Microprocessor capture detection circuit and method

• US 5,873,898 A
• Filed: 04/29/1997
• Issued: 02/23/1999
• Est. Priority Date: 04/29/1997
• 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:
  US08/841,064
• Time in Patent Office: 665 Days
• Field of Search: 607/28
• US Class Current: 607/28
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation
• CPC Class Codes: A61N 1/3716 with reduction of residual polarisation effects

Abstract

The programmable device means such as a microprocessor are employed to discriminate 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. When 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 may be achieved by noting an acceleration (or increasing magnitude of dv/dt) in the sensed signal or waveform.

Claims

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

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

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

a sense amplifier, coupled to the electrode for amplifying and sensing the physiologic electrical signal;

a microprocessor for tracking a negative peak in the physiologic electrical signal, coupled to the sense amplifier, the microprocessor detecting a change in the polarity of the physiologic electrical signal occurring during a capture detect window following application of the electrical stimulating pulse to the heart to thereby detect capture of the heart.

2. The device of claim 1, wherein the device is an implantable medical device that is hermetically sealed and formed of a biocompatible material.

3. The device of claim 1, wherein the change in polarity of the physiologic electrical signal indicates a stimulation polarization artifact sensed by the electrode following delivery of the stimulating pulse by the electrode.

4. The device of claim 3, wherein the microprocessor generates an estimate of the stimulation polarization artifact and stores same in a first array, the microprocessor storing the physiologic electrical signal in a second array, the microprocessor subtracting the first array from the second array to provide an estimate of an evoked response signal.

5. The device of claim 4, the microprocessor further detecting by second order peak tracking an increase in the magnitude of the derivative of the estimate of the evoked response signal, the microprocessor generating an estimate of the derivative of the estimate of the evoked response signal and storing same in a third array as data, the microprocessor monitoring the third array to detect the increase in the magnitude of the data.

6. A method of detecting an evoked response to a cardiac stimulating pulse delivered to a patient'"'"'s heart by at least one electrode connected to an hermetically sealed implantable medical device having a microprocessor disposed therewithin, the method comprising the steps of:

(a) delivering the pulse to the heart with the at least one electrode;

(b) defining a capture detect window in the implantable medical device;

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

(d) detecting, using the microprocessor, a change in polarity of the sensed signal during the capture detect window;

(e) generating in the microprocessor an estimate of a stimulation pulse artifact signal present in the sensed signal when the change in polarity of the sensed signal is detected during the capture detect window.

7. The method of claim 6, further comprising the step of the microprocessor detecting an increase in the magnitude of a derivative of the stimulation pulse artifact signal following generation of the derivative by the microprocessor, to thereby indicate capture of the heart by the stimulating pulse.

8. The method of claim 6, further comprising the step of:

(d) comparing the maximum value of the estimate of the stimulation pulse artifact signal to a predetermined reference value to determine whether or not capture has occurred.

9. 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;

(b) microprocessor means coupled to the amplifying means, for detecting a change in a polarity of the physiologic electrical signal, the microprocessor means comprising means for sampling the physiological signal, means for detecting the change in the polarity of the physiological electrical signal during a capture detect window, the means for polarity change detection further comprising RAM means for storing signal samples as a stored array in the microprocessor, the microprocessor means further having means for processing the stored array to determine whether a change in polaritv has occurred in the physiological signal to thereby indicate capture of the heart.

10. The capture detecting means of claim 9, wherein the means for detecting capture further comprises digital controller/timer means disposed between the microprocessor means and the means for amplifying.

11. The capture detecting means of claim 10, wherein the digital controller/timer means is coupled to a means for sensing patient activity.

12. The capture detecting means of claim 10, wherein the digital controller/timer means is coupled to a means for measuring pressure.

13. The capture detecting means of claim 9, wherein the microprocessor means for processing includes means for generating an estimate of a stimulation polarization artifact signal included in the physiologic signal and means for subtracting the artifact signal from the physiologic signal to generate an estimate of the evoked response signal.

14. The capture detecting means of claim 13, wherein the microprocessor negative peak tracking means stores the estimate of the stimulation polarization artifact signal in a first array, stores the physiologic electrical signal in a second array, and subtracts the first array from the second array to provide an estimate of an evoked response signal.

15. The capture detecting means of claim 14, wherein the microprocessor second order peak tracks the estimate of the evoked response signal to detect an increase in the magnitude of the derivative of the estimate of the evoked response signal, the microprocessor generating an estimate of the derivative of the estimate of the evoked response signal and storing same in a third array as data, the microprocessor monitoring the third array to detect the increase in the magnitude of the data.

16. 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 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, the software programmable device being a microprocessor.

17. The device of claim 16, wherein the device is an implantable medical device that is hermetically sealed and formed of a biocompatible material.

18. The device of claim 16, wherein the change in polarity of the physiologic electrical signal indicates a stimulation polarization artifact sensed by the electrode following delivery of a stimulating pulse by the electrode.

19. The device of claim 16, wherein the software programmable device means generates an estimate of a stimulation polarization artifact signal.

20. The device of claim 19, wherein the software programmable device means stores the estimate of the stimulation polarization artifact signal in a first array, stores the physiologic electrical signal in a second array, and subtracts the first array from the second array to provide an estimate of an evoked response signal.

21. The device of claim 20, wherein the software programmable device means second order peak tracks the evoked response signal to detect an increase in the magnitude of the derivative of the evoked response signal, the microprocessor generating an estimate of the derivative of the estimate of the evoked response signal and storing same in a third array as data, the microprocessor monitoring the third array to detect the increase in the magnitude of the data.