Intracardial electrode and a method of manufacture thereof

An indwelling multi-contact plunge electrode to measure the electrical output from areas of the myocardium on an individual, sequential or combination composite basis. The electrode comprises an outer flexible tube containing a plurality of wire leads having their distal ends projecting angularly through the wall of the tube adjacent the distal end thereof and their proximal ends connected to an electrical plug. The distal end portion of the electrode is stiffened and bent at a substantial angle to the proximal portion and the void in the lumen of the tube not occupied by the wire leads is filled with silicone rubber.

THE INVENTION 
This invention relates generally to new and useful improvements in 
intracardial electrodes and particularly seeks to provide an indwelling 
multicontact plunge electrode that can be used to measure electrical 
outputs at mutiple depths within the myocardial wall of the heart of an 
animate being on an individual, sequential or combination basis. 
Such electrodes must be capable of receiving and transmitting electrical 
impulses from strata of the heart to a recording and/or information 
storage unit for either direct observation or subsequent analysis; and 
should be capable of providing selected single location signals to the 
recording unit or providing sequential signals or providing selected group 
signals thereto as determined by the control settings of the recording 
unit. 
These multiple readings are in direct contrast to the single readings 
heretofore obtainable with known types of single contact plunge probes or 
electrodes and are opposite in sense in comparison with the imposed timed 
electrical stimuli provided by single or plural contact catheters such as 
those employed in atrial pacing of a heart. Typical examples of the latter 
types of pacing catheters are listed on pages 2-9 of the 1975 catalog of 
the United States Catheter and Instruments Corp. (U.S.C.I.). 
It is apparent that scientific investigation of coronary arterial stenoses 
can be greatly aided through the use of electrograms that can only be made 
in connection with multicontact plunge electrodes. In this context, 
attention is drawn to the April 1977 issue of The American Journal of 
Cardiology, Volume 39, pages 529-536, in which a study of John B. 
O'Riordan, MB, and coauthors, is reported. Although that article describes 
the general nature of a multicontact electrode experimentally developed by 
this inventor, it does not describe either the exact construction being 
tested at that time, nor does it constitute a prior printed publication 
with respect to the electrode specifically disclosed and claimed herein. 
Therefore, an object of this invention is to provide a multicontact 
intramyocardial electrode that is particularly adaptable for use in 
connection with recording instruments employed in the scientific 
investigations and observations of coronary arterial stenoses and other 
conditions where multiple depths readouts are required from a single 
electrode. 
Another object of this invention is to provide an electrode of the 
character stated that includes an outer tube or sheath of a fluorinated 
hydrocarbon that is smooth, inert, flexible, thrombo-resistant, 
non-thrombogenic and which may be either radiopaque or non-radiopaque. 
Another object of this invention is to provide an electrode of the 
character stated in which the outer tube or sheath is provided at its 
distal tip with a smooth generally hemispherical closure and contains 
within its lumen from two to twelve insulated lead wires, the distal ends 
of which project angularly through the tube wall at regularly spaced 
intervals along the distal end portion of the tube and have their exposed 
ends substantially coplanar with the outer surface of the tube, the 
proximal ends of which project proximally beyond the proximal end of the 
tube for connection to an electrical plug. 
Another object of this invention is to provide an electrode of the 
character stated in which that portion of the tube lumen not occupied by 
the insulated lead wires preferably is filled with a material such as a 
silicone room temperature vulcanizing rubber to prevent relative movement 
between the lead wires and to render the entire tube structure laterally 
compression resistant while retaining its flexibility. 
A further object of this invention is to provide an electrode of the 
character stated in which the distal end portion containing the exposed 
ends of the lead wires is bent substantially at a right angle to the 
proximal portion and is stiffened by an axially disposed pin having a 
short leg extending into the proximal portion. 
A further object of this invention is to provide a novel method of forming 
an electrode of the character stated. 
A further object of this invention is to provide an electrode of the 
character stated that is intended to be disposable after a single use. 
A further object of this invention is to provide an electrode of the 
character stated that is simple in design, rugged in construction and 
economical to manufacture. 
With these and other objects, the nature of which will become apparent, the 
invention will be more fully understood by reference to the drawings, the 
accompanying detailed description and the appended claims.

