111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20040215300Al
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0215300 Al
`Oct. 28, 2004
`Verness
`( 43) Pub. Date:
`
`(54) ELECTRICAL MEDICAL LEADS
`EMPLOYING CONDUCTIVE AEROGEL
`
`(75)
`
`Inventor: David D. Verness, Forest Lake, MN
`(US)
`
`Correspondence Address:
`MEDTRONIC, INC.
`710 MEDTRONIC PARKWAY NE
`MS-LC340
`MINNEAPOLIS, MN 55432-5604 (US)
`
`(73)
`
`Assignee: Medtronic, Inc.
`
`(21)
`
`Appl. No.:
`
`10/421,455
`
`(22)
`
`Filed:
`
`Apr. 23, 2003
`
`Publication Classification
`
`(51)
`Int. CI? ....................................................... A61N l/05
`(52) U.S. Cl. .............................................................. 607/116
`
`(57)
`
`ABSTRACT
`
`Conductive aerogels are employed in fabrication of electri(cid:173)
`cal medical leads adapted to be implanted in the body and
`subjected to bending stresses. An elongated, flexible and
`resilient, lead body extends from a proximal end to a distal
`end and includes an insulative sheath having an elongated
`lumen through which an elongated conductor extends. A
`layer of conductive aerogel is disposed over the conductor
`deforming upon movement of the conductor within the
`lumen against the aerogel in response to applied stresses.
`
`65
`
`Nevro Corp.
`Ex. 1007
`U.S. Patent No. 8,650,747
`
`

`

`Patent Application Publication Oct. 28, 2004 Sheet 1 of 4
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`US 2004/0215300 A1
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`

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`Patent Application Publication Oct. 28, 2004 Sheet 2 of 4
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`US 2004/0215300 Al
`
`FIG. 2
`
`78
`
`84
`
`74
`
`11
`
`FIG. 3
`G2.
`
`FIG. 4
`
`GD
`...... ~.....,...~ GG
`
`~-b'f
`
`

`

`Patent Application Publication Oct. 28, 2004 Sheet 3 of 4
`
`US 2004/0215300 Al
`
`-
`
`•
`
`~ -u.
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`

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`Patent Application Publication Oct. 28, 2004 Sheet 4 of 4
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`US 2004/0215300 Al
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`•
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`(!) -
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`

