Method and Apparatus for Beat Alignment and Comparison

• US 20090125075A1
• Filed: 01/13/2009
• Published: 05/14/2009
• Est. Priority Date: 11/29/2004
• Status: Active Grant

• Current Assignee: Cameron Incorporated (Schlumberger NV)
• Original Assignee: Cameron Incorporated (Schlumberger NV)
• Inventors: Ostroff, Alan H., Warren, Jay A., Palreddy, Surekha
• Granted Patent: US 8,073,532 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion
• CPC Class Codes: Y10S 128/92 Computer assisted medical diagnostics

Abstract

Methods of using a template having a template data set and template parameters to provide improved alignment of captured cardiac signal data to a stored template. More particularly, in an illustrative method, a captured cardiac signal is first configured using template parameters for a stored template. Then, once configured, the captured cardiac signal is then compared to the stored template. Other embodiments include implantable cardiac treatment devices including operational circuitry configured to perform the illustrative method. In a further embodiment, more than one stored templates may be used. Each template can have independently constructed parameters, such that a single captured cardiac signal may be configured using first parameters for comparison to a first template, and using second parameters for comparison to a second template.

Claims

1. An implantable defibrillator comprising:

a lead electrode assembly including a number of electrodes; and

a canister housing operational circuitry;

wherein;

the lead electrode assembly is coupled to the canister;

the operational circuitry is configured to analyze cardiac events using a template having a template data set and template parameters; and

the operational circuitry is configured to perform the steps of;

capturing a signal using electrodes implanted in a patient'"'"'s torso;

configuring the captured signal in accordance with the template parameters, the template parameters including identification of an amplitude peak as a fiducial point and start and end points surrounding the fiducial point;

aligning the template data set with the configured captured signal using the fiducial point; and

comparing the aligned template data set to the configured captured signal, including comparing the fiducial point identified in the configured captured signal to the fiducial point of the template data set.

2. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured to perform the step of classifying the captured signal as being normal or abnormal such that:

if the configured captured signal correlates to the aligned template data set, the operational circuitry classifies the captured signal as being normal;

or

if the configured captured signal poorly correlates to the aligned template data set, the operational circuitry classifies the captured signal as being abnormal.

3. The implantable defibrillator of claim 2, wherein the operational circuitry is further configured such that the configured captured signal, if determined to be normal, represents a portion of a single cardiac beat including an R-wave.

4. The implantable defibrillator of claim 2 wherein the operational circuitry is configured to:

track the number of normal and abnormal captured signals;

determine whether therapy is indicated using the number of normal and abnormal captured signals; and

if therapy is indicated, deliver therapy.

5. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured such that the template parameters include a manner of selecting data points to form a template window.

6. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured for performing the step of capturing a signal using only subcutaneously implanted electrodes.

7. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured such that the step of comparing the aligned template data set to the configured captured signal includes performing a correlation waveform analysis between the configured captured signal defined between its beginning and ending points, and the aligned template data set.

8. The implantable defibrillator of claim 1, wherein the operational circuitry includes a microcontroller.

9. The implantable defibrillator of claim 1, wherein the operational circuitry includes readable media including an instruction set for performing the capturing, configuring, aligning and comparing steps.

10. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured such that the configured captured signal includes a plurality of amplitude samples, and the comparing step includes comparing amplitudes of samples from the configured captured signal to stored amplitudes for the aligned template data set.

11. The implantable defibrillator of claim 1, wherein the operational circuitry is further configured such that the comparing step includes performing a correlation waveform analysis between the configured captured signal and the aligned template data set.

12. The implantable defibrillator of claim 1 wherein the operational circuitry is configured such that:

the template data set comprises a set of i time-ordered samples {T₀ . . . T_i} of electrical cardiac signals, with a sample, T_f, of the template data set being identified as a highest amplitude or magnitude signal in the template data set and serving as a fiducial point and with a first set of samples {T₀ . . . T<sub>f−

1</sub>} and a second set of samples {T_f+1 . . . T_i} being identified as belonging to a sample window for the template data set;

the step of configuring the captured signal in accordance with the template parameters comprises identifying a sample within a series of sampled signals as a fiducial point, S_f, that has a highest relative amplitude within a set of such sampled signals, and selecting a set of time-ordered samples around S_f including {S₀ . . . S<sub>f−

1</sub>} and {S_f+1 . . . S_i} according to the sample window of the template data set;

the step of aligning the template data set with the captured signal includes aligning time ordered signal samples {S₀ . . . S_i} with time ordered template samples {T₀ . . . T_i} using the fiducial points {S_f, T_f}; and

the step of comparing the aligned template data set to the configured captured signal includes performing correlation analysis of the amplitudes of the aligned data sets {S₀ . . . S_i} and {T₀ . . . T_i}.

