Multi-contact implantable electrode cable with a resorbable stiffening element

An electrode device which has a proximal end and distal end, contains of a number of thin, insulated electrical conductors each with a proximal end and a distal end, the conductors being equipped with implantable electrode contacts means which are electrically connected to the conductors. These contacts are designed to be brought into electrical contact with tissue in one or more cavities in a human body. Each conductor in the cable device is supported by a pre-shaped stiffening element which runs along and is connected to the conductor, made of an elastic polymer material, resorbable in vivo, which is biodegradable and biocompatible. The stiffening element imparts an arched shaped to the conductor, at least in the area in which its contact is located, to cause the contact to press against the adjacent cavity wall. The cable device also includes a longitudinal channel in which a stylet can be inserted for temporary, linear stretching of the cable device and the arched sections of its conductors.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrode cable device of the type 
having a proximal end and a distal end with one or more thin, insulated 
electrical conductors each having a proximal end and a distal end, at 
least one of the conductors having at least one implantable electrode 
contact in electrical connection with the conductor and intended for 
permanent electrical contact with the wall of a cavity in a human body. 
The cable device of this type is devised so the electrode contact can be 
kept pressed, by means of pre-tensioning, against an area of the wall 
forming the cavity in the body. The body cavity can e.g. be an atrium or a 
ventricle of the heart. 
2. Description of the Prior Art 
An electrode cable device of the aforementioned kind is especially designed 
for introduction into a patient's heart and for anchoring the device's 
electrode contact or contacts in the ventricle and/or atrium. Such an 
electrode cable device is usually introduced into the heart via a vein, 
and the electrode contacts are usually anchored in the right ventricle or 
atrium of the heart. The proximal end of the electrode cable device is 
intended for connection to a heart stimulator which has been implanted 
into the body. The electrode cable device can then be used for carrying 
electrical impulses from the heart stimulator to the heart, via the 
implantable electrode contacts, and/or for sensing and registering heart 
signals. 
U.S. Pat. No. 4,522,212 describes an endocardiac electrode device having at 
least three curved spring wires designed for introduction into the heart, 
each curved spring wire carrying an array of electrodes situated to form a 
characteristic geometric pattern across the ventricular contact area 
covered by the spring wires. The active electrode arrays achieve 
recognizable patterns when inside a heart ventricle and can be viewed with 
a fluoroscope. The electrodes are located in relation to each other and on 
the spring wires so the wires, with their electrodes, can easily be 
squeezed into a narrow spring wire bundle which fits inside a catheter 
during the catheter's introduction into the heart. The catheter can then 
be retracted slightly, exposing electrodes on the curved spring wires 
which spring outwardly into a balloon-like shape inside the heart 
ventricle. The curved spring wires consist of curved metal arches with 
external insulation along their entire length, except at the points at 
which electrodes are attached. When the electrode cable device has been 
implanted inside the heart, the spring wires retain their original 
pre-tensioning, thereby exerting constant pre-tensioning pressure on the 
electrodes. 
U.S. Pat. No. 4,699,147 describes a probe, equipped with a plurality of 
electrodes for intraventricular heart catheterization. The probe has a 
catheter with an open, proximal end, an open distal end and four elongate 
conductor devices, with a distal end section and a proximal end section, 
inside the catheter and projecting beyond the open, proximal end of the 
catheter. Each conductor device has a tubular sleeve, six insulated 
wirelike conductors inside the sleeve and a stiff but flexible central 
core wire arranged inside the sleeve and extending along most of the 
sleeve's length. A proximal contact is mounted on each tubular sleeve. The 
distal end section of each conductor device carries six separate shell 
electrodes connected to each wire-like conductor. The section of each core 
wire at the distal end section of the conductor devices can be made to 
assume a desired configuration after the distal end sections of the 
conductor devices are moved from a retracted position inside the catheter 
to a position in which the distal end sections project outside the 
catheter, and the core wires can be made to assume a desired configuration 
in order to jointly form an elliptical wire sleeve. The catheter is 
designed for introduction into an artery or vein and placement of its 
distal end opening in a heart ventricle. From this end opening, the distal 
end sections of the conductor devices can be extended to form the 
elliptical wire shell and then rotated in stages while electrical 
potentials are measured and recorded at different points on the surface of 
endocardiac ventricular wall in contact with the shell electrodes. Even in 
this known type of electrode cable probe, the core wires retain their 
elliptical configuration from the time they are able to bulge outwardly, 
as a result of their pre-tensioned elliptical shaping, and make contact 
with the ventricular wall of the heart. The shell electrodes are kept 
permanently pressed against the ventricular wall of the heart as a result 
of the spring force residing in the core wires of the conductor devices 
and cannot be pulled out of same. If one of the electrodes were to 
fracture after implantation, the pre-shaping can cause the electrode to 
penetrate the heart wall, with possibly fatal consequences. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an electrode device which 
allows positioning and anchoring of a number of small electrode contacts 
at a corresponding number of sites in the ventricle and atrium of a heart. 
