U.S. patent number RE46,494 [Application Number 14/447,747] was granted by the patent office on 2017-08-01 for load-carrying body for reducing torsional and tensile loading on electronic components in an implantable medical electrical lead.
This patent grant is currently assigned to Greatbatch Ltd.. The grantee listed for this patent is Greatbatch Ltd.. Invention is credited to Ryan T. Bauer, Warren S. Dabney, Robert A. Stevenson.
United States Patent |
RE46,494 |
Bauer , et al. |
August 1, 2017 |
Load-carrying body for reducing torsional and tensile loading on
electronic components in an implantable medical electrical lead
Abstract
A load-carrying body for reducing torsional and tensile loading
on electrical components in an implantable medical electrical lead
includes an electronic component disposed in-line with the
implantable medical electrical lead, and a casing for the
electronic component. The electronic component has a proximal end
conductively coupled to a lead conductor and a distal end
conductively coupled to a lead electrode. The casing is
mechanically coupled to the lead so as to isolate the electrical
component from torque or tensile loads applied to the lead, the
lead electrode, or both.
Inventors: |
Bauer; Ryan T. (Plymouth,
MN), Dabney; Warren S. (Lake Oswego, OR), Stevenson;
Robert A. (Canyon Country, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Greatbatch Ltd. |
Clarence |
NY |
US |
|
|
Assignee: |
Greatbatch Ltd. (Clarence,
NY)
|
Family
ID: |
59382732 |
Appl.
No.: |
14/447,747 |
Filed: |
July 31, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12891292 |
May 7, 2013 |
8437865 |
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12873862 |
Jul 17, 2012 |
8224440 |
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12607234 |
May 8, 2012 |
8175700 |
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11558349 |
May 17, 2011 |
7945322 |
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11943854 |
Dec 14, 2010 |
7853325 |
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61256658 |
Oct 30, 2009 |
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61303109 |
Feb 10, 2010 |
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61243643 |
Sep 18, 2009 |
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61314676 |
Mar 17, 2010 |
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61245720 |
Sep 25, 2009 |
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Reissue of: |
12914048 |
Oct 28, 2010 |
8244373 |
Aug 14, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61N
1/06 (20130101); A61N 1/086 (20170801); H01G
4/35 (20130101); H01G 4/40 (20130101); H01F
27/36 (20130101); A61N 1/05 (20130101); A61N
1/056 (20130101); A61N 1/04 (20130101); H01F
17/00 (20130101); A61N 1/057 (20130101); H03H
2007/013 (20130101); A61N 1/0551 (20130101); H03H
1/0007 (20130101); H01F 2017/065 (20130101); G01R
33/285 (20130101); H03H 7/1766 (20130101); A61N
1/3718 (20130101); H03H 7/0115 (20130101); G01R
33/288 (20130101); H03H 2001/0042 (20130101) |
Current International
Class: |
A61N
1/00 (20060101); A61N 1/04 (20060101); A61N
1/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dawson; Glenn K
Attorney, Agent or Firm: Scalise; Michael F.
Parent Case Text
.Iadd.CROSS-REFERENCE TO RELATED APPLICATIONS .Iaddend.
.Iadd.The present application is a reissue application of
application Ser. No. 12/914,048, filed on Oct. 28, 2010, now U.S.
Pat. No. 8,244,373, which is a continuation-in-part of application
Ser. No. 12/891,292, filed on Sep. 27, 2010, now U.S. Pat. No.
8,437,865, which is a continuation-in-part of application Ser. No.
12/873,862, filed on Sep. 1, 2010, now U.S. Pat. No. 8,224,440,
which is a continuation-in-part of application Ser. No. 12/607,234,
filed on Oct. 28, 2009, now U.S. Pat. No. 8,175,700, which is a
continuation-in-part of application Ser. No. 11/558,349, filed on
Nov. 9, 2006, now U.S. Pat. No. 7,945,322, said application Ser.
No. 12/873,862 is a continuation-in-in-part of application Ser. No.
11/943,854, filed on Nov. 21, 2007, now U.S. Pat. No.
7,853,325..Iaddend.
.Iadd.The present application claims priority from provisional
application Ser. No. 61/256,658, filed on Oct. 30, 2009,
provisional application Ser. No. 61/303,109, filed on Feb. 10,
2010, provisional application Ser. No. 61/243,643, filed on Sep.
18, 2009, provisional application Ser. No. 61/314,676, filed on
Mar. 17, 2010, and provisional application Ser. No. 61/245,720,
filed on Sep. 25, 2009..Iaddend.
Claims
What is claimed is:
1. .[.A load-carrying body for reducing torsional and tensile
loading on electronic components in an.]. .Iadd.An
.Iaddend.implantable medical electrical lead, comprising: .Iadd.a)
a lead conductor extending from a proximal lead conductor end to a
distal lead conductor end, wherein the proximal lead conductor end
is connectable to an implantable pulse generator; b) an electrode
configured for contact with body tissue; c) .Iaddend.an electronic
component .[.disposed in-line with an implantable medical
electrical lead, the electronic component.]. having a proximal
.Iadd.electronic component .Iaddend.end conductively .Iadd.and
physically .Iaddend.coupled to .[.a.]. .Iadd.the distal
.Iaddend.lead conductor .Iadd.end, .Iaddend.and a distal
.Iadd.electronic component .Iaddend.end conductively .Iadd.and
physically .Iaddend.coupled to .[.a lead.]. .Iadd.the
.Iaddend.electrode; and .Iadd.d) .Iaddend.a .[.casing for.].