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`US 2004/0215300 A1
`
`Oct. 28, 2004
`
`1
`
`ELECTRICAL MEDICAL LEADS EMPLOYING
`CONDUCTIVE AEROGEL
`
`FIELD OF THE INVENTION
`
`[0001] The present invention relates to implantable medi(cid:173)
`cal devices (IMDs) intended for chronic implantation in the
`body and particularly to electrical medical leads for applying
`electrical stimulation to and/or sensing electrical activity of
`the body, particularly cardiac leads for applying electrical
`stimulation to and/or sensing electrical activity of the heart
`at one or more electrode positioned at a cardiac implantation
`site within a heart chamber or cardiac vessel adjacent a heart
`chamber.
`
`BACKGROUND OF THE INVENTION
`[0002]
`Implantable medical electrical stimulation and/or
`sensing leads intended for chronic implantation in the body
`are well known in the fields of cardiac stimulation and
`monitoring, including cardiac pacing and cardioversion/
`defibrillation, and in other fields of electrical stimulation or
`monitoring of electrical signals or other physiologic param(cid:173)
`eters. In the field of cardiac stimulation and monitoring,
`endocardial leads are placed through a transvenous route to
`locate one or more sensing and/or stimulation electrode
`along or at the distal end of the lead in a desired location in
`a chamber of the heart or a blood vessel of the heart. In order
`to achieve reliable sensing of the cardiac electrogram and/or
`to apply stimulation that effectively paces or cardioverts the
`heart chamber, it is necessary to accurately position the
`electrode surface against the endocardium or within the
`myocardium at the desired site and fix it during an acute
`post-operative phase until fibrous tissue growth occurs.
`
`[0003] The pacemaker or
`implantable cardioverter/
`defibrillator (lCD) implantable pulse generator (lPG) or the
`monitor is typically coupled to the heart through one or more
`of such endocardial leads having a lead body extending
`between a proximal lead connector assembly and distal
`electrode. The proximal lead connector assembly compris(cid:173)
`ing one or more connector element is connected with a
`connector header of the lPG or monitor. The lead body
`typically comprises one or more insulated conductive wire
`surrounded by an insulating outer sleeve. Each conductive
`wire couples a proximal lead connector element with a distal
`stimulation and/or sensing electrode. An endocardial cardiac
`lead having a single stimulation and/or sensing electrode at
`the lead distal end and a single conductive wire is referred
`to as a unipolar lead. An endocardial cardiac lead having two
`or more stimulation and/or sensing electrodes at the lead
`distal end and two or more conductive wires is referred to as
`a bipolar lead or a multi-polar lead, respectively.
`
`[0004]
`In order to implant an endocardial lead within a
`heart chamber, a transvenous approach is utilized wherein
`the lead is inserted into and passed through the sub-clavian,
`jugular, or cephalic vein and through the superior vena cava
`into the right atrium or ventricle as depicted, for example, in
`U.S. Pat. No. 5,545,203. An active or passive fixation
`mechanism is incorporated into the distal end of the endocar(cid:173)
`dial lead and deployed to maintain the distal end electrode
`in contact with the endocardium or within the myocardium
`at the implantation site. An introduction mechanism, e.g., a
`stiffening stylet and/or a guide catheter, is employed to
`advance the distal electrode(s) to the electrode implantation
`site(s).
`
`[0005] More recently, endocardial pacing and cardiover(cid:173)
`sion/defibrillation leads have been developed that are
`adapted to be advanced using particular guide mechanisms
`into the coronary sinus and coronary veins branching there(cid:173)
`from in order to locate the distal electrode(s) adjacent to the
`left ventricle or the left atrium. The distal end of such
`coronary sinus leads is advanced through the superior vena
`cava, the right atrium, the valve of the coronary sinus, the
`coronary sinus, and into a coronary vein communicating
`with the coronary sinus, such as the great vein. Typically,
`coronary sinus leads do not employ any fixation mechanism
`and instead rely on the close confinement within these
`vessels to maintain each electrode at a desired site although
`active fixation mechanisms, e.g., minute helixes that are
`screwed into the vessel wall, can be employed.
`
`[0006] The heart beats approximately 100,000 times per
`day or over 30 million times a year, and each beat stresses
`the lead conductors and insulation. Over the years of implan(cid:173)
`tation, the lead conductors and insulation are subjected to
`cumulative mechanical stresses as well as material reactions
`that can result in degradation of the insulation or fractures of
`the lead conductors with untoward effects on IMD perfor(cid:173)
`mance and patient well-being. The endocardial lead bodies
`of pacing and lCD leads are subjected to continuous stretch(cid:173)
`ing and flexing as the heart contracts and relaxes and are
`formed to be highly flexible, resilient, and durable employ(cid:173)
`ing durable bio-compatible lead conductor and insulator
`materials and structures.
`
`[0007]
`Initially developed chronically implanted unipolar
`and bipolar cardiac pacing leads employed flexible silicone
`rubber tube having a single lumen and two lumens, respec(cid:173)
`tively in which single filar wire conductors formed of
`stainless steel and later of MP35N alloy that were wound
`into wire coils were inserted and electrically coupled to a
`proximal lead connector element and a distal pace/sense
`electrode. Early implantable, endocardial and epicardial,
`bipolar cardiac pacing leads of the type disclosed in U.S.
`Pat. No. 3,348,548, that were clinically implanted in the
`1960s, had two lumens arranged side-by-side and coiled
`wire conductors disposed in each lumen. The wire coil and
`silicone rubber tube of such endocardial pacing leads allow
`the lead body to stretch axially and provide a coil lumen for
`receiving a stiffening stylet during
`transvenous
`lead
`advancement.
`
`[0008] Such lead bodies fabricated at that time were
`relatively large in diameter, and the side-by-side arrange(cid:173)
`ment was believed to be responsible for lead body fractures.
`In addition, effective passive and active distal fixation
`mechanisms were not available, and displacement of the
`distal electrodes were common occurrences. Surgeons
`resorted to stiffening the lead body by leaving the stylet in
`place to prevent dislodgement, but the stiffening stylet then
`often fractured within the wire coil lumen, and the sharp
`broken stylet ends initiated a lead fracture. Moreover, a
`portion of the lead body was (and is to the present time)
`often implanted between the first rib and right clavicle as
`illustrated in the above-referenced '545 patent, and the
`stresses on the lead body caused the relatively large diameter
`lead insulator and body to be crushed and fracture.
`
`[0009] A great deal of effort has been undertaken over the
`years to reduce these complications by developing fracture
`and crush resistant lead bodies and to provide the above-
`
`

