Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Reexamination Certificate
1999-06-08
2004-04-13
Mayo, III, William H. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
C174S103000, C174S108000
Reexamination Certificate
active
06720497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrode cable of the type having a plurality of wires arranged helically along the length of the cable, said cable, which is encased in an outer, tubular sheath made of an electrically insulating material, suitable for use as an electrical connection between an electrical stimulation device, such as a heart stimulator, defibrillator etc. connectable to the proximal end of the cable, and an electrode connected to the distal end of the cable.
2. Description of the Prior Art
A lead device having one or more helices, each formed by at least one conductor, is known from European Application 0 162 178. Each conductor is formed by a number of wires arranged in a bundle by intertwining. All the wires in each conductor can be made of the same or of different materials. When different materials are used, the wires can differ in strength and electrical conductivity. This known lead device can be used as an electrical connection between e.g. a heart stimulator and contact electrodes for implantation in the human body. The objective of this known lead device is to achieve a device which, with the smallest possible external diameter for the helix, displays great fatigue resistance, relatively great electrical conductivity and small electrical resistance.
Each helical conductor in this known lead device has a core made of a wire and a plurality of wires coiled or wound around that core's longitudinal axis. The wires helically coiled around the core are intertwined into a bundle, making the lead device rather stiff and, therefore, scarcely suitable for advancement through the vascular system together with a stylet unit, inserted into a central channel in the lead device, to a desired location in the heart daring an implantation.
Another lead device having one or more helices that is similar to the above device is disclosed in U.S. Pat. No. 5,483,022. The difference is that each wire in the plurality of bundled wires is a wire having a conductive metal core jacketed in a sleeve of a less conductive metal having a higher strength and a better biocompatibility. One of the wires serves as a core similarly to the core in the above device.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a low-resistivity electrode cable which can be used as an efficient electrical connection between a device for electrical stimulation in the human body and an electrode connected to the device. The device can be e.g. a heart stimulator or defibrillator, and the electrode can be e g. an implantable heart electrode. The electrode cable can also be used for nerve stimulation. The electrode cable must be designed so it has very good electrical conductivity while simultaneously displaying optimal strength, tensile strength, flexural strength and fatigue resistance in particular.
In other words, the problem addressed by the invention is to provide an electrode cable with optimal properties in respect to its electrical conductivity, mechanical strength and ability to withstand dynamic stress capable of causing fatigue breakage of the cable, all of which are events which could have fatal consequences for a patient with a heart stimulator.
Another objective of the invention is to provide an electrode cable design making it possible to minimize the use of expensive materials in manufacturing the wires or conductors in the cable.
The problems cited in conjunction with the above objectives have conventionally been addressed to date by the use of either “high-resistivity” electrical conductors (>60&OHgr; for a given reference length) or “low-resistivity” conductors (<15&OHgr; for the same reference length) with a cylindrical spiral (helical) shape, a number of conductors wires (also referred to as wires) being helically wound or intertwined with each other.
In the use of such high-resistivity conductors, total resistance can obviously be reduced by e.g. increasing the total cross-sectional area of the conductive material in the lead, i.e. by increasing the near of wires in the lead and/or increasing the cross-section of each wire in the lead. However, an increase in the number of wires in the lead increases the lead's external diameter which is a disadvantage for a patient in whom such an electrode is to be implanted. The disadvantage is even greater if a plurality of leads must be implanted in the patient. However, an increase in the cross-sectional area of a conductor has an adverse impact on e.g. fatigue resistance. When the number of wires in a helical spiral increases, the pitch of each individual conductor wire also increases, thereby impairing the mechanical properties of the lead.
When the aforementioned type of low-resistivity conductors are utilized, the conductors employ wires made of either a low-resistivity material or a material which is a combination of a low-resistivity material and a high-resistivity material, the latter devised to carry the low-resistivity material. However, such low-resistivity wires have limiting mechanical properties.
The above objects are achieved in an electrode cable according to the invention containing at least a first set of electrically concussive wires, this first set of wires, (and each additional set of wires, if present) including at least one wire devised as a low-resistivity electrical conductor and at least two or three, wire(s) devised as (a) high-resistivity electrical conductor(s), and wherein all the low-resistivity and high-resistivity wires in each set of wires are conductors with the same diameter and are arranged side-by-side in a strip running parallel to the exterior of the cable sheath and extending helically along the cable's length. In a preferred embodiment all wires are conductors with the same diameter in the 0.05 to 0.20 mm range.
The following can be noted to clarify the concepts “low-resistivity” and “high-resistivity” wires (conductors) in the present application. These two concepts are designations whose primary purpose is to indicate that resistivities with clearly differing magnitudes are involved. The ratio between them is particularly important in this context. As is well-known, resistivity is an electrical ,unit measured in &OHgr;m. The following are examples of magnitudes and ratios applicable to low-resistivity and high-resistivity wires respectively.
A example of a low- resistivity wire is a 5.8 m long wire with a cross-sectional area of 0.00785 mm
2
in which a low-resistivity material (silver) constitutes 28% of the conductive material and a high-resistivity material (MP35N) constitutes 72%. This results in a wire (conductor wire) with resistivity on the order of 5.4×10
−8
&OHgr;m. A high-resistivity wire with the exact same geometry as the low-resistivity wire but made only of the high-resistivity material (MP35N) will have a resistivity on the order of about 2.5×10
−7
&OHgr;m. The ratio between the resistivity of the high-resistivity wire and the low-resistivity wire according to this example will amount to about 4.6.
With this kind of hybrid helical wire spiral with one or two low-resistivity wires as the primary electrical conductor means, high-resistivity wires serving as secondary electrical conductor means, providing support for the low-resistivity wires and possessing good mechanical properties, a low-resistivity helical wire can be achieved, which also displays good mechanical properties.
In one preferred embodiment of the electrode cable according to the invention, wire connecting means are arranged on each cable end and accomplish electrical interconnection of all the wires in the respective wire set, thereby achieving their parallel connection in the cable. In this manner, a low-resistivity helical wire is obtained with good mechanical properties.
The wire connecting means on each cable end can e.g. be some appropriate type of metallic clamping means which achieve surface contact with each low-resistivity wire and one or more of the high-resistance wires. The clamping m
Mayo III William H.
Pacesetter AB
Schiff & Hardin LLP
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