.Iadd.rigid, torque bearing member supporting .Iaddend.the
electronic component, .Iadd.wherein a proximal end of .Iaddend.the
.[.casing being.]. .Iadd. torque bearing member is
.Iaddend.mechanically.Iadd., but not conductively .Iaddend.coupled
to the .Iadd.distal .Iaddend.lead .Iadd.conductor end, and a distal
end of the torque bearing member is mechanically, but not
conductively coupled to the electrode, and .Iaddend. .[.so as to
isolate.]. .Iadd.e) wherein the torque bearing member isolates
.Iaddend.the electronic component from torque or tensile loads
applied to the lead .Iadd.conductor.Iaddend., the .[.lead.].
electrode, or both.
2. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 1, .[.including.]. .Iadd.wherein
.Iaddend.a proximal torque coupler .[.disposed.]. .Iadd.is
mechanically and conductively coupled .Iaddend.between .Iadd.and to
.Iaddend.the lead .Iadd.conductor .Iaddend.and the .[.casing.].
.Iadd.electronic component.Iaddend..
3. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 2, wherein .[.the casing includes
a proximal hermetic.]. .Iadd.a .Iaddend.seal .[.isolated by.].
.Iadd.conductively isolates .Iaddend.the proximal torque coupler
from .Iadd.the .Iaddend.torque .[.or tensile loads applied to the
lead.]. .Iadd.bearing member.Iaddend..
4. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 2, wherein the proximal torque
coupler includes a proximal pin mechanically .[.attached to the
lead conductor.]. and conductively coupled to the lead conductor
and the electronic component.
5. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 4, .[.including.]. .Iadd.wherein
.Iaddend.a drive shaft .Iadd.is .Iaddend.disposed between the
proximal pin and the lead conductor.
6. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 1, .[.including.]. .Iadd.wherein
.Iaddend.a distal torque coupler .[.disposed.]. .Iadd.mechanically
and conductively couples .Iaddend.between .Iadd.and to .Iaddend.the
.[.lead.]. electrode and the .[.casing.]. .Iadd.electronic
component.Iaddend..
7. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 6, wherein .[.the casing includes
a distal hermetic.]. .Iadd.a .Iaddend.seal .[.isolated by.].
.Iadd.conductively isolates .Iaddend.the distal torque coupler from
.Iadd.the .Iaddend.torque .[.or tensile loads applied to the lead
electrode.]. .Iadd.bearing member.Iaddend..
8. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of .[.any of claims.]. .Iadd.claim
.Iaddend.1.[.-6.]., wherein the electronic component
.[.comprises.]. .Iadd.is selected from the group consisting of
.Iaddend.a bandstop filter, an electronic switch, a MEMs switch, a
diode array, a multiplexer, a pin diode, a capacitor, a resistor,
an inductor, an electronic sensor, .[.or any combination.].
.Iadd.and combinations .Iaddend.thereof.
9. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 6, wherein the distal torque
coupler includes a distal pin mechanically .[.attached to the lead
electrode.]. and conductively coupled to the .[.lead.]. electrode
and the electronic component.
10. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of .[.any of claims.]. .Iadd.claim
.Iaddend.1.[.-6.]., .[.including.]. .Iadd.wherein .Iaddend.a collar
.Iadd.is .Iaddend.disposed at a distal end of the implantable
medical electrical lead, .Iadd.and .Iaddend.wherein the
.[.casing.]. .Iadd.torque bearing member .Iaddend.is disposed
within the collar.Iadd., .Iaddend.and .Iadd.wherein the torque
bearing member .Iaddend.is translatable along a longitudinal axis
of the collar.
11. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 10, .[.including.]. .Iadd.wherein
.Iaddend.a seal .Iadd.is .Iaddend.disposed between the .[.casing.].
.Iadd.torque bearing member .Iaddend.and the collar .[.for
preventing.]..Iadd., the seal being configured to prevent
.Iaddend.passage of ionic fluid into the lead through .[.its.].
.Iadd.a .Iaddend.distal end .Iadd.of the collar.Iaddend..
12. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 11, wherein the seal
.Iadd.disposed between the torque bearing member and the collar
.Iaddend.is disposed at a distal end, .[.at.]. a proximal end, or
along a middle of the .[.casing.]. .Iadd.torque bearing
member.Iaddend..
13. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim .[.12.]. .Iadd.6.Iaddend.,
.[.including.]. .Iadd.wherein .Iaddend.a collar .Iadd.is
.Iaddend.disposed at a distal end of the implantable medical
electrical lead.Iadd., and .Iaddend.wherein the .Iadd.distal
.Iaddend.torque coupler is disposed within the collar.Iadd.,
.Iaddend.and .Iadd.wherein the distal torque coupler .Iaddend.is
translatable along a longitudinal axis of the collar.
14. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 13, .[.including.]. .Iadd.wherein
.Iaddend.a seal .Iadd.is .Iaddend.disposed between the
.Iadd.proximal .Iaddend.torque coupler and the collar .[.for
preventing.]..Iadd., the seal being configured to prevent
.Iaddend.passage of .[.bionic.]. .Iadd.ionic .Iaddend.fluid into
the lead through .[.its.]. .Iadd.a .Iaddend.distal end .Iadd.of the
collar.Iaddend..
15. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 11, wherein the seal
.Iadd.disposed between the torque bearing member and the collar
.Iaddend.is fixed relative to the .[.casing.]. .Iadd.torque bearing
member.Iaddend..
16. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 11, wherein the seal
.Iadd.disposed between the torque bearing member and the collar
.Iaddend.is fixed relative to the collar.
17. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 10, .[.including.]. .Iadd.wherein
.Iaddend.an insulative conformal coating .Iadd.is .Iaddend.disposed
about at least a portion of the .[.casing.]. .Iadd.torque bearing
member.Iaddend..
18. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 17, wherein the conformal coating
comprises a dielectric ceramic coating.
19. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 17, wherein the conformal coating
is .Iadd.characterized as having been .Iaddend.applied by .Iadd.one
of the group consisting of .Iaddend.sputtering, chemical vapor
deposition, physical vapor deposition, dipping in .[.or.]. .Iadd.a
chemical solution and .Iaddend.applying a chemical solution.
20. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 17, wherein the conformal coating
comprises alumina or parylene.
21. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim .[.10.]. .Iadd.1.Iaddend.,
wherein the .[.casing.]. .Iadd. torque bearing member
.Iaddend.comprises a dielectric ceramic coating.
22. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim .[.10.]. .Iadd.1.Iaddend.,
wherein the .[.casing.]. .Iadd.torque bearing member
.Iaddend.comprises alumina.
23. The .[.load-carrying body.]. .Iadd.implantable medical
electrical lead .Iaddend.of claim 1, .[.including.]. .Iadd.wherein
.Iaddend.a unitary torque coupler .Iadd.is .Iaddend.disposed over
the .[.casing.]. .Iadd.torque bearing member.Iaddend..
Description
FIELD OF THE INVENTION
The present invention generally relates to implantable medical
electrical leads. More particularly, the present invention relates
to an implantable medical electrical active fixation lead
configured to reduce or eliminate torsional and tensile loading on
feed-thru pins, insulators, and brazed joints.
BACKGROUND OF THE INVENTION
A wide assortment of implantable medical devices are presently
known and in commercial use. Such devices include cardiac
pacemakers, cardiac defibrillators, cardioverters,
neurostimulators, and other devices for delivering and/or receiving
electrical signals to/from a portion of the body. Sensing and/or
stimulating leads extend from the associated implantable medical
device to a distal tip electrode or electrodes in contact with body
tissue. These electrodes should be securely fixed to the tissue to
facilitate electrical stimulation or sensing by the implantable
medical device.
In order to work reliably, leads need to be stably located adjacent
to the tissue to be stimulated or monitored. One common mechanism
for accomplishing this has been the use of a fixation helix, which
exits the distal end of the lead and is screwed directly into the
body tissue. The helix itself may serve as an electrode or it may
serve as an anchoring mechanism to fix the position of an electrode
mounted to or forming a portion of the lead itself. This is known
in the art as active fixation. The fixation helix electrode and
lead must be resistant, during and after implantation, to damage
both through torsion and tension. The reason they must be resistant
to torsion is that during the initial implant, the physician
applies a torque tool to the proximal end, which he then twists in
order to drive the helix screw into body tissue. If the physician
does not achieve a desired capture level or desired pacing site,
the physician may unscrew the helix and then pull on the lead to
re-position it at a different site. This pull force creates a
tension on the lead and its associated distal tip electrode
components. Another reason that tensile force may be applied to the
lead is during lead extraction surgeries. Generally, lead
extraction surgery is done to replace a damaged lead or one that
has poor insulation resistance.
One problem associated with implanted leads is that they act as an
antenna and tend to pick up stray electromagnetic signals from the
surrounding environment. This is particularly problematic in an MRI
environment where the currents which are imposed on the leads can
cause the leads to heat to the point where tissue damage is likely.
Moreover, the currents developed in the leads during an MRI
procedure can damage the sensitive electronics within the
implantable medical device. Bandstop filters, such as those
described in U.S. Pat. No. 7,363,090 and U.S. 2007/0112398 A1,
which are herein incorporated by reference, reduce or eliminate the
transmission of damaging frequencies along the leads while allowing
the desired biological frequencies and pacing pulses to pass
efficiently through. However, when implanting the medical
electrical lead, stress can be applied directly to the bandstop
filter or electrical components either through torsion or tensile
loads. Such loads are created because the electrical components are
mechanically connected to the lead, and may damage the electrical
components during the implanting procedure. This is obviously a
negative occurrence which should be avoided.
Accordingly, there is a need for an implantable medical lead having
an electronic component such as a low pass filter or bandstop
filter, wherein the torsional and tensile loads applied to the
electronic component during implantation are reduced or even
eliminated. The present invention fulfills these needs and provides
other benefits.
SUMMARY OF THE INVENTION
The present invention resides in a load-carrying body for reducing
torsional and tensile loading on electronic components in an
implantable medical electrical lead. An electronic component is
disposed in-line with the implantable medical lead, and has a
proximal end conductively coupled to a lead conductor and a distal
end conductively coupled to a lead electrode. A casing for the
electronic component is mechanically coupled to the lead so as to
isolate the electronic component from torque or tensile loads
applied to the lead, the lead electrode or both.
In order to isolate the electronic component from torque or tensile
loads applied to the lead, the lead electrode or both, a proximal
torque coupler is disposed between the lead and the casing, and a
distal torque coupler is disposed between the lead electrode and
the casing. The casing may include a proximal hermetic seal
isolated by the proximal torque coupler from torque or tensile
loads applied to the lead. The casing may also include a distal
hermetic seal isolated by the distal torque coupler from torque or
tensile loads applied to the lead electrode.
The electronic component may comprise a bandstop filter, an
electronic switch, a MEMs switch, a diode array, a multiplexer, a
pin diode, a capacitor, a resistor, an inductor, an electronic
sensor or any combination thereof. The sensor may include a blood
gas sensor, a pressure (hemodynamic) sensor, or the like.
The proximal torque coupler includes a proximal pin mechanically
attached to the lead conductor and conductively coupled to the lead
conductor and the electronic component. A drive shaft may be
disposed between the proximal pin and the lead conductor. The
distal torque coupler includes a distal pin mechanically attached
to the lead electrode and conductively coupled to the lead
electrode and the electronic component.
