METHODS AND APPARATUS FOR DISCRIMINATING POLYMORPHIC TACHYARRHYTHMIAS FROM MONOMORPHIC TACHYARRHYTHMIAS FACILITATING DETECTION OF FIBRILLATION

• US 20070016257A1
• Filed: 09/25/2006
• Published: 01/18/2007
• Est. Priority Date: 08/29/2003
• Status: Active Grant

• Current Assignee: Mark Brown, Shantanu Sarkar
• Original Assignee: Mark Brown, Shantanu Sarkar
• Inventors: Sarkar, Shantanu, Brown, Mark
• Granted Patent: US 8,332,022 B2
• Time in Patent Office: Days
• US Class Current: 607/5
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• 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

Abstract

Methods and apparatus are provided for discriminating high rate polymorphic QRS complexes from high rate monomorphic QRS complexes to increase the specificity of detection of polymorphic VT and VF employing wavelet transform signal processing of the QRS complexes are disclosed. Wavelet transforms are applied to the sampled amplitude values of a sequence of QRS complexes to develop wavelet transform coefficient (WTC) data sets. At least selected ones of the WTC data sets are processed and comparisons are made to determine a wavelet match score. A determination is made as a function of the wavelet match scores of the series of successive QRS complexes that characterizes the most recent QRS complex as more or less likely to signify polymorphic VT or VF.

Claims

1. In an implantable medical device that detects a polymorphic tachyarrhythmia of the heart of a patient as a function of measured time intervals between sensed events in a cardiac signal, a method of improving the specificity of discriminating between a monomorphic tachyarrhythmia and a polymorphic tachyarrhythmia comprising the steps of:

a) provisionally declaring a polymorphic tachyarrhythmia when at least a first number of the measured time intervals satisfy the polymorphic tachyarrhythmia detection criteria;

b) successively sampling, processing, and temporarily storing the cardiac signals to derive a plurality y of data sets of signal amplitudes;

c) successively deriving a plurality y of sets of wavelet transform coefficients from the respective plurality y of data sets of signal amplitudes;

d) comparing at least selected ones of the wavelet transform coefficients of each of the y sets of wavelet transform coefficients to determine a match count x of the y sets of wavelet transform coefficients that match one another within at least a predetermined match tolerance;

e) withholding the final declaration of a polymorphic tachyarrhythmia if the match count x indicates that the corresponding cardiac signals exhibit morphologic stability suggestive of a monomorphic tachyarrhythmia; and

f) making the final declaration of a polymorphic tachyarrhythmia if the match count x indicates that the corresponding cardiac signals exhibit morphological instability suggestive of a polymorphic tachyarrhythmia and the polymorphic tachyarrhythmia is provisionally declared in step a).

2. The method of claim 1, further comprising repeating steps b) through f) as long as step a) is met until step f) is met.

3. The method of claim 2, wherein the implantable medical device further comprises an implantable cardioverter/defibrillator having the capability of delivering a C/D shock therapy and further comprising:

g) delivering a C/D shock therapy when the final declaration of a polymorphic tachyarrhythmia is made in step f).

4. The method of claim 2, wherein step e) comprises:

establishing a withhold count corresponding to z measured time intervals between sensed events of successive cardiac signals; and

repeating steps a) through d) at least z times.

5. The method of claim 2, wherein the implantable medical device further comprises an implantable cardioverter/defibrillator having the capability of delivering a C/D shock therapy and wherein:

step e) comprises establishing a withhold count corresponding to z measured time intervals between sensed events of successive cardiac signals; and

further comprising;

g) repeating steps a) through d) at least z times; and

h) delivering a C/D shock therapy when the final declaration of a polymorphic tachyarrhythmia is made in step f).

6. The method of claim 2, wherein the implantable medical device further comprises an implantable cardioverter/defibrillator having the capability of delivering a C/D shock therapy and delivering an anti-tachycardia therapy and further comprising:

g) delivering a C/D shock therapy when the final declaration of a polymorphic tachyarrhythmia is made in step f); and

h) delivering an anti-tachycardia therapy when the match count x indicates that the corresponding cardiac signals exhibit morphologic stability suggestive of a monomorphic tachyarrhythmia in step e) and a polymorphic tachyarrhythmia is provisionally declared in step a).

7. The method of claim 1, wherein the implantable medical device further comprises an implantable cardioverter/defibrillator having the capability of delivering a C/D shock therapy and delivering an anti-tachycardia therapy and further comprising:

k) delivering a C/D shock therapy when the final declaration of a polymorphic tachyarrhythmia is made in step f); and

I) delivering an anti-tachycardia therapy when the match count x indicates that the corresponding cardiac signals exhibit morphologic stability suggestive of a monomorphic tachyarrhythmia in step e) and a polymorphic tachyarrhythmia is provisionally declared in step a).