`

`US 2004/0215300 Al
`
`Oct. 28, 2004
`
`2
`
`mentioned active and passive fixation mechanisms that
`effectively reduced lead dislodgement. At the same time,
`many other material and structural improvements have been
`made in lead conductors, lead insulators, electrodes, and
`various other electrical medical lead components to reduce
`the lead body diameter and increase its lubricity, to increase
`conductivity of the lead conductor, to increase the number of
`lead-borne electrodes, to decrease stimulation thresholds,
`particularly cardioversion/defibrillation and pacing thresh(cid:173)
`olds, and optimize sensing of the electrogram, to reduce
`inflammation at the electrode-tissue interface, to optimize
`electrode shapes and materials, to incorporate sensors in
`some instances, and to otherwise simplify implantation,
`reduce complications, assure reliable pacing and cardiover(cid:173)
`sion/defibrillation, and increase the implantation lifetime of
`such cardiac leads and other electrical medical leads. In
`particular, many changes have been made in the materials
`used in and the fabrication of lead bodies extending between
`the proximal lead connector assembly and distal elec(cid:173)
`trodes(s) and sensor(s).
`
`[0010] Most current endocardial cardiac leads employ
`multi-filar, parallel-wound, coiled wire conductors electri(cid:173)
`cally connected in common in an electrically redundant
`fashion as a single polarity lead conductor in each of the
`unipolar, bipolar and multi-polar lead configurations. Such
`redundant coiled wire conductors of bipolar and multi-polar
`lead bodies are coaxially arranged about the stiffening stylet
`receiving lumen and insulated from one another by coaxially
`arranged insulating sheaths separating each coiled wire
`conductor from the adjacent coiled wire conductor(s). The
`number of separate lead conductors that can be incorporated
`in a lead body of a given diameter is limited in this coaxial
`winding approach.
`
`[0011]
`In certain cases, the need for increased numbers of
`lead conductors in the lead body has led to the development
`of separately insulated, coiled wire conductors that are
`parallel-wound with a common diameter and are separately
`coupled between a proximal connector element and to a
`distal electrode or terminal in the manner described in
`commonly assigned U.S. Pat. No. 5,007,435, for example.
`The coaxial construction technique may also be combined
`with the parallel-winding technique to multiply the total
`number of separate coiled wire conductors accommodated
`within a specified endocardial lead body outer diameter.
`
`[0012]
`Improvements in stranded wire conductors and
`lead body materials have more recently led to the combi(cid:173)
`nation of substantially straight, stranded wire conductors
`and at least one coiled wire conductor providing a stylet
`lumen as illustrated in commonly assigned U.S. Pat. Nos.
`5,584,873, 6,052,625, and 6,285,910, for example. In these
`lead bodies, ETFE sleeve insulators encase the stranded wire
`conductors, and a PTFE sleeve insulator surrounds the
`multi-filar, coiled wire, conductor. The insulated wire con(cid:173)
`ductors are received in lumens of an elongated lead body
`insulator that also incorporates elongated, empty, compres(cid:173)
`sion lumens.
`
`[0013] Typically, the lumens in lead body insulators
`receiving substantially straight, stranded wire conductors or
`coiled wire conductors are not otherwise filled with a filler
`or the like. However, the above-referenced '203 patent
`discloses coaxial lead bodies of the types disclosed above as
`well as a lead body incorporating multiple, coiled wire
`
`conductors arranged side-by-side within lumens of the lead
