Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1998-09-23
2001-03-20
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C029S857000
Reexamination Certificate
active
06205358
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to implantable medical devices and more particularly to various means for ultrasonically welding, swaging or staking components of implantable medical devices in assemblies such as header modules through the use of appropriately configured covers or lids.
BACKGROUND OF THE INVENTION
The earliest implantable medical devices, e.g., implantable cardiac pacemakers and other body tissue stimulating devices, were formed of an implantable pulse generator (IPG) and a set of electrical leads attached between the IPG and heart or body tissue to be paced or stimulated. Typically, the IPG electrical circuit was powered either by Hg-Zn batteries or by induction of energy transmitted transcutaneously from a skin surface RF power generator and supplied electrical pacing or stimulating pulses to the leads. The IPG batteries and circuits were encapsulated within an epoxy compound partly for ease of manufacture and to allow hydrogen emitted by the Hg-Zn batteries to escape. Electrical connector pins and rings, if present, were initially permanently attached to the circuits. Other early implantable medical devices, e.g. implantable monitors and cochlear implants or the like were also formed in somewhat the same manner.
Such early implantable cardiac pacemakers suffered very short useful lives due to moisture ingress through the epoxy and causing electrical dendritic growth across, and shorting of, adjacent points of the circuit, battery terminals, or discrete transistor terminals. In addition, pacing leads frequently failed due to conductor stress fractures, and batteries depleted prematurely for a variety of reasons.
In the 1960's, IPG connector assemblies were formed integrally with other IPG circuit components and embedded in an epoxy housing to enable attachment of a chosen lead to the IPG circuit for initial implant or defective lead replacement purposes. These integrally formed connector assemblies typically comprised at least one metal, electrical connector block encapsulated therein that were aligned in relation to an elongated lead end receptacle for receiving the proximal lead end. Each connector block was formed to have a bore to receive the lead connector pin or ring, depending on the type of lead intended to be used, and a threaded cross bore receiving a trapped set screw. The electrical connections in connector blocks were typically directly attached to IPG circuits. A silicone rubber suture boot was placed in a mold in alignment with an elongated receptacle. The entire IPG, including connector assembly components, was then encapsulated in epoxy.
In use, a proximal lead connector end was inserted into the appropriate lead connector receptacle until the lead connector pin or ring was received in the bore of the connector block. A set screw was then tightened by a hex wrench to establish firm electrical and mechanical connections and the opening through the molded epoxy housing to access the set screw was sealed. Sutures were tied around the suture boot for sealing engagement against the lead body.
Beginning in the 1970s, hermetically sealed lithium batteries and miniaturized digital and analog integrated circuits (ICs) have been used in implantable medical devices, particularly for implantable cardiac pacemaker and nerve stimulation IPGs. Integrated circuits, batteries and other components were enclosed in hermetically sealed metallic enclosures or “cans” separated from the connector assembly components. Electrical connection between connector blocks and other components of the connector assembly was generally accomplished by electrical feedthroughs supporting feedthrough pins extending through the hermetically sealed can.
Lead connector assembly components external to the hermetically sealed enclosure are still to this date attached to an attachment surface thereof using an in situ molding process to seal the connector assembly components and form the receptacle for a lead or catheter proximal end, etc. For example, in the formation of a lead connector assembly for a cardiac pacemaker IPG, the connector blocks and feedthrough pins are welded together and laid out in a mold with respect to any other associated components and mold plugs. An encapsulating compound is injected into the mold to form the connector header assembly molded to the IPG attachment surface as described, for example, in U.S. Pat. No. 4,041,956, the disclosure of which is hereby incorporated by reference herein in its entirety. This approach is time consuming and not terribly precise. If the resulting connector header assembly fails to meet dimensional tolerances or other quality requirements, it is difficult to rework the IPG.
In 1979 the MEDTRONIC® SPECTRAX® cardiac pacemaker IPGs were introduced having the digital and analog or hybrid ICs and lithium batteries enclosed within a hermetically sealed titanium enclosure having feedthroughs extending through an enclosure attachment surface thereof. Assembly of these components and other details are disclosed in U.S. Pat. Nos. 4,142,532 and 4,182,345, hereby incorporated by reference herein in their respective entireties.
The lead connector assembly, in this case and as used in IPG models to the present time by Medtronic, Inc., is manufactured as a separate pre-formed connector header module that encloses connector components and is attached to an enclosure attachment surface of the hermetically sealed enclosure and to the feedthrough pins. The connector header module is molded of a thermoplastic elastomer such as medical grade polyurethane, has an outer module surface and a number of receptacles and channels disposed within it that in some instances are accessible through windows, channels or recesses extending outwardly to the module surface. The connector header module receives the electrical connector blocks)in connector block receptacles such that the connector block bores are aligned with elongated lead connector receptacles for receiving the proximal lead connector end assemblies. In a typical design, each such connector block is formed with a threaded cross bore receiving a trapped set screw as described above. Each set screw of each connector block in a connector block receptacle is also aligned with a septum receptacle for receiving a silicone rubber set screw septum.
A pre-formed connector header module is generally formed with pin channels for directing the feedthrough pins into contact with the respective connector blocks and with windows to allow the connector blocks and septums to be inserted into their respective receptacles. In each case, the connector block receptacle window or a further window to the module surface is provided for allowing the feedthrough pin end to be welded to the connector block. The windows and pin channels are typically back filled with a medical grade silicone adhesive after the welding step and attachment of the connector header module to the hermetically sealed enclosure.
The receptacle for the connector block and the connector block itself most preferably have fight dimensional tolerances to permit precise alignment of the connector block bore with the lead connector receptacle. In one approach, the connector block receptacle opening dimensions are reduced and the opening edge thereof shaped so that the connector block stretches the opening edge as it is inserted into the connector block receptacle. In other cardiac pacemaker IPGs, each connector block is inserted into a connector block receptacle and ultrasonic energy is applied to the edge of the connector block window to melt it over and tamp it against the exposed surface of the connector block. This ultrasonic tamping technique of dissimilar material parts is similar to that shown in the article entitled “Ultrasonic Joining of Moulded Parts and Semi-Finished Parts of Thermo-Plastic Polymers in Mass Production-Forming with Ultrasound,” Staking, Swaging and Tamping (Guideline DVS 2216, Part 3, 1992),
Welding in the World, Le Soudage Dans Le Monde
, Vol. 31, No. 3, pp. 205-207 (1993), the disclosure o
Haeg Daniel C.
Kelley James F.
Wiklund Craig L.
Evanisko George R.
Medtronic Inc.
Patton Harold R.
Wolde-Michael Girma
Woods Thomas F.
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