0010] According to the present invention, there is provided a
body-implantable lead assembly comprising a lead, one end of the
lead being adapted to be connected to electrical supply for
providing or receiving electrical pulses. The other end of the lead
comprises a distal tip which is adapted to be connected to tissue
of a living body. The lead is characterized by having either a) a
porous electrode at the base of the helix and/or b) an insulating
coating over a portion of the helix so that the impedance is
increased for the helix as compared to a helix of the same size and
materials without an insulating coating. The lead also has an
increased impedance or high impedance which can act to extend the
life of the battery. The high or at least the increased impedance
may be effected in any of a number of ways, including, but not
limited to one or more of the following structures: 1) a fully
insulated tissue-engaging tip with an electrode at the base of the
insulated tip, 2) a partially insulated engaging tip (only a
portion of the surface area of the engaging tip being insulated),
3) a mesh or screen of material at the distal end of the lead, at
the base of an extended engaging tip (whether a fixed or
retractable tip), 4) the selection of materials in the composition
of the mesh and/or tip which provide higher impedance, 5) the
partial insulative coating of a mesh or screen to increase its
pacing impedance, and 6) combinations of any of these features.
There may be various constructions to effect the high impedance,
including the use of helical tips with smaller surface areas (e.g.,
somewhat shorter or thinner tips). There may also be a sheath of
material inert to body materials and fluids and at least one
conductor extending through the lead body. The use of these various
constructions in the tip also allows for providing the discharge
from the tip in a more highly resolved location or area in the
tip.
[0011] According to the present invention, there is provided a
body-implantable lead assembly comprising a lead, one end being
adapted to be connected to electrical supply for providing or
receiving electrical pulses. The lead further comprises a distal
tip which is adapted to be connected to tissue of a living body.
The lead also has a high impedance to extend the life of the
battery. There may be various constructions to effect the high
impedance. There may also be a sheath of material at the distal end
of the lead assembly, with the sheath being inert to body materials
and fluids and at least one conductor extending through the lead
body.
[0012] The distal tip electrode is adapted, for example, for
implantation proximate to the heart while connected with a system
for monitoring or stimulating cardiac activity. The distal tip
electrode includes an electrode tip (preferably with only a
percentage of its entire surface area being electrically
conductively exposed--only a portion of the surface is
insulated--to increase its impedance), preferably a mesh screen
disposed at a distal end of the electrode tip, a fixation helix
disposed within the electrode tip, and a helix guiding mechanism.
The mesh screen preferably is electrically active, and the area of
the mesh screen and the percentage of electrically exposed surface
area of the electrode tip can be changed to control electrical
properties. Further, the mesh screen can entirely cover an end
surface of the electrode tip, or a portion of the end surface in
the form of an annular ring. In one embodiment, the helix guiding
mechanism includes a hole punctured within the mesh screen.
Alternatively, the helix guiding mechanism can include a guiding
bar disposed transverse to a radial axis of the electrode. The
helix is retractable, and is in contact with a movement mechanism.
The movement mechanism provides for retracting the helix, such as
during travel of the electrode tip through veins. The helix is
aligned with the radial axis of the electrode and travels through
the guiding mechanism. The mesh may be tightly woven or constructed
so that there are effectively no openings, or the mesh can be
controlled to provide controlled porosity, or controlled flow
through the mesh.
[0013] In another embodiment, the electrode tip includes a mesh
screen forming a protuberance on the end surface of the electrode
tip. The protuberance is axially aligned with the radial axis of
the electrode. The helix travels around the protuberance as it
passes through the mesh while traveling to attach to tissue within
the heart. The helix also travels around the protuberance as it is
retracted away from the tissue within the heart. If the mesh screen
is insulated around the protuberance, then a high impedance tip is
created. Advantageously, the protuberance allows for better
attachment to the cardiac tissue without having the electrode tip
penetrating therethrough.
[0014] Additionally, a distal tip electrode is provided including
an electrode tip, a mesh screen disposed at a distal end of the
electrode tip, a fixation helix disposed within the electrode tip,
and a helix guiding mechanism. The electrode tip further may
include a piston for moving the helix. The piston further may
include a slot for receiving a bladed or fixation stylet. When
engaged and rotated, the piston provides movement to the helix. The
base provides a mechanical stop for the helix and piston when
retracted back into the electrode tip.
[0015] In another embodiment, the distal tip assembly is adapted
for implantation proximate to the heart while connected with a
system for monitoring or stimulating cardiac activity. A fixation
helix/piston assembly is housed by an electrode collar, housing,
and base assembly. Attached to the proximal end of the helix is a
piston which includes a proximal slot for receiving a bladed or
fixation stylet. When a stylet is engaged in the slot and rotated,
the piston provides movement to the helix. Depending on the
embodiment, the fixation helix/piston assembly may be electrically
active or inactive. The electrode collar, housing, and base all
house the fixation helix/piston assembly. The proximal end of the
electrode collar is attached to the distal end of the housing.
