U.S. patent application number 13/027849 was filed with the patent office on 2011-06-09 for implantable leads permitting functional status monitoring.
Invention is credited to Jeffrey P. Bodner, Eric Hammill, Mohan Krishnan, Paul E. Zarembo, Yongxing Zhang.
Application Number | 20110137383 13/027849 |
Document ID | / |
Family ID | 34550774 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110137383 |
Kind Code |
A1 |
Hammill; Eric ; et
al. |
June 9, 2011 |
IMPLANTABLE LEADS PERMITTING FUNCTIONAL STATUS MONITORING
Abstract
An implantable lead assembly includes a lead body extending from
a proximal end to a distal end having an intermediate portion
therebetween, where the lead body includes an insulating layer. A
conductor is disposed within the insulating layer and the
insulating layer surrounds the conductor. An electrode is coupled
to the lead body, and the electrode is in electrical communication
with the conductor. At least one conductive sleeve is disposed
within the insulating layer. The at least one conductive sleeve
surrounds the conductor and is electrically isolated from the
electrode. The at least one conductive sleeve has a first impedance
value in a first condition.
Inventors: |
Hammill; Eric; (Ham Lake,
MN) ; Zhang; Yongxing; (Irvine, CA) ; Bodner;
Jeffrey P.; (St. Paul, MN) ; Zarembo; Paul E.;
(Vadnais Heights, MN) ; Krishnan; Mohan;
(Shoreview, MN) |
Family ID: |
34550774 |
Appl. No.: |
13/027849 |
Filed: |
February 15, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10698843 |
Oct 31, 2003 |
7904174 |
|
|
13027849 |
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Current U.S.
Class: |
607/72 ;
607/116 |
Current CPC
Class: |
A61N 1/056 20130101 |
Class at
Publication: |
607/72 ;
607/116 |
International
Class: |
A61N 1/32 20060101
A61N001/32; A61N 1/05 20060101 A61N001/05 |
Claims
1. A method comprising: measuring a first impedance of an at least
one conductive sleeve at a first time in an implantable lead
assembly, the implantable lead assembly including a lead body
having a conductor disposed therein, an electrode coupled to the
lead body and in electrical communication with the conductor, an
insulating layer surrounds the conductor, and the at least one
conductive sleeve is disposed within the insulating layer and
surrounds the conductor; measuring a second impedance of the at
least one conductive sleeve at a second time; and sending a signal
if the second impedance is within a predetermined range.
2. The method of claim 1, further comprising: comparing the first
impedance with the second impedance.
3. The method of claim 1, further comprising: wearing away the
insulating layer during an intermediate period between the first
time and the second time.
4. The method of claim 1, further comprising: coupling the
implantable lead assembly to a pulse generator, wherein the pulse
generator is in electrical communication with the at least one
conductive sleeve.
5. The method of claim 4, wherein measuring the first impedance and
measuring the second impedance are performed by the pulse
generator.
6. The method of claim 4, further comprising: storing the impedance
measurements within the pulse generator.
7. The method of claim 1, further comprising: coupling a monitoring
unit to a terminal disposed on the lead body wherein the monitoring
unit is in electrical communication with the at least one
conductive sleeve.
8. The method of claim 7, wherein measuring the first impedance and
measuring the second impedance are performed by the monitoring
unit.
9. The method of claim 1, wherein measuring the first impedance and
measuring the second impedance includes measuring impedance at
preprogrammed times.
10. The method of claim 1, wherein measuring the first impedance
and measuring the second impedance are performed intermittently.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of application Ser. No.
10/698,843, filed Oct. 31, 2003, entitled "Implantable Leads
Permitting Functional Status Monitoring," which is herein
incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present invention relates generally to an implantable
lead assembly that allows status monitoring of implantable
leads.
