Multi-Channel System for Beat to Beat QT Interval Variability

• US 20070203418A1
• Filed: 02/26/2007
• Published: 08/30/2007
• Est. Priority Date: 02/27/2006
• Status: Active Grant

• Current Assignee: Cardiosoft, LLP
• Original Assignee: Cardiosoft, LLP
• Inventors: Starc, Vito
• Granted Patent: US 7,983,742 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]
• CPC Class Codes: A61B 5/35 by template matching
• CPC Class Codes: A61B 5/364 Detecting abnormal ECG interval, e.g. extrasystoles, ectopic heartbeats
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: Y10S 128/92 Computer assisted medical diagnostics

Abstract

The measurement of beat-to-beat QT interval variability (QTV) shows clinical promise for identifying several types of cardiac pathology. However, until now, there has been no device capable of displaying, in real time on a beat-to-beat basis, changes in QTV in all 12 conventional leads in a continuously monitored patient. While several software programs have been designed to analyze QTV, heretofore, such programs have all involved only a few channels (at most) and/or have required laborious user interaction or off-line calculations and post-processing, limiting their clinical utility. This invention discloses a PC-based ECG software program that in real time, acquires, analyzes and displays QTV and PQ interval variability (PQV) in each of the independent channels that constitute the 12-lead conventional and/or Frank X, Y, Z lead ECG. The system also analyzes and displays the QTV and PQV from QT and PQ interval signals that are derived from multiple channels and from singular value decomposition such that the effect of noise and other artifacts on the QTV and PQV results are substantially reduced compared to existing single-channel methods. Moreover, this invention also discloses certain new parameters of T-wave (and QRS and P-wave) morphology, that in initial studies have improved clinical diagnostic utility and/or reproducibility and reliability compared to known existing parameters of T-wave morphology. Finally, it also discloses a method for determining the beat-to-beat variability these T, QRS and P-wave morphologic parameters.

Claims

1. A method for analyzing electrocardiograph signals from a plurality of ECG leads comprising the steps of:

sensing analog fluctuations in voltage simultaneously from the plurality of ECG leads, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;

converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals;

analyzing the digital values of the record in real-time by;

identifying a time of each R wave of a heartbeat;

defining individual signal averaged templates for the T wave and the QRS wave for a series of heartbeats by segmenting each heartbeat of the series of heartbeats at;

i. the beginning and the end of the QRS wave; and

ii. the beginning and the end of the T wave;

utilizing the defined individual templates to determine alteration values for individual T waves and QRS waves of an individual heartbeat, the alteration values comprising shifts in time of the T wave and QRS wave as error functions for the heartbeat; and

assessing changes in QT interval for each heartbeat using the T wave template, the QRS wave template, and the series of heartbeats to determine beat-to-beat variability of the QT intervals of the heartbeats.

2. The method of claim 1 further comprising the step of recording the digital values in a record before the step of analyzing the digital values of the record.

3. The method of claim 1, further comprising the step of constructing a singular value decomposition from at least two converted digital values.

4. The method of claim 1, further comprising the steps of:

iteratively refining the template by adjusting the template based on a plurality of more recently received beat data and;

iteratively assessing the time variation of each beat as it is received to the iteratively refined template.

5. The method of claim 1, further comprising the steps of

defining a norm for each wave as an estimate of the noise of matching for each wave of a selected beat;

and

selecting only selected ones of the beats for averaging on the basis of the similarity in the QT signal value and of the beat quality as assessed by the norm.

6. A method of analyzing ECG waveforms from a plurality of leads, comprising the steps of:

automatically identifying individual beginning and ending points for the P, QRS, and T wave intervals of the ECG waveforms;

automatically forming signal averaged templates for the P wave, the QRS wave, and the T wave of the ECG;

utilizing the defined individual templates to determine alteration values for individual P waves, QRS waves and T waves of an individual heartbeat, the alteration values comprising shifts in time of the wave P, QRS, and T waves as error functions for the heartbeat; and

statistically describing for all leads the beat-to-beat variability of the last predetermined number of recorded beats for the PQ and QT intervals.

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

constructing initial global templates from a selected plurality of beats;

creating the mode of a probability function of the RR interval for the beats;

determining the maximum of the mode of the probability function for the beats; and

selecting fewer than all of the beats that are closest to the determined maximum.

8. The method of claim 7, further comprising the step of obtaining a template ECG wave for the same beats by averaging the superimposed ECG signals based on the fiducial point of the QRS wave.