Furthermore, the proximal end of the housing is attached to the
distal end of the base, and the proximal end of the base is
directly attached to the conductor coils of the lead.
[0016] A mesh screen may be attached to the distal tip of the
electrode collar. The mesh screen, in another embodiment, is
electrically active and serves as the electrode on the distal tip
assembly. The tip may then be fully insulated to increase the
impedance of the tip or may be partially insulated (with
preselected areas of the helix tip being insulated and other areas
being non-insulated) to adjust the impedance of the tip to the
specific or optimal levels desired. The area of the mesh screen can
be modified to cover differing portions of the end surface of the
distal tip assembly to control electrical properties of the lead.
The fixation helix travels through a guiding mechanism, where the
guiding mechanism allows the fixation helix to be extended and
retracted. In one embodiment, the helix guiding mechanism includes
a hole formed within the mesh screen. Alternatively, the helix
guiding mechanism can include a guiding bar disposed transverse to
a radial axis of the electrode collar. The mesh screen and/or
guiding bar also serve as a full extension stop when the helix is
fully extended. The base serves as a stop when the fixation
helix/piston assembly is fully retracted.
[0017] The provided electrode tip supplies a retractable helix and
a mesh screen which advantageously allows for sufficient tissue
in-growth. The guide mechanism provides a convenient way to direct
the rotation of the helix. A further advantage of the electrode tip
is the provided mechanical stop. The mechanical stop aids in
preventing over-retraction of the helix during the installation or
removal of the electrode tip.
[0018] In yet another embodiment, the electrode uses a partially
insulated fixation helix to provide a relatively high pacing
impedance electrode. The fixation helix is insulated using
insulating coatings over a portion of the fixation helix.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a first side elevational view illustrating a lead
constructed in accordance with one embodiment of the present
invention.
[0020] FIG. 2A is a cross-sectional view of an electrode tip of a
lead for monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention.
[0021] FIG. 2B is an end view of the electrode tip of the lead
shown in FIG. 2A.
[0022] FIG. 3A is a cross-sectional view of an electrode tip of a
lead for monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention.
[0023] FIG. 3B is an end view of the electrode tip of the lead
shown in FIG. 3A.
[0024] FIG. 4A is a cross-sectional view of an electrode tip of a
lead for monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention
[0025] FIG. 4B is an end view of the electrode tip of the lead
shown in FIG. 4A.
[0026] FIG. 5A is a cross-sectional view of an electrode tip of a
lead for monitoring and stimulating the heart constructed in
accordance with one embodiment of the present invention
[0027] FIG. 5B is an end view of the electrode tip of the lead
shown in FIG. 5A.
[0028] FIG. 6 shows a partially insulated helical tip according to
the present invention which increases the impedance of the tip as
compared to a fully non-insulated helical tip.
DETAILED DESCRIPTION OF THE INVENTION
[0029] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which specific
aspects of the broader invention may be practiced. These
embodiments are described in sufficient detail to enable those
skilled in the art to practice both the broad concepts of the
invention as well as more limiting specific constructions, and it
is to be understood that other embodiments may be utilized and that
structural changes may be made without departing from the spirit
and scope of the present invention as disclosed herein. Therefore,
the following detailed description is not to be taken in a limiting
sense, and the scope of the present invention is defined by the
appended claims.
[0030] As noted previously, there are a number of ways in which
increased impedance may be effected for mechanically fastened
electrode connections in atrial/ventricular implantable catheters
(AVIC) systems. These include at least the following: 1) a fully
insulated tissue engaging tip (at least with respect to all
surfaces that are in electrical contact or electrically active
physical relationship to heart muscles so that a pace would be
effective if discharged at that portion of the tip), 2) a partially
insulated engaging tip (only a portion of the surface area of the
engaging tip being insulated, preferably there is sufficient
coating so that there is at least 5%, or at least 10%, or at least
20 or 30%, or at least 40, 50 or 60%, or at least 70, 75, 80 or 90%
of the surface area of the tip which can discharge to heart muscle
[or as percentages of the entire tip or as percentages of the
entire tip that extends physically beyond the end plane of the
catheter and which may therefore penetrate tissue or muscle]), 3) a
porous, electrically conductive element, such as a mesh or screen
of material at the proximal end of the helix or the distal end of
the lead (excluding the helix), at the base of an extended engaging
tip, 4) the selection of materials in the composition of the mesh
and/or tip which provide higher impedance, 5) the partial
insulative coating of a porous conductive element, such as the mesh
or screen to increase its impedance, and 6) combinations of any of
these features. There may be various constructions to effect the
increased or high impedance, including the use of helical tips with
smaller surface areas (e.g., somewhat shorter or thinner tips).
