Controllable electrode device for in vivo tissue stimulation

An electrode device for intracorporeal stimulation of body tissue, particularly for intracardial stimulation of the heart, has an electrode cable containing an elongated, flexible conductor having an exterior covered with a layer of insulation, and an interior forming a channel for the introduction of an elongated member for transmitting a pushing force to the distal (i.e., treatment site) end of the electrode for controlling the configuration of the electrode device as it is inserted in a patient. An electrode head is disposed at the distal end of the conductor. For making the electrode device pliant and elastic to facilitate implantation, even using an inserted stylet which need not be retracted, the elongated member in the interior of the conductor is made longitudinally stiff but has relatively large lateral flexibility.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a controllable electrode device for 
intracorporeal stimulation of body tissue, particularly of the type suited 
for intracardial stimulation of a heart. 
2. Description of the Prior Art 
Electrode devices are generally known in the art for intracardial 
stimulation of heart which include an electrode cable containing an 
elongate, flexible conductor having an exterior provided with a layer of 
insulation and an interior forming a channel which is capable of receiving 
an elongated member, such as stylet, for transmitting a pushing force to 
the distal end of the electrode, at which the electrode head is disposed. 
As used herein, "distal" means distal relative to a yet-to-be-connected 
stimulation device, or alternatively, that end of the electrode disposed 
at the treatment site. 
In electrode devices of this type, it is of great importance for the 
electrode cable to be sufficiently pliant so that it is able, during 
advancement during implantation into a patient's heart via a vein, to 
follow the course of the vein without damaging the venous wall. In most 
instances, the electrode cable is introduced using a stylet, which is 
inserted into a channel inside the cable, and which is made of a material 
which achieves the desired stiffness necessary to advance the electrode 
cable in a vein. At difficult passages, for example, where the cable must 
bend sharply, the stylet is often retracted slightly, so that the distal 
end of the electrode cable displays maximum pliancy. After such a passage 
has been negotiated, the stylet is again advanced to the distal end of the 
electrode cable in order to push this end, for example, into the atrium or 
ventricle until the electrode head bears against the heart wall, for 
stimulation of the heart. When the electrode is in place, the stylet is 
withdrawn, which is a procedure that may damage the conductor, which often 
forms the channel for the stylet, at the locations of sharp bends in the 
vein in which the electrode cable has been inserted. 
An electrode device of this type, having an electrode cable which is 
advanced in a vein with the aid of a stylet, is described, for example, in 
German OS 3 043 189. 
Another electrode device of this type is described in the U.S. Pat. No 
4,677,990. The stylet described therein is thinner at its anterior end 
than along the rest of the stylet, so the distal end of the cable can be 
bent into a J-shape. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electrode device 
having an electrode cable with a conductor having a channel therein for 
receiving an insertion instrument, such as a stylet, which is relatively 
pliant and elastic, even with the stylet in place. 
It is a further object of the present invention to provide such an 
electrode device wherein the stylet does not need to be retracted during 
advancement of the electrode cable through a vein. 
The above objects are achieved in accordance with the principles of the 
present invention in an electrode device wherein the elongated, insertion 
member is longitudinally stiff while having relatively great lateral 
flexibility. As used herein, "longitudinal" means the direction along 
which the electrode device is to be inserted in a vein, and "lateral" 
means directions substantially perpendicular to the longitudinal 
direction. When the elongated member (stylet) is inserted into the channel 
of the electrode cable, the stylet is laterally supported by the conductor 
and the layer of insulation. Because the stylet is longitudinally stiff, 
it can impart the pushing force to the distal end of the electrode cable 
required for electrode advancement. With the use of a stylet having 
relatively great lateral flexibility and pliancy, the stylet does not have 
to be retracted within the electrode cable during the passage of difficult 
locations in the vein. 
In a simple embodiment of the invention, the elongated member is a wire 
consisting of plastic material. The wire may be made, for example, of 
nylon. 
In a preferred embodiment of the invention, the elongated member consists 
of at least two intertwined wires. This results in very great lateral 
flexibility with relatively great longitudinal stiffness. 
The intertwined wires may be made of metal or of a plastic material. 
