Microprocessor capture detection circuit and method

• US 6,163,724 A
• Filed: 08/27/1999
• Issued: 12/19/2000
• Est. Priority Date: 09/18/1998
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Schuelke, Robert John, Peck, Bradley C., Blow, Brian A., Hemming, Michael Todd, Morrison, Scott M.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US09/385,655
• Time in Patent Office: 480 Days
• Field of Search: 607/9, 607/28
• US Class Current: 607/28
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation

Abstract

A software programmable device means such as a microprocessor discriminates between evoked response signals and post-pace polarization signals sensed by an implantable medical device. The polarity of the positive or negative change in voltage in respect of time (or dv/dt) of the waveform incident on the lead electrodes is monitored during a short period of time immediately following a paced event. It has been discovered that the post-pace polarization signal exhibits a relatively constant polarity during the capture detect window, and that the evoked response signal may cause the polarity of post-pace polarization signal to reverse during the capture detect window . The sign of the post-pace polarization polarity, either positive or negative, is determined by the design of the specific output circuitry. The evoked response signal may reverse the polarity of the sensed signal in either case, from positive to negative or from negative to positive, during the time window of interest. In another embodiment of the present invention, and when the magnitude of the post-pace polarization is so great that the evoked response does not reverse the polarity of the waveform, discrimination of the evoked response is achieved by noting an acceleration (or increasing magnitude of dv/dt) in the sensed signal or waveform.

Claims

1. A sense amplifier system including electrical circuits implemented in an implantable pulse generating device to identify and process evoked response signals based on post-pace polarization signals, the sense amplifier system comprising:

at least one lead electrode having a positive and negative polarity;

a pre-amp circuit;

a peak tracking circuit;

a band-pass filter circuit;

a rectifier circuit;

a comparator circuit;

a digital blanking/masking/processing circuit; and

a microprocessor coupled to said pre-amp circuit;

said pair of lead electrodes being positioned to sense said evoked response signals and being operably connected to said digital blanking circuit via said pre-amp circuit, said peak tracking circuit, said band pass filter circuit, said rectifier circuit and said comparator circuit to thereby yield a detectable bit for identification and processing by the microprocessor.

2. The system of claim 1, wherein the evoked response signals include an atrial physiologic electrical signal.

3. The system of claim 1, wherein the evoked response signals include a ventricular physiologic electrical signal.

4. The system of claim 1, wherein the post-paced polarization signals relate to a stimulation polarization artifact signal sensed by the electrode following delivery of a stimulating pulse by the pulse generating device.

5. The system of claim 4 wherein the microprocessor generates an estimate of the stimulation polarization artifact signal included in the physiologic signal, the microprocessor subtracting the artifact signal from the physiologic signal to generate an estimate of the evoked response signal.

6. The system of claim 5 wherein the microprocessor performs to process second order peak tracking of the evoked response signal and detects an increase in the magnitude of the derivative of the estimate of the evoked response signal.

7. A method of detecting an evoked response to delivery of a cardiac stimulating pulse to a patient'"'"'s heart by an electrode capable of sensing a physiologic electrical signal and delivering stimulating pulses, the electrode being coupled to a hermetically sealed implantable medical device, the method comprising the steps of:

(a) coupling the electrode to an input of a sense amplifier system wherein the sense amplifier system includes electrical circuits including a microprocessor implemented to identify and process evoked response signals and post-pace polarization signals the identification and processing method including;

(b) defining a capture detect window following delivery of a stimulating pulse;

(c) detecting with the microprocessor, during the capture detect window, a change in the polarity of the physiologic electrical signal sensed at the electrode, the change in polarity of the physiologic signal corresponding to a post-pace polarization artifact signal;

(d) storing the physiologic signal in a first array;

(e) generating and storing in a second array, an estimate of the stimulation polarization artifact signal, and

(f) subtracting, in the microprocessor, the estimate of the stimulation polarization artifact signal stored in the first array from the physiologic signal stored in the second array to provide an estimate of the evoked response signal.