A collar may be disposed at a distal end of the implantable medical
electrical lead. In such case, the casing is typically disposed
within the collar and is translatable along a longitudinal axis of
the collar. A seal is typically disposed between the casing and the
collar for preventing passage of ionic fluid into the lead through
its distal end. The seal may be disposed at a distal end, a
proximal end, or along the middle of the casing. In various
configurations, the seal may be fixed relative to the casing or,
alternatively, fixed relative to the collar.
The seal prevents ingress of bodily fluids inside the lead body and
electrically isolates the electronic component and the pins of the
casing. Isolating the pins extending in non-conductive relationship
with the casing from each other is very important. For example, a
bandstop filter may present an impedance of 2000 ohms at resonance.
This desirably impedes the flow of MRI induced RF current into body
tissue through the electrode. However, if the pins are not isolated
from each other, a parallel path through body fluids (ionic fluid)
could result in a parallel path of approximately 80 ohms. This
conduction through surrounding fluid would degrade the MRI RF
signal attenuation of the bandstop filter. Accordingly, it is
important to be able to isolate the opposite ends of the pins of
the electronic component.
An insulative conformal coating may be disposed about at least a
portion of the casing. The conformal coating may comprise a
dielectric ceramic coating, an alumina or parylene, and may be
applied by sputtering, chemical vapor deposition, physical vapor
deposition, dipping in or applying a chemical solution. The casing
may comprise a dielectric ceramic coating comprised of alumina.
The aforementioned drive shaft may be associated with a proximal
pin extending from the casing. This drive shaft may comprise a
hollow stylet-receiving rigid tube.
Other features and advantages of the present invention will become
apparent from the following more detailed description which
illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the invention. In such
drawings:
FIG. 1 is a wire-formed diagram of a generic human body showing a
number of exemplary implanted medical devices;
FIG. 2 is a schematic illustration of a human heart with an
implanted medical electrical lead;
FIG. 3 is an outline illustration of the head and left pectoral
region of a patient undergoing implantation of a medical electrical
lead;
FIG. 3A is an enlarged view of area 3A in FIG. 3;
FIG. 4 is a schematic diagram of a unipolar active implantable
medical device;
FIG. 5 is a diagram similar to FIG. 4, illustrating a bipolar
active implantable medical device;
FIG. 6 is a diagram similar to FIGS. 4 and 5, illustrating a
biopolar lead wire system with a tip and ring electrode, typically
used in a cardiac pacemaker;
FIG. 7 illustrates a bipolar cardiac pacemaker lead wire showing
the tip and ring electrodes;
FIG. 8 is an enlarged, fragmented schematic illustration of the
area illustrated by the line 8-8 in FIG. 7;
FIG. 9 is a schematic illustration similar to FIG. 8, showing the
undesirability of permitting a parallel electrical path through
body fluids around an impeding electrical component;
FIG. 10 is a sectional view of an exemplary medical electrical lead
embodying the present invention;
FIG. 11 is an enlarged sectional view of the area illustrated by
the line 11-11 in FIG. 10;
FIG. 12 is an electrical schematic diagram of the bandstop filter
illustrated in FIG. 11;
FIG. 13 is a sectional view similar to FIG. 10, showing an
exemplary load carrying body embodying the present invention;
FIG. 14 is an enlarged sectional view taken generally along the
line 14-14 of FIG. 13;
FIG. 15 is a sectional view similar to FIG. 14, showing an
alternative configuration;
FIG. 16 is an exploded perspective view of the assembly of FIG. 15;
and
FIG. 17 is a sectional view similar to FIG. 15, of another
exemplary load carrying body embodying the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a wire formed diagram of a generic human body showing a
number of implanted medical devices. 10A represents a family of
hearing devices which can include the group of cochlear implants,
piezoelectric sound bridge transducers and the like. 10B represents
a variety of neurostimulators and brain stimulators.
Neurostimulators are used to stimulate the Vagus nerve, for
example, to treat epilepsy, obesity and depression. Brain
stimulators are pacemaker-like devices and include electrodes
implanted deep into the brain for sensing the onset of the seizure
and also providing electrical stimulation to brain tissue to
prevent the seizure from actually occurring. 10C shows a cardiac
pacemaker which is well-known in the art. 10D includes the family
of left ventricular assist devices (LVAD's), and artificial hearts,
including the artificial heart known as the Abiocor. 10E includes
an entire family of drug pumps which can be used for dispensing of
insulin, chemotherapy drugs, pain medications and the like. 10F
includes a variety of bone growth stimulators for rapid healing of
fractures. 10G includes urinary incontinence devices. 10H includes
the family of pain relief spinal cord stimulators and anti-tremor
stimulators. 10H also includes an entire family of other types of
neurostimulators used to block pain. 10I includes a family of
implantable cardioverter defibrillators (ICD) devices and also
includes the family of congestive heart failure devices (CHF). This
is also known in the art as cardiac resynchronization therapy
devices, otherwise known as CRT devices.
FIG. 2 is a schematic illustration of a human heart 12 with an
implanted medical electrical lead 14. The medical electrical lead
14 includes an electrical or electronic component 16 in series with
the active fixation distal helix electrode(s) 36. Once the medical
electrical lead 14 is in the desired location, it is typically
attached to cardiac tissue with a helical tip 36 (active) or even
passive fixation electrode(s) (not shown).
FIG. 3 is an outline illustration of the head 18 and left pectoral
region 20 of a patient 22 undergoing implantation of a medical
electrical lead 14. FIG. 3A is an enlarged view of area 3A in FIG.
