Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1999-04-12
2001-01-30
Jastrzab, Jeffrey R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06181972
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to leads for implantable medical devices, more particularly, cardiac stimulation leads.
BACKGROUND OF THE INVENTION
Typically, cardiac stimulation leads comprise a hollow insulating sleeve in a flexible material with an internal electric conductor (two conductors in the case of a bipolar lead), finished at its distal extremity by a bearing surface which is intended to come in contact with the endocardium. The bearing surface is equipped with an electrode (the so-called “distal” electrode in the case of a bipolar lead), making it possible to carry out the stimulation of the myocardium. The distal stimulation electrode generally presents a flattened frontal extremity, constituting an active surface, in touching contact with the wall of the myocardium. The design of such an extremity of the lead must satisfy various requirements, which, until now, have been contradictory.
The first requirement, which is essential, is to provide a high impedance at the heart/electrode interface, in order to decrease the current necessary for the stimulation and, consequently, to increase the lifespan of the pulse generator. To increase the interface impedance, it is desirable to reduce the dimensions of the active surface of the stimulation electrode (see, in particular, Cl{acute over (e)}menty et al.
{acute over (E)}conomies d'{acute over (e)}nergie: le r{acute over (o)}le de la sonde [Energy Saving: The Role of the Lead], Stimucoeur
1998, 26 no. 4, pp. 184-187).
However, a reduction in the dimensions of the lead extremity involves an increase in the pressure at the heart/electrode interface leading to increases in the stimulation threshold, and potentially to perforations of the myocardium.
In one particular known geometry, the stimulation electrode is a ring which has a flattened annular surface a flattened frontal (distal) end, whose central area is insulated. One can thus have a current conducting surface without reducing the total surface area (conducting and non-conducting) bearing against the endocardium. This structure reflects a first compromise solution as between the aforementioned constraints.
In addition, the choice of a material for the electrode, such as a microporous vitreous carbon in the place of a metal, e.g., platinum, makes it possible to combine an excellent biocompatibility with satisfactory electric performance (in particular, low energy losses by polarization). However, even in this case, the contact impedance remains relatively low, about 500 Ohm.
Further, the annular shape of the electrode leads to losses of current directly in blood, through the part of the ring which is not in contact with the myocardium. This constitutes an additional factor, prejudicial to the lifespan of the pulse generator, from the reduction in the impedance of contact.
OBJECTS AND SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to propose a lead structure which makes it possible to alleviate the aforementioned disadvantages, having a high contact impedance, preferably easily being able to reach 1000 Ohm, while maintaining an optimal surface contact between the electrode and the endocardium. Thus, it also will be seen that a preferred structure of the present invention makes it possible to take advantage of a particular phenomena likely to improve still further the effectiveness of a stimulation, in particular, the application of “point effects” and the presence of high potential gradients. These advantages, as they will become apparent, are obtained with a structure which advantageously provides very little trauma for the patient, thus minimizing any risk of perforation of the myocardium.
To this end, the lead of the present invention broadly concerns a cylindrical body presenting a distal end and a contact surface for making contact with the endocardium, which contact surface is electrically insulated, and a stimulation electrode, which is electrically conducting, and connected to a conductor of the lead. The stimulation electrode is characterized in that it comprises at least one active element presenting at its exposed (distal) extremity a protrusion relative to the body contact surface, wherein the active element presents, on at least a part of its protruding surface to be maintained in contact with the endocardium, a radius of curvature less than 0.5 mm, preferably less than or equal to 0.3 mm. It should be understood that the protrusion is a projecting body, namely one that provides a step or surface discontinuity as between the active element and the contact surface.
Very advantageously, the contact impedance of the lead at the heart/electrode interface, when the lead is conventionally installed in a patient's heart, is at least 800 Ohm, more preferably approximately 1000 Ohm.
The material of the active element is preferably a microporous vitreous carbon.
In a first embodiment, the lead of the present invention includes an active element which is a plurality of active elements each having a distinct shape, also called a “protuberance”, which includes an exposed distal extremity tip. The exposed extremity tip projects outwardly from the contact surface. The plurality of protuberances are mechanically interconnected and the distal extremity tips of two adjacent protuberances are separated by an interval defined by a part of the contact surface, and thus the endocardium when the lead is fixed in position against the endocardium.
According to various alternative implementations, this first embodiment may include one or more of the following features: the extremity area each of active element protuberance is hemispherical. The contact surface of the lead to be placed in contact with the endocardium is hemispherical. Each of the active element protuberances is located at a distance from an axis of the lead and regularly distributed around this axis; preferably there are three protuberances equiangularly distributed at 120° around an axis of the lead. Each protuberance preferably comprises a cylindrical stem whose diameter lies between 15% and 30% of the diameter of the contact surface. The exposed distal extremity of the protuberances are approximately coplanar, the distal extremity of the contact surface is preferably approximately located in the plane of the exposed extremities of the protuberances.
In accordance with a second embodiment of the invention, the active element of the lead of the present invention is an element having a flat form preferably extending in a radial plane, from the lead extremity lead, while protruding from the contract surface along a meridian thereof. When the surface contact is hemispherical, the active element can be in the shape of a flat disc.
One also can envisage two active elements of a flat form, preferably extending in two orthogonal radial planes from the lead extremity. Other configurations and structures are possible as will be understood by a person of ordinary skill in the art in view of the discussion which follows.
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J.C. Daubert, et al.; “Quel avenir pour la stimulation comme traitement primaire de l'insuffisance cardiaque?”,Stimuvoeur, 1997, vol. 25, issue 3, pp. 170-176.
Bailly Alain
Guedeney Dominique
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