It is a further object to provide such an electrode device which applies 
the electrode contacts against internal surface areas of the walls of the 
ventricle and atrium initially with a given pressure (pre-tensioning) 
exerted by pressure-exerting stiffening elements, after which, following a 
given period of time when the electrode elements have become 
anchored/embedded in heart tissue, the electrode device firmly seats the 
electrode contacts in the respective heart wall area without the continued 
exertion of any residual pressure by any stiffening arrangement. 
The above objects are achieved in accordance with the principles of the 
present invention in an electrode device having a stiffening element which 
is used at an initial stage of electrode implantation to keep the 
electrode contacts pressed against the respective cavity wall, and which 
successively degrades and dissolves after the requisite 
anchoring/embedding of the electrode contacts has occurred, when the 
stiffening element is no longer needed. 
A related object of the invention is to select a material for the 
stiffening element which is slightly bendable but which initially is stiff 
enough to hold the electrode contacts in place against tissue and which, 
by the action of body fluids, gradually loses its stiffening properties 
over a given, appropriate period of time. 
A primary feature of the inventive electrode cable device is that its 
conductor, or each conductor in a multi-electrode version, is supported by 
an elongate, pre-shaped stiffening element, connected to and running along 
the conductor, made of abendable material which is resorbable in vivo. 
This stiffening element is devised and arranged to impart an arched or 
helical shape to at least the section of the conductor on which its 
contact is located. The electrode cable device also has a channel, which 
extends longitudinally through the device, into which a stylet can be 
removably inserted to permit temporary, substantially linear straightening 
of the cable device and its conductor's arched or helical section. 
The bendable material, which is resorbable in vivo, is, according to the 
invention, a material which is biodegradable or soluble within an 
appropriate period of time after it comes into contact with blood. The 
resorbable or degradable material is preferably selected from the groups 
of proteins/amino acid polymers, polyhydroxycarboxyl acids and/or 
carbohydrate polymers. The proteins/amino acid polymers group can contain 
gelatin, collagen, polyserine, polythreonine, polyphenylalanine or the 
like. The polyhydroxycarboxyl acids group can contain polylactides and/or 
polyglycolides. The carbohydrate polymers group can contain dextran, 
starch, hyaluronic acid, cellulose or the like. 
Breakdown or degradation time for the material resorbable in vivo should be 
at least several hours but should generally be on the order of about 24 
hours to three to four weeks or, in some instances, months. 
In an embodiment in which the electrode cable device has at least one pair 
(preferably two pairs) of thin, insulated electrical conductors, each 
conductor in each pair can have an electrode contact, serving as a 
microelectrode, arranged on a convex, arching section of its conductor, 
which bulges out from the center line (longitudinal axis) of the cable 
device, the conductors in each pair of conductors arching outwardly in 
opposite directions. 
With a cable device devised in this way, both conductors, equipped with 
stiffening elements, in each conductor pair form a convex 
position-retaining means in the body cavity in which the conductor pair is 
located. 
When the electrode cable device according to the invention is to be used 
for placing groups of electrode contacts in separate body cavities, such 
as the atrium and ventricle of a heart, a version is used in which two 
groups of electrode contacts are disposed in their respective cavity 
(chamber) by two longitudinally separate contact areas of the device. Each 
contact area is intended for a separate body cavity. When such a cable 
device has four pairs of insulated electrical conductors, the electrode 
contacts can suitably be distributed among the contact areas with the 
contacts for two pairs of conductors respectively disposed in two contact 
areas. 
When the electrode contact means are grouped for activity in different 
contact areas (in different body cavities), the electrical conductors plus 
attendant stiffening elements form bundled cable strings within the cable 
section in which the conductors have no contacts, e.g. between the 
above-mentioned contact areas. The pre-shaped stiffening elements, which 
are connected to the conductors and extend along same, can be devised in 
different ways. In a particularly simple embodiment, each stiffening 
element is a tubular sleeve on the exterior of the conductor. 
Alternatively each stiffening element can be a continuous band-shaped or 
wire-like element running along and attached to the conductor. 