3. The medical electrical lead 14 is implanted through a venous
access in the left (or right) pectoral region 20 of the patient 22
and delivered endocardially through the veins and into the heart
using an introducer 24, connector pin 26, guide wire 27, and stylet
knob 28.
FIG. 4 is a general diagram of a unipolar active implantable
medical device (AIMD) 10. The AIMD housing 30 is typically
titanium, ceramic, stainless steel or the like. Inside of the
device housing 30 are the AIMD electronic circuits. Usually AIMDs
include a battery, but that is not always the case. A unipolar lead
32 is routed from the AIMD 10 to a distal electrode 34 where it is
embedded in or affixed to body tissue. In the case of a spinal cord
stimulator 10H, the distal electrode 34 could be in the spinal
cord. In the case of a deep brain stimulator 10B, the distal
electrode 34 would be placed deep into the brain, etc. In the case
of a cardiac pacemaker 10C, the distal electrode 34 would typically
be placed in the cardiac right ventricle.
FIG. 5 is very similar to FIG. 4 except that it is a bipolar
system. In this case, the electrical simulation and sensing may be
between the two distal electrodes 34 and 34'. In the case of a
cardiac pacemaker 10C, this would be known as a bipolar lead system
with one of the electrodes known as the distal tip electrode 36 and
the other electrode which would float in the blood pool known as
the ring electrode 38 (see FIG. 6). In contrast, the electrical
tissue simulation and sensing path in FIG. 4 is between the distal
electrode 34 through body tissue to the conductive housing 30 of
the implantable medical device 10 (the bipolar system of FIG. 5 can
be typically programmed into the unipolar mode shown in FIG.
4).
FIG. 6 illustrates a single chamber bipolar lead system with a
distal tip electrode 36 and ring electrode 38 typically as used in
a cardiac pacemaker 10C.
In all of these applications, a patient exposed to the fields of an
MRI scanner or other powerful emitter used during a medical
diagnostic procedure, could have currents induced in the leads 32
and, in turn, can cause heating by I.sup.2R losses in the lead
conductor 32 or by heating caused by current flowing from an
electrode 36, 38 into body tissue. If these currents become
excessive, the associated heating can cause damage or even
destructive ablation to body tissue.
The distal tip electrode 36 is designed to be implanted into or
affixed to the endocardial or myocardial tissue of the heart. The
ring electrode 38 is designed to float in the blood pool. Because
the blood is flowing and is thermally conductive, the ring
electrode 38 structure is substantially cooled during MRI scans. In
theory, the ring electrode 38 could also touch the myocardial or
trabecular tissue and become encapsulated. When electrodes 36
and/or 38 are encapsulated they become thermally insulated by
surrounding body tissue and can readily heat up due to the RF pulse
currents of an MRI field.
FIG. 7 illustrates a single chamber bipolar cardiac pacemaker lead
wire showing the distal tip electrode 36 and the distal ring
electrode 38. This is a coaxial wound system where the ring
electrode lead conductor 40 is wrapped around the tip electrode
lead conductor 42. There are other types of pacemaker lead systems
in which these two conductors lay parallel to one another (known as
a bifilar lead system).
FIG. 8 is a schematic illustration of the area 8-8 in FIG. 7. In
the area of the distal tip electrode 36 and ring electrode 38,
bandstop filter 44 has been placed in series with the tip electrode
conductor 42. The bandstop filter 44 consists of a passive
component inductor L in parallel with a capacitor C which is
designed to be resonant at an MRI pulsed RF frequency. The
resistive losses R.sub.C and R.sub.L of the capacitor and the
inductor are carefully controlled such that the bandstop filter 44
has a resulting 3 dB bandwidth to achieve substantial attenuation
along a selected range of MRI RF pulsed frequencies. Accordingly,
at MRI pulsed frequencies, a very high impedance is presented
thereby reducing the flow of undesirable RF current into body
tissue. A bandstop filter 44 could also be placed in series with
the ring electrode lead wire 40. The bandstop filter 44 shown is
exemplary of any type of passive component network (any combination
of inductors, resistors or capacitors) that could be used in the
present invention. An electronic switch, a MEMS switch as taught by
U.S. Pat. No. 6,944,489, a diode array, an electronic switch, an
inductor, a multiplexer or any combination thereof, could also
advantageously be used with or instead of the bandstop filter
44.
Referring once again to FIG. 8, it is important that the implanted
bandstop filter 44 have a high insulation resistance (IR) between
points "a" and "b", which are external to the electronic element.
In this case, the bandstop filter 44 would provide a high impedance
at resonance (above 1000 ohms) to reduce the flow of RF currents
induced in the lead into body tissue. However, if both ends of the
bandstop filter 44 were exposed to ionic containing fluids (i.e.
body fluid), then external conduction paths would occur.
Experiments by the inventors have shown that a parallel resistance
of 80 ohms could result, which would significantly and undesirably
reduce the impedance of the bandstop filter 44 at resonance. This
parallel IR is shown in FIGS. 8 and 9 as R.sub.FL which represents
the conduction through body fluid which would occur from end to end
(points a to b) if the bandstop filter 44 were not properly
insulated and isolated. For a typical bandstop filter, let's assume
that its impedance at resonance at 64 MHz was 2000 ohms. If it
undesirably had ionic fluids exposed to its external contacts at
points a and b, this would mean that an 80 ohm insulation
resistance now appears in parallel with the 2000 ohm impedance.