`body insulator. The lumens are also reinforced against
`crushing with a liquid polymer, e.g., Silastic® silicone
`rubber, silicone rubber adhesive or polyurethane, that solidi(cid:173)
`fies in place. However, encasing the turns of the coiled wire
`conductors along the length of the lead body with such
`materials can stiffen the lead body unduly and may increase
`the likelihood of stress-related fracture at other points along
`the lead body.
`[0014] To some extent, it has been recognized that the
`relative movement of lead conductors with respect to the
`surrounding wall of silicone rubber tube can abrade the
`conductors or tube, perhaps due to the abrasive action of
`silica of the silicone rubber compound, and cause the lead
`body to fail. In commonly assigned U.S. Pat. No. 5,796,044,
`coiled wire, single filar and multi-filar, conductors are dis(cid:173)
`closed that are sheathed loosely within a separate, coiled,
`insulating sheath allowing a gap or space to be present
`between the exterior surface of the coiled wire conductor
`and the adjacent interior surface of the insulating sheath. The
`insulating sheath is loosely fitted around the coiled wire
`conductor to avoid concentrating corrosion effects at the site
`of a defect, allowing any corrosion that may occur as a result
`of the defect to be spread over a larger wire surface. The
`coiled insulating sheath is preferably included within the
`lumen of a non-coiled outer insulating sheath.
`[0015]
`It is suggested in U.S. Pat. No. 3,333,045 that the
`tube lumen be backfilled with a liquid silicone fluid or
`powdered ETFE to lubricate the surfaces of the lumens of
`silicone rubber tube receiving stranded, drawn-brazed
`stranded (DES) wires, loosely coiled into coiled wire con(cid:173)
`ductors. Incorporating such non-conductive lubricating or
`reinforcing materials within the conductor lumen of a lead
`body insulator may or may not reduce the possibility of lead
`conductor fracture through abrasion or crushing. The elec(cid:173)
`trical connection between the distal electrode or sensor and
`the proximal lead connector element is interrupted if a
`fracture of the lead conductor does occur with or without the
`lubricating or reinforcing materials within the lead conduc(cid:173)
`tor lumen.
`[0016]
`It has been proposed to include other materials or
`mechanisms to provide a form of redundancy with the coiled
`or straight stranded wire conductor to compensate for a
`complete fracture or the reduced conductivity attendant to a
`partial fracture of the conductor. In U.S. Pat. No. 4,033,355,
`the coiled wire conductor is tightly fitted within a conductive
`silicone rubber tube, e.g., silicone rubber compounded with
`conductive particles, e.g., carbon. The tight fitting is deter(cid:173)
`mined to be necessary to ensure that the wire coil turns make
`intimate contact with the conductive silicone rubber so that
`a section of conductive silicone rubber bridges any fractured
`ends of the wire conductor. An internal block of conductive
`silicone rubber surrounding a section of the coiled wire
`conductor within the lead connector assembly of the cardiac
`pacing lead disclosed in U.S. Pat. No. 3,924,639 is provided
`to make a temporary electrical connection with the lead
`conductor. The use of conductive silicone rubber as dis(cid:173)
`closed in the '355 patent raises the same issues of reduced
`lead body flexibility and abrasion possibly increasing the
`risk of fracture as the use of the tight fitting electrically
`insulating silicone rubber disclosed in the above-referenced
`'203 patent. While such silicone rubber materials can be
`made conductive by incorporating suspended conductive
`
`