A channel for temporarily receiving a stylet can be formed by a 
longitudinal channel inside the cable string sections, with a round 
cross-section. 
The distal ends of the conductors in an anterior contact area are 
appropriately connected to the channel at the distal end of the cable 
device. 
The pre-shaped stiffening element running along each conductor, as 
described above, is made of a bendable material which is resorbable in 
vivo. This material should be biodegradable and dissolve in the body 
within an appropriate period of time after being in contact with blood. 
The period of time must be such that the respective electrode contact has 
time to become embedded in the tissue of the wall of the respective body 
cavity before the stiffening element degrades and dissolves through the 
action of blood. The degradation and removal by the blood of the 
stiffening element after a given period of time accordingly completely 
removes stiffening element along each conductor after this given period of 
time during which the electrode contact has become embedded into the wall 
of the adjacent body cavity, thereby eliminating the continued presence of 
a stiffening, pressure-application means for the electrode contact after 
it is no longer needed, thereby conveying a major advantage. 
The risk of a future fracture of the arched, electrode contact-carrying 
wires causing fatal consequences, as is present with the aforementioned 
known types of electrode contact devices is accordingly avoided. 
This possibility obviously poses a life-threatening risk to a patient in 
whom a conventional pre-shaped conductor is implanted, since fatigue 
fracture of a spring-biased wire, in the heart as an "electrode holder", 
could have fatal consequences if any part of the broken wire spring 
penetrates the wall of the ventricle or atrium, an event which may lead to 
death caused by internal bleeding.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 schematically depicts an electrode cable device 2 according to the 
invention. The cable device has a proximal end 4 and a distal end 6 and, 
in this instance, eight thin, flexible, insulated electrical conductors 8, 
10, 12, 14, 16, 18, 20 and 22, each with a proximal end and a distal end. 
Each conductor in the electrode cable device 2 is supported by an 
associated, elongate stiffening element 24, 26, 28 and 30, connected to 
the conductor. Each such stiffening element 24-30 extends along at least 
part of the conductors. In the illustrated instance, the stiffening 
element 24 passes axially through the electrode cable device 2, and the 
stiffening element 24 accordingly supports both the electrical conductors 
8 and 16. In the corresponding manner, the stiffening element 26 supports 
both the insulated electrical conductors 10 and 18. The stiffening 
elements 28 and 30 correspondingly support the electrical conductors 12 
and 20, and 14 and 22, respectively. 
The proximal ends of the pre-shaped stiffening elements 24-30 are connected 
to one end of a common electrode cable connector 32 on the proximal end 4 
of the electrode cable device 2. The electrode cable connector 32 is for 
connecting the electrode cable device 2 to a heart stimulator or pacemaker 
(not shown). At the lower end, as shown in FIG. 1, the connector 32 is 
equipped with a stylet orifice 34 through which a stylet 36, shown in FIG. 
2, can be inserted into a channel 38 in the electrode cable device 2. The 
channel 38 extends axially along the length of the cable device 2 from the 
connector 32 to an electrode contact 41 at the distal end 6 of the cable 
device 2. The channel 38 can be e.g. a thin, relatively stiff but flexible 
tube having a longitudinal channel 40 into which the stylet 36 can be 
introduced in order to achieve axial stretching of the electrode cable 
device 2, from the state shown in FIG. 1 to a substantially straight state 
shown in FIG. 2, making it much easier to introduce the electrode cable 
device 2 (preferably via a vein) into the heart. The stylet 36 is 
manipulated during its insertion in and out of the channel 38 with fixed 
handle 42 at the proximal end of the stylet 36. 
In this instance, each of the thin, insulated electrical conductors 8-22 is 
electrically connected to an associated implantable electrode contact 44, 
46, 48, 50, 52, 54, 56 and 58. The electrode contacts 44-58, devised as 
microelectrodes, are intended to be brought into permanent electrical 
contact with tissue in the wall of the cavity in a human body in which 
they have been implanted. 
The electrode cable device 2 shown in FIGS. 1 and 2 is designed, 
preferably, for transmitting electrical signals between a heart 
stimulator, connected to the connector 32, and the two cavities in a human 
heart in which the contacts 44-58 are to be implanted to achieve 
electrical contact. The four electrode contacts 52, 54, 56 and 58 are 
arrayed in a first contact area of the cable device 2, whereas the other 
four electrode contacts 44, 46, 48 and 50 are arrayed in a second contact 
area, separate from the first contact area along the longitudinal 
direction of the cable device 2, which is closer to the proximal end 4 of 
the cable device 2 than the first contact area (with contacts 52-58). 