Referring to the drawings in detail, a 4-lead electrode, as one example, 
includes an outer tube or sheath 5, preferably formed from a fluorinated 
hydrocarbon such as a FEP (hexafluoropropylene-tetrafluoroethylene 
copolymer) or TFE (tetrafluorocthylene) resin, commercially available as 
"Teflon" FEP or "Teflon" TFE from DuPont, which may be from about 50 to 
150 cm. in length or more and, for a No. 3 French size, should have an 
O.D. (outside diameter) of 0.038" and an I.D. (inside diameter) of 0.026". 
These electrodes can be fabricated within the size range of No. 2 French to 
about No. 6 French, in which the O.D.s would range from 0.025" to 0.075" 
and the I.D.s preferably would range from 0.016" to 0.065". 
The distal tip of the tube 5 is formed into a smooth generally 
hemispherical closure 6 and the prominal end of the tube is open. 
The distal end portion of the tube 5, for a four lead electrode, is 
provided with four longitudinally aligned angularly oriented perforations 
7, the axes of which are disposed at about a 30.degree. angle with respect 
to the longitudinal axis of the tube. Preferably, the distalmost 
perforation 7 should be located approximately 0.030" from the closure 6 
and the spacing between the perforations should be on the order of 5 mm. 
Four wire leads 8, 9, 10 and 11 are contained within the lumen of the tube 
5 and have their distal ends extending through the perforations 7 and 
their proximal ends projecting about 10 cm. proximally beyond the proximal 
end of the tube for connection to an electrical plug 12. The distal ends 
of the leads 8-11 are ground and polished into generally coplanar 
relationship to the outer surface of the tube 5 to provide exposed 
contacts. The exposed proximal ends of the leads 8-11 are individually 
protected by "spaghetti" tubes 13 and an outer sleeve 14 protects the 
proximal end portion of the unit. Preferably the "spaghetti" tubes 13 and 
the sleeve 14 are formed from the same type of material as used to form 
the tube 5, although any other suitable type of inert plastic material 
such as polyethylene, polypropylene or polyurethane could be used instead. 
Each of the leads 8-11 preferably is formed from 300 Series stainless steel 
ribbon wire having a cross-section of 0.003".times.0.010", although the 
range of usable cross-sectional sizes may extend from about 
0.0015".times.0.004" to about 0.010".times.0.025". Precious metals such as 
silver, gold or platinum could also be used for the leads. 
It is important that the leads 8-11 be coated by a smooth, low-friction, 
flexible, continuous, insulating coating such as that provided by a FEP or 
TFE resin; and a preferred method of applying such a coating to the leads 
is disclosed in U. S. Pat. No. 3,922,378, granted Nov. 25, 1975, in which 
a wire substrate is immersed in a dispersion bath of the selected resin 
and removed therefrom, then the coated substrate is initially dried, then 
heated to a predetermined temperature over a predetermined period of time 
and finally slowly cooled over a predetermined period of time to a 
temperature as low as or lower than a predetermined lower temperature. 
The distal end portion of the tube 5 is provided with an axially disposed 
stainless steel wire stiffening pin 15 that extends from a location 
adjacent the distal closure 6 to a location proximal of the proximalmost 
of the perforations 7 and includes rounded ends 16, 16 in order to avoid 
either scraping of the insulating coating on the leads 8-11 or perforating 
the end closure 6. 
The distal end portion of the electrode that includes the perforation 7, 
the distal ends of the leads 8-11 and the major portion of the pin 15, is 
bent at about 90.degree. to the proximal portion of the electrode to 
define a plunge portion that can be directly introduced into the 
myocardium of a heart and to leave a proximally extending short leg 17 of 
the pin 15 against which the insertion force is exerted. 
That portion of the void in the lumen of the tube 5 that is not occupied by 
the leads 8-11 and the stiffening pin 15 is filled by a cured flexible 
insulating material 18 such as a silicone RTV (room temperature 
vulcanizing) rubber, which protects the leads 8-11 from potential damage 
due to relative movements due to torsion or flexing and renders the 
complete assembly of the electrode substantially resistant to lateral 
compression. 
Because the method of assembly of this electrode is quite important to the 
utility and functional integrity of the finished product, a brief 
description thereof now will be presented. 
First, the tubing 5 is cut to length (50-150 cm. or more) and then the 
distal end portion is pierced to provide the angularly disposed, 
longitudinally aligned, perforations 7. Then the coated wire leads 8-11 
are inserted from the outside of the tube 5 through the performations 7 
into and proximally through the lumen of the tube, leaving distal ends of 
the leads projecting externally of the wall of the tube and the proximal 
ends of the leads projecting substantially beyond the proximal end of the 
tube. This insertion of the leads 8-11 is readily effected because the 
wires are relatively stiff and because frictional resistance to their 
passage is at a minimum due to the low friction characteristics of both 
the wire coatings and the tube 5. 
Next a solution of the RTV silicone rubber is prepared and 
vacuum-introduced into the void of the lumen of the tube 5 that is not 
occupied by the leads 8-11. This requires a vacuum on the order of 28" hg. 
in order to assure a complete flow-through of the RTV solution. 
Preferably, the silicone rubber solution comprises 80 parts of a RTV base, 
as commercially available from the General Electric Company, and 20 parts 
of G.E.'s 910 diluent, although the range of base to diluent may extend 
from about 95 parts base and 5 parts diluent to 60 parts base and 40 parts 
diluent. 
Next, the pin 15 is axially inserted from the open distal end of the tube 5 
into the filled lumen thereof to a distance such that the distal end of 
the pin is located slightly distally beyond the distal one of the 
perforations 7. 
Next, the RTV filled tube is cured either by storage overnight at room 
temperature or by heating at about 150.degree. C. for about 30 minutes. 
Then the outer surface of the tube 5 is wiped clean and a small amount of 
the cured RTV is removed from the open distal end of the tube 5 to enable 
the distal tip thereof to be shaped by heat, mechanical deformation and 
grinding and polishing into the generally hemispherical closure 6. 
Next, the proximal ends of the leads 8-11 are connected to the plug 12 
after adding the "spaghetti" 13 and the protective sleeve 14; and then 
electrical continuity of the leads from the perforations 7 to the plug 12 
is checked and each contact pin of the plug is appropriately marked with 
the identity of its associated lead. 
Next, the distal end portion of the electrode is cleaned and then bent at a 
substantial right angle to the proximal portion, leaving the leg 17 of the 
pin 15 extending into the proximal portion. 
Finally, the outwardly projecting distal ends of the leads 8-11 are clipped 
off close to the outer surface of the tube 5 and are finely ground and 
polished into substantially coplanar relationship therewith. It should be 
noted that since the leads 8-12 are oriented at an acute angle relative to 
the longitudinal axis of the tube 5, the exposed ground and polished 
contact areas thereof are larger than their 90.degree. cross-sectional 
areas. 
It is of course to be understood that variations in arrangements, materials 
of construction and proportions of parts may be made within the scope of 
the appended claims.