There may also be other elements associated with the catheter
and/or leads, such as a sheath of material inert to body materials
and fluids, circuitry, microcatheters, and at least one conductor
extending through the lead body.
[0031] One aspect of the present invention comprises an implantable
electrode with a helical tip comprising:
[0032] an electrode having a distal end and a proximal end; and
[0033] a helix disposed within the electrode, which helix is
aligned along a radial axis of the electrode towards the distal
end, and which helix is either retractable or fixed; and
[0034] the implantable electrode having at least one feature
selected from the group consisting of:
[0035] a) the helix having a coating of an insulating material on
its surface which covers at least 5% of its surface area but less
than 95% of its surface area (which is exposed beyond the distal
end of the electrode),
[0036] b) the helix extending beyond the distal end of the
electrode and the distal end of the electrode having a porous
conductive surface at a base of the helix,
[0037] c) a porous conductive element such as a screen or mesh at a
base of the helix, which is retractable/extendable, with the helix
being either active or inactive (electrically), and
[0038] d) a partially insulated (partially insulation coated)
porous conductive element (e.g., screen or mesh) at the base of an
active or inactive, retractable/extendable or fixed helix.
[0039] The implantable electrode preferably has the helix with a
coating of insulating material on its surface which covers from
5-100% (to 100% where there is an additional electrode element
within the system) or 5-95% of surface area of the helix beyond the
distal end of the electrode. Alternatively, the surface of the
helix is that which is considered to be in electrically
discharge-functional physical relationship with tissue or muscle
into which it is embedded. For purposes of measuring or determining
the distal end of the electrode, the tip extends beyond a tubular
or cylindrical housing or structural portion which is considered
the electrode, and the tip is an engaging portion that extends
beyond the housing portion of the electrode. The distal end of the
electrode is usually characterized as the end of the cylindrical
housing or tubing carrying the tip, circuits, conductive elements,
guides, etc. It is more preferred that the helix of the implantable
electrode has a coating of insulating material on it surface which
covers from 5-95% or 10-90% of the surface area of said helix
beyond the distal end of the electrode.
[0040] A lead 10 is illustrated in FIG. 1. The lead 10 comprises a
lead body 11, an elongate conductor 13 contained within the lead
body, and a lead tip 20 with an optional retractable tip assembly
24 contained in the lead tip 20. In addition, a stylet 14 is shown
inserted into the lead body 11. A helix 100 (FIGS. 2A-5A), which
consists of an electrical conductor coil, is contained in the
retractable lead tip 24. In an alternative practice of the
invention, the helix 100 extends and retracts by rotation of the
stylet 14, as will be discussed further below. A Brady lead body is
shown, although the invention could be incorporated with other
leads, such as Tachy leads. The lead body 11 consists of electrical
conductors 13 which are covered by a biocompatible insulating
material 22. Polymers, such as silicone rubber, fluorinated resins,
polyacrylates, polyamides ceramic or composite materials or other
insulating material can be used for covering the lead body 11.
[0041] In one embodiment shown in FIGS. 3 and 3A, the helix 100 is
formed of electrically conductive material offering low electrical
resistance and also resistant to corrosion by body fluids. A
biocompatible metal, such as titanium or platinum-iridium alloy is
an example of a suitable material. Alternatively, the helix 100 is
electrically inactive or insulated. In one embodiment, the helix
100 may be coated with an insulative material (not shown) or may be
constructed of a rigid, corrosion resistant,
non-electrically-conductive material (e.g., a ceramic). A housing
182, described in further detail below, is made from an
electrically conductive material and covered with an insulating
material such as a synthetic or natural polymer such as a silicone
rubber. The housing 182 is directly connected to an electrical
conductor within the lead 120. These materials are additionally
suitable because they tend to be biologically inert and well
tolerated by body tissue.
[0042] The helix 100 defines a lumen and thereby is adapted to
receive a stiffening stylet 14 that extends through the length of
the lead. The stylet 14 stiffens the lead 120, and can be
manipulated to introduce an appropriate curvature to the lead,
facilitating the insertion of the lead into and through a vein and
through an intracardiac valve to advance the distal end of the lead
120 into the right ventricle of the heart (not shown). A stylet
knob 154 is coupled with the stylet 14 for rotating the stylet 14
and advancing the helix 100 into tissue of the heart.
[0043] In one embodiment, as shown in FIGS. 2A and 2B, a lead 310
has an electrode tip 320 which is provided with a mesh screen 330.
