Method and apparatus for performing stimulation threshold searches

In a pacing system, wherein a pace pulse generator is selectively coupled to an active pace/sense electrode adapted to be placed in operative relation to a heart chamber and to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode to deliver pace pulses to the heart chamber in a bipolar pace vector or a remote indifferent pace/sense to deliver pace pulses to the heart chamber in a unipolar pace vector, and a sense amplifier coupled to the active pace/sense electrode and selectively coupled, to provide a prevailing sense vector, to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode whereby the prevailing sense vector is a bipolar sense vector or to a remote indifferent pace/sense whereby the prevailing sense vector is a unipolar sense vector, apparatus for periodically conducting a pacing threshold search in the pacing channel comprising the sense amplifier and the pace pulse generator coupled with the active and indifferent pace sense electrodes comprising;

• timing means for triggering the commencement of the pacing threshold search:
• means for conducting the pacing threshold search to determine if the stimulation energy threshold determined in the prevailing sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• means operable if the high output pace pulse energy is determined to be required for selectively coupling the sense amplifier to an alternate one of the indifferent pace/sense electrodes sense in the other one of the bipolar sense vector or unipolar sense vector to thereby sense in an alternate sense vector;
• means for again conducting the pacing threshold search to determine if the stimulation energy threshold determined in the alternate sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• and
• means for setting the prevailing sense vector to a default one of the bipolar or unipolar sense vectors and the pace pulse energy to the high output energy if the high output pace pulse energy is again determined to be required.

In a pacing system, wherein a pace pulse generator is selectively coupled to an active pace/sense electrode adapted to be placed in operative relation to a heart chamber and to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode to deliver pace pulses to the heart chamber in a bipolar pace vector or a remote indifferent pace/sense to deliver pace pulses to the heart chamber in a unipolar pace vector, and a sense amplifier coupled to the active pace/sense electrode and selectively coupled, to provide a prevailing sense vector, to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode whereby the prevailing sense vector is a bipolar sense vector or to a remote indifferent pace/sense whereby the prevailing sense vector is a unipolar sense vector,

• a method of periodically conducting a pacing threshold search in the pacing channel comprising the sense amplifier and the pace pulse generator coupled with the active and indifferent pace sense electrodes comprising;
• (a) triggering the commencement of the pacing threshold search:
• (b) operating the pace pulse generator to apply a sequence of pace pulses varying in pulse energy to the heart chamber in the selected pace vector to evoke a response of the heart chamber to the pace pulse energy that captures the heart chamber if the pace pulse energy exceeds a stimulation energy threshold of the heart chamber;
• (c) operating the sense amplifier to sense the evoked response to an applied pace pulse that exceeds the stimulation energy threshold through the prevailing sense vector to determine the stimulation energy threshold in the prevailing sense vector;
• (d) determining if the stimulation energy threshold determined in the prevailing sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• (e) if the high output pace pulse energy is determined to be required, selectively coupling the sense amplifier to an alternate one of the indifferent pace/sense electrodes sense in the other one of the bipolar sense vector or unipolar sense vector;
• (f) repeating step (b) while operating the sense amplifier to sense the evoked response to each applied pace pulse that exceeds the stimulation energy threshold through the alternate one of the bipolar or unipolar sense vectors to determine the stimulation energy threshold in the alternate sense vector;
• (g) determining if the stimulation energy threshold determined in the alternate sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• and
• (h) if the high output pace pulse energy is determined to be required in step (g), setting the prevailing sense vector to a default one of the bipolar or unipolar sense vectors and the pace pulse energy to the high output energy.

In a pacing system, wherein a pace pulse generator is selectively coupled to an active pace/sense electrode adapted to be placed in operative relation to a heart chamber and to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode to deliver pace pulses to the heart chamber in a bipolar pace vector or a remote indifferent pace/sense to deliver pace pulses to the heart chamber in a unipolar pace vector, and a sense amplifier coupled to the active pace/sense electrode and selectively coupled, to provide a prevailing sense vector, to one of an indifferent pace/sense electrode proximate to the active pace/sense electrode whereby the prevailing sense vector is a bipolar sense vector or to a remote indifferent pace/sense whereby the prevailing sense vector is a unipolar sense vector, apparatus for periodically conducting a pacing threshold search in the pacing channel comprising the sense amplifier and the pace pulse generator coupled with the active and indifferent pace sense electrodes comprising;

• timing means for triggering the commencement of the pacing threshold search:
• pace pulse energy timing and control means for operating the pace pulse generator to apply a sequence of pace pulses varying in pulse energy to the heart chamber in the selected pace vector to evoke a response of the heart chamber to the pace pulse energy that captures the heart chamber if the pace pulse energy exceeds a stimulation energy threshold of the heart chamber;
• means responsive to the sensing of the evoked response to an applied pace pulse that exceeds the stimulation energy threshold by the sense amplifier sensing through the prevailing sense vector for determining the stimulation energy threshold in the prevailing sense vector;
• means for determining if the stimulation energy threshold determined in the prevailing sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• said pace pulse energy timing and control means operable if the high output pace pulse energy is determined to be required to selectively couple the sense amplifier to an alternate one of the indifferent pace/sense electrodes sense in the other one of the bipolar sense vector or unipolar sense vector and to again apply a sequence of pace pulses varying in pulse energy to the heart chamber in the selected pace vector to evoke a response of the heart chamber to the pace pulse energy that captures the heart chamber if the pace pulse energy exceeds a stimulation energy threshold of the heart chamber;
• means responsive to the sensing of the evoked response to each applied pace pulse that exceeds the stimulation energy threshold by the sense amplifier sensing through the alternate one of the bipolar or unipolar sense vectors for determining the stimulation energy threshold in the prevailing sense vector;
• means for determining if the stimulation energy threshold determined in the alternate sense vector requires setting the pace pulse energy to a high output pace pulse energy to reliably capture the heart chamber;
• and
• setting means operable if the high output pace pulse energy is again determined to be required for setting the prevailing sense vector to a default one of the bipolar or unipolar sense vectors and the pace pulse energy to the high output energy.