`

`US 2004/0215300 Al
`
`Oct. 28, 2004
`
`3
`
`particles to a certain degree, but the conductivity does not
`match that of the lead conductor itself.
`[0017] Endocardial leads that have an increased resistance
`to fracture and the capability of continued function after
`fracture of a lead conductor are disclosed in commonly
`assigned U.S. Pat. Nos. 6,018,683, 6,061,598, 6,119,042 and
`6,285,910 and in the above-referenced '044 patent. The
`endocardial leads are provided with a monofilar or multi(cid:173)
`filar coiled wire conductor that extends along the length of
`the lead body between a proximal electrical connector
`element and a distal electrode in a conventional manner. In
`addition, a stranded wire conductor extends loosely along
`the coiled wire conductor from a point along the lead body
`located proximal to the point of expected breakage of the
`coiled wire conductor to a point along the lead body located
`distal to the point of expected breakage. In certain embodi(cid:173)
`ments, the proximal and distal ends of the stranded wire
`conductor are electrically and mechanically coupled to the
`coiled wire conductor, limiting the extensibility of the coiled
`wire conductor, rendering the coiled wire conductor less
`susceptible to axially applied tensile forces, and also pro(cid:173)
`viding for continued electrical connection between the con(cid:173)
`nector element and the electrode in the event that the coiled
`wire conductor fractures intermediate the proximal and
`distal ends of the stranded wire conductor. In other embodi(cid:173)
`ments, the stranded wire conductor is coupled only at its
`proximal or distal end to the coiled wire conductor or may
`simply be located in the same lumen as the coiled wire
`conductor without mechanical connection to the coiled
`conductor. Due to the confines of the lumen, the stranded
`and coiled wire conductors come into contact at numerous
`points along their respective lengths so that a mechanical
`connection is not necessary.
`[0018] The fabrication of electrical medical lead bodies
`often requires directing lead conductors through cavities in
`the lead body insulator other than conductor lumens per se
`in order to make electrical connections to lead connector
`elements or distal electrodes or sensors. For example, the
`lead body insulator of the endocardial leads disclosed in the
`above referenced '625, '873, '683, '598, '042 and '910
`incorporate bifurcation sleeves or trifurcation sleeves in
`order to connect two or three, respectively, connector assem(cid:173)
`blies to selected lead conductors that are diverted through
`branch sleeve cavities or lumens. These sleeve lumens are
`typically backfilled with liquid silicone rubber adhesive that
`solidifies within the cavity about the short segments of
`conductor wire traversing the cavity and immobilizes them.
`At times, the immobilization of the lead conductor segment
`can cause or does not prevent the lead conductor traversing
`the sleeve lumen to fracture due to chronically applied
`stress.
`It is therefore desirable to provide a relatively
`[0019]
`simple, electrically redundant, bridging of a fractured wire
`conductor traversing a cavity, lumen or other space of the
`lead body.
`
`BRIEF SUMMARY OF THE INVENTION
`In accordance with one aspect of the present inven(cid:173)
`[0020]
`tion, cavities, lumens or other spaces (herein referred to
`collectively as lumens) of a cardiac lead body adjacent to a
`lead conductor are filled with a solid rigid electrically
`conductive foam, particularly a conductive aerogel, that
`presents a "deformable space" to the lead conductor travers(cid:173)
`ing the lumen.
`
`[0021] The solid rigid, conductive aerogel foam is in
`intimate contact with the un-insulated surface of the lead
`conductor providing a redundant conductive path alongside
`the conductor. A fracture of the lead conductor section that
`increases conductor resistance or results in an open circuit is
`bridged by a continuous segment of the conductive aerogel
`that the lead conductor contacts.
`
`In fabrication, the lead conductor is preferably
`[0022]
`coated with a fluid conductive aerogel that solidifies about
`the lead conductor between the lead conductor and an
`insulating tube, sheath or layer surrounding the lead con(cid:173)
`ductor.
`
`[0023] The solidified conductive aerogel is relatively rigid
`but can be stretched, crushed, or deformed when a sufficient
`force is applied. During chronic implantation, the solidified,
`conductive, aerogel is stretched, compressed or deformed by
`flexing of the lead conductor within the lead body insulator
`due to externally applied stresses, whereby the lead conduc(cid:173)
`tor is allowed to flex within the space created by the
`deformation thereby releasing stress on the lead conductor.
`The solidified conductive aerogel is also deformed if a
`crushing force is applied to the lead body. The deformation
`crushes the conductive aerogel upon itself to the extent that
`the lead conductor is bent or crushed but the conductive
`aerogel does not itself fracture and makes contact with the
`lead conductor to bridge any lead conductor fracture due to
`crushing or severe bending. The crushed conductive aerogel
`retains its conductivity providing a conductive bridge across
`any lead conductor fracture.
`
`[0024] Conductive or non-conductive aerogels can be
`employed to fill spaces in other IMDs where it would be
`desirable to restrict motion of conductors or other compo(cid:173)
`nents disposed within the space that would lead to fracture
`or failure over prolonged exposure to applied stresses.
`
`[0025] This summary of the invention has been presented
`here simply to point out some of the ways that the invention
`overcomes difficulties presented in the prior art and to
`distinguish the invention from the prior art and is not
`intended to operate in any manner as a limitation on the
`interpretation of claims that are presented initially in the
`patent application and that are ultimately granted.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0026] These and other advantages and features of the
`present invention will be more readily understood from the
`following detailed description of the preferred embodiments
`thereof, when considered in conjunction with the drawings,
`in which like reference numerals indicate identical structures
`throughout the several views, and wherein:
`
`[0027] FIG. 1 is a conventional lCD lead having a trifur(cid:173)
`cation in the lead body in which the present invention may
`be advantageously practiced;
`
`[0028] FIG. 2 is an end cross-section taken along lines 2-2
`of FIG. 1 illustrating a first aspect of a first embodiment of
`the present invention;
`
`[0029] FIG. 3 is a side cross-section view of a sub(cid:173)
`assembly of FIG. 2 of a coiled wire conductor coated with
`a conductive aerogel layer disposed between inner and outer
`non-conductive tubes;
`
`