The mesh screen 330 completely encapsulates the diameter of the
lead, and may serve, at least in part, as a pacing/sensing
interface with cardiac tissue. If the helix 100 is electrically
active, it too can help serve as a portion of a pacing or sensing
interface. The mesh screen 330 is of a porous construction,
preferably made of electrically conductive, corrosion resistant
material. Using a mesh screen 330 having a porous construction
allows for fibrotic ingrowth. This provides for a further anchoring
of the lead tip 320 and also increases the sensing capability of
the lead 310 by increasing the surface area in contact with the
cardial tissue. The mesh screen 330 may be attached to an electrode
collar 40, which is electrically active. In a retractable catheter
system, a housing 380, which is electrically conductive,
encapsulates the piston 350 and the fixation helix 100. Insulation
382 is disposed about the housing 380 and collar 40.
[0044] Disposed within the lead 310 is a lead fastener 100 for
securing the lead 310 to cardiac tissue. The lead fastener 100 can
be disposed along the radial axis 15 of the electrode lead 310. In
this embodiment, the lead fastener comprises a fixation helix 100.
The fixation helix 100 can be made electrically active or inactive
as discussed above. Attached to the fixation helix 100 in a
retractable tip system is a piston 350. The piston 350 is
configured to mate with a bladed locking stylet 14 at a stylet slot
354, and acts as an interface between the stylet 14 and the helix
100. The stylet 14, coupled with the piston 350 at the stylet slot
354, extends and retracts the fixation helix 100 when the stylet 14
is rotated. The piston 350 can either be electrically active or
inactive. The piston 350 also has a slot 352, which allows the
piston 350 to mate with a base 360.
[0045] Fitted with a knob 362, as shown in FIG. 2A, the base 360
mates with the slot 352 of the piston 350. The base 360 serves as a
stop once the fixation helix 100 is fully retracted. The
electrically conductive base 360 also allows passage of a bladed
locking stylet 14 and attachment of electrode coils (not
shown).
[0046] In addition, the lead 310 has a guide groove 370. The groove
370 is formed by puncturing a hole (not shown) within the mesh
screen 330, although the guide groove 370 can be formed by other
methods known by those skilled in the art. Having a circular
cross-section, the guide groove 370 may have a diameter greater
than that of the conductor forming the helix 100. The groove 370 is
disposed within the mesh screen 330, and directs the fixation helix
100 from its retracted position, as illustrated in FIG. 2A, to an
extended position (not shown). The groove 370 also reversibly
directs the fixation helix 100 from an extended position to the
retraction position.
[0047] In a second embodiment, as shown in FIGS. 3A and 3B, a lead
110 has an electrode tip 120 which is provided with a mesh screen
130. The mesh screen 130 completely encapsulates the diameter of
the lead or electrode tip 120, and serves as the pacing/sensing
interface with cardiac tissue. The screen 130 is of a porous
construction, made of electrically conductive, corrosion resistant
material. Using a mesh screen 130 having a porous construction
allows for fibrotic ingrowth. This provides for a further anchoring
of the lead tip 120 to tissue and also increases the sensing
capability of the lead 110. The sensing capability is enhanced
because the mesh screen 130 has more surface area than
corresponding solid material. The ingrowth of fibrotic tissue into
the mesh screen 130 increase the sensing capability of the lead 110
by increasing the surface area in contact with the cardiac tissue.
Furthermore, the geometry of the mesh screen 130, particularly any
protuberance, as will be discussed below, creates a high pacing
impedance tip.
[0048] The mesh screen 130 may form a protuberance 135 from a flat
edge portion 137 of the mesh screen 130 in a generally central
portion of the electrode tip 120. The protuberance 135 may be
generally circular in cross-section, but may be any shape (e.g.,
truncated cylindrical, truncated pyramidal, oval, ellipsoidal,
etc.) as a result of design or circumstance which provides a flat
or conformable surface (preferably not a rigid, sharp face which
will not conform to tissue) abutting tissue, and preferably has a
diameter smaller than a diameter of the lead 110. In addition, the
protuberance 135 is aligned with the radial axis 15 of the lead
110. Sintered to an electrode collar 40, a process known by those
skilled in the art, the mesh screen 130 is attached to the
electrode tip 120. The electrode collar 40 is electrically
active.
[0049] Disposed within the electrode lead 110 is a lead fastener
for securing the electrode lead 110 to cardiac tissue. The lead
fastener can be disposed along the radial axis 15 of the electrode
lead 110. In this embodiment, the lead fastener comprises a
fixation helix 100. The fixation helix 100 can be made electrically
active or inactive to change sensing and pacing characteristics, as
discussed above. Attached to the fixation helix 100 is a piston
150. The piston 150 is configured to mate with a bladed locking
stylet 14, thereby providing a movement assembly. The stylet 14
extends and retracts the fixation helix 100 when the stylet 14 is
rotated. The piston 150 can either be electrically active or
inactive. The piston 150 also has a slot 152. The slot 152 of the
piston 150 allows the piston 150 to mate with a base 160 upon full
retraction.