Using the parallel resistance Rp formula wherein
R.sub.P=(R.sub.1R.sub.2)/(R.sub.1+R.sub.2)=(80)(2000)/(2000+80)=7-
6.9 ohms. This would be disastrous for the operation of the
bandstop filter 44. Instead of presenting 2000 ohms at resonance to
the MRI pulsed frequency, it would present only 76.9 ohms. This
would result in a great deal of RF current flowing through the
distal electrode into body tissue which is highly undesirable. It
is a feature of the present invention that along with a torque
coupler--tensile stress isolator, insulating seals and/or
insulating conformal coatings be provided such that this low value
of parallel insulation resistance does not occur in parallel with
the electronic circuit element. The electronic circuit element of
the present invention is not limited to just L-C parallel resonant
bandstop filters. It is equally important for inductors, electronic
switches, MEMS switches, pin diodes, L-C trap filters, low pass
filters, diode arrays, electronic multiplexers, electronic sensors,
or any other type of active or passive electronic circuit wherein
torque and tensile load protection is needed along with a high
insulation resistance is needed from one end of it to the other end
of it, as described as points a and b in FIGS. 8 and 9.
FIG. 9 is very similar to FIG. 8 except that the electronic device
44, in this case, is an electronic switch 45 which is shown in the
open position. The electronic switch 45 can actually consist of a
pin diode, a MEMS switch, an electronic switch, an electronic
sensor, or even a diode array. It is shown in the open position
indicating that it's in the MRI compatible position. In other
words, MRI RF currents induced onto lead 42 would be unable to flow
through distal electrode 36 into body tissue and potentially damage
said body tissues.
FIG. 10 illustrates an exemplary lead 14 which embodies a lead body
46, a coaxial conductor 48 for the ring electrode 38, a coaxial
conductor 42 for the tip (active fixation helix) electrode 36, a
collar 50, and the translatable casing 52 which houses electronic
components. The translatable casing 52 includes a pin 54 and a pin
56. The translatable casing 32 is optionally hermetically sealed at
one or both ends. The pin 54 is electrically and mechanically
connected to the tip electrode lead wire conductor 42 and the pin
56 is attached to a distal helix electrode 36. The distal helix
electrode 36 is also known as an active fixation electrode. The pin
54, the casing 52, and the pin 56 all form what is defined herein
as a casing subassembly 58. This is further illustrated in FIG. 11,
which shows the cross-section of an inductor L and a capacitor C
inside casing 52, which are physically disposed in series, but are
electronically connected in parallel to form an L-C resonant
bandstop filter 44. This is further described in U.S. 2010/0100164,
which is incorporated herein by reference.
Referring once again to FIG. 10, there will typically be a laser
weld (not shown) electrically and mechanically connecting the tip
conductor 42 to a conductive drive shaft 60, there is also a laser
weld (not shown) connecting the casing pin 56 to the distal tip
electrode 34. During transvenous insertion, the active fixation
helix tip 36 is retracted (as shown) so that it will not stab or
poke into body tissues during endocardial lead insertion. When the
physician has positioned it in the desirable location (perhaps
inside the cardiac right ventricle), then the physician takes a
special torque tool and twists the proximal end of lead body 46
which causes the entire conductor 42 and drive shaft 60 to rotate.
As the casing 52 and distal helix electrode 36 .[.rotates, it.].
.Iadd.rotate, helix electrode .Iaddend.engages a guide 62 which
causes the helix 36 to extend and screw into body tissue. The guide
62 may be formed as part of the collar 50 and engages the tip
electrode 36 when the tip conductor 42 is rotated. The rotation
causes the helical tip electrode 36 to rotate within the collar 50
and thereby translate in a forward manner. At the same time the tip
electrode 36 is advancing relative to the collar 50, it is engaging
with body tissue by being screwed directly into the tissue to
thereby form an attachment. The tip electrode 36 can be rotated in
the opposite direction by rotating the tip conductor 42 and thereby
disengaged from the tissue for removal and/or reattachment at a
different location. This is a method of active affixation which is
well known in the art.
An O-ring 64 is disposed on the proximal end of and subassembly 58.
In this case, the seal 64 is only to prevent the intrusion of ionic
containing body fluids into the interior of lead body 46. In this
case, a conformal coating 66 is disposed over the exterior of the
casing 52 and all the way over the pin 54 and even over a portion
of a conductive drive shaft 60. The conformal coating 66 may be a
material for electrical isolation and/or also aid in reducing
friction. The conformal coating 66 may also be a dielectric ceramic
coating that can be applied in a multitude of ways, such as by
sputtering, chemical vapor deposition, physical vapor deposition,
or dipping in a chemical solution. The conformal coating 66 may
also be made of a variety of materials sufficient to provide
insulation, such as alumina. In another exemplary embodiment and to
provide further electrical isolation, the casing 52 can also be
manufactured as a ceramic tube, and also from materials such as
alumina. It is to be understood that such a ceramic tube casing 52
can be used with or without the conformal coating 66.
The lead tip conductor 42, the casing sub-assembly 58 and the
distal helix 36 are shown in the retracted position. As the helix
is extended, the conformal coating 66 on the inside diameter of
seal 64 will slide back and forth as it is part of the drive shaft
60. This provides a high degree of electrical resistance or
isolation between the terminal pins 54 and 56 such that undesirable
currents do not flow through body fluids from end to end outside of
the electronic component casing 52. Seal supports 68 abut the seal
64 on both ends and fix the seal 64 in place. The seal supports 68
can be made from a range of materials, including but not limited to
a polymer, polyurethane, metal, elastomer, ceramic, composite or
any other suitable material.
FIG. 11 is generally taken from section 11-11 of FIG. 10. Shown is
the interior of the translatable casing 52 illustrating bandstop
filter components L and C. Terminal pins 54 and 56 extend in
non-conductive relationship with the translatable casing 52.
