Notch filter noise rejection system in a cardiac control device
First Claim
1. A physiological event signal sensing system in a cardiac medical device, comprising:
- means for sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference;
means for sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs;
means for combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs/n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function;
means for comparing said notch filter output signal with a predetermined threshold level; and
,means responsive to said notch filter output signal exceeding the predetermined threshold level for determining the occurrence of a heartbeat.
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Abstract
A physiological event signal sensing system in a cardiac control or monitoring device for detecting spontaneous cardiac electrical events which may be obscured by continuous or burst EMI line frequency noise. The noise rejecting sensing system of this invention senses and samples cardiac signals which may include a noise component which is produced by power line interference in addition to a physiological signal component. The sampling frequency is selected to be an integer multiple of at least one common power line frequency. The system notch filters the cardiac signal to remove line frequency components, using either or both lowpass and highpass notch filtering coefficients, then limits the filtered output to the amplitude of the corresponding filter input to remove filter output signals caused by the sudden termination of line frequency noise which is characteristic of burst noise.
142 Citations
28 Claims
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1. A physiological event signal sensing system in a cardiac medical device, comprising:
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means for sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference; means for sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs; means for combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs/n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function; means for comparing said notch filter output signal with a predetermined threshold level; and
,means responsive to said notch filter output signal exceeding the predetermined threshold level for determining the occurrence of a heartbeat. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A physiological event signal sensing system in a cardiac medical device, comprising:
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means for sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference; means for sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs; means for combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs/n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function; rectifying means responsive to said sampling means for rectifying said sampled cardiac signal and responsive to said combining means for rectifying said notch filter output signal; means for comparing each of said rectified notch filter output signal samples to the corresponding time sample of said rectified sampled cardiac signal to determine the sample having a smaller value in each pair of compared corresponding time samples; means responsive to said comparing means for setting each sample of said notch filter output signal to said smaller value to provide a minimized notch filter output signal; means for comparing said minimized notch filter output signal with a predetermined threshold level; and
,means responsive to said notch filter output signal exceeding the predetermined threshold level for determining the occurrence of a heartbeat. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A physiological event signal sensing system in a cardiac medical device, comprising:
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means for sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference; means for sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs; means for combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs/n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function; integrating means responsive to said sampling means for integrating said sampled cardiac signal and responsive to said combining means for integrating said notch filter output signal; means for determining the ratio of said integrated notch filter output signal to said integrated sampled cardiac signal, means for comparing said ratio with a predetermined threshold level; and means responsive to said notch filter output signal exceeding the threshold level for determining the occurrence of a heartbeat.
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27. A method of operating a physiological event signal sensing system in a cardiac medical device, comprising the steps of:
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sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference; sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs; combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs /n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function; comparing said notch filter output signal with a predetermined threshold level; and
,determining the occurrence of a heartbeat when said notch filter output signal exceeds a predetermined threshold level.
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28. A method of operating a physiological event signal sensing system in a cardiac medical device, comprising the steps of:
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sensing a cardiac signal, said cardiac signal including a physiological component and including a noise component which is produced by power line interference; sampling the instantaneous amplitude values of said cardiac signal at a sampling frequency of Fs; combining said amplitude values for n consecutive samples to derive a notch filter output signal retaining said physiological component while attenuating said power line noise component, wherein n is preselected so that Fs/n defines the frequency of the power line noise component and wherein said amplitude values are combined according to a predetermined notch filter function; rectifying said sampled cardiac signal; rectifying said notch filter output signal; comparing each of said rectified notch filter output signal samples to the corresponding time sample of said rectified sampled cardiac signal to determine the sample having a smaller value in each pair of compared corresponding time samples; setting each sample of said notch filter output signal to the smaller value resulting from said comparing step to provide a minimized notch filter output signal; comparing said minimized notch filter output signal with a predetermined threshold level; and
,determining the occurrence of a heartbeat when said minimized notch filter output signal exceeds a predetermined threshold level.
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Specification