Electrode for artificial pacemaker

An electrode for implantation in the heart to control atrio-ventricular block by artificial pacemaker including plural electrically conductive wires grouped in a bundle with spring metal arcuate prongs formed on one end thereof. A sheath is provided to compress the prongs for insertion of the electrode through a cannula to place the electrode against the heart. The electrode is implanted in the heart by advancing the prongs through the pericardium into the myocardium.

This invention relates generally to electrodes for implantation into body 
organs and more particularly to an electrode for artificial pacemakers for 
implantation into the heart muscle to stimulate heart activity. 
Previous designs of pacemaker electrodes employ the use of a puncturing 
needle to penetrate the myocardium of the right ventricle. Electrodes are 
introduced through this needle and allowed to move about freely within the 
heart chamber making contact with the endocardium. Major risks are 
present, including electrode tip migration within the ventricular cavity, 
hemorrhage from cardiac puncture and thrombus formation on the wire. 
The applicants are aware of the following U.S. Pat. Nos. 
3,814,104 Irnich et al (June 4, 1974) 
3,976,082 Schmitt (Aug. 24, 1976) 
3,754,555 Schmitt (Aug. 28, 1973) 
3,902,501 Citron et al (Sept. 2, 1975) 
3,844,292 Bolduc (Oct. 29, 1974) 
These systems are not comparable to the present invention in that they are 
transvenous electrodes and pace the endocardium. The "prongs" or tines of 
these devices are bulky and do not have the unique characteristics of the 
light spring spiral prongs of the present invention. 
The following U.S. Pat. Nos. RE 27,569 Ackerman (Feb. 6, 1973) and 
3,866,615 Hewson (Feb. 18, 1975), are illustrative of the above-mentioned 
prior art devices in which the electrode pierces the ventricle. 
The U.S. Pat. No. to Quinn 3,416,534 (Dec. 17, 1968) discloses an electrode 
similar to that of the present invention in which a heavy, helical 
"cork-screw" type implantation device is provided to enter the myocardium. 
Aside from obvious disadvantages such, for example, as the inability to 
remove the electrode once it is implanted and the reliance on single 
electrode contact, the Quinn device cannot be controlled in depth of 
penetration of the electrode, thereby resulting in the danger of 
penetration of the ventricle with the dangers attendant thereon. 
The present invention provides an electrode which does not enter the heart 
chamber but rather anchors securely within the myocardium itself. The 
invention provides an electrode in which positive fixation of the 
electrode tips is accomplished to prevent electrode tip migration. The 
configuration of the tips provided by the invention provides assurance of 
intimate electrical contact, avoiding the possibility of intermittent 
conductivity fluctuations. The nature and configuration of the electrode 
tip provides the lowest possible pacemaker's threshold due to the intimate 
contact provided thereby and the positive contact and increased electrode 
area presented by the multiple tips. By avoidance of penetration of the 
ventricle, the present invention precludes the risk of hemorrhage due to 
cardiac puncture and the thromboemboli which could be generated within the 
heart chamber by such penetration. 
In a preferred embodiment the present invention provides an electrode for 
implantation in the myocardium to control atrioventricular block by 
artificial pacemaker, including a plurality of resilient electrically 
conductive wires grouped in coextensive parallel relationship in a bundle, 
means proximate one end of the bundle to fix the wires rotationally with 
respect to one another with the ends of the wire beyond the means deformed 
to describe arcuate pronged segments radiating from the axis of the 
bundle, insulation surrounding the bundle between the other ends of the 
wires and the means to fix the wires; and a tubular constraint removably 
disposable around the bundle to compress the prongs to the diameter of the 
bundle to permit insertion of the bundle through a cannula for subsequent 
expansion of the prongs and entry into the myocardium. 
These and other advantages and objects of the invention will become better 
understood to those skilled in the art by reference to the following 
detailed description when viewed in light of the accompanying drawings 
wherein like components throughout the figures thereof are indicated by 
like numerals and wherein:

DESCRIPTION OF A PREFERRED EMBODIMENT 
In FIG. 1 the device in accordance with the invention is shown in broken 
away section and consists of a bundle shown generally at 9 comprising four 
wires 10 disposed in parallel coextensive relationship to one another and 
having arcuate prongs 12 on one end thereof. The wires 10 are crimped 
together by a crimp 14 proximate the prongs 12 so that the prongs are 
fixed rotationally with respect to one another. The bundle 9 is completed 
by an insulated coating 16 formed around the wires 10 to electrically 
insulate them from their surroundings. The insulation 16 extends from the 
crimp 14 to the free ends of the wires 10. A tubular sheath 18 surrounds 
the bundle 9 for purposes to be described below. 
The wires 10 are preferably made of a corrosion resistant alloy such, for 
example, as spring steel alloy manufactured under the trademark ELGILOY, 
now owned by American Gauge and Machine Company, Elgin, Illinois. ELGILOY 
is a spring steel first used in watches and clocks, now used in diverse 
applications and has the following composition: cobalt, 40%; chromium, 
20%; nickel, 15%; molybdenum, 7%; manganese, 2%; carbon, 0.15%; beryllium, 
0.04%; iron, 15.81%. 
The wire strands 10 are thin, preferably on the order of 0.010 inch in 
diameter and are tempered to achieve a "spring effect" as will be 
described in detail below. The prongs 12 are preferably formed to describe 
the arc of a circle 5/32 inch in diameter and are approximately 1/2 inch 
in length and are bowed or curved in the same direction. The sheath 18 is 
preferably 18 gauge in size to fit over the resultant bundle 9. The 
thickness of the insulative coating 16 on the bundle of wires 10 is not in 
excess of 0.005 inch so that the final bundle assembly will slide freely 
within the 18 gauge tube. 
The prongs 12, in the unconstrained configuration of FIG. 1, are disposed 
at approximately 90.degree. to one another to radiate outwardly from the 
axis of the bundle 9 as shown. 
By withdrawing the bundle 9 within the sheath 18 as shown in FIG. 2, it can 
be seen that the prongs are compressed to be constrained within the 
confines of the sheath 18 for purposes to be described below. 
In FIGS. 3-8 one method involved in fabricating the electrode of FIGS. 1 
and 2 is illustrated. In FIG. 3 an untempered ELGILOY wire 10 is coiled on 
one end with approximately four turns, forming a 5/32 inch diameter spring 
coil 20. Four wires with coils thus formed thereon are then inserted 
through a tubular crimp 14 of approximately 0.032 inch OD by 0.026 ID by 
0.125 inch length as is shown in FIG. 4 and the crimp 14 is then 
compressed to fix the wires rotationally with respect to one another. In 
FIG. 5, the coils are bent at right angles to one another, forming a "four 
leaf clover" configuration as is best seen in the end view shown in FIG. 
6. The assembly is then heat set at 410.degree. C. for 5 hours and cooled 
slowly to room temperature. The tempered wires are then passed through the 
18 gauge sheath 18 as is shown in FIG. 7 to open the coils 20 to their 
final twisted shape as is seen in that figure. Each of the coils 20 are 
then cut to form the prongs 12 of approximately 1/2 inch in length. The 
entire bundle of wires 10 between the free end thereof and the crimp 14 is 
then coated with a dielectric insulating coating 16 of a suitable material 
such, for example, as polyurethane. 
FIGS. 9-13 illustrate a use of the device in accordance with the invention. 
As shown in FIG. 9, implantation of the electrode is initiated by 
insertion of a 16 gauge cannula 22 with a trocar 24 through the chest wall 
26 (5th intercostal space) toward the cardiac maximal impulse 28. When the 
chest wall is entered, the trocar 24 is removed, leaving the empty cannula 
22 in the mediastinum as shown in FIG. 10, with the tip thereof resting 
against the pericardium 30 as seen in the figure. As seen in FIG. 11, the 
sheath 18 containing the bundle 9 in the configuration of FIG. 2 is then 
inserted through the cannula 22 with the end thereof resting against the 
pericardium. The bundle 9 is then advanced about 5 millimeters within the 
sheath 18 such that the electrode prongs 12 penetrate the pericardium into 
the myocardium 32 as is seen in FIG. 12. The cannula 22 and sheath 18 are 
then removed, leaving the electrode bundle 9 in the configuration of FIG. 
13. The exterior ends of the wires 10 in the bundle are then connected to 
a conventional electronic pacemaker for stimulation of the heart in a 
manner well known in the art. Typically, an indifferent electrode, to 
complete the circuit, can be provided by a separate 2-0 steel suture (or 
other type) placed through the skin at the chest (not shown). 
The utility of the invention has been demonstrated by 15 tests conducted on 
animals. Five animals underwent 50 repeated wire placements under direct 
vision through a left thorocotomy. The prongs were observed to advance, 
seek out, and embed in the myocardium without major difficulties. Pacing 
thresholds varied from 0.5-1.5 milliamperes, well within acceptable 
limits. Five animals were under 72 hour electrode implantation and removal 
with intermittent pacing. Intramyocardial position was confirmed by chest 
roentgenograms and electrocardiograms. Pacing thresholds were acceptable 
at an average level of 2.7 milliamperes. Five animals were continuously 
paced for 72 hours and exhibited a mean threshold of 2.9 milliamperes. 
Comparison of intermittent and continuous pacing showed that there was no 
significant difference. 
An autopsy conducted on the animals revealed that all prongs were well 
embedded in the myocardium with minimal evidence of injury. The prongs 
coursed a plane 3 millimeters below the epicardium, providing a safety 
margin of 5-8 millimeters of myocardium from electrode intrusion into the 
heart chamber itself. 
What has been described above is intended as exemplary to enable those 
skilled in the art in the practice of the invention.