Apparatus and method for capture detection in a cardiac stimulator

• US 5,443,485 A
• Filed: 09/08/1993
• Issued: 08/22/1995
• Est. Priority Date: 09/08/1993
• Status: Expired due to Term

• Current Assignee: Intermedics Incorporated (Boston Scientific Corporation)
• Original Assignee: Intermedics Incorporated (Boston Scientific Corporation)
• Inventors: Housworth, Craig M., Schroeppel, Edward A.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): Getzow, Scott M.
• Application Number:
  US08/117,854
• Time in Patent Office: 713 Days
• Field of Search: 607/11, 607/13, 607/28
• US Class Current: 607/28
• CPC Class Codes: A61B 5/283 Invasive
• CPC Class Codes: A61B 5/29 for permanent or long-term implantation
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

A capture detection circuit for an implantable cardiac stimulator. A signal detected by an electrode in the heart following delivery of a stimulating pulse is amplified, bandpass and highpass filtered, rectified, integrated over a selected window of time starting at a selected delay after delivery of the stimulating pulse, and applied to two comparators having different reference values. If the integrated signal exceeds the first reference value, the first comparator output goes high. If the integrated signal exceeds the second reference value, the second comparator goes high. If both comparators remain low, non-capture is indicated. If the first comparator goes high and the second comparator remains low, capture is indicated. If the second comparator goes high, an intrinsic contraction is indicated. The window of integration can be extended to distinguish capture from intrinsic contraction.

Claims

1. In a cardiac stimulator having an electrode and having a cardiac stimulation pulse generator means for delivering a cardiac stimulation pulse to the heart, the improvement comprising a capture detector for detecting an electrical signal at said electrode that is evoked in said heart in response to said cardiac stimulation pulse having:

a highpass filter having an input in circuit communication with said electrode and having an output;

an absolute value circuit having an input in circuit communication with the output of said highpass filter and having an output;

an integrator having an input in circuit communication with the output of said absolute value circuit and having an output;

a comparator having a first input in circuit communication with the output of said integrator and having a second input in circuit communication with a reference value, said comparator having an output; and

means for causing said integrator to integrate over a selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse;

whereby said output of said comparator has a value that is indicative of whether capture has occurred.

2. The cardiac stimulator of claim 1, and further including a second comparator having a first input in circuit communication with the output of said integrator and having a second input in circuit communication with a second reference value, said second comparator having an output.

3. The cardiac stimulator of claim 2, in which the second reference value is greater than the first reference value.

4. The cardiac stimulator of claim 3, in which the second reference value is about an order of magnitude greater than the first reference value.

5. The cardiac stimulator of claim 2, in which said means for causing said integrator to integrate extends the window of integration in the event that the first comparator output indicates that the first input to the first comparator exceeded the reference value during the selected window of time.

6. The cardiac stimulator of claim 1, in which said highpass filter is adapted and configured to pass frequencies above about 40 Hz.

7. The cardiac stimulator of claim 1, and further including a bandpass filter having an input and an output and connected in circuit communication with said highpass filter in series connection therewith.

8. The cardiac stimulator of claim 7, in which said bandpass filter has a pass band of about 22 Hz to about 60 Hz.

9. The cardiac stimulator of claim 1, in which said means for causing said integrator to integrate extends the window of integration in the event that the comparator output indicates that the first input to the comparator exceeded the reference value during the selected window of time.

10. A method of verifying cardiac capture by sensing via a pacing electrode a cardiac signal evoked in response to a cardiac stimulation pulse delivered via said same pacing electrode, comprising the steps of:

sensing a waveform signal at said pacing electrode following delivery of said cardiac stimulation pulse;

bandpass filtering said sensed waveform signal through a pass band selected to pass a band of frequencies characteristic of the evoked cardiac signal;

processing said bandpass-filtered waveform signal to render a waveform signal representing the absolute value of said bandpass-filtered signal;

integrating said absolute value processed waveform signal over a selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse; and

comparing said integrated waveform signal to a reference value during said selected window of time and generating a capture detect signal if said integrated waveform signal exceeds said reference value during said selected window of time.

11. A method of verifying cardiac capture by sensing via an electrode a cardiac signal evoked in response to a cardiac stimulation pulse, comprising the steps of:

sensing a waveform signal at said electrode following delivery of said cardiac stimulation pulse;

highpass filtering said sensed waveform signal through a filter selected to pass frequencies characteristic of the evoked cardiac signal;

processing said highpass-filtered waveform signal to render a waveform signal representing the absolute value of said bandpass-filtered signal;

integrating said absolute value processed waveform signal over a selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse; and

comparing said integrated waveform signal to a reference value at the end of said selected window of time and generating a capture detect signal if said integrated waveform signal exceeds said reference value during said selected window of time.

12. The method of claim 11, in which the electrode via which the cardiac signal is sensed is the same electrode via which the stimulation pulse is delivered.

13. A method of verifying cardiac capture by sensing via an electrode a cardiac signal evoked in response to a cardiac stimulation pulse, comprising the steps of:

sensing a waveform signal at said electrode following delivery of said cardiac stimulation pulse;

bandpass filtering said sensed waveform signal through a pass band selected to pass a band of frequencies characteristic of the evoked cardiac signal;

processing said bandpass-filtered waveform signal to render a waveform signal representing the absolute value of said bandpass-filtered signal;

integrating said absolute value processed waveform signal over a selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse; and

comparing said integrated waveform signal to a first reference value at the end of said selected window of time, and comparing said integrated waveform signal to a second reference value at the end of said selected window of time, and generating a capture detect signal if said integrated waveform signal exceeds said first reference value during said selected window of time, but does not exceed said second reference value during said selected window of time.

14. The method of claim 13, in which said second reference value is greater than said first reference value.

15. A method of verifying cardiac capture by sensing via an electrode a cardiac signal evoked in response to a cardiac stimulation pulse, comprising the steps of:

sensing a waveform signal at said electrode following delivery of said cardiac stimulation pulse;

bandpass filtering said sensed waveform signal through a pass band selected to pass a band of frequencies characteristic of the evoked cardiac signal;

processing said bandpass-filtered waveform signal to render a waveform signal representing the absolute value of said bandpass-filtered signal;

integrating said absolute value processed waveform signal over a selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse; and

comparing said integrated waveform signal to a first reference value at the end of said selected window of time, and comparing said integrated waveform signal to a second reference value at the end of said selected window of time, and if said integrated waveform signal exceeds said first reference value during said selected window of time, but does not exceed said second reference value during said selected window of time, continuing to integrate said absolute value processed waveform signal over an extended window of time, and generating a capture detect signal if said integrated waveform signal does not exceed said second reference value during said extended window of time.