Implantable cardiac device having event recording capability with compression
First Claim
1. An implantable cardiac stimulation device having a system for compressing cardiac signals, the stimulation device having a sensing system adapted to sense cardiac signals, a pulse generator configured to generate stimulation pulses in the absence of cardiac signals, and a telemetry circuit that is adapted to transmit the cardiac signals in a compressed format to an external programmer capable of restoring the compressed cardiac signals, the system comprising:
- a converter, coupled to the sensing system, configured to convert the sensed cardiac signal to a plurality of digital samples;
a subtractor, coupled to the converter, configured to subtract a current digital sample with a reference value to produce a delta value; and
a controller, coupled to the converter, the subtractor and the telemetry circuit, configured to convert the cardiac signal into a compressed format, the compressed format comprising a first digital sample, corresponding to a starting amplitude of the cardiac signal, followed by one of a compressed delta value when the delta value is below a first threshold, or an uncompressed delta value when the delta value is above the first threshold, the uncompressed delta value being preceded by a first indicator signal;
whereby the cardiac signal is compressed in a substantially lossless fashion.
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Abstract
An implantable cardiac device is disclosed having a converter that provides a digital electrocardiogram signal to a controller which is stored in memory or transmitted via the telemetry circuit in an improved compressed fashion. The improved compression scheme comprises sampling the electrogram signal, transmitting the starting value in an uncompressed format followed by a plurality of delta signals in a compressed format. The delta signals may be determined by subtracting successive signals or by subtracting a predicted value from the current value. In either case, the delta signal is then transmitted in a truncated number of bits, e.g., 2 or 4 bits. When the delta signal is too large to be represented in the compressed number of bits, the controller then provides an indicator signal followed by the delta signal in the uncompressed format. In addition, whenever successive delta signals are below a minimum threshold (e.g., zero), they may be compressed into a count.
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Citations
35 Claims
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1. An implantable cardiac stimulation device having a system for compressing cardiac signals, the stimulation device having a sensing system adapted to sense cardiac signals, a pulse generator configured to generate stimulation pulses in the absence of cardiac signals, and a telemetry circuit that is adapted to transmit the cardiac signals in a compressed format to an external programmer capable of restoring the compressed cardiac signals, the system comprising:
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a converter, coupled to the sensing system, configured to convert the sensed cardiac signal to a plurality of digital samples; a subtractor, coupled to the converter, configured to subtract a current digital sample with a reference value to produce a delta value; and a controller, coupled to the converter, the subtractor and the telemetry circuit, configured to convert the cardiac signal into a compressed format, the compressed format comprising a first digital sample, corresponding to a starting amplitude of the cardiac signal, followed by one of a compressed delta value when the delta value is below a first threshold, or an uncompressed delta value when the delta value is above the first threshold, the uncompressed delta value being preceded by a first indicator signal; whereby the cardiac signal is compressed in a substantially lossless fashion. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An implantable cardiac stimulation device having a system for compressing cardiac signals, the stimulation device having a sensing system adapted to sense cardiac signals, a pulse generator configured to generate stimulation pulses in the absence of cardiac signals, and a telemetry circuit that is adapted to transmit the cardiac signals in a compressed format to an external programmer capable of restoring the compressed cardiac signals, the system comprising:
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converting means, coupled to the sensing system, for converting the sensed cardiac signal to a plurality of digital samples, and for producing a first digital sample corresponding to a starting amplitude of the cardiac signal and a plurality of delta values each indicative of a subsequent change in amplitude of the cardiac signal; and processing means for converting the first digital sample and the plurality of delta values into an encoded string of compressed and uncompressed values, the encoded string comprising the first digital sample in an uncompressed format followed by the plurality of delta values in one of the compressed or uncompressed formats, the processing means for transmitting one of a compressed or uncompressed delta value based on whether a compression criteria has been met, and identifying means for identifying whether the delta value is in one of the compressed or uncompressed formats; whereby the cardiac signal is compressed in a substantially lossless fashion. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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31. A method, for use with an implantable cardiac stimulation device, of compressing a patient'"'"'s cardiac signal in a compressed format for subsequent reconstruction in an external device, the method comprising the steps of:
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converting the cardiac signal into a plurality of digital samples, each digital sample comprising a first number of digital bits; determining a delta value based on the difference between a reference value and a current digital sample; determining when the delta value meets a predefined criteria and for producing a first indicator signal when the criteria is not met; triggering the transmission of an initial first number of bits as a starting value; triggering the transmission of a compressed digital signal when the predefined compression criteria is met, the compressed digital signal having a second number of digital bits that is less than the first number of digital bits; and triggering the transmission of the first indicator signal followed by the uncompressed delta value when the predefined criteria is not met. - View Dependent Claims (32, 33, 34, 35)
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Specification