Capture detection circuit for pulses and physiologic signals

• US 6,144,881 A
• Filed: 09/18/1998
• Issued: 11/07/2000
• 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:
  US09/157,220
• Time in Patent Office: 781 Days
• Field of Search: 600/510, 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

A method and apparatus for discriminating between evoked response signals and post-pace polarization signals sensed by a sense amplifier of 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. The post-pace polarization signal exhibits a relatively constant polarity during the capture detect window, and 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. The evoked response signal may reverse the polarity of the sensed signal from positive to negative or from negative to positive, during the time window of interest. 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. In one embodiment, sensing of the evoked response is based upon a relationship between a maximum magnitude of a derivative of a sensed signal and a predetermined threshold reference value. The evoked response is declared when the maximum amplitude of the a derivative of the sensed signal equals or exceeds the threshold reference value.

Claims

1. A capture detection circuit in an implantable medical device having at least one electrode for delivering electrical pulses and sensing a physiologic electrical signal based on a relationship between a maximum magnitude of a derivative of a sensed signal and a predetermined threshold reference value, the capture detection circuit comprising:

(a) a differentiator circuit, coupled to the electrode, for differentiating the physiologic electrical signal sensed by the electrode to provide a derivative of the sensed signal, and

(b) signal processing means coupled to the differentiator circuit, for determining the relationship between the maximum magnitude of the derivative of the sensed signal to and the predetermined threshold reference value, capture being deemed to have occurred when the value of the maximum magnitude of the derivative of the sensed signal is greater than or equal to the predetermined threshold reference value.

2. 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;

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

a differentiator, coupled to the electrode, for differentiating the physiologic electrical signal to provide a derivative of the sensed signal; and

processing means for detecting capture by a stimulating pulse based on a relationship between a maximum magnitude of a derivative of a sensed signal and a predetermined threshold reference value.

3. A method of detecting an evoked response to a cardiac stimulating pulse delivered to a patient'"'"'s heart by an electrode based on a relationship between a maximum magnitude of a derivative of a sensed signal and a predetermined threshold reference value, the method comprising the steps of:

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

(b) differentiating the sensed signal; and

(c) comparing the differentiated sensed signal to the predetermined reference value to determine whether or not capture has occurred.