BACKGROUND
[0003] Implantable leads are a critical component in medical device
applications. In any implantable medical device (IMD) application,
and particularly in pacemaker or implantable cardiac defibrillator
applications, it is important to be able to monitor and report the
performance and functional status of leads. In some IMD
applications, the lead status is monitored for malfunctions, for
example, when the lead fractures and is unable to perform.
[0004] In one example, the impedance of a lead conductor coupled
with an electrode is measured to monitor the status of a lead as
described in U.S. Pat. No. 4,958,632. Exposure of the lead to the
surrounding environment of the body or fracture of the lead causes
measurable changes in the conductor impedance, which signals that
the lead has malfunctioned or is beginning to fail. However,
conventional lead status monitoring techniques are not able to
detect breaches of the lead insulation until the lead conductor
impedance changes, which occurs only when the lead has begun to
malfunction. In other words, the techniques are only able to detect
failure of the lead as the lead conductor begins to fail.
[0005] U.S. Pat. No. 6,317,633, is another example of lead
conductor monitoring through impedance measurements. However, the
system does not address the issue that the lead conductor impedance
only changes upon onset of failure in the lead conductor, and not
before, when only the insulation has been partially breached and
the lead is still fully functional.
[0006] What is needed are implantable leads that overcome the
shortcomings of previous implantable leads. What is further needed
are implantable leads that permit functional status monitoring of
lead insulation before the onset of lead conductor failure, which
would allow replacement of a lead before degradation in
performance.
SUMMARY
[0007] An implantable lead assembly includes a lead body extending
from a proximal end to a distal end, the lead body includes an
insulating layer. A conductor is disposed within the insulating
layer, and the insulating layer surrounds the conductor. An
electrode is coupled to the lead body, the electrode is in
electrical communication with the conductor. At least one
conductive sleeve is disposed within the insulating layer. The at
least one conductive sleeve surrounds the conductor and is
electrically isolated from the electrode. The at least one
conductive sleeve has a first impedance value in a first
condition.
[0008] Several options for the implantable lead assembly follow. In
one option, the at least one conductive sleeve is exposed to a
surrounding environment in a second condition and the at least one
conductive sleeve has a second impedance value that is within a
predetermined range. In another option, a second conductive sleeve
is disposed within the insulating layer and is electrically
isolated from the electrode. In yet another option, the second
conductive sleeve surrounds the conductor and the at least one
conductive sleeve. In still another option, a second conductor is
disposed within the insulating layer, and the second conductive
sleeve surrounds the second conductor.
[0009] In another embodiment, a method comprises measuring a first
impedance of an at least one conductive sleeve at a first time in
an implantable lead assembly. The implantable lead assembly
includes a lead body having a conductor disposed therein and an
electrode coupled to the lead body. The electrode is in electrical
communication with the conductor. An insulating layer surrounds the
conductor and at least one conductive sleeve is disposed within the
insulating layer. The conductive sleeve surrounds the conductor.
The method further includes measuring a second impedance of the at
least one conductive sleeve at a second time. Additionally, the
method includes sending a signal if the second impedance is within
a predetermined range.
[0010] Several options for the method follow. In one option, the
method includes comparing the first impedance with the second
impedance. The method includes coupling the implantable lead
assembly to a pulse generator, in another option. The pulse
generator is in electrical communication with the conductive sleeve
in one option. In another option, measuring the first impedance and
the second impedance are performed by a pulse generator. In still
another option, the method further includes coupling a monitoring
unit to a terminal disposed on the lead body. The monitoring unit
is in electrical communication with the conductive sleeve in one
option. In a further option, measuring the first impedance and
measuring the second impedance are performed by the monitoring
unit.
[0011] The implantable lead assembly allows for detection of
breaches in lead insulation before malfunction of a lead conductor.
With the above described design, exposure of the conductive sleeve
to a surrounding environment through wear of the lead insulation
measurably changes the impedance of the conductive sleeve. This
measurable change of impedance signals wear of the lead insulation
before the lead conductor itself is exposed to the surrounding
environment. In other words, the implantable lead assembly detects
wear of lead insulation before the lead conductor can malfunction
or fail thus preventing a potential tragedy for a patient.
