Implantable medical device with autosensitivity algorithm for controlling sensing of cardiac signals
First Claim
1. A cardiac pacing system having a pacing device and a lead for connecting patient cardiac signals to said pacing device, said device having at least one DSP channel having DSP means for amplifying and processing said cardiac signals, said DSP means further having sensitivity means for setting the sensitivity level for use in detection of a said cardiac signal, gain control means for adjusting the gain used in said amplifying, and event means for determining when a said cardiac signal is determined to be a valid cardiac event, further comprising:
- amplitude sample means for enabling said DSP means to amplify and process cardiac signals periodically at a first sampling interval in the range of 1 minute to 60 minutes;
amplitude means for obtaining and storing signal amplitude data representative of the amplitude of sampled cardiac signals that have been amplified by said DSP means;
noise sample means for enabling said DSP means to sample noise in said DSP channel following each sampled cardiac signal;
noise means for obtaining and storing noise amplitude data representative of sampled noise in said DSP channel; and
check means for comparing said stored signal amplitude data with said stored noise amplitude data periodically at a predetermined check interval greater than at least one hour and for adjusting said sensitivity level in accord with each said comparison.
1 Assignment
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Accused Products
Abstract
A cardiac pacing system and method incorporate DSP processing and software algorithms for collecting signal amplitude data and noise data, and organizing the data for automatic checking of signal channel gain and signal detection sensitivity. Unfiltered signals are used to obtain values representative of maximum amplitude, which values are stored in a gain histogram, from which determination of the percentage of clipped signals can be made. Gain is adjusted by limiting clipping to a predetermined range of allowed clipping, to optimize use of the DSP range. The signals, both P waves and R waves for a dual chamber system, are also processed by DSP and parameters representing maximum amplitudes are stored in amplitude histograms. At the same time, noise is analyzed for respective windows of time following each ventricular event, and noise amplitude data is stored in noise histograms. After a predetermined waiting period, the signal amplitude and noise histograms are analyzed and compared, and for each channel the sensitivity is adjusted to fall between a calculated noise floor and the lowest bin of the amplitude histogram that contains valid data.
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Citations
56 Claims
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1. A cardiac pacing system having a pacing device and a lead for connecting patient cardiac signals to said pacing device, said device having at least one DSP channel having DSP means for amplifying and processing said cardiac signals, said DSP means further having sensitivity means for setting the sensitivity level for use in detection of a said cardiac signal, gain control means for adjusting the gain used in said amplifying, and event means for determining when a said cardiac signal is determined to be a valid cardiac event, further comprising:
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amplitude sample means for enabling said DSP means to amplify and process cardiac signals periodically at a first sampling interval in the range of 1 minute to 60 minutes;
amplitude means for obtaining and storing signal amplitude data representative of the amplitude of sampled cardiac signals that have been amplified by said DSP means;
noise sample means for enabling said DSP means to sample noise in said DSP channel following each sampled cardiac signal;
noise means for obtaining and storing noise amplitude data representative of sampled noise in said DSP channel; and
check means for comparing said stored signal amplitude data with said stored noise amplitude data periodically at a predetermined check interval greater than at least one hour and for adjusting said sensitivity level in accord with each said comparison. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. An implantable medical device system, said system having signal channel means for receiving and processing medical signals from the patient in whom it is implanted, said channel means having sensitivity means for setting a sensitivity threshold for discriminating between valid signals and noise, said channel means further comprising:
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amplitude sample means for sampling a received signal for a first sample time every predetermined first sample interval and for storing data representative of the amplitude of said sampled signal;
noise sample means for sampling noise in said channel for a second sample interval that has a predetermined time relation to said first sample time, and for storing data representative of the sampled noise;
event analysis means for determining a valid signal only when a sampled signal has an amplitude above said sensitivity threshold;
an amplifier circuit having a signal range with an upper limit and adjustable gain;
adjust means operable every second interval for processing said stored amplitude data and said stored noise data, said adjust means having gain adjust means for adjusting said gain as a function of the percentage of said sampled signals having a maximum signal amplitude above said upper limit and sensitivity adjust means for adjusting said sensitivity threshold as a function of said stored amplitude data and said stored noise data; and
data reduction means for reducing said stored noise data and said stored amplitude data before continuing sampling of data in a manner that gives greater weight to data taken during each second interval than data stored in prior second intervals. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39)
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40. A method of receiving and processing signals from a patient'"'"'s heart, the method employing an implantable signal channel, comprising:
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setting a first interval of 1 minute to 1 hour, and periodically sampling every said first interval to obtain a heart signal, and storing data relating to each said sampled signal;
periodically sampling, during a time period in a predetermined time relation to each said sampling of a signal, noise present in said channel, and storing data relating to said noise;
periodically checking sensitivity in accord with predetermined check criteria, said checking being done after a plurality of said first intervals, said checking comprising;
removing a first amount of stored signal data according to predetermined signal error criteria to obtain adjusted signal data;
removing a second amount of stored noise data according to predetermined noise error criteria to obtain adjusted noise data; and
calculating and setting a sensitivity threshold for detection of valid signals as a function of said adjusted signal and noise data. - View Dependent Claims (41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54)
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55. An implantable cardiac system, having at least one signal processing channel for receiving cardiac signals, said channel having an amplifier circuit with an adjustable gain and having event validation means for validating when a received signal is valid and is not noise, comprising:
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gain histogram means for collecting gain data representative of the amplification of sampled ones of received signals and storing said gain data in a gain histogram;
amplitude histogram means for collecting amplitude data representative of the amplitude of said sampled received signals and storing said amplitude data in an amplitude histogram;
noise histogram means for collecting noise data representative of channel noise associated with each sampled signal and storing said noise data in a noise histogram; and
setting the gain of said amplifier circuit and setting a sensitivity threshold for said event validation means on a periodic basis and as a function of the data in said histograms. - View Dependent Claims (56)
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Specification