[0050] The base 160 is modified with a knob 162 to mate with the
slot 152 of the piston 150. The knob 162 mates with the piston 150
to prevent over-retraction once the helix 100 has been fully
retracted. The stylet 14 operates to advance the fixation helix
100. As the implanter rotates the stylet 14, the stylet 14 engages
the piston 150 at the stylet slot 154 and rotates the piston 150,
which moves the fixation helix 100 through a guide groove 170. The
guide groove 170 is for ensuring that the fixation helix 100 is
properly guided out of and into the end of the electrode. Once the
fixation helix 100 is fully retracted, the base 160 serves as a
mechanical stop. The base 160 also allows passage of a bladed
locking stylet 14 and attachment of electrode coils. Additionally,
the base 60 is electrically active.
[0051] The electrode lead 110 also has a guide groove 170. The
groove 170 is formed by puncturing a hole within the mesh screen.
Having a circular cross-section, the groove 170 has a diameter
greater than that of the conductor forming the helix 100. The
groove 170 is disposed within the mesh screen 130, and directs the
fixation helix 100 from its retracted position, as illustrated in
FIG. 2A, to an extended position (not shown). During implantation,
after the electrode is in contact with tissue at the desired
location in the heart, the stylet 14 is rotated which causes the
piston to advance the fixation helix out of the groove 170. As the
fixation helix 100 is placed in an extended position, the helix 100
travels through groove 170 and circles around the protuberance 135.
The groove 170 also directs the fixation helix 100 from an extended
position to the retracted position. Advantageously, the mesh screen
130 prevents the implanter from overextension and advancing the
helix 100 too far into the tissue. An electrically conductive
housing 180 encapsulates both the piston 50 and the fixation helix
100. Insulation 182 covers the housing 180, the collar 40, and a
portion of the mesh screen 130. The insulation 182 over the mesh
screen 130 controls the impedance of the electrode tip 120.
[0052] In a third embodiment as shown in FIGS. 4A and 4B, a lead 10
has an electrode tip 20 which is provided with a mesh screen 30.
The mesh screen 30 completely encapsulates the diameter of the lead
tip. Sintered to an electrode collar 40, the mesh screen 30 is
attached to the electrode tip 20. The electrode collar 40 is
electrically active. A housing 80 is disposed about the helix 100,
and is electrically active. Insulation 82, encompasses the housing
80 and collar 40.
[0053] Disposed within the lead 10 is a lead fastener for securing
the lead 10 to cardiac tissue. The lead fastener can be disposed
along the radial axis 15 of the lead 10. In this embodiment, the
lead fastener comprises a fixation helix 100. The fixation helix
100 can be made electrically active or inactive to change sensing
and pacing characteristics.
[0054] The helix 100 is of a well known construction. Using a
conductor coil such as helix 100 has been shown to be capable of
withstanding constant, rapidly repeated flexing over a period of
time which can be measured in years. The helix 100 is wound
relatively tightly, with a slight space between adjacent turns.
This closely coiled construction provides a maximum number of
conductor turns per unit length, thereby providing optimum strain
distribution. The spirally coiled spring construction of helix 100
also permits a substantial degree of elongation, within the elastic
limits of the material, as well as distribution along the conductor
of flexing stresses which otherwise might be concentrated at a
particular point.
[0055] Attached to the fixation helix 100 is a piston 50. The
piston 50 is configured to mate with a bladed locking stylet 14.
The piston 50 advances the fixation helix 100 once the lead is
placed in position within the heart. The piston 50 can either be
electrically active or inactive. The piston 50 also has a slot 52
and a stylet slot 54. The stylet 14 couples with the stylet slot 54
and extends or retracts the fixation helix 100 when the stylet 14
is rotated. The slot 52 of the piston 50 allows the piston 50 to
mate with a base 60 when the helix 100 is retracted to prevent over
retraction. The base 60 is configured with a knob 62 to mate with
the slot 52 of the piston 50. Once the fixation helix 100 is fully
retracted, the base 60 serves as a stop at full retraction. The
base 60 also allows passage of a bladed locking stylet 14 and
attachment of electrode coils. In addition, the base 60 is
electrically active.
[0056] The lead 10 also includes a guiding bar 70. Extending across
the diameter of the tip, the guiding bar 70 is generally
cylindrical in shape. The guiding bar 70 directs the fixation helix
100 from its retracted position, as illustrated in FIG. 2A, to an
extended position (not shown) as the piston 52 advances the helix
100. The guiding bar 70 also directs the fixation helix 100 as it
is retracted from an extended position to the retraction position
through the mesh screen. Although a guiding bar 70 is described,
other types of guiding mechanisms can be used such as helical
passageways, threaded housings, springs, and are considered within
the scope of the invention. Additionally, the lead 10 is provided
with a seal (not shown) for preventing entry of body fluids and
tissue from entering the lead through the opening therein. The seal
could be a puncture seal between the piston 50 and the base 60.
