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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to a lead bearing an electrode for electrically
connecting an organ inside a living animal body to an electrical device.
Notwithstanding its various uses, this invention will be described for
purposes of this description for use as an endocardial pacing and sensing
lead for connecting an artificial cardiac pacemaker to cardiac tissue.
There are generally two types of body-implantable leads used with cardiac
pacemakers -- one which requires surgery to expose the myocardial tissue
to which the electrode is in some manner or another affixed and another in
which a lead with an electrode or electrodes located at its distal end is
inserted in and guided through a body vessel such as a vein into the heart
where the electrodes contact, and in some cases are secured to the heart
through the endothelial tissue lining the inside of the heart. The former
leads are generally referred to as myocardial type leads while the latter
are generally referred to as endocardial type leads. Examples of prior
myocardial leads may be found in U.S. Pat. No. 3,216,424, 3,416,534,
3,472,234, and 3,737,579. Examples of prior art endocardial leads may be
found in U.S. Pat. No. 3,348,548, 3,754,555, 3,814,104, 3,844,292, and
3,974,834 and in publications such as "New Pacemaker Electrodes" by Max
Schaldach appearing in Vol. 17 Transactions: American Society for
Artificial Internal Organs, 1971, pp. 29-35; German Offenlegungsschrift
No. 2,516,848 entitled "Transvenous Stimulation Electrode for Heart
Pacemakers" published Oct. 28, 1976; and German Offenlegungsschrift No.
2,539,553 entitled "Electrode Assembly for Medical Purposes" published
Mar. 10, 1977. These prior art teachings relate to various types of
endocardial leads which are simple to manufacture and importantly are
relatively easy to use by the implanting physician. The attributes of an
endocardial lead which are most desirable are that the electrode be
capable of being firmly secured into the wall of the cardiac tissue to
prevent dislodgement while avoiding perforation of the electrode all the
way through the cardiac tissue. In addition, it is important that the
means used to secure the lead to the cardiac tissue be protected from
causing damage to the vein, heart valve, or other tissue through which the
lead is inserted into the heart. Other features of importance include
electrodes having the desired shape and surface area requirements and
means for securing the electrode to the heart without applying any
permanent twisting or torque to the lead which will cause it to be
stressed while in chronic use. Another problem with prior art leads has
been that it is difficult to know exactly to what extent the means for
securing the electrode to the cardiac tissue has been successfully
achieved when the lead is in its final placement. Still another concern
is, whether once in place, the electrode and/or securing means can be
totally withdrawn out of the vein or at least disengaged from cardiac
tissue and appropriately repositioned. The above cited prior art
references have attempted with varying degrees of success to provide
endocardial leads having some of the desirable features without any of the
attendant problems or undesirable characteristics as described above.
The body-implantable lead of the present invention provides those features
most desirable in an endocardial lead without those undesirable problems
or characteristics. The present invention provides a body-implantable lead
in which the electrode is of the desirable ring type having a desired
shape and surface area. The electrode is a substantially elongated member
having an opening passing therethrough in which is partially housed a
helix. While the lead is being inserted and guided through the vein to the
heart, the portion of the helix which extends out of the distal end of the
electrode is prevented from causing any injury or damage to the vein,
valve, or other tissues. Once in the desired location and position in the
heart, the lead may be rotated so that the helix may very simply be
screwed into the heart through the endocardial tissue. The helix once
secured in place serves to hold the ring electrode in firm engagement with
the cardiac tissue for providing the desired electrical stimulation as
well as the detection to electrical signals from the heart. In the
preferred embodiment the helix is electrically insulated from the
electrode so that it serves only to secure the electrode in firm
engagement with the tissue but in an alternate embodiment without the
insulating member the helix may also be part of the electrode system if
desired. Another feature of the present invention is that sealing means
are provided in the opening in the electrode for preventing body fluids
and tissue from reaching the proximal end of the electrode through the
opening in the distal end.