`

`US 2004/0215300 Al
`
`Oct. 28, 2004
`
`4
`
`[0030] FIG. 4 is an end cross-section view of the sub(cid:173)
`assembly of FIG. 2 of a stranded wire cable conductor
`coated with a conductive aerogel layer disposed within a
`non-conductive layer or tube;
`
`[0031] FIG. 5 is a side section view of the trifurcation of
`the lead body of FIG. 1 illustrating a second aspect of the
`first embodiment of the present invention; and
`
`[0032] FIG. 6 is a schematic, cross-section, side view of
`a fracture in a segment of the stranded lead conductors of
`FIGS. 2, 4, and 5 and the bending, crushing and stretching
`of the conductive aerogel coating bridging the fracture.
`
`DETAILED DESCRIPTION OF 1HE
`INVENTION
`
`In the following detailed description, references are
`[0033]
`made to illustrative embodiments of methods and apparatus
`for carrying out the invention. It is understood that other
`embodiments can be utilized without departing from the
`scope of the invention.
`
`In accordance with the present invention, conduc(cid:173)
`[0034]
`tive aerogels are incorporated into IMDs and preferred
`embodiments
`incorporating conductive aerogels
`into
`implantable medical lead bodies are described herein. As
`characterized by D. R. Rolison et al., "Aerogels ... are
`nanoscale mesoporous materials of low density and high
`surface area ... in which nano-meter solid domains (the
`"being") are networked through a continuous highly porous
`volume of free space (the "nothingness") ... " (see "Elec(cid:173)
`trically conductive oxide aerogels: new materials in electro(cid:173)
`chemistry", J. Mater. Chern., 2001, 11:963-80). A typical
`aerogel is 99.8% air (nothingness) and 0.2% matter (being)
`and is the lightest known material weighing about 3 milli(cid:173)
`grams per cubic centimeter and one of the best known
`thermal insulators. Aerogel is sometimes called "solid
`smoke" because of its extraordinarily low density and the
`bluish cast it takes when light shines on it.
`
`[0035] The first non-conductive aerogels were created in
`the 1930s of silicon dioxide and have largely remained a
`scientific curiosity, but various potential uses of non-con(cid:173)
`ductive and more recently developed conductive aerogels
`are outlined in the Rolison et al. article, including use as
`insulators, sensor elements, Cerenkov detectors, in Space
`Shuttle missions and in the "Stardust" mission launched
`Feb. 7, 1999, to intercept the tail of comet Wild-2 in 2004,
`capture samples of the comet's tail and return to earth with
`the samples.
`
`[0036] The Rolison article describes a variety of conduc(cid:173)
`tive aerogels, including the early-developed aerogels ren(cid:173)
`dered conductive by incorporating carbon soot into the
`"being" or incorporating various metal oxides into the
`"being". Preferred conductive aerogels can be formed incor(cid:173)
`porating platinum and gold particles or various metal oxides
`within the aerogel. Aerogels are produced from certain gels
`described in the Rolison article, for example, by heating the
`gel under pressure, which causes the liquid in the gel to
`become supercritical (in a state between a liquid and a gas)
`and lose its surface tension. In this state, the liquid may be
`removed from the gel by applying additional heat, without
`disrupting the porous network formed by the gel's solid
`component. Exemplary methods of fabricating and potential
`uses of the conductive metal oxide aerogels in electrochemi-
`
`cal cells, capacitors, catalytic converters, and the like are
