Capture detection circuit for pulses and physiologic signals

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.