SUMMARY OF THE INVENTION
The above features and advantages of the present invention, as well as
others, are accomplished by providing a body-implantable lead having
tissue securing means at the distal end thereof for securing an electrode
in contact with tissue at a desired location and movable means for
preventing the tissue securing means from causing injury as the lead is
inserted in and guided through a body vessel to the desired location. The
lead further comprises a proximal end adapted to be connected to a medical
device, the tissue securing means and electrode means at the distal end
thereof, and an electrical conductor extending therebetween encased in
material means substantially inert to body fluids and tissue. The
electrode means comprises a substantially elongated member having a
chamber therein along its length. The tissue securing means are located
partially within and extending beyond at the distal end of the electrode
means for securing the electrode means in firm engagement with the
endocardial tissue at the desired location. Sealing means located in the
chamber are provided for preventing body fluids and tissue from reaching
the proximal end of the electrode means through the lumen extending to the
distal end of the electrode means. The movable means positioned within the
chamber are provided for protecting the tissue securing means from causing
injury to the body vessel, valve or other tissues as the lead is inserted
and guided through a body vessel to the desired location.
Preferably, the tissue securing means is a helix having several spaced
turns. The movable means is an elongated cylindrical rod located in the
chamber in the electrode means. The distal end of the rod is positioned
within the coils at the proximal end of the helix. A stylet pressure fit
at its proximal end to the proximal end of the lead passes through the
lumen defined by the conductor coil comprising the conductive lead means.
The lumen communicates with the opening in the proximal end of the
electrode means such that the distal end of the stylet when fully inserted
passes into the opening in the proximal end of the electrode means and
engages the proximal end of the rod moving the distal end of the rod out
of the opening at the distal end of the electrode means and within the
coils of the helix extending beyond the distal end of the electrode means.
In this manner the point and turns of the helix extending beyond the
distal end of the electrode means are protected from causing injury or
damage to the vein, valve, or other tissues as the lead is inserted and
guided to the desired location. Once the lead is at the desired location
the first stylet is totally withdrawn from the lead freeing the rod for
automatic retraction back into the chamber in the distal end of the
electrode means. A second stylet, which cannot contact the rod either
because it is not long enough or of sufficiently large cross-sectional
diameter that it does not pass through the opening in the proximal end of
the electrode means, is inserted in the lead. The lead is then rotated a
desired amount causing the helix to be screwed into the endocardial and
myocardial tissues to secure and permanently maintain the ring electrode
in the desired contact with the tissue. Other features, advantages and
objects of the present invention will hereinafter become more fully
apparent from the following description of the drawings, which illustrate
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a view of a preferred embodiment of the body-implantable,
intravascular lead of the present invention including in part an inside
elevation partly in longitudinal section of the electrode end portion of
the lead;
FIGS. 2 through 5 show stylets useable in conjunction with the lead of the
present invention;
FIG. 6 shows a cross section viewed of a keyway defining the opening into
which the correspondingly shaped end of the stylet of FIG. 6 may be
placed; and
FIG. 7 shows the lead of FIG. 1 being lodged in and permanently secured to
the tissue forming the apex of the right ventricle of the heart.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the preferred embodiment of the invention depicted in FIG.
1, there is shown an intravascular endocardial lead comprising an
elongated lead portion 10, a distal electrode end portion 12 and a
proximal terminal end portion 13. The lead, in unipolar configuration,
comprises a closely wound, coiled conductor 14 in the form of a spring
spirally wound about and along the axis of the conductor. The spring coil
14 extends through the length of the lead 10 in a lumen of a jacket or
sleeve 16 of electrically insulating material.
The spiral conductor 14 is formed of electrically conductive material
offering low electrical resistance and also resistant to corrosion by body
fluids. A platinum-iridium alloy is an example of a suitable material.
Sleeve 16 is formed of an electrically insulating material, and preferably
a silicone rubber such as clean room grade Silastic available from Dow
Corning Corporation or a polyether urethane such as Pellethane.RTM.
CPR.RTM. 2363-80AE available from the Upjohn Company. These materials are
additionally suitable because they are inert and well tolerated by body
tissue.
At the proximal end 13 of the lead 10, the conductor 14 is received in and
crimped to tubular terminal pin 18. Terminal pin 18 projects beyond sleeve
16 and is adapted for insertion in receptacles provided on the pulse
generator, which can comprise any suitable implantable pulse generator
such as that shown for example in U.S. Pat. No. 3,057,356.