In the illustrated instance, the first contact area with the contacts 52-58 
is intended for the left ventricle in a heart, whereas the second contact 
area with the contacts 44-50 is intended for the left atrium of a heart. 
The electrode contacts 44-50 and 52-58, respectively, are intended to 
achieve permanent electrical contact with tissue in the wall of the cavity 
in which they are arranged. In order to achieve this desired permanent 
electrical contact with the wall of the cavity in question, the electrode 
contacts are kept, at an initial stage of their implantation, pressed 
against the wall of the cavity with pressure exerted by pre-shaped 
stiffening element 24, 26, 28 and 30, running along the conductors, which 
support the conductors 8-22. These four elongate stiffening elements 
24-50, connected to and running along the conductors, are made of a 
bendable material which is resorbable in vivo. The stiffening elements 
24-30 are pre-shaped in such a way that they impart an arched shape to 
their respective conductors, at least in the parts of the conductors in 
which the contacts 44-58 are located. The stiffening elements 24-30 and 
the electrical conductors 8-22 supported by them are arranged in pairs so 
they lie on a common plane, the conductors in each such conductor pair 
arching outwardly in opposite directions. This circumstance is not very 
apparent in FIG. 1 but is clearly depicted in the sectional views in FIGS. 
3 and 4, showing the 111--111 and IV--IV section lines in FIG. 1. 
The electrode cable device 2 shown in FIG. 1 therefore contains four pairs 
of insulated electrical conductors, viz. pairs 8-12, 10-14, 16-20 and 
18-22. The conductor pairs 16-20 and 18-20 have their electrode contacts 
52-58 located in the first contact area of the cable device 2, in which 
section 111--111 is located, whereas the other two conductor pairs 8-12 
and 10-14 have their electrode contact means 44-50 located in the second 
contact area, in which section IV--IV is located. 
The electrical conductors B-22 with their associated stiffening elements 
24-30 made of resorbable material and the channel 38 for the stylet 36 are 
bundled into a single string in a first cable section LI, located between 
the proximal end 4 of the cable device 2, and the second contact area 
(containing the IV--IV section), located between the two axially separate 
contact areas. 
The stiffening element, such as the element 24, for each insulated 
electrical conductor, such as conductors 8 and 16, is formed by a sleeve, 
enclosing the conductor, made of resorbable material, the sleeve being 
casing-like or tubular. At section Va in FIG. 1, the two conductors 8 and 
16 run parallel to each other, the stiffening element 24' being 
sleeve-like and displaying the figure eight-shaped cross-section shown in 
FIG. 5a. In FIG. 5b, which shows the section Vb, the stiffening element 
24" can have a circular, tubular shape, since only a single conductor 16 
is involved, since the conductor 8 only extends to the electrode contact 
44. 
As an alternative to a tubular or sleeve-shaped structure, the stiffening 
elements 24, 26, 28 and 30 for each insulated electrical conductor could 
be formed by a band-shaped or wire-shaped stiffening element running along 
and attached to the conductor. FIGS. 5c and 5d show examples of such a 
band-shaped stiffening element, respectively designated 24a' and 24a", the 
stiffening element is broader at section Vc shown in FIG. 5c than at 
section Vd shown in FIG. 5d. 
FIG. 6 shows a cross-section V1--V1 through the posterior cable section L1, 
bundled into a single cable string, in FIG. 1. Here, the stiffening 
element 24b for e.g. the conductors 8 and 16, is devised as a string-like 
element with an approximately quarter circle-shaped cross-section, the 
three other stiffening elements 26b, 28b and 30b displaying a 
corresponding quarter circle-shaped cross-section, so the four 
string-shaped elements 24b, 26b, 28b and 30b jointly give the cable device 
a circular cross-section for the posterior cable section L1. 
The channel 38 for the stylet 36 then is a longitudinal channel 40 inside 
the cable section LI with a cross-section which, in total, is circular. 
FIG. 7 shows a corresponding cross-section VII--VII through the anterior 
channel section L2. Since this channel section only contains the 
conductors 16, 18, 20 and 22 for the electrode contacts 52, 54, 56 and 58, 
the string-shaped channel section L2 acquires the cross-sectional shape 
shown in FIG. 7 with only one conductor in each quarter circle string. 
As shown at the top of FIG. 1, the distal ends of the conductors 16, 18, 20 
and 22 in the anterior, first contact area are connected to the channel 38 
located on the distal end 60 of the cable device 2. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventor to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of his contribution to the art.