9. A method of analyzing ECG waveforms, comprising the steps of:

sensing analog fluctuations in voltage simultaneously from a plurality of ECG channels, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;

converting these signals to digital values corresponding substantially to their analog values;

creating signal averaged templates of at least one of the P, QRS, and T-wave signals from the plurality of analog signals;

subjecting the signal averaged templates to singular value decomposition and analyzing their eigenvalues; and

displaying the result in a user perceptible form.

10. The method of claim 9, wherein the step of subjecting the signal averaged templates to singular value decomposition includes the steps of calculating normalized volumes and modified complexity ratios for the P, QRS and T waves defined by:

$\mathrm{normalized}<br><br><br><br>\mathrm{volume}=100\times <br><br>\left(w_2*w_3\right)/w_1^2$ $\mathrm{modified}<br><br><br><br>\mathrm{complexity}<br><br><br><br>\mathrm{ratio}=100\times <br><br>\underset{i=3}{\overset{n}{\sum <br><br>}}<br><br>w_i^2/\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>w_i^2$

wherein w_i signifies the given eigenvalue of the given wave, wave portion or wave combination, and wherein n is the number of ECG channels selected by the user and the number of eigenvalues being analyzed.

11. The method of claim 10, further comprising the step of determining the beat-to-beat variability of the normalized volume and modified complexity ratio of the T, QRS or P wave, or of any portion or combination of these waves.

12. A method for analyzing electrocardiograph signals from a plurality of ECG leads comprising the steps of:

sensing analog fluctuations in voltage simultaneously from the plurality of ECG leads, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;

converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals;

analyzing the digital values of the record in real-time by;

identifying a time of each R wave of a heartbeat;

defining individual signal averaged templates for the P wave and the QRS wave for a series of heartbeats by segmenting each heartbeat of the series of heartbeats at;

i. the beginning and the end of the P wave; and

ii. the beginning and the end of the QRS wave;

utilizing the defined individual templates to determine alteration values for individual P waves and QRS waves of an individual heartbeat, the alteration values comprising shifts in time of the P wave and QRS wave as error functions for the heartbeat; and

assessing changes in PR interval for each heartbeat using the P wave template, the QRS wave template, and the series of heartbeats to determine beat-to-beat variability of the PR intervals of the heartbeats.

13. The method of claim 12 further comprising the step of recording the digital values in a record before the step of analyzing the digital values of the record.

14. The method of claim 12, further comprising the step of constructing a singular value decomposition from at least two converted digital values.

15. The method of claim 12, further comprising the steps of:

iteratively refining the template by adjusting the template based on a plurality of more recently received beat data and;

iteratively assessing the time variation of each beat as it is received to the iteratively refined template.

16. The method of claim 12, further comprising the steps of

defining a norm for each wave as an estimate of the noise of matching for each wave of a selected beat;

and

selecting only selected ones of the beats for averaging on the basis of the similarity in the QT signal value and of the beat quality as assessed by the norm.

17. A system for analyzing electrocardiograph signals from a plurality of ECG leads comprising:

means for sensing analog fluctuations in voltage simultaneously from the plurality of ECG leads, the fluctuations in voltage resulting from electrical activity of a heart and defining a plurality of analog signals;

means for converting such signals having an analog value to digital values corresponding substantially to the analog value of the signals;

means for analyzing the digital values of the record in real-time by;

identifying a time of each R wave of a heartbeat;

defining individual signal averaged templates for the T wave and the QRS wave for a series of heartbeats by segmenting each heartbeat of the series of heartbeats at;

i. the beginning and the end of the QRS wave; and

ii. the beginning and the end of the T wave;

means for utilizing the defined individual templates to determine alteration values for individual T waves and QRS waves of an individual heartbeat, the alteration values comprising shifts in time of the T wave and QRS wave as error functions for the heartbeat; and

means for assessing changes in QT interval for each heartbeat using the T wave template, the QRS wave template, and the series of heartbeats to determine beat-to-beat variability of the QT intervals of the heartbeats.

18. The system of claim 17, wherein the system is included in an implantable device.

19. The system of claim 17, wherein the means for assessing changes in QT interval develops an output signal that is provided to one of a group consisting of means for monitoring the condition of the patient'"'"'s heart;

means for monitoring the progression of disease in the patient'"'"'s heart;

means for controlling the rhythm of the patient'"'"'s heart;

means for raising an alarm when predetermined limits are exceeded; and

means for controlling a drug dispensing pump.