Hermetic seals 70 and 72 are shown which form a hermetic seal
between the pins 54 and 56 and the translatable casing 52. This
protects the inductor L and capacitor C (or other electronic
components) from intrusion of body fluids. It is well known in the
art that intrusion of moisture, body fluids or other contaminants
can cause electronic circuits to short out. It is not an absolute
requirement that the translatable casing 52 be hermetically sealed.
Electronic components, such as inductor L and capacitor C
components, could be utilized that are inherently non-toxic and
biocompatible. Components for direct body fluid exposure are
described in U.S. Pat. No. 7,535,693 the contents of which are
hereby incorporated by reference. However, in the case where there
are hermetic seals 70, 72, it is important that the hermetic seals
be protected from damage due to excessive torque or tensile loads.
In the case where there are no hermetic seals, it's even more
important that delicate electronic components be protected from
damaging torque or tensile stresses.
The present invention is applicable to any type of active or
electronic circuits that may be disposed in or adjacent to a
translatable electronic casing 52. The flexible seal 64 of FIG. 10
prevents the entrance of ionic body fluids into the inside of the
lead body 46. The seal 64 can be formed in a multitude of ways
appreciated by those skilled in the art, such as multiple wipers,
o-rings, thin disks or sheets, and various molded profiles. See,
for example, U.S. application Ser. No. 12/873,862, the contents of
which are incorporated herein.
There is a secondary optional O-ring seal 74 as shown in FIG. 10.
The O-ring seal 74 is disposed between the inside diameter of the
lead collar 50 and the outside diameter of the electronic component
casing 52. The purpose of seal 64 and the O-ring seal 74 is to
ensure that ionic body fluids cannot be disposed across the
important electrical path between pins 54 and 56. Ionic body fluids
could represent a parallel path as low as 80 ohms. Over time, due
to bulk permeability, body fluids will penetrate into the interior
of the lead body 46. However, this is an osmotic type of action.
The resulting fluids that would occur over long periods of time
inside the lead body 46 would be distilled and free of ionic
contaminants (de-ionized). This means that they would be less
conductive of high frequency electrical signals from one end to the
other of the electronic component casing 52. The presence of
optional O-ring 74 is desirable in that it also presents a high
impedance to such a parallel circuit path. The casing 52 may also
have a conformal insulative coating 66 for further electrically
isolating terminals 54 and 56 such that a parallel path through
body fluid is further impeded. The insulative coating may be formed
from any suitable material, such as a dielectric material,
including, but not limited to parylene, ETFE, PTFE, polyamide,
polyurethane and silicone. It will be understood that the exemplary
embodiment of FIG. 10 may work with or without such coatings.
FIG. 12 is an electrical schematic illustration of the bandstop
filter illustrated in FIG. 11.
FIG. 13 is a perspective illustration of an exemplary unitary
torque coupler 76 embodying the present invention. The torque
coupler 76 is made of a rigid and non-conductive material. The form
of the torque coupler 76 may vary and be formed to match the
medical electrical lead's 46 collar 50. A helical electrode tip 36
is attached to the distal torque coupler pin 78. A proximal torque
coupler pin 80 is attached to drive shaft 60. Torque and tensile
loads applied to the lead 46 are transmitted through the unitary
torque coupler 76 while not being transmitted within the electronic
components 44 located inside. The torque coupler 76 also protects
the mechanically sensitive hermetic seals 70 and 72.
FIG. 14 is a sectional view taken from section 14-14 of FIG. 13. As
was previously mentioned, the torque coupler 76 is of a rigid and
insulative material. It has sufficient strength properties to
transmit torque and tensile loads thereby protecting the casing 52
of the electronic module 44. There is a unique coupling mechanism
provided by the proximal torque coupler pin 80, which is generally
electrically and mechanically attached to proximal pin 54 either by
laser welding, brazing of the like. In order to mechanically grasp
and adhere to the material of the torque coupler 76, it may have
one or more disc-like rings 82 in order to increase its surface
area. The rings may have sprocket spokes to lock it to the unitary
torque coupler. In general, there is more torque on the proximal
side than on the distal side. Accordingly, in the preferred
embodiment as shown in FIG. 14, there would be two friction rings
82 on the proximal side and only one on the distal side. The casing
52 is hermetically sealed by hermetic seals 70 and 72. The unitary
torque coupler 76 not only protects the delicate electronics 44
inside of the casing 52, but it also protects the delicate hermetic
seals 70 and 72. An optional overall insulative coating 66 may be
applied. The torque coupler 76 may be formed by a mold into which a
biocompatible epoxy is poured and then later cured into a hard
state.
During implantation by a physician, the lead body 46 is held in
place while the center conductor 42 is rotated using a physician
torque tool. As the entire assembly rotates, it is pushed forward
by guide 62 which causes the distal helix end 36 to protrude and
screw into body tissue. The torque that is applied to the lead
conductor 42 is transmitted to drive shaft 60 and in turn to the
proximal torque coupler pin 80. The torque is then transmitted
mostly into the rigid body of the torque coupler 76 itself thereby
bypassing pins 54 and 56. The torque that is transmitted by the
torque coupler 76 is further transmitted to the distal torque
coupler pin 78. This arrangement, importantly, protects the casing
52, the electronics 44 and the sensitive hermetic seals 70 and
72.
FIG. 15 shows an alternate torque coupler arrangement. In this
case, the torque coupler is divided into two discrete torque
couplers, one consisting of a proximal torque coupler 84 and the
other consisting of a distal torque coupler 86. In this case, the
torque couplers 84, 86 are also of a rigid insulative material.