8. The method of claim 1, wherein:

step b) further comprises framing a sample data set of signal amplitude values as a data frame related to the detection of a feature of interest of the cardiac signal; and

step c) further comprises wavelet transforming the data frame of signal amplitude values to generate a set of wavelet transform coefficients.

9. The method of claim 1, wherein step d) comprises:

comparing at least certain wavelet transform coefficients of the most recent set of wavelet transform coefficients among the plurality y of sets of wavelet transform coefficients to at least certain wavelet transform coefficients of the preceding (y-1) sets of wavelet transform coefficients and determining (y-1) match values representing the degree that the compared wavelet coefficients of the most recent set match the wavelet transform coefficients of the (y-1) sets;

comparing each of the (y-1) match values to a match count threshold; and

determining the match count x of the (y-1) match values that meet the match count threshold.

10. The method of claim 9, wherein:

step d) comprises comparing the match count x to a morphologic stability match count threshold; and

step e) comprises withholding the final declaration of a polymorphic tachyarrhythmia if the match count x meets the morphologic stability match count threshold.

11. The method of claim 10, wherein step f) comprises making the final declaration of a polymorphic tachyarrhythmia if the match count x does not meet the morphologic stability match count threshold and a polymorphic tachyarrhythmia is provisionally declared in step a).

12. The method of claim 10, wherein step e) comprises:

establishing a withhold count corresponding to z measured time intervals between sensed events of successive cardiac signals; and

repeating steps a) through d) at least z times.

13. The method of claim 9, wherein step f) comprises making the final declaration of a polymorphic tachyarrhythmia if the match count x does not meet the morphologic stability match count threshold and a polymorphic tachyarrhythmia is provisionally declared in step a).

14. The method of claim 1, wherein step d) comprises:

each time that step c) is performed to derive the most recent set of wavelet coefficients, comparing at least certain wavelet transform coefficients of the most recent set of wavelet transform coefficients to at least certain wavelet transform coefficients of a selected preceding set of wavelet transform coefficients and determining a match value representing the degree that the compared wavelet coefficients of the most recent set match the wavelet transform coefficients of the preceding set;

accumulating y match values;

comparing each of the y match values to a match count threshold; and

determining the match count x of the y match values that meet the match count threshold.

15. The method of claim 14, wherein step e) comprises:

comparing the match count x to a morphologic stability match count threshold; and

withholding the final declaration of a polymorphic tachyarrhythmia if the match count x meets the morphologic stability match count threshold.

16. The method of claim 15, wherein step f) comprises making the final declaration of a polymorphic tachyarrhythmia if the match count x does not meet the morphologic stability match count threshold and a polymorphic tachyarrhythmia is provisionally declared in step a).

17. The method of claim 15, wherein step e) comprises:

establishing a withhold count corresponding to z measured time intervals between sensed events of successive cardiac signals; and

repeating steps a) through d) at least z times.

18. The method of claim 14, wherein step f) comprises:

comparing the match count x to a morphologic stability match count threshold; and

making the final declaration of a polymorphic tachyarrhythmia if the match count x does not meet the morphologic stability match count threshold and a polymorphic tachyarrhythmia is provisionally declared in step a).

19. The method of claim 1, wherein step d) comprises:

determining m median wavelet transform coefficient magnitudes from the wavelet transform coefficients in each of (y-1) wavelet transform coefficient data sets preceding, in time, a current wavelet transform coefficient data set having p wavelet transform coefficient magnitudes;

ordering the set m of the median wavelet transform coefficient magnitudes into a plurality of scales;

comparing the median wavelet transform coefficient magnitudes in each scale to a scale threshold of the scale to derive a subset of median wavelet transform coefficient magnitudes m_i that meet the scale thresholds;

determining a subset of current wavelet transform coefficient magnitudes p_i each corresponding in wavelet number to the wavelet numbers of the subset of median wavelet transform coefficient magnitudes m_i; and

deriving a selective wavelet coefficient stability index (SWCSI) to be employed as the match count x in steps e) and f) by;

$\mathrm{SWCSI}=\underset{i=\underset{\mathrm{coefficients}}{\mathrm{selected}}}{\overset{\text{\hspace{1em}<br><br>}}{\sum <br><br>}}<br><br>\frac{<br><br>p_i-m_i<br><br>}{<br><br>m_i<br><br>}.$

20. The method of claim 19, further comprising determining the scale threshold of each scale as a percentage of the absolute maximum median wavelet transform coefficient magnitude in the scale.