Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
1999-08-03
2001-07-31
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
Reexamination Certificate
active
06269272
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to cardiac stimulator leads, and more particularly to a cardiac stimulator lead having an extendable and retractable screw-in fixation mechanism.
DESCRIPTION OF THE RELATED ART
Conventional cardiac stimulator systems consist of a cardiac stimulator and at least one elongated flexible cardiac lead that is connected proximally to a header structure on the cardiac stimulator and is implanted distally at one or more sites within the heart requiring cardiac stimulation or sensing. The cardiac stimulator is normally a pacemaker, a cardioverter/defibrillator, a sensing instrument, or some combination of these devices.
At the time of implantation, the distal end of a cardiac lead is inserted through an incision in the chest and manipulated by the physician to the site requiring electrical stimulation with the aid of a flexible stylet that is removed prior to closure. At the site requiring electrical stimulation, the distal end of the lead is anchored to the endocardium by an active mechanism, such as a screw-in electrode tip, or alternatively, by a passive mechanism, such as one or more radially spaced tines. The proximal end of the lead is then connected to the cardiac stimulator and the incision is closed. The implantation route and site are usually imaged in real time by fluoroscopy to confirm proper manipulation and placement of the lead.
A conventional cardiac stimulator lead normally consists of an elongated, flexible, tubular, electrically insulating sleeve that is connected proximally to a connector that is adapted to couple to the header of a cardiac stimulator, and distally to a tubular tip electrode. One or more ring-type electrodes may be secured to the sleeve at various positions along the length of the sleeve. The proximal end of the lead sleeve is connected to the connector by application of various biocompatible adhesives to various portions of the connector and the sleeve. The tip electrode ordinarily consists of a tubular structure that has an increased diameter portion that forms an annular shoulder against which the distal end of the lead sleeve abuts. The exterior surface of the tubular structure is normally smooth, as is the interior surface of the distal end of the lead sleeve.
In conventional active fixation tip electrodes, engagement with the endocardium is often achieved by projecting a corkscrew from the electrode. This is normally carried out by twisting the corkscrew. As the corkscrew spirals outward from the tip, the piercing point of the corkscrew pierces the endocardium, enabling the corkscrew to be screwed into the tissue by further twisting. The axial movement of the corkscrew relative to the tip electrode is usually accomplished by providing the electrode with a set of internal threads cut to match the pitch of the coils of the corkscrew. A stylet is inserted into the lead and temporarily coupled to the corkscrew. The stylet is twisted by hand to rotate the corkscrew.
The most common method of verifying a proper engagement of the endocardium by the corkscrew is by touch. Following deployment of the corkscrew, the physician applies a gentle, axial, tensile force on the lead connector. An absence of appreciable longitudinal movement of the lead is an indication that the corkscrew has successfully penetrated and engaged the tissue. However, a sudden longitudinal movement of the lead is an indication that the corkscrew either did not engage enough tissue or did not engage any tissue at all. In such circumstances, the physician must retract the corkscrew, reposition the tip of the lead proximate the targeted tissue, and redeploy the corkscrew. This process may be very time consuming, particularly where very precise electrode positioning is medically indicated and the targeted tissue is difficult to reach, e.g. requires complex bending and manipulation of the stylet. The problem of tissue engagement verification may be aggravated by other aspects of conventional tip electrode and corkscrew design. In most conventional leads, the corkscrew is deployed by a set of internal threads in the tip electrode. The threads extend from some point within the electrode to the opening at the distal end of the electrode from which the corkscrew deploys. A by-product of this design is that the corkscrew deploys as soon as the stylet is twisted. This may not be problematic where the tip is positioned and maintained in close contact with the targeted tissue. However, if the tip is not bearing directly against the targeted tissue or not positioned within a fraction of the total length of the corkscrew at the time the stylet is twisted, the corkscrew may deploy and either not engage any tissue at all or only penetrate a small distance into the tissue. In the former situation, the corkscrew will have to be retracted and second attempt made. In the latter scenario, two undesirable outcomes may result. First, a less than optimum amount of tissue penetration may result. Second, minimal tissue penetration by a fully extended corkscrew may result in the conducting tip of the electrode having only intermittent physical contact with the targeted tissue or no contact at all.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a cardiac stimulator lead is provided. The lead includes a connector for connecting to a cardiac stimulator and a tubular insulating sleeve that has a first end coupled to the connector and a second end. An electrode is coupled to the second end and has a longitudinal bore. A washer is disposed in the bore for restricting the influx of body fluids into the sleeve. A conductor wire is disposed in the sleeve and coupled between the connector and the electrode for transmitting electric signals between the cardiac stimulator and the electrode.
A corkscrew is coupled to the electrode and is extendable from and retractable into the bore. The lead includes means for transmitting torque from the pin member to the corkscrew. The cork screw has a selected pitch and is mounted on a threaded shaft. Threads on the shaft have a different pitch from the pitch of the cork screw, preferably a pitch less than that of the cork screw, and most preferably a pitch about half that of the corkscrew. When the corkscrew is advanced out of the lead, it engages the cardiac wall. Because of the larger pitch of the corkscrew, the corkscrew drives into the heart wall faster than the corkscrew is exposed outside the tip of the lead. This pulls the lead tip securely against the heart wall. If the tip is also an electrode, a better electrical connection is made between the electrode and the heart.
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Getzow Scott M.
Intermedics Inc.
Schwegman Lundberg Woessner & Kluth P.A.
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