Electrode system for pacemakers

An electrode system for pacemakers has at least one ventricular electrode, intended for placement in contact with heart tissue in the ventricle in order to sense electrical activity and stimulate and connected to a conductor for transmitting signals to and from the electrode. The part of the conductor nearest to the ventricular electrode is in the form of an insulated needle, helix or screw for puncturing or screwing into the part of the atrial wall facing the septum during implantation and having a sufficient length to permit the conductor to extend into the septum or superior part of the outer ventricular wall.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrode system for pacemakers, of the 
type having at least one ventricular electrode, intended for placement in 
contact with heart tissue in the ventricle in order to sense electrical 
activity and stimulate and connected to a conductor for transmitting 
signals to and from the electrode. 
2. Description of the Prior Art 
Stimulation in both single chamber and dual chamber pacemakers with 
ventricular stimulation, i.e. VVI and DDD pacemakers, normally takes place 
in the apex. A conventional pacemaker of this type for treating patients 
suffering from e.g. bradycardia requires two additional electrodes, each 
with its own connecting conductor, one of these electrodes being placed in 
the heart's atrium and the other in the ventricle. The task of the 
electrodes is to sense electrical activity in the heart and to emit 
stimulation pulses when spontaneous electrical activity ceases. 
One example of an electrode system of this type is described in e.g. U.S. 
Pat. No. 4,567,901. In this known system, the electrode cable is 
subdivided in a precurved area into an atrial section and a ventricular 
section, said sections in turn being curved so the atrial electrode and 
the ventricular electrode carried by them come to be disposed at the 
desired sites in the heart when the electrode system is implanted. Such an 
electrode system with a precurved electrode cable subdivided into two 
separate sections is a complex system which is difficult to implant in the 
patient. 
There thus exists a need to achieve an Electrode system for DDD pacemakers 
with the electrode conductors bundled in a single cable. 
In attempts to achieve such a simplification of the electrode system, 
electrode systems have been used previously with the conductors bundled in 
a single cable, at one end of which an ordinary stimulation and sensing 
electrode is arranged for implantation in the conventional manner in the 
ventricle near the apex. This type of electrode system also includes one 
or a plurality of electrodes arranged on the cable in the atrium of the 
heart. However, these atrial electrodes are "floating", i.e. they are 
normally not in direct contact with electrically active tissue, so 
effective stimulation is impossible, and sensing with the aid of these 
electrodes is more difficult. 
In one attempt to bring the atrial electrode(s) into contact with the heart 
tissue in the atrium in order to stimulate there, the part of the cable 
carrying the atrial electrode(s) has been preshaped so the electrode(s) 
press(es) against the heart tissue in the atrium, cf U.S. Pat. No. 
4,154,247. The cable is thus preshaped into a curve, loop or the like so a 
ring electrode on the cable makes contact with the atrial wall. This 
preshaping of the cable, however, makes implantation more difficult, and 
the contact with the atrial wall is unreliable. 
Studies have shown that it would be advantageous with pacemakers providing 
ventricular stimulation to stimulate high up in tile ventricle, e.g. high 
up in the septum or occasionally, for practical reasons, in the superior 
part of the outer ventricular wall. Stimulation in the apex has proved to 
be capable of rapidly resolving acute problems, but some excess mortality 
has been observed in patients receiving this type of stimulation compared 
to stimulation in the upper atrial wall. Stimulation high up in the septum 
has been found to be similar to natural stimulation, since depolarization 
then comes through the septum and subsequently spreads across the 
ventricle with more efficient heartbeats as a result. 
SUMMARY OF THE INVENTION 
An object of the present invention is to eliminate the shortcomings of the 
above-described, known techniques and to achieve an electrode system 
making possible stimulation high up in the ventricle with both single and 
dual chamber pacemakers providing ventricular stimulation. 
The above object is achieved in accordance with the principles of the 
present invention in an electrode system for pacemakers having at least 
one ventricular electrode having an exposed conductor portion capable of 
penetrating heart tissue, for screwing into or puncturing the part of the 
atrial wall facing the septum during implantation, and having a length so 
that it proceeds into the., septum or superior part of the outer 
ventricular wall. The tissue-penetrating portion of the electrode can be 
in the form of a helix, screw or needle. With a structure according to the 
invention, an electrode system is achieved with which the ventricular 
electrode is introduced into the septum or the superior part of the outer 
ventricular wall, i.e. the ventricular electrode will sense and excite 
tissue high up in the ventricle. 