The pin 18 and the spiral conductor 14 are hollow defining a lumen and
thereby adapted to receive a stiffening stylet 20 that extends through the
length of the lead 10. The stylet 20 stiffens the lead 10, and its
proximal end, adjacent the proximal end 13 of the lead, is formed to
provide means, such as the knob 21, which is knurled on its outer surface
for rotating the stylet about its axis to thereby direct the distal end 12
of the lead as it is inserted through the vein. The stylet imparts
rigidity to the proximal portion of the leads and can be manipulated to
introduce an appropriate curvature to the distal, electrode end portion
facilitating the insertion of the lead into and through a vein and through
an intracardiac valve, for example one of the jugular veins and the
tricuspid valve, to advance the distal end 12 of the led into the right
ventricle of the heart. In the present invention two different stylets are
used, each having a slightly different purpose as will hereinafter be
explained.
At the distal end of the lead 10 an electrode body in the form of an
elongated member 22 is provided. Electrode body 22 has an opening 24 which
passes completely therethrough along its longitudinal axis from its
proximal end 26 to its distal end 28. Integrally formed as part of
electrode body 22 and located at its distal end 28 is a raised portion 30
which serves as the ring electrode of lead 10. The outer surface of ring
electrode 30 is somewhat rounded and smooth having the desired shape and
surface area for the required stimulation and detection of electrical
signals from the heart. Electrode body 22 in the preferred embodiment is a
substantially cylindrical member having a circular cross section but may
take a number of other configurations. Electrode body 22, preferably is
made of a corrosion resistant, electrically conductive material, e.g.,
platinum or a platinum alloy, a metal oxide or a carbon compound. In the
specific embodiment shown, electrode 22 is made of a platinum-iridium
alloy. The entire outer surface of electrode body 22 except the raised
portion forming ring electrode 30 is insulated as shown by the continuous
covering provided by sleeve 16 which conforms to the shape of the outer
surface of electrode body 22. In this way the entire lead is electrically
insulated when it is connected to the pulse generator from the body except
at the ring electrode 30.
Opening 24 passing through electrode body 22 is sectioned into two chambers
32 and 34. Chamber 32 located at the proximal end 26 of electrode body 22
is somewhat smaller in cross section than chamber 34 which is located
toward the distal end 28. A restriction 36 is provided on the inner
surface of opening 24 and located between the chambers 32 and 34.
Distal end 38 of conductor coil 14 is located in chamber 32 whereby the
lumen defined by coil 14 communicates with the distal end of chamber 32
and with chamber 34 located on the distal side of restriction 36. The
distal end 38 of coil 14 is physically maintained, and mechanically and
electrically connected to electrode body 22 via a crimped portion 40 in
the proximal end 26 of electrode body 22. This mechanical connection
between coil 14 and electrode body 22 could be accomplished in ways other
than crimping.
Coil 14 is of a well known construction similar to the conductor coils
disclosed in U.S. Pat. Nos. 3,348,548 and 3,974,834. A lead such as 10
using a conductor coil such as coil 14 has been shown to be capable of
withstanding constant, rapidly repeated flexing over a period of time
which can be measured in years. The conductor coil is wound relatively
tightly, although there can be a slight space between adjacent turns. This
closely coiled construction provides a maximum number of conductor turns
per unit length, thereby providing optimum strain distribution. The
spirally coiled spring construction of conductor 14 also permits a
substantial degree of elongation, within the elastic limits of the
material, as well as distribution along the conductor of flexing stresses
which otherwise might be concentrated at a particular point. Both the
conductor 14 and the insulating sleeve 16 are elastic, and this, together
with the coiled construction of the conductor, assures maximum
distribution of flexing strains. Conductor 14 may also comprise a
multi-filar redundant coil of thinner, highly elastic wire.
