Implantable cardiac stimulation device having T-wave discrimination of fusion events during autocapture/autothreshold assessment

• US 6,324,427 B1
• Filed: 01/26/1999
• Issued: 11/27/2001
• Est. Priority Date: 01/26/1999
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Inventors: Florio, Joseph J.
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US09/237,617
• Time in Patent Office: 1,036 Days
• Field of Search: 607/9, 607/14, 607/27, 607/28
• US Class Current: 607/28
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold

Abstract

A system and method for discriminating a fusion beat from an evoked response during the autocapture/autothreshold routines of an implantable stimulation device is provided. The presently disclosed system and method reliably verifies capture in an implantable stimulation device by accurately discriminating a fusion beat from an evoked response based on an analysis and comparison of the morphology, amplitude, polarity, pattern and/or timing intervals of resulting T-waves. The disclosed system for discriminating a fusion beat includes a pulse generator; a means for sensing voltage signals evidencing depolarization and repolarization of cardiac tissue; and a microprocessor based means for determining, based on an analysis of the subsequent T-waves, whether a voltage signal that occurs during the capture detection window is a depolarization voltage signal, which evidences capture, or a fusion beat.

Claims

1. In an implantable pacemaker, a method of discriminating between a fusion event or an evoked response, the method comprising the steps of:

selectively generating stimulation and backup pulses at a predetermined rate;

sensing a first response during a first detection window following a stimulation pulse;

sensing T-waves during a second detection window that follows the stimulation pulse;

determining if a current T-wave corresponds to a true evoked response or a fusion beat; and

increasing the stimulation pulse rate when fusion beats occur thereby minimizing the generation of backup pulses subsequent to the generation of stimulation pulses.

2. The method of claim 1, wherein the step of determining if the current T-wave corresponds to a true evoked response or a fusion beat comprises the steps of:

determining a reference T-wave;

defining an acceptable value range for an attribute of the reference T-wave;

measuring the same attribute of the current T-wave;

defining the first sensed response as an evoked response when the measured attribute of the current T-wave is within the acceptable value range of the reference T-wave attribute; and

defining the evoked response as a fusion event when the measured attribute of the current T-wave is not within the acceptable value range of the reference T-wave attribute.

3. The method of claim 2, wherein the step of defining an acceptable range comprises the step of:

automatically performing statistical analysis of a plurality of T-waves to determine an acceptable value range for the at least one attribute of the reference T-wave.

4. The method of claim 3, wherein the attribute is selected from the group consisting of T-wave morphology, amplitude, polarity, pattern and stimulus to T-wave time interval.

5. The method of claim 4, wherein more than one T-wave attributes are used to define the reference T-wave and the same more than one attributes are measured for the current T-wave.

6. A method for discriminating a fusion event from an evoked response in an implantable pacemaker during an autocapture/autothreshold routine, wherein the autocapture/autothreshold routine adjusts the output energy of stimulation pulses in response to sensing and not sensing a response to a stimulation pulse, the method comprising the steps of:

defining at least one attribute of a reference T-wave wherein the definition includes an acceptable variance in that attribute;

sensing a first response corresponding to a stimulation pulse delivered during the autocapture/autothreshold routine;

measuring the same at least one attribute as was defined for the reference T-wave for a T-wave corresponding to the stimulation pulse;

comparing the at least one attribute of the T-wave to the same at least one attribute of the reference T-wave;

defining the first sensed response to the stimulation pulse as an evoked response if the measured attribute of the T-wave is within the acceptable variance of the reference T-wave definition; and

defining the first sensed response to the stimulation pulse as a fusion event if the measured attribute of the T-wave is not within the acceptable variance of the reference T-wave definition.

7. The method of claim 6, further comprising the step of:

blocking the autocapture/autothreshold routines from making any adjustments to the output energy of the stimulus pulses when the first sensed response is defined as a fusion beat; and

increasing a rate of the stimulation pulses so as to overdrive the fusion beat.

8. The method of claim 6, wherein the at least one attribute of the reference T-Wave and measured T-wave is selected from the group consisting of morphology, amplitude, polarity, pattern and stimulus to T-wave time interval.

9. In an implantable pacemaker, a method for classifying a voltage signal sensed in response to a stimulation pulse as an evoked response or a fusion beat, the method comprising the steps of:

generating stimulation pulses to a patient'"'"'s heart;

defining an acceptable value range for at least one attribute of the patient'"'"'s T-waves, said range extending a predetermined amount above and below a prescribed reference value;

sensing the voltage signal in response to a stimulation pulse;

sensing the T-wave that follows the sensed voltage signal;

measuring the at least one attribute of the sensed T-wave;

classifying the sensed voltage signal as a fusion beat if the measured attribute of the T-wave is beyond the prescribed acceptable value range; and

classifying the sensed voltage signal as an evoked response if the measured attribute of the T-wave is within the prescribed acceptable value range.

10. The method of claim 9, wherein the at least one attribute of the T-wave is selected from the group consisting of T-wave pattern, amplitude, polarity, morphology and stimulus to T-wave timing interval.

11. The method of claim 9, wherein the step of prescribing an acceptable value range for the at least one attribute of T-waves comprises:

detecting a plurality of T-waves and setting the prescribed reference value as the average value of such attribute detected in the plurality of T-waves; and

determining an acceptable value range for the at least one attribute comprising detecting the variation of the attribute from the prescribed reference value in the plurality of T-waves and setting the acceptable value range to such variation.

12. An implantable stimulation device, comprising:

a pulse generator which generates stimulation pulses at a predetermined rate;

a timing circuit, triggered by the generation of a stimulation pulse, that defines a first and second detection window;

a sensing circuit that senses a first response during a first detection window following a stimulation pulse and a second response during the second detection window; and

a processor circuit, coupled to the sensing circuit, that determines if a T-wave which is sensed in the second detection window corresponds to a true evoked response or a fusion beat, the processor circuit further having means for increasing the rate when fusion beats occur, the processor circuit still further having autocapture/autothreshold routine means operative to adjust the output energy of stimulation pulses in response to sensing and not sensing a response to a stimulation pulse.

13. The implantable stimulation device of claim 12, further comprising:

means for measuring a reference T-wave;

means for measuring the same attribute of the current T-wave; and

means for comparing the reference T-wave to the current T-wave.

14. The implantable stimulation device of claim 13, wherein processor circuit comprises:

means for defining an acceptable value range for an attribute of the reference T-wave;

means for defining the first sensed response as an evoked response when the measured attribute of the current T-wave is within the acceptable value range of the reference T-wave attribute; and

means for defining the evoked response as a fusion event when the measured attribute of the current T-wave is not within the acceptable value range of the reference T-wave attribute.

15. The implantable stimulation device of claim 14, wherein the at least one attribute of the reference T-wave and the measured T-wave is selected from the group consisting of morphology, amplitude, polarity, pattern and stimulus to T-wave time interval.

16. The implantable stimulation device of claim 15, wherein at least two attributes of the reference T-wave are defined and the same at least two attributes of the measured T-wave are measured.

17. The implantable stimulation device of claim 16, wherein the defined attributes of the reference T-wave and the measured attributes of the measured T-wave comprise morphology, amplitude, polarity, pattern and stimulus to T-wave time interval.