They could be poured in place, such as a non-conductive
thermal-setting epoxy or polyimide. They could also be pre-machined
from hard plastics, ceramics or the like. In addition, ceramic
powders could be pressed into a fixture and then sintered at high
temperature in order to make a rigid non-conductive torque
coupler.
Each of the distal and proximal torque coupler pins 78 and 80
includes a locking sprocket 88. Similarly, each of the proximal and
distal torque couplers 84 and 86 include a locking
sprocket-receiving recess 90 configured for receiving a respective
locking sprocket 88 therein. These features are better illustrated
in FIG. 16, which also shows that the proximal and distal torque
couplers 84 and 86 also have a castle parapet configuration 92 on
one side for mating reception with a similar castle parapet
structure 94 provided on respective ends of the casing 52. In this
case, the casing 52 is of a strong and rigid material such that it
will not deform during application of torsional loads. These
gear/sprocket-like features of the torque couplers 84, 86, torque
coupler pins 78, 80 and the casing 52 prevent the torque couplers
84 and 86 from slipping relative to the casing 52 and the
respective pins 78 and 80 while under load. In a preferred
embodiment, an adhesive (not shown) would be applied to the
sprocket 86 engagement surfaces 90 and 92 so that the entire system
would be also resistant to tensile loads. In other words, tensile
and torque loads applied to the pins 78 and 80 are transmitted
through the torque couplers 84 and 86 directly to the casing 52,
thereby isolating the electrical components 44 from such torque or
tensile loads.
FIG. 16 is an exploded view of various components disposed within
the lead body 46 and the collar 50, from FIG. 15. Beginning on the
left hand or proximal side one can see the lead tip conductor 42
which attaches to the conductive drive shaft 60. The conductive
drive shaft 60 (which is optional) is secured by welding, brazing
or the like, to the proximal torque coupler pin 80. The torque
coupler pin 80 includes a locking sprocket 88 configured for
locking reception within the locking sprocket recess 90 of the
proximal torque coupler 84. The proximal pin 54 is fixed within a
pin receiving recess 96 provided within the proximal torque coupler
pin 80 (see FIG. 15). The distal end of the pin 54 includes a head
98 to which the electronic component (bandstop filter 44) is
conductively coupled. Similarly, the distal pin 56 is disposed
within a pin receiving recess 100 (FIG. 15) provided within the
distal torque coupler pin 78 and is fixed in place by means of a
weld or the like. A distal pin 56 extends through the distal
hermetic seal 72, and includes a head 102 which is conductively
coupled to the electronic components (bandstop filter 44) disposed
within the casing 52. A sprocket 88 is configured for locking
reception within the locking sprocket recess 90 provided in the
distal torque coupler 86. The tip electrode 36 is fixed to the
distal torque coupler pin 78. Importantly, the proximal and distal
torque couplers 84 and 86 each include a castle parapet structure
92 that mates with a corresponding castle parapet structure 94
provided on respective ends of the casing 52. As described
previously, this structure ensures that the electrical components
within the casing 52 are isolated from torque or tensile loads
applied to the lead 14, the lead electrode 36, or both.
FIG. 17 is a sectional view similar to FIGS. 14 and 15. In this
case, the pin 54 has a unique cup shape to receive a conductive
shaft 104. This shaft 104 is attached to a ferrule 106 which is in
turn connected to the lead conductor 42. Since it is very important
that torque not be transmitted from lead conductor 42 through the
shaft 104 to the pin 54, hermetic terminals this small generally
consist of a single sapphire ceramic or an alumina ceramic.
Metallization is attached to these pins by first sputtering and
then gold brazing. An elongated torque coupler 108 is connected to
the ferrule 106 and is in turn connected to the parapet structure
94 that is located on the end of the casing 52 in order to lock it
in place. The elongated torque coupler 108 operates in accordance
with the present invention so that torque or tensile loads that are
transmitted via the lead conductor 42 bypass the conductive shaft
104 and the hermetic seal 70.
From the foregoing, it will be appreciated that the present
invention relates to a lead body adapted for in-vivo implantation
in a living subject, said lead body comprising a proximal end
configured for electrical and mechanical connection to a therapy
delivery or monitoring device, and a distal end which is connected
to a translatable active fixation electrode in contact with body
tissues. The distal end of the lead body encompasses a collar in
which a casing is enclosed. The casing includes electronic
components which can either be active or passive. One or both ends
of the casing 52 (or alternatively the entire casing), is protected
by a novel torque coupler. The torque coupler protects either the
sensitive hermetic seals of casing 52 or the internal electronic
components 44 from damage due to torque applied to torque or
tensile loads applied to lead conductor 42, the tip electrode 36,
or both. In a preferred embodiment, the casing includes a passive
inductor and capacitor element configured to form a parallel
resonant L-C bandstop filter. The casing is translatable within the
collar, which causes a distal helix electrode to rotate and
literally be screwed into body tissue. The helix electrode is also
known as an active fixation electrode. The casing is part of a
casing assembly which includes a seal which is disposed between the
casing assembly and the collar whereby the seal prevents passage of
ionic body fluids in the living subject into the lead body fluid
distal end. Conformal coatings can be placed over the translatable
casing so that high resistance path is provided from one end of the
active or passive electronic circuit to the other. The active or
passive electronic circuit can include L-C bandstop filters, L-C
trap filters, low pass filters, electronic sensors, passive or
active electronic switches, MEMS switches, pin diode switches,
non-linear circuit elements, such as diodes and the like. The
conformal coating may be a dielectric material for electrical
isolation and/or also aid in reducing friction.
Although several embodiments have been described in detail for
purposes of illustration, various modifications may be made to each
without departing from the scope and spirit of the invention.
* * * * *