Alternatively, O-rings could be used to seal the electrode.
[0057] In a fourth embodiment as shown in FIGS. 5A and 5B, a lead
210 has an electrode tip 220 which is provided with a mesh screen
230. The mesh screen 230 forms an annular ring having an open
center, where the annular ring is centered at a radial axis 15 of
the electrode lead 210. The mesh screen 230 provides more surface
area than a smooth tipped electrode which aids in sensing. The
removal of the center portion of the mesh screen creates a high
impedance pacing tip due to the nature of the surface geometry.
Sintered, fused, bonded, adhesively secured or mechanically
attached to an electrode collar 40, the mesh screen 230 is attached
to the electrode tip 220. The electrode collar 40 is electrically
active.
[0058] Disposed within the lead 210 is a lead fastener for securing
the lead 210 to cardiac tissue. The lead fastener can be disposed
along the radial axis 15 of the electrode lead 210. In this
embodiment, the lead fastener comprises a fixation helix 100. The
fixation helix 100 can be made electrically active or inactive as
discussed above. Attached to the fixation helix 100 is a piston
250. The piston 250 has a stylet slot 254 and is configured to mate
with a bladed locking stylet 14. The stylet 14, coupled with the
piston 250 at the stylet slot 254, extends and retracts the
fixation helix 100 when the stylet 14 is rotated. The piston 250
can either be electrically active or inactive. The base 260 serves
as a stop once the fixation helix 100 is fully retracted. The base
260 also allows passage of a bladed locking stylet 14 and
attachment of electrode coils. The base 60 is electrically
active.
[0059] Additionally, the electrode lead also has a guiding bar 270.
The guiding bar 270 directs the fixation helix 100 from its
retracted position, as illustrated in FIGS. 5A and 5B, to an
extended position (not shown). The guiding bar 270 also directs the
fixation helix 100 from an extended position to the retracted
position. Although a guiding bar 270 has been described, other
types of mechanisms could be used to extend the helix, and are
considered within the scope of the invention. A housing 280
encapsulates the piston 250 and the fixation helix 100, and
insulation 282 is disposed over the housing 280 and collar 40.
[0060] Insulation generally covers the housing, the collar, and a
portion of the electrical discharge surface (e.g., the cathode, the
helix and/or the porous material or mesh). The insulation over the
mesh screen further controls the impedance of the electrode tip.
The insulated coating, whether present on the helix or the mesh or
other elements which are potentially electrically active or on
which electrical activity is to be suppressed, should be
biocompatible, non-thrombogenic, and otherwise safe for
implantation. The insulation coating should be of dimensions which
effect the insulation, increase the impedance (where desired), but
which dimensions do not interfere with the performance of the tip,
the lead or the helix or the health of the patient. The insulation
is present as a coating (a material which tends to conform to the
surface rather than completely reconfigure it, as would a lump of
material). The coating usually should be at least 0.5 microns in
thickness, usually between 0.5 and 100 microns, preferably between
1.0 and 30 or 50 microns, more preferably between 1 and 20 microns,
still more preferably between 1.5 and 15 microns, and most
preferably between 1.5 or 2.0 microns and 10 or 15 microns. The
coating may be provided by any convenient process, such as
electrophoretic deposition, dip coating, spin coating, in situ
polymerization, vapor deposition, sputtering and the like. Any
insulating material is useful, such as polymers, ceramics, glasses,
and the like, but because of their convenience in application,
flexibility and availability, polymers are preferred. Polymers from
such classes as polyesters, polyamides, polyurethanes, polyethers,
polysiloxanes, polyfluorinated resins, polyolefins, polyvinyl
polymers, polyacrylates (including polymethacrylates), and the like
may be used with various leads and tips according to the practice
of the present invention. PARYLENE is a preferred material, as
described herein, with a thickness of between 1.5 and 10
microns.