Notification of lead insulation wear allows the implantable lead
assembly to be safely replaced before failure of the lead.
Furthermore, impedance measurements can be safely and easily
performed by pulse generators (e.g., pacemakers), which can also
alert a patient that the implantable lead assembly needs
replacement. Additionally, a pulse generator can measure impedance
at a variety of preprogrammed times, intermittently, or
continuously, and also store the readings for later use by a
physician. Further still, a separate monitoring unit can be
attached to the implantable lead assembly to take impedance
measurements as well.
[0012] These and other embodiments, aspects, advantages, and
features of the present invention will be set forth in part in the
description which follows, and in part will become apparent to
those skilled in the art by reference to the following description
of the invention and referenced drawings or by practice of the
invention. The aspects, advantages, and features of the invention
are realized and attained by means of the instrumentalities,
procedures, and combinations particularly pointed out in the
appended claims and their equivalents.
[0013] While multiple embodiments are disclosed, still other
embodiments of the present invention will become apparent to those
skilled in the art from the following detailed description, which
shows and describes illustrative embodiments of the invention.
Accordingly, the drawings and detailed description are to be
regarded as illustrative in nature and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram of a system with a lead for use
with a heart and constructed in accordance with one embodiment.
[0015] FIG. 2 is a side view of an implantable lead assembly
constructed in accordance with one embodiment.
[0016] FIG. 3 is an enlarged side view of an implantable lead
assembly constructed in accordance with one embodiment.
[0017] FIG. 4 is a perspective view of an implantable lead assembly
constructed in accordance with another embodiment.
[0018] FIG. 5 is a cross-sectional view of an implantable lead
assembly constructed in accordance with one embodiment.
[0019] FIG. 6 is a cross-sectional view of an implantable lead
assembly constructed in accordance with another embodiment.
[0020] FIG. 7 is a cross-sectional view of an implantable lead
assembly constructed in accordance with yet another embodiment.
[0021] FIG. 8 is a cross-sectional view of an implantable lead
assembly constructed in accordance with still yet another
embodiment.
[0022] FIG. 9 is a side view of an implantable lead assembly
constructed in accordance with one embodiment with a portion of a
pulse generator.
[0023] FIG. 10 is a perspective view of an implantable lead
assembly constructed in accordance with yet another embodiment.
[0024] FIG. 11 is a perspective view of an implantable lead
assembly constructed in accordance with yet another embodiment
along with a monitoring unit.
[0025] FIG. 12 is a perspective view of an implantable lead
assembly constructed in accordance with another embodiment showing
wear.
[0026] FIG. 13 is a block diagram illustrating one embodiment of a
method of use for the implantable lead assembly.
[0027] While the invention is amenable to various modifications and
alternative forms, specific embodiments have been shown by way of
example in the drawings and are described in detail below. The
intention, however, is not to limit the invention to the particular
embodiments described. On the contrary, the invention is intended
to cover all modifications, equivalents, and alternatives falling
within the scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION
[0028] 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 the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized and that structural changes may be made without
departing from the scope of the present invention. Therefore, the
following detailed description is not to be taken in a limiting
sense, and the scope of the subject matter of this application is
defined by the appended claims and their equivalents.
[0029] FIG. 1 is a block diagram of a system 100 for delivering
and/or receiving electrical pulses or signals to stimulate and/or
sense the heart. The system for delivering pulses 100 includes a
pulse generator 105 and an implantable lead assembly 110. The pulse
generator 105 includes a source of power as well as an electronic
circuitry portion. The pulse generator 105 is a battery-powered
device which generates a series of timed electrical discharges or
pulses used to initiate depolarization of excitable cardiac tissue.
The pulse generator 105 is generally implanted into a subcutaneous
pocket made in the wall of the chest. Alternatively, the pulse
generator 105 is placed in a subcutaneous pocket made in the
abdomen, or in other locations.