13. The implantable defibrillator of claim 1 wherein the operational circuitry is configured such that:

the template parameters include one or more size parameters indicating how many samples are part of the template, and one or more position parameters indicating a position of a fiducial point in the template; and

the step of configuring the captured signal in accordance with the template parameters includes identifying a fiducial point in the captured signal, and defining a signal window around the fiducial point using the one or more size parameters and the one or more position parameters.

14. The implantable defibrillator of claim 1 wherein the operational circuitry is also configured to:

track the number of normal and abnormal captured signals;

determine whether therapy is indicated using the number of normal and abnormal captured signals; and

if therapy is indicated, deliver therapy.

15. An implantable defibrillator comprising a canister and a lead electrode assembly, the lead electrode assembly being coupled to the canister, with operational circuitry disposed in the canister for performing cardiac signal analysis and delivering electrical cardiac stimulus using a plurality of electrodes disposed on the canister and lead electrode assembly, wherein the operational circuitry is configured such that it performs a method comprising:

capturing electrical cardiac signals;

storing a template comprising template data and template parameters, the template data including a number of sample values disposed about a fiducial point, the template parameters indicating a number of data points in the template and a relative location of the fiducial point within the number of data points;

configuring a captured electrical cardiac signal using the template parameters such that a fiducial point of the captured electrical cardiac signal is defined with a predetermined number of samples on either side of the fiducial point;

calculating a correlation of the configured captured electrical cardiac signal to the template data by aligning the template data fiducial point with the fiducial point of the configured captured electrical cardiac signal and comparing the template data including the template data fiducial point to the configured captured electrical cardiac signal;

using the calculated correlation to determine whether the captured electrical cardiac signal is normal or abnormal;

tracking the number of normal and abnormal captured signals;

determining whether therapy is indicated using the number of normal and abnormal captured signals; and

if therapy is indicated, delivering therapy.

16. The implantable defibrillator of claim 15 wherein the operational circuitry comprises a microcontroller configured to control the operation of steps of capturing electrical cardiac signals, storing a template, configuring a captured electrical cardiac signal, calculating a correlation and using the calculated correlation to determine whether the captured electrical cardiac signal is normal or abnormal.

17. A method of cardiac signal analysis comprising:

an implanted defibrillator capturing a cardiac electrical signal;

the implanted defibrillator comparing the cardiac electrical signal to a first stored template by defining a first fiducial point in the cardiac electrical signal, a first start point and a first end point for the cardiac electrical signal and using the first fiducial point, first start point and first end point for the cardiac electrical signal to align the template to the cardiac electrical signal;

the implanted defibrillator comparing the cardiac electrical signal to a second stored template by defining a second fiducial point in the cardiac electrical signal, a second start point and a second end point for the cardiac electrical signal and using the second fiducial point, second start point and second end point for the cardiac electrical signal to align the template to the cardiac electrical signal;

the implantable defibrillator using the results of comparison to the first and second stored templates to determine whether the cardiac electrical signal indicates malignant function of the patient'"'"'s heart; and

if the patient'"'"'s heart function is malignant, the implantable defibrillator delivering stimulus to the patient.

18. The method of claim 17 wherein the first stored template, first fiducial point, first start point and first end point are defined independently of the second stored template, second fiducial point, second start point and second end point.

19. A method of analyzing a patient'"'"'s cardiac rhythm using a template having a template data set, the method comprising:

defining a set of template parameters including features of a fiducial point for the template and template start and end points relative to the fiducial point;

performing the following method steps on a number of selected captured cardiac signals;

a. configuring the captured signal in accordance with the template parameters;

b. aligning the template data set with the captured signal; and

c. comparing the template data set to the captured signal to determine whether the captured signal is normal or abnormal;

tracking the number of normal and abnormal captured signals; and

determining whether therapy is indicated.

20. The method of claim 19, wherein the configuring step includes identifying a fiducial point in the selected captured cardiac signals.

21. The method of claim 19, further comprising:

capturing a number of cardiac signals;

analyzing the individual captured cardiac signals to determine whether the captured cardiac signals likely represent a cardiac event; and

selecting those individual captured cardiac signals which likely represent a cardiac event.