In a further embodiment of the invention, the elongated member consists of 
a relatively thin wire, on which relatively stiff tubular or ring-shaped 
elements are strung over most of the length of the wire. One end of the 
wire is provided with a stop for the tubular or ring-shaped elements. This 
results in a stylet which can be changed from being extremely stiff to one 
being extremely pliant. This stylet does not require any lateral support. 
The tubular or ring-shaped elements can consist of a stiff material, or a 
combination of several still materials. For example, the distal end of the 
stylet may be provided with elements which are somewhat softer than the 
other elements, so that the distal end is more flexible in the passage 
through a vein. 
In another embodiment of the invention, the stop may be an elongated 
element consisting of a relatively soft material. In this manner, the 
distal end of the electrode cable can be made very pliant.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An electrode device for intracardial stimulation of a heart is shown in 
FIG. 1. The electrode device included an electrode cable 1 containing an 
elongated, flexible conductor 2 having an exterior provided with a layer 
of insulation 3 and an interior forming a channel 4. An electrode head 6 
is disposed at a distal end 5 of the conductor 2 for stimulating heart 
tissue in a patient. The electrode cable 1 also contains a connector part 
7 for electrically and mechanically connecting the cable 1 to a heart 
stimulation apparatus (not shown). 
A stylet 8, consisting in this embodiment of at least two intertwined 
wires, is inserted in the channel 4. The wires may consist of metal or a 
plastic material. The proximal end of the stylet 8 is equipped with a 
handle 9. A portion 10 of the stylet 8 next to the handle 9 is laterally 
stiffened in this embodiment with, for example, solder (if the stylet 8 is 
made of metal) or with glue (if the stylet 8 is made of a plastic 
material). Such stiffening can be advantageous, especially if this part of 
the stylet 8 is outside of the electrode cable 1 and is therefore not 
laterally stiffened by the conductor 2 and the layer of insulation 3. When 
the electrode cable 1 must be pliant, particularly at its distal end and 
midsection, other portions of the stylet 8 can be stiffened in the same 
manner. 
In another embodiment, not shown in the drawings, the stylet may consist of 
a homogenous plastic material, such as nylon, with properties making it 
longitudinally stiff but with relatively great lateral flexibility. 
Another stylet 11 is shown in FIG. 2. The stylet 11 consists of a 
relatively thin wire 12, on which relatively stiff tubular or ring-shaped 
elements 13 are strung, the elements 13 extending over the length of the 
wire 12. The distal end of the wire is equipped with a stop 14 for the 
elements 13. The proximal end of the wire 12 is equipped with an 
additional stop 15 for the elements 13. The stop 15 can be slidably 
arranged on the wire 12. In order to achieve a soft distal end, the 
element or elements 13 at the portion 16 of the stylet 11 closer to the 
distal end can be made of material which is somewhat softer than the other 
elements 13. Alternatively, the stop 14 amy be in the form of an elongated 
element made of a softer material than the elements 13. This version is 
shown in FIG. 2 in dashed lines. 
When the stylet 11 as shown in FIG. 2 is placed inside the channel 4 in the 
electrode cable 1 (shown in FIG. 1), the stiffness of the electrode cable 
1 can be controlled by the operator advancing the stop 15 against the 
proximate-most element 17, or holding onto the element 17 at the same time 
as the operator pulls on the wire 12. This presses the elements 13 
together, thereby stiffening the stylet 11. When the operator releases 
pressure so the wire 12 slackens, the stylet 11, and accordingly the 
electrode cable 1, become more pliant. This is shown in FIG. 2 by the 
dashed lines indicating the distal portion 16 of the stylet 11. 
The invention is not limited to the embodiments shown and described herein. 
The basic inventive concept is to provide a stylet which is longitudinally 
stiff because of the electrode lateral support provided by the electrode 
cable, but which also displays great lateral flexibility. The primary 
advantage of the invention disclosed herein is to facilitate advancement 
of the electrode cable in a vein, compared to advancement which can be 
achieved with prior art electrodes using a stylet. 
Because the electrode cable disclosed herein can be advanced in a vein with 
virtually no loss of pliancy, the risk of undesirable venospasm, injuries 
to veins, and incorrect introduction into coronary vessels and inferior 
veins, such as the inferior vena cava, is reduced. With a laterally 
flexible stylet, the risk of damage to the conductors of the electrode 
cable when the stylet is withdrawn from the electrode cables channel is 
also reduced. 
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.