[0030] The implantable lead assembly 110, shown in more detail in
FIG. 2, has a lead body 111 extending from a proximal end 112,
where it is coupled with the pulse generator 105, and extending
through an intermediate portion to a distal end 114, which is
coupled with a portion of a heart 115, in the implanted condition
(one example is shown in FIG. 1). In another example, the lead body
distal end 114 is disposed adjacent to the heart 115, in the
implanted condition. The distal end 114 of the implantable lead
assembly 110 includes at least one electrode 116 which electrically
couples the implantable lead assembly 110 with the heart 115. In
one option, the electrode 116 is coupled with the lead body 111.
The electrode 116, in one option, is either a unipolar or
multipolar type electrode. In another option, multiple electrodes
are provided. At least one electrical conductor 118, as shown in
phantom lines in FIG. 3, is disposed within the implantable lead
assembly 110 and electrically couples the electrode 116 with the
proximal end 112 of the implantable lead assembly 110. The
electrical conductor 118 carries electrical current and pulses
between the pulse generator 105 and the electrode 116 located in
the distal end 114 of the implantable lead assembly 110. In yet
another option, multiple electrical conductors 118 are disposed
within the implantable lead assembly 110, as shown in FIG. 8.
[0031] The lead body 111, in one option, includes an insulating
layer 120 formed of a biocompatible polymer suitable for
implementation within the human body. The insulating layer 120 is
made from a silicone rubber type polymer, in one option. In another
option, the insulating layer 120 includes polyurethane. In yet
another option, the insulating layer 120 includes
polytetrafluoro-ethylene (PTFE). In still another option, the
insulating layer 120 includes ethylene-tetrafluoroethylene (ETFE),
or polysiloxane urethane. The insulating layer 120 surrounds the
electrical conductor 118. The implantable lead assembly 110 travels
from the pulse generator 105 and into a major vein. The distal end
114 of the implantable lead assembly 110, in one option, is placed
inside or adjacent to the heart 115. In another option, the distal
end 114 of the implantable lead assembly 110 is placed, or
"floats," inside a vein or within a chamber of the heart 115.
[0032] As shown in FIGS. 3 and 4 in phantom lines, a conductive
sleeve 122 is disposed within the insulating layer 120, in one
option. The conductor 118 is disposed within the conductive sleeve
122, so the conductive sleeve 122 surrounds the conductor 118. In
other words, the conductive sleeve 122 defines a perimeter around
the conductor 118. In one option, the conductive sleeve 122 is
comprised of discrete conductive elements and defines a broken
perimeter around the conductor 118. Optionally, the conductive
sleeve 122 is aligned with a longitudinal axis defined by the
conductor 118. The conductive sleeve 122 is electrically isolated
from the electrode 116 and conductor 118 by the insulating layer
120. In another option, the insulating layer 120 also surrounds the
conductive sleeve 122, thereby isolating the conductive sleeve from
a surrounding environment (for example bodily fluids). When
surrounded by the insulating layer 120, the conductive sleeve 122
has a first impedance value in a non-breached first condition. In
one option, the conductive sleeve 122 is in an open circuit when
isolated from the surrounding environment and has an infinite first
impedance value. In another option, shown in FIG. 4, the insulating
layer 120 (FIG. 3) includes a first insulating portion 124
interposed between the conductor 118 and the conductive sleeve 122,
and a second insulating portion 126 that surrounds the conductive
sleeve 122. In still another option, the conductive sleeve 122 is
exposed to a surrounding environment in a breached second condition
as described below. Optionally, the conductive sleeve 122 extends
from the proximal end of the implantable lead body 111 (FIG. 3)
along substantially one third of the lead body length, where a
large amount of wear is likely to occur.
