The present invention relates generally to an implantable cardiac stimulation lead and, more particularly, to a technique for dramatically increasing the number of stimulating sites available without a concurrent increase in the number of conductors in the lead.
The implantable cardiac stimulation leads with which the present invention is concerned may take the form of pacemakers capable of pacing and sensing in at least one chamber of the heart. Indeed, the present invention, may relate to a programmable dual chamber pacemaker wherein the basic configuration of the pacemaker, e.g. unipolar or bipolar, can be changed, including the grounding configuration and ground potentials used within the pacemaker.
Generally, a heart stimulator, commonly known as a xe2x80x9cpacemakerxe2x80x9d or xe2x80x9cpacerxe2x80x9d, uses one or two flexible leads having one end connected to the pacer and the other end connected to electrodes placed in close proximity to the heart. These leads are used to stimulate or pace the heart. Also, these leads are used to sense the heart activity by picking up electrical signals from the heart.
In order to properly pace or sense, the pacer has to be able to deliver a stimulating pulse to the heart or sense an electrical signal from the heart, and this requires that there be an electrical return path. If, within a given heart chamber, a unipolar lead is usedxe2x80x94containing a single conductorxe2x80x94the return path is the conductive body tissue and fluids. The return path is connected to the pacer by connecting the pacer electrical common or ground to the pacer metal enclosure, typically referred to as the pacer case or housing. The case, in turn, makes contact with the body tissue and/or fluids.
An alternative solution to using a unipolar lead in a given heart chamber is to use a double lead/electrode in the heart chamber, known as a bipolar lead. In a bipolar lead, a second conductor is spiraled over and insulated from a first conductor along the length of the lead. At the distal end of the lead, one of the conductors is connected to a first electrode, referred to as the xe2x80x9ctipxe2x80x9d electrode, and the second conductor is connected to a second electrode, referred to as a xe2x80x9cringxe2x80x9d electrode. The ring electrode is generally situated 10 to 20 mm from the tip electrode. The tip electrode is typically placed in contact with heart tissue, while the ring electrode is in electrical contact with the blood. Because both body tissue and fluids are conductive, the ring electrode of a bipolar lead, in contact with the body fluids, serves as an electrical return for both pacing and sensing.
As indicated, pacing or sensing using the pacer case or enclosure as part of the electrical return path is known as unipolar pacing or sensing. Pacing or sensing using the lead ring electrode and associated lead conductor as the electrical return path is known as bipolar pacing or sensing.
There are numerous factors to consider when deciding whether unipolar or bipolar pacing and/or sensing should be used. Bipolar pacing has, in general, the advantage of requiring less energy than unipolar pacing. Further, bipolar sensing is less prone to crosstalk and myopotential sensing than is unipolar sensing. Crosstalk generally refers to a pacer mistakenly sensing a heart activity in one heart chamber immediately after the other chamber is paced. Bipolar sensing reduces crosstalk resulting from a pacing stimulus in the opposite chamber. Bipolar pacing is preferred if pectoral or diaphragmatic stimulation occurs.
Unipolar pacing and sensing offers the advantage, in general, of simpler circuitry within the pacemaker and a smaller diameter lead. Some physicians prefer unipolar over bipolar pacing and/or sensing as a function of other implantation and heart conditions. Depending on the lead orientation, unipolar sensing may be better than bipolar sensing.
An item of prior art which is pertinent to the present invention is U.S. Pat. No. 4,991,583 to Silvian which discloses a method of operation and an apparatus provided for independently configuring one or both channels of a conventional pacer to either a unipolar or bipolar pacing mode of operation and either a unipolar tip-to-case, unipolar ring-to-case, or a bipolar tip-to-ring sensing mode of operation, despite positive potentials that appear at the tip or ring electrodes.
Another disclosure of interest is provided by U.S. Pat. No. 5,895,416 to Barreras, Sr. et al. which discloses a lead system which steers the electrical field to the appropriate location by switching transistors off and on.
Still another pertinent disclosure is provided by U.S. Pat. No. 6,085,118 to Hirschberg et al. which discloses a lead system which determines the function of an electrode by use of a switching system.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.
The present invention discloses an implantable cardiac stimulation lead system for use with a stimulation device which includes an implantable housing containing a pulse generator which emits stimulation pulses. The lead system includes a first electrode for delivering stimulation pulse current to tissue, a plurality of second electrodes for returning to the stimulation device the pulse current after traversing the tissue, and a matrix switching system. X and Y electrical conductors extend between the stimulating device and the matrix switching system. The matrix switching system includes a switching device to connect each of the Y electrical conductors to each single X electrical conductor and to each of the second electrodes such that each switching device is actuated by a corresponding pulse from the pulse generator applied to corresponding X and Y conductors connected thereto and such that the total number of electrical conductors required is fewer than the number of the second electrodes.
A primary feature, then, of the present invention is the provision of an improved implantable cardiac stimulation lead.
Another feature of the present invention is the provision of such a technique which dramatically increases the number of stimulating sites available without a concurrent increase in the number of conductors in the lead.
Yet another feature of the present invention is the provision of such a technique according to which an implantable cardiac stimulation lead can be provided with multiple stimulation sites with minimal enlargement of lead size.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.