System and method for predicting ventricular tachycardia by derivative analysis

• US 4,492,235 A
• Filed: 02/11/1982
• Issued: 01/08/1985
• Est. Priority Date: 02/11/1982
• Status: Expired due to Fees

• Current Assignee: Arrhythmia Research Technology, Inc.
• Original Assignee: Arrhythmia Research Technology, Inc.
• Inventors: Sitrick, David H.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/347,988
• Time in Patent Office: 1,062 Days
• Field of Search: 128/695-696, 128/702-705, 128/708, 364/415, 364/417
• US Class Current: 600/518
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A system for predicting ventricular tachycardia from electrocardiograph input waveforms. A high pass filter provides an output responsive to the input waveforms. A time derivative of the filter output is generated to produce waveforms which can be compared to a standard. In one embodiment, the input waveforms are digitized prior to processing by the filter means. In another embodiment, digitized input waveforms are signal averaged prior to processing by the filter. The filter can be a finite impulse response filter of an infinite impulse response filter. In an alternate embodiment, a ventricular tachycardia prediction system for use with ECG waveforms having cyclical characteristics is disclosed. The ECG waveforms are periodically sampled during each of a plurality ECG cycles. A filter unidirectionally filters the signals for each ECG cycle so as to provide a filter output systematically related to the high frequency content of the input. A reference signal is provided for ventricular tachycardia prediction. The filter output is compared to the reference signal, and a propensity for episodes of ventricular tachycardia is indicated responsive to the comparison.

Claims

1. A system for predicting ventricular tachycardia from electrocardiograph input waveforms comprising:

filter means for providing a high pass filter output responsive to said input waveforms,

means for providing a time derivative output of said filter output responsive to the filter output,

means for predicting ventricular tachycardia responsive to said time derivative output.

2. The system as in claim 1 further comprising:

means for digitizing said input waveforms prior to processing by said filter means.

3. The system as in claim 2 further comprising:

means for signal averaging the digitized input waveforms prior to processing by said filter means.

4. The system as in claim 1 wherein said filter means is a finite impulse response filter.

5. The system as in claim 1 further characterized in that said filter means is an adaptive high pass filter.

6. A system for predicting ventricular tachycardia from electrocardiograph input waveforms comprising:

filter means for providing a filter output responsive to said input waveforms,

means for providing a time derivative output of said filter output responsive to the filter output,

means for predicting ventricular tachycardia responsive to said time derivative output.

7. A ventricular tachycardia prediction system for use with an ECG input having cyclical characteristics comprising:

means for periodically sampling the ECG input during each of a plurality of ECG cycles,

filter means for unidirectionally filtering the signals for each ECG cycle, so as to provide a filter output systematically related to the high frequency content of the ECG input;

means for providing a reference signal;

means for comparing the filter output to the reference signal; and

means for indicating a propensity for episodes of ventricular tachycardia responsive to said means for comparing.

8. The system as in claim 7 wherein said samples are filtered in the same time order as the ECG input was sampled.

9. The system as in claim 7 wherein said samples are filtered in the reverse time order as that which the ECG input was sampled.

10. The system as in claim 8 or 9 wherein said filter means is further comprised of:

means for averaging samples for a plurality of ECG cycles prior to deriving the filter output.

11. The system as in claim 7 further comprising:

means for determining the duration of the QRS portion of the ECG signal responsive to said filter output;

second means for comparing said determined duration to said second reference signal, and

means for indicating the prediction of ventricular tachycardia responsive to said second means for comparing.

12. The system as in claim 7 wherein said reference signal corresponds to a filter output indicative of a high frequency, low level, energy component in the tail of the ECG waveform.

13. A method for predicting ventricular tachycardia in a patient from cyclically recurring ECG inputs, comprising the steps of:

sampling and storing a plurality of points each ECG cycle at a fixed rate of N samples per cycle;

identifying a reference point p of the waveform,

deriving a filter output Q_n responsive to unidirectionally filtering the stored samples,

providing a preselected reference signal,

comparing the filter output to said reference signal and

indicating the prediction of potential ventricular tachycardia responsive to said comparison.

14. A method for analyzing electrocardiograph signals to determine the presence or absence of a predetermined level of high frequency energy in the late QRS signal, comprising the steps of:

sampling a series of analog QRS signals at spaced time segments,

converting each segment sample to a digital signal equivalent,

applying a portion of said digital signals in a single time direction to a filter;

determining an arithmetic value of the amplitude of the output of said filter; and

comparing said value with said predetermined level.

15. The method of claim 14 further characterized in that said filter has a high pass response.

16. The method of claim 14 further comprising the step of generating an indication signal which is a function of said comparison.

17. The method of claim 14 further including the step of averaging the digital values of said series of QRS signals to obtain an averaged composite QRS signal before the application thereof to said filter.

18. The method of claim 17 wherein said portion of said digital signals comprises signals representing at least the last 40 milliseconds of the averaged QRS signal.

19. The method of claim 16 further including the step of measuring the duration of said averaged QRS signal.

20. A system for analyzing electrocardiograph signals to determine the level of high frequency energy in the late QRS signal comprising:

means for converting X, Y, and Z lead electrocardiographic input signals to digital signals representative of times spaced samples;

means for examining said X, Y, and Z digital signals and selecting therefrom the QRS waveform portions thereof;

means for signal averaging a multiplicity of said selected QRS waveforms for each of said X, Y, and Z inputs and providing composite, digital signals representative of the averaged X, Y, and Z QRS waveforms;

filter means having a preselected response;

means for applying to said filter means in a forward time order the digital signals representative of the late portion of each of said X, Y, and Z QRS waveforms;

means for providing a reference signal; and

means for comparing the output of said filter means with said reference signal to determine the presence of a high frequency, low level, energy component in the filter output predictive of ventricular tachycardia.

21. The system of claim 20 wherein said comparing means compares only a portion of said filter'"'"'s output.

22. The system of claim 21 wherein said portion of said filter'"'"'s output represents the filtered last 40 milliseconds of the QRS waveform.

23. The system of claim 22 wherein said comparing means combines selected portions of said filter'"'"'s output for each of the X, Y, and Z signal samples and determines an arithmetic value of said combined portions.

24. The system of claim 23 wherein said arithmetic value is the root mean square of said combined portions.

25. The system as in claim 24 wherein said arithmetic value is the sum of the absolute values of the filter outputs for each of said X, Y, and Z signals.

26. The system of claim 20 further comprising:

means for applying to said filter means the digital signals representative of the early portion of each of said X, Y, and Z QRS waveforms;

means for extracting from said filter'"'"'s output the time of commencement of said QRS waveforms;

means responsive to said extraction means and said comparing means for determining the width of said QRS waveform;

means for providing a width reference signal,

means for indicating the prediction of probable ventricular tachycardia responsive to a comparison of the determined QRS width and the width reference signal.