[0033] In one option, the conductive sleeve 122 is a thin coating
of conductive material applied to an insulating layer so as to
surround the insulating layer and the conductor 118 disposed
therein. The coating of conductive material, in one option, is
metallic and is applied by sputtering or vapor deposition. In
another option, the conductive sleeve 122 is a conductive polymer.
A conductive polymer is applied to the implantable lead assembly
110 (FIG. 3) by dipping the implantable lead assembly in a
conductive polymer monomer solution, in one option. Optionally, the
polymer is applied by plasma polymerization of an electrically
conductive polymer on to the implantable lead assembly 110. In
another option, the polymer includes conductive additives, for
example, graphite, silver or platinum. In yet another option, the
polymer itself is intrinsically conductive. In still another
option, the conductive sleeve 122 includes a shape memory alloy
formed into a tubular shape by extrusion, or by rolling or coiling
of thin alloy films into a tube. In a further option, the
implantable lead assembly 110 is created with alternating layers of
polymer, where metallic fillers are added to the polymer at various
layers to create the conductive sleeve 122.
[0034] As shown in FIG. 5, in one option, the conductive sleeve 122
is disposed substantially adjacent to the outer surface of the lead
body 111. The conductive sleeve 122 surrounds the first insulating
portion 124 and conductor 118 so as to define a perimeter around
the conductor, as described above. The first insulating layer
includes silicone, in one option. The conductive sleeve 122 is
interposed between the first insulating portion 124 and the second
insulating portion 126, thereby electrically isolating the
conductive sleeve 122 from the electrode 116 (FIG. 4) and conductor
118. The second insulating portion 126 includes polyurethane, in
another option. In yet another option, the conductor 118 is coated
with a thin insulating layer of ETFE, which is interposed between
the conductor 118 and the first insulating portion 124.
[0035] In another option, as shown in FIGS. 6 and 7, multiple
conductive sleeves are disposed within the implantable lead
assembly 110. As shown in FIG. 6, the insulating layer includes a
first insulating portion 124, second insulating portion 126 and
third insulating portion 128. The first insulating portion 124
surrounds the electrical conductor 118. The second insulating
portion 126 is disposed around and surrounds the first insulating
portion 124. A first conductive sleeve 130 is interposed between
the first insulating portion 124 and second insulating portion 126.
The first conductive sleeve 130 surrounds the conductor 118 so as
to substantially define a perimeter. The third insulating portion
128 surrounds the second insulating portion 126, and a second
conductive sleeve 132 is interposed between the second insulating
portion and the third insulating portion. Like the first conductive
sleeve 130, the second conductive sleeve 132 is electrically
isolated from the electrode 116 and conductor 118. In one option,
the second conductive sleeve 132 surrounds the conductor 118 and
first conductive sleeve 130, substantially defining a perimeter
around both structures. In another option, the first insulating
portion 124, second insulating portion 126 and third insulating
portion 128 include different insulating materials as described
above with respect to insulating layer 120. In still another
option, the first insulating portion 124, second insulating portion
126, and third insulating portion 128 include substantially similar
insulating materials.
[0036] Referring specifically to FIG. 7, in one option, the first
conductive sleeve 130 surrounds the conductor 118 and is adjacent
thereto. A thin insulating layer of ETFE, PTFE, or other insulating
material is interposed between the conductor 118 and first
conductive sleeve 130, thus isolating the conductor from electrical
communication with the first conductive sleeve, in another option.
Because the first conductive sleeve 130 surrounds the conductor
118, the first conductive sleeve substantially defines a perimeter
around the conductor, as described above. A first insulating
portion 124 surrounds the first conductive sleeve 130. A second
insulating portion 126 surrounds the first insulating portion 124.
The second conductive sleeve 132 is interposed between the first
insulating portion 124 and the second insulating portion 126. The
second conductive sleeve 132 surrounds the conductor 118 and first
conductive sleeve 130 so as to substantially define a perimeter
around the conductor and first conductive sleeve. In one option,
the first insulating portion 124 and second insulating portion 126
include different insulating materials, as was described above,
with respect to insulating layer 120. In still another option, the
first insulating portion 124 and second insulating portion 126
include substantially similar insulating materials.