A tissue securing member in the form of a relatively rigid circular
corkscrew or helix 42 is provided having a proximal end 44 of several
closely wound turns located in the chamber 34 at the distal end 28 of
electrode body 22. Helix 42 has a distal end 46 formed by about two spaced
turns which extend out of chamber 34 beyond the end of ring electrode 30
approximately 0.08 inches. These turns end in a sharpened tip 48 at a
point on the inside circumference of the wire making up helix 42. An
insulating hollow sleeve 50 is provided tightly fitting in at the distal
end 28 inide chamber 34. Sleeve 50 may be made of Delrin.RTM. or other
suitable body compatible, insulating material. A crimp is provided in
electrode body 22 near its distal end 28 at crimped portion 52. Crimped
portion 52 serves to hold proximal end 44 of helix 42 in fixed position
from lateral or rotational movement by squeezing or crimping the adjacent
portion of sleeve 50 and several closely wound turns at the proximal end
28 of helix 42. Again, this fixing of helix 42 in position could be
accomplished in other ways than by crimping. Sleeve 50 serves to help fix
helix 42 in place as well as insulate helix 42 from electrode body 22 so
that helix 42 serves only as a means of securing and maintaining ring
electrode 30 in firm engagement with endocardial tissue as will later be
described. In this arrangement helix 42 forms no part of the electrode
structure. Of course, if it were desired in certain applications that
helix 42 form a part of the electrode structure, this could be
accomplished by eliminating insulating sleeve 50. Helix 42 in its
uncrimped section 46 has a nominal outside diameter of approximately 0.06
inches with the nominal outside diameter of sleeve 16 and ring electrode
30 being about 0.13 inches. Helix 42 is a platinum-iridium coil made of
approximately 0.012 inch outer diameter wire.
Also provided in chamber 34 is an elongated plunger or rod 54 which is
generally circular in cross section. Rod 54 may be made of Delrin.RTM.
plastic or any other suitable body compatible material such as a hardened
epoxy, nylon or urethane. Rod 54 has a proximal end 56 at which is located
a flattened head 58 and a distal end 60 which is somewhat greater in
cross-sectional diameter than proximal end 56 of rod 54. Distal end 60 of
rod 54 provides a relatively close fit within the portion of helix 42
distally of the crimped turns at proximal end 44 as well as within the
spaced turns of distal end 46 of helix 42. In its unextended position
distal end 60 remains totally within chamber 34 and does not extend beyond
the distal end of electrode body 22.
A boot 62 is provided in chamber 34 near head 58 of rod 54. This boot 62
has a leg portion 64 which extends outwardly from rod 54 and fits tightly
against the inner surface of chamber 34. Boot 62 may snap tightly and fit
onto rod 62 or may be secured in a groove provided on the outer surface of
rod 54 near head 58. Leg 64 has an end portion 66 extending from the end
of leg 64 which fits against and under the proximal end of sleeve 50. Boot
62 may be made of a silicone rubber or other body compatible, flexible
material. Boot 62 serves to seal off body fluids and tissue coming into
chamber 34 at the distal end 28 of electrode body 22 from reaching chamber
32 or the distal end 38 of coil 14. Boot 62 is sufficiently flexible so as
to allow movement of rod 54 whereby distal end 60 of rod 54 moves distally
outward from chamber 34 beyond the end of ring electrode 30 through the
spaced turns all the way to the very distal end of helix 42 as shown in
dotted lines, the purposes of which will be later explained in conjunction
with the operation of the present invention.
It will be understood from the following description that the boot 62 as
shown in FIG. 1 is compressed upon itself as distal end 70 of stylet 20
bears against head 58 of rod 54, to move rod 54 to its advanced position.
In a further embodiment (not illustrated), the cylindrical boot 62 may be
fixed at one of its ends near the restriction 36 and at its other end to
the distal side of the head 58 nearest helix 42. In this second
embodiment, the body of the boot would be stretched as the end 70 advances
the rod 54 into the advanced position and would also provide the requisite
sealing of the lead body within conductor 14 from body fluids and tissue.
FIGS. 2 through 5 show stylets that may be used in conjunction with the
lead 10 of the present invention. Stylet 20 shown inserted in lead 10 in
FIG. 1 has a length L.sub.1 and a cross sectional diameter D.sub.1. When
fully inserted in lead 10 through terminal pin 18 knurled knob 21 of
stylet 20 is pressure fit on the end of pin 18. Length L.sub.1 of stylet
20 passes through the lumen defined by coil 14 and as seen in FIG. 1,
stylet 20 has a distal end 70 which presses against head 58 of rod 54.
