Cardiac pacer having active notch filter system

• US 4,436,093 A
• Filed: 09/28/1982
• Issued: 03/13/1984
• Est. Priority Date: 11/04/1980
• Status: Expired due to Fees

• Current Assignee: Norland Corporation
• Original Assignee: Norland Corporation
• Inventors: Belt, Kenneth W.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/425,223
• Time in Patent Office: 532 Days
• Field of Search: 128/696, 128/901, 128/419 PG, 128/419 PT, 128/704
• US Class Current: 607/9
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A battery powered external pacer operable in fixed-rate and demand modes includes a sense amplifier having an active notch filter system for attenuating power line interference. The filter system comprises four separate data channels each including a transmission gate synchronously driven by pacer clock pulses for frequency stability. Charges developed on capacitors in each data channel are summed by an output capacitor to avoid the need for amplifiers in each channel. A detector having two comparators for detecting positive and negative directed R-wave components derives heart pulses from the amplified signal. A pulse-driven reference supply having very low power consumption provides operating bias required by the detector. A battery monitor having a single comparator simultaneously monitors supply voltage for low and unusable voltage levels.

Claims

1. In a cardiac pacer of the type responsive to an applied cardiac sense signal which includes a desired signal component and a power line-induced interference component, a sense amplifier comprising:

means comprising a plurality of selectable sample-and-hold channels for independently sampling the instantaneous amplitude of said cardiac signal;

sampling means for sequentially and repeatedly selecting said channels whereby each channel is selected for an equal period of time over a complete selecting cycle; and

signal summation means for combining the outputs of said channels to derive an output signal including said desired signal component;

said channels being selected at a frequency of nf, where n is a whole integer and f is the frequency of the power line component, whereby said interference component is attenuated from said output signal.

2. A cardiac pacer as defined in claim 1 wherein said sample-and-hold channels each include a signal storage capacitor, and said signal summation means comprise a summing capacitor coupled to each of said signal storage capacitors.

3. A cardiac pacer as defined in claim 1 wherein each of said channels includes an analog switch device, and wherein said sampling means selectively render said switch devices conductive.

5. A cardiac pacer as defined in claim 1 wherein said sampling period is substantially less than t/K, where t is the duration of one complete sampling cycle, and K is the number of said sample-and-hold channels.

4. A cardiac pacer as defined in claim 4 wherein the pacer further includes an oscillator, and wherein said sampling means include frequency divider means, and digital phase shift means for applying the output of said frequency divider means to said analog switch means.

6. In a cardiac pacer of the type responsive to an applied cardiac sense signal which includes a desired signal component and a power line-induced interference component, a sense amplifier comprising:

means comprising a plurality of selectable sample-and-hold channels each including a signal storage capacitor and an analog switch device for independently sampling the instantaneous amplitude of said cardiac signal;

sampling means for sequentially and repeatedly rendering said analog switch devices conductive whereby each channel is selected for a predetermined sampling period over each complete selecting cycle;

signal summation means including a summing capacitor coupled to said signal storage capacitors for combining the outputs of said channels to derive an output signal including said desired signal component; and

said channels being selected at a frequency of nf, where n is a whole integer and f is the frequency of the power line component, whereby said interference component is attenuated from said output signal.

7. A cardiac pacer of the type responsive to an applied cardiac sense signal which includes a desired signal component and a power line-induced interference component, comprising:

a continuous-wave signal source;

pulse control circuit means operable from said continuous-wave signal and responsive to an applied pulse occurrence signal for controlling the production of output pulses from the pacer;

means comprising a plurality of selectable sample-and-hold channels for independently sampling the instantaneous amplitude of said cardiac signal;

sampling means operative from said continuous-wave signal source for sequentially and reapeatedly selecting said channels whereby each channel is selected for a predetermined sampling period over each complete selecting cycle;

signal summation means for combining the outputs of said channels to derive a pulse occurrence signal including said desired signal component for application to said pulse control circuit means; and

said channels being selected at a frequency of nf, where n is a whole integer and f is the frequency of the power line component, whereby said interference component is attenuated from said pulse occurrence signal prior to application of said pulse occurrence signal to said pulse control circuit means.

8. A cardiac pacer as defined in claim 7 wherein said sampling means include frequency divider means for reducing the frequency of said continuous wave signal, and digital phase shift means for applying the output of said frequency divider means to said analog switch means.

9. A cardiac pacer as defined in claim 8 wherein said sample-and-hold channels each include a signal storage capacitor and an analog switch device, said signal summation means comprise a summing capacitor, and said sampling means individually render each of said analog switch devices conductive.

10. A cardiac pacer as defined in claim 7 wherein said sampling period is substantially less than t/K, where t is the duration of one complete sampling cycle and K is the number of sampling channels.

11. In a cardiac pacer of the type responsive to an applied cardiac sense signal including a desired signal component and a power line-induced interference component, a sense amplifier comprising:

means comprising a plurality of selectable sample-and-hold channels for independently sampling the instantaneous amplitude of said cardiac signal;

sampling means for sequentially and repeatedly selecting said channels whereby each path is selected for a predetermined sampling period once during each complete selecting cycle;

signal summation means for combining the outputs of said channels to derive an output signal including said desired signal component; and

said channels being selected for sampling periods substantially less than t/K and at a frequency of nf, where t is the duration of one selecting cycle, K is the number of sample-and-hold hold channels, n is a whole integer and f is the frequency of the power line component, whereby said interference component is attenuated from said output signal.

12. A cardiac pacer as defined in claim 11 wherein said sample-and-hold channels each include a signal storage capacitor, and said signal summation means comprise a summing capacitor coupled to associated ones of said signal storage capacitors.

13. A cardiac pacer as defined in claim 11 wherein each of said channels includes an analog switch device, and wherein said sampling means selectively render said devices conductive.

14. A cardiac pacer as defined in claim 13 wherein the pacer further includes an oscillator, and wherein said sampling means include frequency divider means, and digital phase shift means for applying the output of said frequency divider means to said analog switch means.