[0037] Referring now to FIG. 8, implantable lead assembly 110 is
shown with multiple conductors 118 and corresponding multiple
conductive sleeves 130, 132, 134 disposed therein. The first
conductive sleeve 130 surrounds a conductor 118, in one option. The
conductor 118 is coated with a thin insulating layer of ETFE, PTFE
or other insulating material to electrically isolate the conductor
118 from the first conductive sleeve 130. In another option, the
second conductive sleeve 132 surrounds another conductor 118. As
discussed above, the conductor 118 is coated is thereby
electrically isolated from the conductor 118. A third conductive
sleeve 134 surrounds an additional conductor 118, in yet another
option. The conductor 118 is also coated with a thin insulating
layer of ETFE or PTFE to electrically isolate the third conductive
sleeve 134 from the conductor 118. In one option, the conductors
118 and conductive sleeves 130, 132, 134 are disposed within
insulating layer 120 of implantable lead assembly 110. As described
above, in one option, each conductive sleeve 130, 132, 134 is
disposed adjacently to a conductor 118. In another option however,
each conductive sleeve 130, 132, 134 is offset from the respective
conductor 118. In this option, the conductive sleeves 130, 132, 134
are disposed within the insulating layer 120, but still otherwise
surround the respective conductors 118. Optionally, one or two of
the conductive sleeves 130, 132, 134 is offset from the respective
conductor 118, while the remaining conductive sleeves are adjacent
the respective conductor. In still another option, one or more than
one of conductive sleeves 130, 132 and/or 134 surrounds multiple
conductors 118. In a further option, the conductors 118 extend
parallel to the longitudinal axis of the implantable lead assembly
110 as do the conductive sleeves 130, 132, 134. As the conductive
sleeves 130, 132, 134 surround the respective conductors 118, each
conductive sleeve substantially defines a perimeter around the
respective conductor, as described in the above embodiments.
[0038] As shown in FIGS. 1 and 9, in one option, the conductive
sleeve 122 is coupled to the pulse generator 105 when the proximal
end 112 of the implantable lead assembly 110 is coupled with the
pulse generator 105. In another option, the pulse generator 105 is
operable to measure the impedance value of the conductive sleeve
122. In other words, the conductive sleeve 122 is in electrical
communication with the pulse generator 105, permitting impedance
measurement by the pulse generator.
[0039] Referring now to FIGS. 10 and 11, in one option, the
implantable lead assembly 110 includes a terminal 136 disposed on
the outer surface of the lead body 111. In another option, the
terminal 136 extends from the outer surface of the lead body 111,
through insulating layer 120, to the conductive sleeve 122. The
terminal 136 is in electrical communication with the conductive
sleeve 122, in yet another option. In a further option, when needed
(as described below), a monitoring unit 138 (FIG. 11) is coupled to
the implantable lead assembly 110, specifically the terminal 136,
and is in electrical communication with the terminal 136. The
monitoring unit 138 is also in electrical communication with the
conductive sleeve 122 through the terminal 136. In still another
option, the monitoring unit 138 is operable to measure the
impedance value of the conductive sleeve 122. Optionally, the
monitoring unit 138 is implanted with the pulse generator 105 (FIG.
1) and implantable lead assembly 110. In another option, the
monitoring unit 138 is disposed outside the body, and a cable
couples the monitoring unit to the terminal 136 of implantable lead
assembly 110. In one option, the monitoring unit 138 and pulse
generator 105 both measure impedance of the conductive sleeve 122.
In another option, only the monitoring unit 138 measures the
impedance of the conductive sleeve 122. In yet another option, the
monitoring unit 138 measures and records the impedance of
conductive sleeve 122.