8. A medical device capable of providing intra-cardiac electrical stimuli to a patient'"'"'s heart, comprising:

an electrode having a positive and negative polarity for delivering electrical stimulating pulses, and sensing a physiologic electrical signal including changes in the polarities thereof originating, in the patient'"'"'s heart;

a pulse generator, coupled to the electrode, for generating electrical stimulating pulses to be applied to the heart by the electrode;

a sense amplifier including;

a pre-amp circuit coupled to the electrode, for amplifying and sensing the physiologic electric signals;

a peak tracking circuit;

a band-pass filter circuit;

a rectifier circuit;

a comparator circuit;

a digital blanking/masking/processing circuit; and

a microprocessor coupled to said pre-amp circuit,

said electrode being positioned to sense said evoked response signals and being operably connected to said digital blanking circuit via said pre-amp circuit, said peak tracking circuit, said band pass filter circuit, said rectifier circuit and said comparator circuit to thereby yield a detectable bit for identification and processing by the microprocessor;

based on a change in the polarity of the physiologic electrical signal.

9. The device of claim 8, wherein the change in polarity of the physiologic electrical signal corresponds to a stimulation polarization artifact sensed by the electrode following delivery of a stimulating pulse by the electrode and a basis on which said detectable bit for identification and processing by the microprocessor is generated.

10. The device of claim 8, wherein the microprocessor subtracts an estimate of the stimulation polarization artifact from the physiologic electrical signal to provide an estimate of an evoked response signal for each post-pacing episode.

11. A method of detecting and processing an evoked response to a cardiac stimulating pulse delivered to a patient'"'"'s heart by an electrode, the method comprising the steps of:

(a) acquiring, using the electrode, a sensed signal during a capture detect window following delivery of the stimulating pulse;

(b) detecting, using a microprocessor and by one of negative peak tracking and second order peak tracking, a change in polarity of the sensed signal, and

(c) if a change in polarity of the sensed signal is detected in step (b), generating in the microprocessor an estimate of a stimulation pulse artifact signal present in the sensed signal.

12. The method of claim 11, further comprising the step of the microprocessor detecting an increase in the magnitude of the derivative of the stimulation pulse artifact signal for each post pacing episode.

13. Means for detecting capture in an implantable medical device having at least one means for delivering electrical pulses and sensing a physiologic electrical signal, the capture detecting means comprising:

(a) means for amplifying the physiologic electrical signal sensed by the delivering and sensing means, the amplifying means being coupled to the delivering and sensing means; and

(b) microprocessor means for negative peak tracking, coupled to the amplifying means, for detecting a change in the polarity of the physiologic electrical signal.

14. The capture detecting means of claim 13, wherein the physiologic electrical signal is an atrial physiologic electrical signal based on evoked response signals.

15. The capture detecting means of claim 13, wherein the physiologic electrical signal is a ventricular physiologic electrical signal based on evoked response signals.

16. The capture detecting means of claim 13, wherein the change in polarity of the physiologic electrical signal is a stimulation polarization artifact sensed by the delivery and sensing means for each post pacing episode.

17. The capture detecting means of claim 13, wherein the microprocessor negative peak tracking means generates an estimate of a stimulation polarization artifact signal for each post pacing episode.

18. A medical device capable of providing intra-cardiac electrical stimuli to a patient'"'"'s heart, comprising:

means for delivering electrical stimulating pulses and sensing a physiologic electrical signal including changes in the polarity thereof originating in the patient'"'"'s heart;

means for generating electrical stimulating pulses, coupled to the delivering and sensing means, for generating electrical stimulating pulses to be applied to the heart by the delivering and sensing means;

means for sensing and amplifying the physiologic electrical signal coupled to the delivering and sensing means;

software programmable device means for negative peak tracking, coupled to the amplifying and sensing means, for detecting a change in the polarity of the physiologic electrical signal.

19. The device of claim 18, wherein the software programmable device means for negative peak tracking is a microprocessor and is incorporated with the said means for sensing and amplifying.