When fully inserted the distal end 70 of stylet 20 moves the distal end 60
of rod 54 out of the distal end 28 of electrode body 22 and beyond ring
electrode 30 into the dotted position shown in FIG. 1. In this extended
position, distal end 60 of rod 54 serves to protect the tip 48 and spaced
turns at distal end 46 of helix 42 from causing any damage to the vein,
valve or other tissue through which lead 10 is inserted and guided. Thus
stylet 20 serves to move rod 54 into its extended protective position as
shown dotted in FIG. 1.
A second stylet may then be required to be used for screwing distal end 46
of helix 42 into endocardial and myocardial tissue. Either stylet 72, 74,
or 84 may be used for this purpose. These stylets each have knurled knobs
76, 78 and 86 respectively fixed on the proximal ends thereof. The knobs
are all the same as knob 21 on stylet 20. Stylets 72, 74 and 84 are made
so as to be readily visibly and tactily distinguishable from stylet 20.
Stylet 72 has the same cross section diameter D.sub.1 as stylet 20 but has
a shorter length L.sub.2 than the length L.sub.1 of stylet 20. Length
L.sub.2 is sufficiently shorter than length L.sub.1 of stylet 20 that when
stylet 72 is fully inserted into lead 10, its distal end 80 does not reach
or contact rod 54 so that rod 54 remains in its retracted or unextended
position wholly within electrode body 22. Stylet 72 thus allows the tip 48
of helix 42 and the spaced turns at distal end 46 of helix 42 to pierce
endocardial tissue and allows a sufficient portion of the spaced turns to
be screwed into the tissue as stylet knob 76 and proximal end 13 of lead
10 are rotated. Helix 42 thereby advances through endocardial tissue into
myocardial tissue to be retained therein and inhibited from dislodgement
therefrom by the spaced turns at the distal end 46 of helix 42. In such
position ring electrode 30 is secured in position to firmly maintain
contact with the cardiac tissue to permit appropriate electrical
stimulation and detection of electrical signals to take place through ring
electrode 30. Alternatively to stylet 72, stylet 74 is provided, which
although having the same length L.sub.1 as stylet 20 has a cross-sectional
diameter D.sub.2 somewhat greater than diameter D.sub.1 of stylet 20.
Because of this greater diameter D.sub.2 when stylet 74 is inserted in
lead 10, the distal end 82 is unable to pass through restriction 36 and
therefore cannot reach rod 54, leaving rod 54 in its unextended position.
Stylet 74 is then used to secure helix 42 into endocardial tissue in the
same manner as described above with respect to stylet 72.
The stylet 84 of FIG. 5 has a main body diameter of D.sub.2 and a distal
end portion 88 that is flattened to have a cross section that may be the
same dimension as D.sub.1. FIG. 6 depicts a cross section of the distal
end 12 of lead 10 at the restriction 36. The restriction 36' depicted in
FIG. 6 is rectangular in shape having dimensions D.sub.1 + and D.sub.2 +
closely slightly larger than those dimensions D.sub.1 and D.sub.2 of the
portion 88 of stylet 84. In use, the distal portion 88 extends through
restriction 36 to extend rod 54 in the manner herein described and, upon
partial retraction allows the rod to retract when the helix is to be
screwed in. The key relationship of restriction 36' and portion 88 allows
torque to be transmitted directly from knob 86 to restriction 36' to
facilitate screwing the helix into the heart.
A mark at the proximal end of the stylet 84 may be provided to show the
amount by which the stylet should be withdrawn to allow rod 54 to retract.
In addition rod 54 may be made with a radio-opaque material so that its
position may be determined during insertion under fluoroscopy. Of course,
restriction 36' and portion 88 could have other matching or keyed
configurations.
Turning now to FIG. 7, there is shown an illustration of the partially
introduced lead 10 of the present invention in a vein (position A) and the
completed introduction and permanent securement of the helix 42 in the
tissue forming the apex of the right ventricle of a heart (position B).
In FIG. 7, the heart 130 in cross section comprises the four chambers,
namely, the right ventricle 131, the right atrium 132, the left atrium 133
and the left ventricle 134. In the placement of an endocardial lead, it is
preferable to use a venous approach on the low pressure side of the heart,
that is, through a vein, e.g., the right or left external jugular veins or
the right or left cephalic veins 135, the superior vena cava 136, the
right atrium 132, the tricuspid valve 137 and the right ventricle 131.