[0040] As shown in FIG. 1, in operation, the implantable lead
assembly 110 is coupled to the pulse generator 105. The electrode
116 of the implantable lead assembly 110 is electrically coupled
with the heart 115. As described above, the pulse generator 105 is
operable to measure the impedance of the conductive sleeve 122, in
one option. In another option, the pulse generator 105 is operable
to measure the impedance of the conductive sleeves 130, 132, 134
(FIGS. 5, 6 and 7). When desired, the impedance of the conductive
sleeve 122 is measured at a first time by the pulse generator 105.
The conductive sleeve 122 impedance is measured at a later
measurement is compared against the first impedance measurement by
the pulse generator. A change of impedance to within a
predetermined range is indicative of wear of the insulating layer
120 of the implantable lead assembly 110. In other words, if wear
has ablated the insulating layer 120 and exposed the conductive
sleeve 122 to the surrounding environment, the impedance of the
conductive sleeve 122 will change from the first impedance value to
the second impedance value within a predetermined range. As shown
in FIG. 12, wear of the insulating layer 120 creates a breach or
opening 140 in the implantable lead assembly 110. As shown in
phantom lines in FIG. 12, after sufficient wear, the opening 140
extends from the outer surface of the implantable lead assembly 110
to the conductive sleeve 122. In this second breached condition,
the surrounding environment contacts the exposed conductive sleeve
122 and thereby changes the impedance value of the conductive
sleeve. A closed circuit is formed between the pulse generator 105,
conductive sleeve 122, and the surrounding environment (for example
body fluids) which contacts the pulse generator. In one option, the
predetermined range of impedance values is less than or equal to
about 2000 ohms. If the second impedance value is within the
predetermined range, a signal is sent that is capable of alerting a
patient or physician, for example, that the implantable lead
assembly 110 needs to be replaced. In another option, the second
impedance value is compared against the first impedance value and a
signal sent if the second impedance value is substantially lower
(for example, less than or equal to 2000 ohms) than the first
impedance value (for example, an infinite impedance). In still
another option, the impedance measurements are stored within the
pulse generator 105 for future access by a physician. Optionally,
the impedance measurements are taken at preprogrammed times. The
pulse generator 105 makes impedance measurements intermittently, in
yet another option. Alternatively, the pulse generator 105 measures
impedance continuously. In a similar manner, impedance measurements
and comparisons therebetween as herein described may be taken with
conductive sleeves 130, 132, 134, described in the above
embodiments.
[0041] Referring again to FIGS. 10 and 11, in operation the
implantable lead assembly 110 is coupled with the monitoring unit
138, which is operable to make impedance measurements. The
monitoring unit 138 is coupled to the terminal 136 and also in
electrical communication thereto, in one option. In another option,
the terminal 136 is coupled to the conductive sleeve 122 and in
electrical communication thereto. The monitoring unit 138 is
thereby in electrical communication with the conductive sleeve 122
through the terminal 136. In still another option, the monitoring
unit 138 is operable to measure the impedance of the conductive
sleeves 130, 132, 134 (FIGS. 5, 6 and 7). When desired, the
impedance of the conductive sleeve 122 is measured at a first time
by the monitoring unit 138. The conductive sleeve 122 impedance is
measured at a later second time by the monitoring unit 138. As
described above, a change of impedance to within a predetermined
range is indicative of wear of the insulating layer 120 of the
implantable lead assembly 110 and exposure of the conductive sleeve
122 to the surrounding environment. In one option, the
predetermined range of impedance values is less than or equal to
about 2000 ohms. If the second impedance measurement is within the
predetermined range, a signal is sent that is capable of alerting a
patient or physician that the implantable lead assembly 110 needs
to be replaced. In another option, the second impedance value is
compared against the first impedance value and a signal sent if the
second impedance value is substantially lower (for example, less
than or equal to 2000 ohms) than the first impedance value (for
example, an infinite impedance). Optionally, the impedance
measurements are stored within the monitoring unit 138 for future
access by a physician. In another option, the impedance
measurements are taken at preprogrammed times. In yet another
option, the monitoring unit 138 makes impedance measurements
intermittently. Alternatively, the monitoring unit 138 measures
impedance continuously. In a similar manner, impedance measurements
and comparisons therebetween as herein described may be taken with
conductive sleeves 130, 132, 134.
