Pacemaker artifact suppression in coronary monitoring

• US 4,105,023 A
• Filed: 01/19/1977
• Issued: 08/08/1978
• Est. Priority Date: 01/19/1977
• Status: Expired due to Term

• Current Assignee: Warner-Lambert Company (Pfizer Inc.)
• Original Assignee: American Optical Corporation
• Inventors: Marchese, Thomas F., Argon, Rauf S.
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): Rose, Arthur S.
• Application Number:
  US05/760,487
• Time in Patent Office: 566 Days
• Field of Search: 128/2.06 B, 128/2.06 G, 128/2.06 R, 128/2.05 T, 128/419 PT, 128/206 F
• US Class Current: 600/510
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/308 for electrocardiography [ECG]
• CPC Class Codes: A61B 5/7217 of noise originating from a therapeutic or surgical apparatus, e.g. from a pacemaker
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

In heart monitoring systems for use with patients whose hearts may be stimulated by an artificial pacer and which system includes heart rate indicating means, there is provided circuitry for suppressing the recharge waveform portion of a pacer signal artifact in addition to suppression of the discharge pulse portion of the signal artifact, thereby to prevent inaccuracies in the heart rate indication arising from the pacer signal artifact. In addition to suppressing the discharge pulse portion of a pacer signal artifact with conventional means, the invention recognizes that the recharge waveform of the pacer signal may cause a false impression of a QRS complex which actuates heart rate indicating means and provides novel circuitry for suppressing such recharge waveform.

Circuitry is provided for recognizing the occurrence of a pacer discharge pulse and for generating a suppression signal in timed relation thereto which, when arithmetically added to the recharge waveform portion, acts to cancel or suppress such recharge portion. The suppression signal is of inverse polarity to the recharge waveform portion and is generated by sampling the pacer signal artifact substantially at the beginning of the recharge waveform to determine the magnitude thereof. In a preferred embodiment, a pacer signal artifact and the termination of the discharge pulse portion thereof is identified by novel rate and duration measuring circuitry.

Claims

1. In a heart monitoring system including means for sensing a patient'"'"'s ECG signals, means responsive to the QRS complex of sensed ECG signals for indicating the patient'"'"'s heart rate, and signal suppression means for suppressing the pacer discharge pulse portion of a heart pacer signal artifact possibly appearing in the sensed ECG signal to prevent false actuation of the heart rate indicating means thereby, the pacer signal artifact being comprised of the pacer discharge pulse portion and a recharge waveform portion, the improvement wherein said suppression means additionally incudes:

means responsive to a pacer signal artifact in the sensed ECG signal for generating a recharge waveform suppression signal of opposite polarity to the recharge waveform portion of the pacer signal, and means for arithmetically summing the recharge waveform suppression signal with the sensed ECG signal to additionally suppress said recharge waveform portion, the magnitude and duration of said recharge waveform suppression signal being such as to thereby also prevent false actuation of the heart rate indicating means by said recharge waveform portion of the pacer signal artifact.

2. The heart monitoring system of claim 1 wherein the magnitude of said recharge waveform suppression signal is substantially proportional to the magnitude of the respective recharge waveform portion of the pacer signal.

3. The heart monitoring system of claim 2 wherein said recharge waveform portion of the pacer signal has a magnitude sufficient for a particular interval to actuate the heart rate indicating means and wherein said recharge waveform suppression signal exists at least for an interval substantially concurrent with said particular interval of said recharge waveform portion.

4. The heart monitoring system of claim 2 wherein the magnitude of said recharge waveform suppression signal is substantially equal to the magnitude of the respective recharge waveform portion of the pacer signal.

5. The heart monitoring system of claim 1 wherein said suppression means includes means responsive to a pacer signal artifact for generating a strobe signal substantially at the beginning of the recharge waveform portion thereof and said recharge waveform suppression signal generating means comprises a transient generator providing an output signal the magnitude of which is a function of the magnitude of the input signal applied thereto, and switch means responsive to said strobe signal for extending said beginning of said recharge waveform portion of the pacer signal artifact to said transient generator as said input signal thereto.

6. The heart monitoring system of claim 5 wherein said recharge waveform portion of said pacer signal artifact is an exponential charging function having a particular time constant and said transient generator comprises an RC circuit, the value of said RC circuit being selected to provide an exponential decay of the opposite polarity as said input signal with a time constant which corresponds substantially with said particular time constant of said exponential charging function of said recharge waveform portion.

7. The heart monitoring system of claim 6 wherein said RC circuit comprises parallel-connected resistance means and capacitance means, said parallel-connected resistance means and capacitance means being connected in series with said switch means and said summing means.

8. The heart monitoring system of claim 5 wherein said strobe signal generating means comprises means for obtaining a representation of the time derivative of the sensed ECG signal including any possible pacer, the timer derivative representation of a pacer discharge pulse including first and second spikes of opposite polarities at the beginning and end respectfully of the pacer discharge pulse, means responsive to said time derivative representation for providing a trigger signal each time the magnitude of the time derivative representation exceeds a threshold corresponding with the respective opposite polarities of the time derivative representation, the threshold for each polarity being selected such that a first trigger signal is provided at the start of a pacer discharge pulse and a second trigger signal is provided at the end of a pacer discharge pulse, means responsive to said first trigger signal for initiating a predetermined timing interval following a predetermined delay, the termination of a normal pacer discharge pulse occurring during said timing interval, and means responsive to said second trigger signal occurring during said predetermined interval for generating said stroke pulse.

9. The heart monitoring system of claim 8 wherein the thresholds respectively corresponding with the opposite polarities of said time derivative representations are substantially equal, said thresholds being representative of a minimum slew rate of said sensed signal including any possible pacer discharge pulse.