`described in the Rolison article.
`
`It is my belief that such aerogels, particularly
`[0037]
`conductive aerogels, can be advantageously used in many
`IMD applications. Particular exemplary uses in the context
`of an electrical medical lead having a flexible and resilient
`lead body that is likely to be subjected to bending and
`compression stresses when implanted in the body are
`described as follows.
`
`In fabrication, one or more lead conductor is
`[0038]
`extended through a conductor lumen, and a mass of fluid
`conductive aerogel is deposited within at least a portion of
`and extending for a distance along the elongated lumen in
`contact with the conductor. The deposition is preferably
`effected by coating the surface of the conductor with a fluid
`conductive aerogel before the aerogel coated conductor is
`covered by an insulating sheath or fitted into a lumen of an
`insulating tube or tube. The coating can be formed by
`extrusion of the fluid conductive aerogel over a continuous
`length of the conductor. The fluid conductive aerogel solidi(cid:173)
`fies in intimate contact with the conductor to provide a
`generally rigid support of the lead conductor and a deform(cid:173)
`able space thereover.
`
`[0039] The solidified conductive aerogel is relatively rigid
`but can be crushed or deformed or stretched axially when a
`sufficient force is applied. Thus, the conductive aerogel
`becomes a deformed space. Preferably, one or more further
`non-conductive polymer layers can be extruded over the
`conductive aerogel layer.
`
`It will be understood that the present invention can
`[0040]
`be practiced in the context of any electrical medical lead,
`e.g., any conventional cardiac pacing leads, lCD leads,
`neurostimulation leads, etc., and that the figure merely
`illustrate one exemplary electrical medical lead. FIG. 1
`therefore illustrates an exemplary endocardial lead 100,
`embodied as a transvenous I CD lead of the type disclosed in
`the above-referenced '625 patent, in which the present
`invention is advantageously practiced. The lead 100 com(cid:173)
`prises an elongated lead body 10 extending between proxi(cid:173)
`mallead connector assemblies 30, 36 and 46 and a lead body
`distal end 13. The lead body 10 is a complex structure
`having distinct proximal, intermediate, and distal regions
`through which four electrical lead conductors that are elec(cid:173)
`trically insulated from one another by components of a lead
`body insulator extend.
`
`[0041] The distal region of the lead 100 includes a number
`of components, in this embodiment, including an elongated,
`open-coil, proximal cardioversion/defibrillation electrode
`26, an elongated open-coil, distal cardioversion/defibrilla(cid:173)
`tion electrode 24 and a distal tip-ring assembly. The elon(cid:173)
`gated open-coil structure retains flexibility in along the
`lengths of the proximal and distal cardioversion/defibrilla(cid:173)
`tion electrodes 26 and 24. The distal tip-ring assembly
`includes distal tip pace/sense electrode 12, tine sheath 16
`carrying tines 14, tip-ring spacer component 18, ring-shaped
`pace/sense electrode 20, and ring-coil spacer component 22.
`The tine sleeve 16 fabricated of silicone rubber or a rela(cid:173)
`tively softer polyurethane, and the tip-ring and ring-tip
`spacers 18 and 22 fabricated of relatively harder plastics, for
`example polyurethane having a Shore hardness of at least
`75D, to provide a relatively rigid distal tip-ring assembly
`extending to the distal end of distal defibrillation.
`
`