[0042] In another embodiment, a method 200 is shown in FIG. 13,
which comprises measuring a first impedance of a conductive sleeve
at a first time in an implantable lead assembly, as principally
shown in block 202. The implantable lead assembly includes a lead
body having a conductor disposed therein, an electrode is coupled
to the lead body. The electrode is in electrical communication with
the conductor. An insulating layer surrounds the conductor. The
conductive sleeve is disposed within the insulating layer and also
surrounds the conductor. The method further includes measuring a
second impedance of the conductive sleeve at a second time, as
shown in block 204. As shown in block 206, the method also includes
sending a signal if the second impedance is within a predetermined
range. In one option, the predetermined range of impedance values
is less than or equal to about 2000 ohms.
[0043] Several options for the method follow. For example, in one
option, the method further includes comparing the first impedance
with the second impedance. In another option, the method further
includes wearing away the insulating layer during an intermediate
period between the first time and the second time. In still another
option, the method includes coupling the implantable lead assembly
to a pulse generator, where the pulse generator is in electrical
communication with the conductive sleeve. In yet another option,
the method further includes measuring the first impedance and
second impedance with the pulse generator. The method further
includes storing the impedance measurements within the pulse
generator, in another option. Additionally, in another option, the
method further includes coupling a monitoring unit to a terminal
disposed on the lead body, where the terminal is in electrical
communication with the conductive sleeve. Optionally, the method
includes measuring the first impedance and second impedance of the
conductive sleeve with the monitoring unit. In another option,
measuring the first impedance and second impedance of the
conductive sleeve includes measuring impedance at preprogrammed
times. In yet another option, the method includes intermittently
measuring impedance of the conductive sleeve. In still another
option, the method conversely includes continuously measuring
impedance.
[0044] The above described design for an implantable lead assembly
allows for detection of breaches in lead insulating layers before
malfunction of a lead.
[0045] Exposure of the conductive sleeve to a surrounding
environment through wear of the lead insulation measurably changes
the impedance of the conductive sleeve. This change of impedance,
when within a predetermined range, signals wear of the lead
insulation before the lead conductor itself is exposed to the
surrounding environment. In other words, the implantable lead
assembly detects wear of lead insulation before the lead conductor
can malfunction or fail thus preventing a potential tragedy for a
patient. Notification of lead insulation wear allows the
implantable lead assembly to be safely replaced before failure of
the lead.
[0046] Furthermore, impedance measurements are safely and easily
performed by pulse generators (e.g. pacemakers), which also alert a
patient and physician that the implantable lead assembly needs
replacement. Additionally, a pulse generator can measure impedance
at a variety of preprogrammed times or intermittently, and then
also store the readings for later use by a physician. Further
still, a separate monitoring unit may be attached to the
implantable lead assembly to take impedance measurements as well.
The implantable lead assembly and the methods described above may
also be used in other implantable medical lead applications beyond
cardiac pacemakers, for example neurological recording and
stimulation.
[0047] It is to be understood that the above description is
intended to be illustrative, and not restrictive. Many other
embodiments will be apparent to those of skill in the art upon
reading and understanding the above description. It should be noted
that embodiments discussed in different portions of the description
or referred to in different drawings can be combined to form
additional embodiments of the present invention. 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.
[0048] Various modifications and additions can be made to the
exemplary embodiments discussed without departing from the scope of
the present invention. For example, while the embodiments described
above refer to particular features, the scope of this invention
also includes embodiments having different combinations of features
and embodiments that do not include all of the described features.
Accordingly, the scope of the present invention is intended to
embrace all such alternatives, modifications, and variations as
fall within the scope of the claims, together with all equivalents
thereof.
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