[0061] In yet another embodiment, a partially insulated fixation
helix is used to provide a relatively high impedance electrode
design. Leads comprising a distal or electrode end and a proximal
or connector end may be used. A "miniature" wire-in-basket porous
electrode may be sintered upon the distal end of a metallic pin,
provided with a blind hole. Circumferential to this subassembly, a
sharpened wire fixation helix may be positioned and attached at a
general location proximal to the electrode by any convenient means
which allows electrical continuity. This attachment includes, but
is not limited to, crimping, spot welding, laser welding, the use
of grooves upon the surface of the pin, the use of thin metallic
overband (also not shown) or any combination thereof. A portion of
this fixation helix is provided with an extremely thin layer of a
biostable, biocompatible polymer, which, inter alia, provides
electrical insulation between the fixation helix and the cardiac
tissue. In one embodiment, the insulated portion is the majority of
the fixation helix, leaving a relatively small uninsulated region
of fixation helix. This approach offers increased impedance to
reduce energy dissipation in pulsing functions, such as pacing
functions. Other varying embodiments include, but are not limited
to, a portion which is approximately or substantially equal to half
of the fixation helix, and a portion which is approximately or
substantially equal to a minority of the fixation helix. Such
embodiments provide different amounts of uninsulated region and
different amounts of impedance. The thin coating of electrically
insulating coating must usually be at least 1 micron in thickness
to provide a significant insulating effect, depending upon its
insulating ability and properties. The thickness of the coating is
limited primarily by physical limitations on the system. The
coating can not be so thick as to interfere with the fastening
ability of the helix or to increase the size of the helix beyond
that which is tolerable for the use of the helix and the patient.
Typically, the coating is at least one micron up to about 100
microns, more typically the coating is between 1 and 30 microns,
preferably between 1.5 and 20 microns, more preferably between 1.5
and 15 microns, and most preferably between 2 and 10 microns. The
material used for the coating should, of course, be biocompatible
and even more preferably non-thrombogenic. Materials such as
PARYLENE.TM., polyurethanes, polyacrylates (including
polymethacrylates), polyesters, polyamides, polyethers,
polysiloxanes, polyepoxide resins and the like can be used.
PARYLENE material includes a thermoplastic film polymer base upon
para-xylylene. Crosslinked polymers within these classes may be
preferred for their resistance to breakdown and their physical
durability. As the coating is to be maintained within the body of a
recipient, the coating composition should not be water-soluble or
aqueous soluble within the parameters and environment encountered
within animal bodies (e.g., it should not be soluble within blood,
serum or other body fluids with which it might come into
contact).
[0062] To the proximal end of this pin, a metallic conductor coil
may be conveniently attached to provide electrical connection to
the implantable pacemaker (not shown) by means of a connector. In
one embodiment, local (e.g., steroid or other medicinal) therapy is
provided by a (e.g., circumferential) steroid/polymer matrix
positioned immediately proximal to the porous electrode. In one
embodiment, the circumferential steroid/polymer matrix is provided
with a distal taper. Other embodiments include other distal
configurations, including, but not limited to, non-tapered or
"inflated" configurations. In one embodiment, an internalized,
medicinal or biologically active (e.g., steroid) releasing matrix
is used. Proximal to this biologically active (e.g., steroid)
eluting matrix, a generally cylindrical polymeric tubing (this is
the preferred shape, but the shape is a matter of choice) 820 is
used to provide electrical insulation of this entire assembly. In
one embodiment, the lead is "unipolar." In one embodiment, an
ablative protective covering positioned over the entirety of distal
end is used (not shown). One example of such a covering is the
mannitol "Sweet Tip".RTM. electrode of Guidant Corporation's
Cardiac Rhythm Management Group. In one embodiment, a "bipolar"
lead is provided with the distal electrode features described.
[0063] During an in vitro evaluation of this electrode design,
polymeric coatings intended to partially insulate the fixation
helix were prepared and evaluated. In one embodiment, the PARYLENE
coating is extremely thin (.about.3.mu.), providing a coating with
uniform coverage which is adherent to the metallic substrate, and
which is controllable to provide an abrupt margin. The silicone
rubber coating is known to be somewhat thicker (.about.10.mu.),
uniform in coverage, somewhat less adherent to the metallic
substrate, and controllable to an abrupt margin. Other coatings may
be used without departing from the spirit and scope of the present
invention.
[0064] The PARYLENE or other insulative coating effectively
increases in vitro "pacing impedance." Application of a
non-continuous or partially extensive coating of an electrically
insulating polymer such as PARYLENE to the metallic fixation helix
produces the desired increase in impedance compared to an
uninsulated helix as well as other existing designs. For example,
it has been demonstrated that one embodiment using a coated
fixation helix provides a pacing impedance of over approximately
800 ohms which is larger than the impedance of some electrodes
using an uncoated fixation helix. The post-implant pacing impedance
of an embodiment using a coated fixation helix remains higher than
that of typical electrodes using an uncoated fixation helix. In one
experiment, a coated fixation helix using PARYLENE as an insulating
layer provided over 1200 ohms average pacing impedance on the day
of implantation and over 900 ohms ten days after the implant.
[0065] Additionally, post-implant average voltage threshold of the
PARYLENE insulated miniaturized electrode is less than the other
high impedance electrodes. Such performance is considered to be
desirable. In one experiment, an embodiment with a coated fixation
helix 802 having a voltage threshold of approximately 0.2 volts on
the day of implant was measured at about 0.7 volts at ten days
after the implant (using a 0.5 ms pulse width). An electrode with
an uncoated fixation helix demonstrated over 0.8 volts average
voltage threshold at ten days after the implant, illustrating the
benefits of the coated fixation helix.