`

`US 2004/0215300 Al
`
`Oct. 28, 2004
`
`5
`
`[0042] The lead body insulator in the intermediate region
`comprises an elongated tubular lead body insulator 11,
`depicted in cross-section in FIG. 2. The lead body insulator
`11 in the proximal region comprises a trifurcation sleeve 28
`depicted in FIG. 3, joining the proximal end of the elongated
`tubular lead body insulator 11 with the distal ends of
`insulating sleeves 31, 37 and 47 extending proximally from
`the trifurcation sleeve 28 to the proximal lead connector
`assemblies 30, 36, and 46, respectively. The trifurcation
`sleeve 28 includes an axially extending sleeve trunk 29 and
`trifurcation branches 33, 39 and 49. Each of the sleeve trunk
`29 and trifurcation branches 33, 39 and 49 encloses a sleeve
`cavity or lumen that proximal segments of lead conductors
`extend through. The trifurcation branches 33, 39 and 49 can
`be unintentionally stressed in movement outward in the
`directions of arrows A and B, respectively, during handling
`at implantation or chronically due to body motion.
`
`[0043] The lead body insulator 11 in the distal region is
`preferably fabricated of polyurethane and supports various
`insulating components and spacers supporting the distal
`array of components, e.g., electrodes 12, 20, 24 and 26 and
`the distal passive fixation tine sheath 16 as disclosed in detail
`in the above-referenced 625 patent. The lead body 10
`comprises four mutually insulated, elongated conductors
`disposed within the lead body insulator 11 that are not
`visible in FIG. 1. Three of the insulated conductors are
`stranded wire conductors, each coupled to one of ring(cid:173)
`shaped pace/sense electrode 20, elongated wire coil, distal
`cardioversion/defibrillation electrode 24 and elongated wire
`coil, proximal cardioversion/defibrillation electrode 26. A
`fourth, wire coil, conductor is coupled to distal tip pace/
`sense electrode 12.
`
`[0044] Connector assembly 30 supports a single connector
`pin 34, coupled to the conductor coupled to the distal
`cardioversion/defibrillation electrode 24, and is provided
`with sealing rings 32 to seal the connector assembly 30
`within the connector bore of an lCD lPG connector header
`upon implantation. Similarly, connector assembly 46 is
`provided with a single connector pin 50 coupled to the
`conductor coupled to the proximal cardioversion/defibrilla(cid:173)
`tion e