Notch filter noise rejection system in a cardiac control device

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;
• 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.

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;
• 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.

A method of operating a physiological event signal sensing system in a cardiac medical device, comprising the steps of:

• 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.

A method of operating a physiological event signal sensing system in a cardiac medical device, comprising the steps of:

• 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.