[0066] An additional benefit is that the coated fixation helix
embodiments may provide an improvement in both the implant as well
as post-implant average S-wave amplitude detection.
[0067] The miniaturized high impedance, positive fixation porous
electrode technology described here provides the following
advantages over the prior art. For one example, the coated fixation
helix embodiments provide an electrode where the benefits of high
impedance pacing are realized through downsizing the porous
electrode and insulating the fixation helix. Downsizing of the
porous electrode may be accomplished, for example, by having a
smaller porous (e.g., mesh) electrode supported on a non-conductive
surrounding support element (e.g., a polymeric or composite film
with a mesh central area, particularly a mesh truncated conical or
pyramidal area of flexible, conductive mesh). An area of the
completely conductive mesh may also be discontinuously coated
leaving a conductive central or conductive raised area,
particularly surrounding a contact, engaging element, or helix.
Further, an external steroid collar provides a fabrication
advantage since such a component can be readily mass produced
compared to smaller components with elaborate profiles. Still
further, fabrication of a lead with this external collar is
streamlined. The higher impedance design conserves battery power to
provide longer battery life with fewer battery replacements. Other
benefits exist which are not described in detail herein, however,
which those skilled in the art will appreciate.
[0068] FIG. 6 shows a high impedance catheter tip 800 with a
partially insulated tip 802 and a partially insulated mesh 808. The
partially insulated tip (or helix) 802 extends from a base,
proximal end 830 to a distal, pointed end 834 with a middle portion
836 lying between proximal end 830 and distal end 834. Helix 802
comprises one fully insulated section 804 which begins at distal,
pointed end 834 and extends to, and ends with, middle portion 836
and one uninsulated section 806 which extends from the end of the
fully insulated section within middle portion 836 to base, proximal
end 830. The partially insulated mesh 808 comprises a first area
810 of the mesh 808 which is insulated and second are 812 of the
mesh 808 which is not insulated. The impedance of the catheter tip
can be readily controlled by the amount of surface area of the
helical tip itself and the area of the mesh (if present) which is
insulated. With a fixed conductivity in the tip and the mesh (if
present), the impedance can be increased by increasing the
percentage of the surface area of the tip or mesh which is
insulated.
[0069] A hole 820 is shown in the mesh 808. The mesh 808 may be
flat and flush with the end 822 of the catheter 816 or may be
partially wrapped (not shown) over the end 820 or inside the end
820 to affix the mesh to the catheter 816. The mesh 808 may also be
hemispherical, truncated conical, truncated pyramidal or any other
shape which may assist in allowing the mesh 808 to more compliantly
contact tissue (not shown) surface to transmit the pacing signal or
discharge. Within the catheter 816 may be a soluble, elutable or
dispersible material which carries medication or biologically
active material along with the catheter. For example,
anti-inflammatants, antibiotics, analgesics, pain-reducing
medication, vitamins, anti-viral medication, or the like may be
transmitted to the attachment site along with the catheter by
inclusion within a material 814 carried within or on the catheter
816.
[0070] The coating of insulation on the helical tip or mesh may be
applied by any convenient method, including, but not limited to
coating (e.g., dip coating), printing, spraying, brush application,
resist application and removal and the like. The insulation may
also contain active ingredients (such as those recited within
material 814) to benefit the patient. The insulation carrying the
active material must not be soluble, so a polymer or other material
that is porous or has elutable materials must be used. The material
delivery does not have to be coextensive with the life of the
implant or the tip, and delivery of the material may be desirable
only over a short time period after insertion of the helical tip
and catheter.
[0071] A soluble or dispersible protective cap may also be placed
over the helical tip to reduce the possibility of any incidental
damage while catheterizing or moving the tip within a patient. As
previously noted, the cap material should preferably be
biocompatible or even digestible and may include such materials as
natural and synthetic materials such as sugars, starches, gelation
(unhardened), gums, resins, polymers, and the like. All components
of the catheter and tip which are exposed to the tissue or fluids
within a patient should be non-thrombogenic, and bio-acceptable.
There are extensive classes of commercially available materials
which meet these needs for metal, polymeric, composite and other
materials described within the practice of the present
invention.
[0072] It is to be understood that the above description is
intended to be illustrative, and not restrictive. Although the use
of the lead has been described for use in a cardiac pacing system,
the lead could as well be applied to other types of body
stimulating systems. Many other embodiments will be apparent to
those of skill in the art upon reviewing the above description. The
scope of the invention should, therefore, be determined with
reference to the appended claims, along with the full scope of
equivalents to which such claims are entitled.
* * * * *