Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-10-29
2004-03-09
Evanisko, George R. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06704602
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to inter-device communications between medical devices and most particularly to systems that employ sub stimulation threshold pulses for such communications.
BACKGROUND
The high cost and general level of difficulty in communicating with an implanted medical device using a low cost external instrument has prevented widespread usage of the data which is currently available from pacemaker and other implantable medical devices to augment traditional transtelephonic home follow-up.
Health care systems are increasingly emphasizing and rewarding those products which reduce the cost of obtaining, communicating, and managing patient data. Therefore inexpensive devices for remotely monitoring the essential status of pacemaker patients and patients with other implantable medical devices is highly desirable. Even small improvements may have significant economic and medical benefit.
Difficulties arise in transferring large amounts of data between an implanted medical device and external monitors or other medical communications systems. Telemetry using RF or E fields and H fields is commonly practiced in, for example, the field of implantable devices such as pacemakers and defibrillator/cardioversion devices in communicating information between the implant and the external transceiving device for example, a programmer. This has limitations as well, primarily on the cost for the external device which goes up considerably if it needs to receive telemetry. Also, the energy cost of transmitting information from the implanted device to outside the patient's body is higher than using subthreshold electrical pulses and this therefore depletes the implant's battery, weighing against using telemetry too. The overriding consideration for employing external devices to receive data through skin contact electrodes is the simplicity and low cost of the one-way (receiving) device. (The receiving device could even be worn like a wrist watch and receive subthreshold communications for later retransmission).
Therefore to enable better device transmitted communications as the data amounts and transfer rates are desirably increased, a communications protocol and implementing hardware that facilitates such communications has been developed and is the subject of this document.
A list of references where similar or related inventions in the same or other unrelated fields were contemplated follows, and is incorporated into this disclosure by this reference thereto.
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Additionally the Cardiac Telecom HEARTTrac(tm) cardiac monitoring system may provide additional information about such communications but at this date the inventors have not had an opportunity to review this matter.
There still is a need for a very inexpensive method of getting large amounts of data from an implanted device to an external device that is as yet unsatisfied by this art. This is especially true in rural areas and in places where sophisticated telemetry systems may be difficult to use or obtain.
SUMMARY OF THE INVENTION
In general this invention provides a way for an implantable medical device to communicate a limited amount of stored data or sensor or status data such as battery status and lead condition to an inexpensive external instrument. Additionally it would be an advantage to be able to also transmit marker data for electrocardiograms. Rather than relying on the more traditional telemetry communications channel which requires a large amount of support circuitry and so forth, we are using certain subthreshold electrical pulsing capability present in some current implantable medical devices for this purpose. This subthreshold pulsing may be delivered along different pathways for minute ventilation, lead impedance, and capture detection, as well as for this new communications purpose. In a preferred embodiment this circuit
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outputs pulses at rates up to 125 Hz. By modulating a series of such pulses we can easily send data at 10 to 100 bps or even higher data rates. Preferably, communication occurs on a dedicated set of such pulses.
The pulse train can be by modulated to include data in several ways. The form (its amplitude or width for example) of the wave of the communications pulse may be varied in discrete steps. Including or omitting pulses at a given time in a segment length of time can represent various forms of data. Pairing of pulses to send a data bit may be employed. For example, a zero (0) bit could be represented by a pulse followed by a missing pulse, while a one (1) would be represented by a missing pulse followed by a pulse. By limiting ourselves to having at least one missing pulse every two pulse locations, we eliminate the possibility of a 00 or 11 configuration and enhance reliability in reading and allows for easier synchronization by this limitation too. Again, since it is so much less costly we make the communication be only one way. However, so that the implanted device is not communicating constantly to a turned off or disconnected receiver, it is also preferable to trigger a communications episode or session from external to the implanted device. This can be done with a simple “telemetry system” or a substitute for one like a magnet and an internal reed switch that is in the implant device circuitry and which when triggered by the presence of the magnet, begins a communications episode. (Of course, if a more sophisticated external device is used this sub threshold communication may run simultaneously with or be triggered by the H or E field telemetry. But the preferred embodiments will use simple triggers like sounds or magnets or externally applied electrical pulses, or a short burst of H or E field signal produced by an inexpensive external trigger device.) More specifically, each pulse is adapted to avoid pacing, or any tissue stimulation, and to avoid or minimize its effect on the lead to tissue interface. The size of the electrical pulse energy is therefore below the threshold required for cardiac or skeletal muscle stimulation. These pulses can be safely applied by a pacemaker electrode in a pattern which makes them easily and reliably detectable and interpretable by a simple external device.
A few modifications to currently known devices for delivering subthreshold pulses allows for delivery of modulated pulses. A simple detection algorithm can be implemented in external receivers which normally read electrograms of the patient by use of skin electrodes. The data read can be translated, error-checked, or otherwise modified to transmit the data to the external device. The external device can store this or transmit it to other devices or employ it directly to display diagnostically useful information or device related information for attending technicians or physicians.
In general then the invention is a communications system for communicating between an implanted medical device and a device external to a living body containing said implanted medical device wherein communications of data from within said implanted medical device to said external device is accomplished by a communications circuit for producing modulated biphasic subthreshold pulses in a pattern of modulations predetermined to represent data and insufficiently energetic to cause a physiologically significant reaction in living body tissue, and wherein said modulated pulses are transmitted across two electrodes electrically connected to said implanted device, said electrodes linkable in an electrical circuit from said communications circuit through tissues of said living body, such that said transmission can be received by an external device through a plurality of electrodes connected to said extern
Berg Gary
Ernst Jill H.
Nelson Chester G.
Stomberg Charles
Wilkinson Jeffrey D.
Chapik Daniel G.
Evanisko George R.
Medtronic Inc.
Soldner Michael C.
Wolde-Michael Girma
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