Microprocessor capture detection circuit and method

• US 5,954,756 A
• Filed: 04/09/1998
• Issued: 09/21/1999
• Est. Priority Date: 04/09/1998
• Status: Expired due to Term

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Peck, Bradley C., Blow, Brian A., Hemming, Michael Todd, Morrison, Scott M.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US09/058,378
• Time in Patent Office: 530 Days
• Field of Search: 607/28
• US Class Current: 607/28
• CPC Class Codes: A61N 1/371 Capture, i.e. successful stimulation

Abstract

The present invention employs software programmable device means such as a microprocessor 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. 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 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 circuit;

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

(c) detecting with a 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;

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

(e) 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.