Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Of electrical article or electrical component
Patent
1996-04-24
1998-12-29
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Of electrical article or electrical component
264102, 264618, 264642, 419 2, 419 8, B28B 124, B22F 700
Patent
active
058536523
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to medical electrical leads and methods of manufacture thereof and, in particular, to a method of manufacturing a sintered porous platinized electrode used in a steroid eluting pacing cardiac lead which produces an electrode having increased dimensional consistency over previously used manufacturing methods.
2. Description of the Prior Art
The safety, efficacy and longevity of an implanted pacemaker system depends, in part, on the performance of the pacing leads, the electronic circuits and the integrity of the pulse generator, and the capacity and reliability of the pulse generator power source. These inter-related components of an implanted pacemaker system optimally are matched in a fashion that accommodates ever increasing demands on the modes of operation and function of the system in conjunction with an overall reduction in system size, an increase in system longevity and an increased expectation in system reliability.
During the past thirty years, the technology of cardiac pacing has significantly advanced. Implantable pacing systems offer an ever increasing variety of pacing modalities, thereby substantially broadening the indications for pacemaker use. In conjunction with this advancement, there has been extensive research and development to optimize the performance of pacing leads and their reliability while concurrently simplifying their manufacture.
In the past ten years, substantial improvements in chronic pacemaker sensing and stimulation thresholds have been achieved which, in turn, have allowed the development of smaller and longer-lived pacemakers that can be used with smaller leads. As new circuits are developed with lower "overhead" current drains, however, and as the circuits increase in complexity to allow for ever increasing pacemaker capabilities in their programmable functions, modes and memory, pacemaker longevity depends increasingly more on the characteristics of the lead. In addition, many doctors prefer pacing leads be made ever thinner, to occupy less space in the venous system, without diminishing or detracting from the mechanical strength and integrity of the lead body.
Recently, various investigators have emphasized materials and their relationship to the considerations involved in optimizing electrode design. For example, Bornzin, U.S. Pat. No. 4,502,492 owned by Medtronic, Inc. discloses a low polarization, low threshold electrode design which was commercialized as the TARGET TIP.RTM. lead during the early to mid-1980's. That design featured a generally hemispherical electrode with circular grooves, fabricated from platinum and coated over its external surface with a plating of platinum black. This combination of the relatively low (8 mm.sup.2) macroscopic electrode surface area and relatively high microscopic electrode surface area (due to the use of platinum black) contributed to the achievement of state-of-the-art thresholds for that time period. Other manufacturers marketed electrodes of other materials and configurations including totally porous platinum mesh (Cardiac Pacemakers, Inc.), porous surface sintered (Cordis Corporation), glassy and vitreous carbons (Siemens Inc.), and laser drilled metal (Telectronics Ltd.) electrodes in that same time period.
A considerable breakthrough in the development of low threshold electrode technology occurred with the invention of the steroid eluting porous pacing electrode of Stokes, U.S. Pat. No. 4,506,680 and related Medtronic U.S. Pat. Nos. 4,577,642; 4,606,118 and 4,711,251, all incorporated herein by reference. The electrode disclosed in the Stokes '680 patent was constructed of porous, sintered platinum or titanium, although carbon and ceramic compositions were also mentioned. Proximate the electrode a plug of silicone rubber impregnated with the sodium salt of dexamethasone phosphate, or a water soluble form of other glucocorticosteroids, was placed. The silicone rubber plug allowed the release of the steroid through the interstitial g
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Schildgen Gary R.
Wait Charles R.
Fiorilla Christopher A.
Jaro Michael J
Medtronic Inc.
Patton Harold
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