In an embodiment of the electrode system according to the invention, 
especially devised for DDD pacemakers, the system includes an atrial 
electrode, intended for placement in contact with heart tissue inside the 
atrium for sensing electrical activity and stimulation, and connected to a 
conductor for transmitting signals to and from the electrode, the 
conductors for the electrodes being arranged in a single cable. From the 
site of the atrial electrode, the conductor extends to the ventricular 
electrode, the atrial electrode being positioned in the lower part of the 
atrium when the ventricular electrode has been applied high up in the 
ventricle in this manner, a substantially "linear" electrode system is 
achieved which facilitates implantation, and the atrial electrode is in 
contact with heart tissue in the lower part of the atrium for sensing 
electrical activity and stimulation in the atrium, the ventricular 
electrode being implanted high up in the ventricle. 
According to further embodiments of the electrode system according to the 
invention, the ventricular electrode is formed by a non-insulated terminal 
part of the otherwise insulated tissue-penetrating conductor which 
protrudes from the middle of a cowl forming the atrial electrode. Upon 
implantation, the needle, helical or screw-shaped conductor pierces or is 
screwed into the septum down to excitable heart tissue, the cowl then 
pressing against the inside of the lower atrial wall. The cowl can be made 
of carbon, platinum or titanium nitride.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a schematic cross-section of a heart with the electrode system 
according to the invention introduced into the right atrium 2. 
The electrode system includes an atrial electrode in the form of a cowl 4 
made of carbon, platinum or titanium nitride which, in an implanted 
electrode system, presses against the inside of the lower part of the wall 
of the atrium 2, to one side of the heart valve 6. The atrial electrode 
can thus be used both for sensing electrical activity in and stimulating 
the atrium. 
From the middle of the cowl 4 an insulated, tissue-penetrating conductor 8 
protrudes formed by a conductor wire 8a covered by insulation 8b. The 
tissue-penetrating conductor 8 may, for example, be helical or 
screwshaped. The terminal part 10 of the helical or screw-shaped conductor 
8 has no insulation and forms the ventricular electrode. The 
tissue-penetrating conductor 8 is intended for penetration, such as by a 
screwing action, into the septum 12, and has a length sufficient to permit 
the terminal part 10 to reach excitable ventricular tissue. The electrode 
system is installed simply by rotating the electrode system around its 
longitudinal axis so the tissue-penetrating conductor 8 is screwed into 
the septum 12, so that it is anchored therein. 
FIG. 3 shows an alternative version in which an insulated needle 20 
protrudes from the middle of the cowl 4. The tip 18 of the needle 20 has 
no insulation and forms the ventricular electrode. When the electrode 
system is implanted, the needle 20 is pushed into the septum 12 so the tip 
18 reaches excitable tissue. 
The electrodes 10 and 18 thus are each electrically insulated from the 
electrode 4, and the ventricular electrode 10 or 18 senses electrical 
activity and stimulates tissue high up in the ventricle. As noted above, 
studies have shown that stimulation high up in the septum is more 
advantageous than stimulation in the apex since the former stimulation 
more closely resembles conditions in natural stimulation. 
Alternately, the ventricular electrode 10 can be introduced into the 
superior part of the outer ventricular wall. For practical reasons, this 
version, shown with dashed lines in FIG. 1, could be preferable in certain 
situations. 
As shown in FIG. 2, the wires (such as 8a) from the respecting electrodes 
4, 10 or 18 for transmitting signals to and from the electrodes are 
arranged in a single cable 14 which runs to the pulse generator and 
sensing circuitry, such as an atrial sense and pace unit 22 and a 
ventricular sense and pace unit 23 in a pacemaker 21, which also contains 
other electronic equipment. Devising the electrode system with a single 
cable, even with DDD pacemakers, offers significant advantages, 
particularly during implantation, as noted above. The electrode system can 
then be easily introduced into the atrium through the vena cava. The same 
applies to the embodiment of FIG. 3. 
The electrode system could also include an atrial indifferent electrode 16 
in the form a metal ring arranged on the cable 14, cf. FIGS. 2 and 3. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventors to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of their contribution to the art.