Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1999-03-18
2002-06-04
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06400992
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to medical electrical leads for sensing or electrical stimulation of body organs or tissues and their method of fabrication, such leads having multiple electrical conductors encased in a lead body, and particularly to implantable cardiac leads for delivering electrical stimulation to the heart, e.g., pacing pulses and cardioversion/defibrillation shocks, and/or sensing the cardiac electrogram (EGM) or other physiologic data.
BACKGROUND OF THE INVENTION
Implantable medical electrical stimulation and/or sensing leads are well known in the fields of cardiac stimulation and monitoring, including cardiac pacing and cardioversion/defibrillation, and in other fields of electrical stimulation or monitoring of electrical signals or other physiologic parameters of the body. A pacemaker or cardioverter/defibrillator implantable pulse generator (IPG) or a cardiac monitor is typically coupled to the heart through one or more of such endocardial leads. The proximal end of such leads typically is formed with a connector which connects to a terminal of the IPG or monitor. The lead body typically comprises one or more insulated, conductive wire surrounded by an insulating outer sleeve. Each conductive wire couples a proximal lead connector element with a distal stimulation and/or sensing electrode. An endocardial cardiac lead having a single stimulation and/or sensing electrode at the distal lead end and a single conductive wire is referred to as a unipolar lead. An endocardial cardiac lead having two or more stimulation and/or sensing electrodes at the distal lead end and two or more conductive wires is referred to as a bipolar lead or a multi-polar lead, respectively.
In order to implant an endocardial lead within a heart chamber, a transvenous approach is utilized wherein the lead is inserted into and passed through a pathway comprising the subclavian, jugular, or cephalic vein and through the superior vena cava into the right atrium or ventricle. It is necessary to accurately position the sense and/or stimulation electrode surface against the endocardium or within the myocardium at the desired site in order to achieve reliable sensing of the cardiac electrogram and/or to apply stimulation that effectively paces or cardioverts the heart chamber. The desired heart sites include the right atrium, typically the right atrial appendage, the right ventricle, typically the ventricular apex, and the coronary sinus and great vein.
The transvenous pathway can include a number of twists and turns, and the lead body can be forced against bony structures of the body that apply stress to it. Moreover, the heart beats approximately 100,000 times per day or over 30 million times a year, and each beat stresses at least the distal portion of the lead body. The lead conductors and insulation are subjected to cumulative mechanical stresses, as well as material reactions as described below, that can result in degradation of the insulation or fractures of the lead conductors with untoward effects on device performance and patient well being.
Early implantable, endocardial and epicardial, bipolar cardiac pacing leads employed separate coiled wire conductors in a side by side configuration within a silicone rubber sheath and incorporated a lumen for receiving a stiffening stylet inside the lumen of at least one of the conductor coils to facilitate advancement through the transvenous pathway. The stiffening stylet was advanced through a proximal connector pin opening to stiffen the lead body during the transvenous introduction and location of the distal electrodes deeply inserted into the right ventricular apex and was then withdrawn. The relatively large diameter and stiff lead body provided column strength that was relied upon to maintain the distal electrodes embedded into the trabeculae of the right ventricular apex. Fibrous tissue growth about the distal lead body was also relied upon to hold the distal pace/sense electrodes in position.
Similar atrial, J-shaped lead bodies were developed that relied upon the lead body stiffness and shape to lodge and maintain distal pace/sense electrodes lodged into the right atrial appendage after the stiffening stylet was removed from the lead conductor lumen. In the case of early J-shaped atrial leads formed of silicone rubber, the lead body was reinforced with an outward extending silicone rubber rib to maintain the J-shape bend when the stylet was removed. In later J-shaped atrial leads, internally encased metal coils or wires have been employed to maintain the J-shape bend.
Such relatively large and stiff lead bodies were disadvantageous in a number of respects. The available bio-compatible conductor material alloy presented an impedance that limited current carrying capacity. The large diameter body made it difficult to implant more than one lead through the venous system. The relatively high column strength was often still insufficient to maintain the pace/sense electrodes in the atrial appendage or ventricular apex, and physicians often resorted to leaving the stylets in place, resulting in fracture of the lead conductor and lead body sheath when the stylet wire broke. Once the lead bodies fibrosed in, they were difficult to retract from the heart if they needed to be replaced. Finally, the lead conductors tended to fracture at stress sites, in bipolar leads sometimes due to stresses applied unevenly to the side-by-side arrangement of the conductor coils.
In the efforts to solve these problems, more flexible lead bodies were developed using smaller diameter coiled wire conductors and other insulating materials, most notably polyurethane compositions. Passive and active fixation mechanisms incorporated were into the distal end of the endocardial lead to fix the electrode at a desired site in a heart chamber during the acute post-operative phase before fibrous tissue growth envelops the lead body. Passive fixation mechanisms, e.g., a plurality of soft, pliant tines that bear against the trabeculae in the right ventricle or the atrial appendage to urge the distal tip electrode against the endocardium, do not invade the myocardium. Active fixation mechanisms are designed to penetrate the endocardial surface and lodge in the myocardium without perforating through the epicardium or into an adjoining chamber. The most widely used active fixation mechanism employs a sharpened helix, which typically also constitutes the distal tip electrode, that is adapted to be rotated by some means from the proximal end of the lead outside the body in order to screw the helix into the myocardium and permanently fix the electrode at the desired atrial or ventricular site.
The side by side, bipolar, coiled wire lead body design was also replaced by a coaxial configuration which is more resistant to fracture and smaller in diameter and which was typically formed of polyurethane or silicone rubber inner and outer sheathes. More recently, each such coiled wire conductor of both unipolar and bipolar leads was formed of a plurality of multi-filar, parallel-wound, coiled wire conductors electrically connected in common in an electrically redundant fashion as shown in commonly assigned U.S. Pat. No. 5,007,435, for example, incorporated herein by reference. Such redundant coiled wire conductors of bipolar and multi-polar lead bodies are coaxially arranged about the stiffening stylet receiving lumen and insulated from one another by coaxially arranged insulating sheaths separating each coiled wire conductor from the adjacent coiled wire conductor(s).
In the implantation of a cardiac device of the types listed above, and in the replacement of previously implanted cardiac leads, two or more transvenous cardiac leads are typically introduced through the venous system into the right chambers or coronary sinus of the heart. It has long been desired to minimize the diameter of the transvenous cardiac lead body to facilitate the introduction of several cardiac leads by the same transvenous approach. Moreover, a number of multi-polar, endocardial cardiac
Borgersen Svenn E.
Kramer Hans W.
Kamm William E.
Medtronic Inc.
Wolde-Michael Girma
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