Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1998-12-09
2001-03-13
Layno, Carl H. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S032000, C607S060000, C128S903000
Reexamination Certificate
active
06201993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for detecting a radio frequency (RF) signal transmitted between an implantable medical device (IMD) and an external medical device in a telemetry session and for discriminating the transmitted RF signal from transient and steady state noise corrupting it.
2. Description of the Prior Art
In the field of programmable IMDs, it has become common to provide an interactive, transceiver system for both remotely programming operating functions, modes and parameters of the implanted device, and for telemetering out data related thereto on command by RF telemetry to an external medical device, commonly denoted a “programmer”. Such IMDs include cardiac pacemakers, cardiac and other physiologic monitors, implantable drug dispensers, nerve, muscle, and brain stimulators of various types, cochlear implants, blood pumps, cardiomyostimulators, and tachyarrhythmia-control devices, e.g., implantable cardioverter/defibrillators (ICDs) for delivery of staged therapies to the ventricles and/or the atria, etc.
At the present time, both analog and digital information or data is typically transmitted by uplink RF telemetry from such IMDs to the external programmer upon receipt of a downlink telemetry interrogation command from the external programmer. The analog information has typically included battery voltage, physiologic signal amplitudes sensed in real time from sensors or sense electrodes, e.g., sampled cardiac electrocardiogram or EGM amplitude values, and, in the case of implanted pacemaker and ICD IPGs, pacing pulse and/or cardioversion shock amplitude, energy, and pulse width and lead impedance. Digital information includes digitized operating data, e.g., markers signifying device operations and data typically stored in RAM or ROM and transmitted in response to an interrogation command from such IMDs. Such stored data includes historic statistics related to device performance, episodic physiologic data stored in response to detection of an episode of interest or delivery of a therapy, e.g., cardiac electrogram segments, current programmed operating modes and parameter values, implant data, and patient and IMD identifier codes. Uplink telemetry is therefore employed to interrogate the IMD functions and memory and to confirm re-programming of operating modes and parameter values programmed in an downlink telemetry transmission.
Commonly assigned U.S. Pat. No. 5,683,432, incorporated by reference herein in its entirety, sets forth a history of the types of communication links that have been employed to communicate with an IMD, specifically including magnetic field coupling, reflected impedance coupling, and RF coupling. Static and dynamic magnetic field coupling techniques are only usable for limited programming of the IMD and have largely been abandoned, although use of static dynamic field coupling continues in the Medtronic Itrel II implantable neural stimulator. In a reflected impedance coupling system, information is transferred using the reflected impedance of an internal (implanted) L-R or L-C tuned circuit RF energized by an inductively coupled, external, L-R or L-C tuned circuit. Advantageously, such a system uses little or no current to transmit information. Disadvantageously, however, the maximum data rate of reflected impedance coupling systems is relatively slow, and the distance or rate at which information may be transferred is limited.
In RF coupled systems, which are perhaps the most commonly employed communication systems in modem implantable device systems, the RF carrier is modulated with information and is transferred from a transmitting antenna L-R or LC tuned circuit to a receiving antenna L-R or L-C circuit. Generally speaking, the modulated RF carrier induces a voltage in the receiving coil that tracks the modulated carrier signal which is then demodulated in order to recover the transmitted data. An example of a pacemaker programmer for use with programmable cardiac pacemakers having RF telemetry capabilities is disclosed in U.S. Pat. No. 4,550,370, incorporated by reference herein in its entirety.
Significant attenuation of the uplink and downlink RF telemetry signals occurs because the stainless steel or titanium canister commonly used to hermetically enclose an IMD and its antenna coil acts as a low-pass filter for the transmitted RF signals. Uplink telemetry transmission power cannot be increased to compensate for such attenuation because IMD battery power consumption must be minimized. The attenuation increases as frequency is increased, and so communications systems that are currently used have a maximum frequency of less than 200 kHz, which limits data transmission rate. Depending upon the type of modulation and demodulation used in an RF communication system, the data or bit rate cannot exceed a predetermined fraction of the carrier frequency; otherwise, the ability to reliably distinguish between modulation representing a digital (binary) “1” from a digital “0” is compromised. As a result of these constraints, the transmission range through the canister is limited to about 2-3 inches. A wide variety of proposals have been advanced in the prior art involving relocation of the telemetry antenna coil to or use of different antenna types at a location outside the canister of the IMD and use of higher frequencies in the megahertz range to increase operating range and data transmission rate but they have yet to be realized.
Since the time that such telemetry systems first became available, IMDs have proliferated in types and successive models or generations of each type that have been steadily improved in longevity and designed with increased programmable functions and capabilities. At first, in some instances, a single external programmer was designed to function with a single type or family of IMDs that could not be used to program or interrogate other IMD types or families or new generations thereof. A new programmer would have to be provided to the physicians as successive programmable IMD models and IMD functions became clinically available. In some instances, this problem was perceived and dealt with by providing the capability of upgrading the programmer so that it could communicate with the newly available
IMDs and at least confirm the identity of the IMD during a programming session for safety and record keeping reasons before proceeding to the programming and interrogation functions.
Microprocessor-based programmers were developed by Medtronic, Inc. and other manufacturers which operated under the control of dedicated, plug-in ROM modules or cartridges to enable the operation of the programming and interrogation telemetry with regard to specific model or series of models of IMDs. In such systems, the programmer is incapable of communicating with a given IMD model unless the appropriate plug-in module or cartridge is first installed. For example, for many years, particular Medtronic® MemoryMod® ROM cartridges were developed and supplied to enable the physician to upgrade the programmer to program and a-interrogate a specific set of new generation Medtronic® pacemaker implantable pulse generator models.
More sophisticated, computer based programmers have been developed that is also can be upgraded, including, for example, the Medtronic® Model 9710 and 9760 programmers and the more recent Medtronic® Model 9766 and 9790 programmers which employ the Medtronic® Model 9765 programming head. It is possible to load updated software for programming new generation IMDs onto a hard disk drive from floppy disks or compact discs or through a modem and many of the other alternative ways that programs are added to personal computers, for example.
Telemetry sessions between an IMD and the external programmer are typically initiated and conducted in the manner described in commonly assigned, U.S. Pat. No. 5,168,871, incorporated herein by reference herein in its entirety. Current telemetry systems are designed to provide two-way telemetry by RF signal transmission and li
Jurek David R.
Kruse John M.
Atlass Michael B.
Layno Carl H.
Medtronic Inc.
Patton Harold R.
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