During introduction of the lead 10, it must travel a convoluted course
through the veins and must pass through the valve 137 without causing any
damage to the tissue. It is also desirable that the lead 10 have a small
cross section so that it will easily pass through the veins without
causing excessive stretching of the veins.
In position A of FIG. 7, the distal end 12 of lead 10 is shown in part. To
get to this position stylet 20 is fully inserted in proximal end 13 of
lead 10 with knob 21 pressure fit on the end of terminal pin 18. In this
position distal end 70 of stylet 20, for example, presses against head 58
of rod 54 moving the rod into its extended position. In extended position,
distal end 60 of rod 54 is located inside the spaced turns at the distal
end 46 of helix 42 and extends past the tip 48. In this extended position
the distal end 60 of rod 54 serves to protect the spaced turns at distal
end 46 and point 48 of helix 42 from causing any damage to the vein, the
superior vena cava 136, the right atrium 132, valve 137 or right ventricle
131 as lead 10 is inserted into vein 135 and guided into the apex at the
bottom of the right ventricle 131 or in other suitable sites in the right
ventricle or right atrium.
Once lead 10 is appropriately situated, for example in the apex of the
right ventricle 131 as seen in position B, stylet 20 is withdrawn from
lead 10, causing rod 54 to automatically be retracted back inside chamber
34 into its unextended position. Then either of stylets 72 or 74 is
inserted through pin 18 into lead 10. As described earlier, the distal
ends 80 or 82 of these respective stylets do not contact rod 54 so that
the rod remains in its retracted or unextended position totally within
chamber 34 of electrode body 22. Therefore tip 48 and the spaced turns at
the distal end 46 of helix 42 are ready to be screwed into the endocardial
tissue in the apex of the right ventricle or other suitable location. Knob
76 or 78 and proximal end 13 of lead 10 are rotated causing tip 48 to
pierce the endocardial tissue and the spaced turns of helix 42 are fully
screwed into myocardial tissue by the continued rotation. Alternatively,
the lead 10 may be turned about the stylet 72 or 74 to screw in the helix
42. Once fully screwed into the myocardial tissue the ring electrode 30 is
secured into firm engagement with the tissue for providing the electrical
stimulation and detection of electrical signals. In the event that for any
reason rod 54 was not automatically retracted back inside chamber 34 when
stylet 20 was completely withdrawn, the screwing of helix 42 into the
tissue will cause the rod to be retracted back into chamber 34 to its
unextended position. Once lead 10 is in secured position, the stylet 72 or
74, whichever was used is fully withdrawn from the lead.
In removing lead 10 from its secured position as seen in position B, first
either stylet 72 or 74 is inserted and by manipulation of knob 76 or 78
respectively and the proximal end 13 of lead 10, the helix 42 is unscrewed
from the tissue. Of course, rod 54 remains in its retracted or unextended
position. Once helix 42 is unscrewed, stylet 20 is fully reinserted into
lead 10 so that distal end 70 moves rod 54 into its extended position. Tip
48 and the spaced turns at the distal end 46 of helix 42 extending out of
ring electrode 30 are protected so that as lead 10 is withdrawn out of the
ventricle 131, back through valve 137, atrium 132, superior vena cava 136
and vein 135, no damage or injury to any of this tissue is caused.
In vivo testing of lead 10 reveals that the helix can be easily and
repeatedly introduced through the vein, through the valve and screwed into
the endocardium, unscrewed and withdrawn from the body through the same
path without causing any significant damage to the tissue that the lead
contacts. The ease of using the lead of the present invention and the
positive securement afforded by a corkscrew or helix together with the
extendable protective rod make it very desirable compared to many prior
endocardial lead designs.
Although a unipolar lead design has been illustrated in the description of
the preferred embodiment, it will be understood that bipolar leads (that
is a lead carrying two electrodes and conductors) may as readily employ
the novel protective rod-ring electrode design of the present invention.
It should be understood that although the use of the lead 10 has been
described for use in a cardiac pacing system, lead 10 could as well be
applied to other types of body stimulating systems.
It should be further understood, of course, that the foregoing disclosure
relates only to the best mode known to the inventor of many possible modes
of practicing the invention and that numerous modifications may be made
therein without departing from the spirit and scope of the invention as
set forth in the appended claims.
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