Heart rate correction system and methods for the detection of cardiac events

• US 9,042,969 B2
• Filed: 08/12/2009
• Issued: 05/26/2015
• Est. Priority Date: 08/12/2009
• Status: Active Grant

• Current Assignee: Angel Medical Systems, Inc.
• Original Assignee: Angel Medical Systems, Inc.
• Inventors: Hopenfeld, Bruce
• Primary Examiner(s): Koharski, Christopher D
• Assistant Examiner(s): Dinga, Roland
• Application Number:
  US12/461,442
• Publication Number:
  US 20110040199A1
• Time in Patent Office: 2,113 Days
• Field of Search: 600/508, 600/509, 600/515
• US Class Current: 600/509
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening

Abstract

A device for detecting a cardiac event is disclosed. Detection of an event is based on a test applied to a parameter whose value varies according to heart rate. Both the parameter value and heart rate (RR interval) are filtered with an exponential average filter. From these filtered values, the average change in the parameter and the RR interval are also computed with an exponential average filter. Before computing the average change in the parameter, large changes in the parameter over short times, which may be caused by body position shifts, are attenuated are removed, so that the average change represents an average of small/smooth changes in the parameter'"'"'s value that are characteristic of acute ischemia, one of the cardiac events that may be detected. The test to detect the cardiac event depends on the heart rate, the difference between the parameter'"'"'s value and its upper and lower normal values, and its average change over time, adjusted for heart rate changes. The upper and lower normal parameter values as a function of heart rate are determined from long term stored data of the filtered RR values and parameter values. Hysteeresis related data and transitory deviations from normal (e.g. vasospasm related data) are excluded from the computation of normal upper and lower parameter bounds.

Claims

1. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform of a heart rate of said patient over a plurality of heart beats, said heart rate defining a first parameter;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured for;

(i) computing a digitized heart rate time series data from said digitized waveform over said plurality of heart beats;

(ii) low pass filtering and averaging of the digitized heart rate time series data, thereby producing a filtered and averaged heart rate time series signal;

(iii) performing a test to detect the cardiac event, wherein the test is based on the filtered and averaged heart rate time series signal, said test comparing a second parameter value of at least one beat with a heart rate dependent threshold, wherein the threshold is selected as a function of according to the filtered and averaged heart rate time series signal.

2. The system of claim 1 wherein the heart rate time series data is filtered with a recursive filter.

3. The system of claim 1 wherein the recursive filter is an exponential average filter.

4. The system of claim 1 wherein the filter involves the computation of a moving average.

5. The system of claim 1 herein the processor and the device are disposed in a housing suitable for implantation into an animal.

6. The system of claim 1 wherein the processor is further configured to compute a change in heart rate value from the filtered heart rate time series signal, and wherein the test to detect the cardiac event is based on the change in heart rate value.

7. The system of claim 1 wherein the cardiac event is acute ischemia.

8. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform of a heart rate of said patient over a plurality of heart beats, said heart rate defining a first parameter;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured for;

(i) computing both heart rate time series data and a second parameter value data from the digitized waveform over said plurality of heart beats;

(ii) low pass filtering and averaging of the heart rate time series data and the second parameter value data, thereby a producing filtered and averaged heart rate time series data and filtered parameter value data;

(iii) based on the filtered and averaged heart rate time series data and filtered parameter value data, generating upper and lower normal boundaries of the value of the filtered parameter as a function of heart rate;

(iv) performing a cardiac event detection test that involves comparing a value of the second parameter of at least one beat with its associated heart rate dependent upper and lower normal boundaries.

9. The system of claim 8 wherein the cardiac event detection test involves comparing the difference between the parameter value and its associated upper boundary with a threshold.

10. The system of claim 8 wherein the heart rate time series data and the parameter value data are filtered with the same filter.

11. The system of claim 10 wherein the heart rate time series data and the parameter value data are filtered by computing a moving average.

12. A cardiac event detection system for detecting a cardiac event in a patient comprising:

(a) at least two sensors for sensing an analog signal from said patient'"'"'s heart;

(b) a device coupled to said sensors, said device having an analog-to-digital circuit system contained therein for digitizing said electrical signal to produce a digitized waveform of a heart rate of said patient over a plurality of heart beats, said heart rate defining a first parameter;

(c) a processor electrically coupled to said analog-to-digital circuit system, said processor configured for;

(i) computing both heart rate time series data and a second parameter value data from the digitized waveform over said plurality of heart beats;

(ii) low pass filtering and averaging of the heart rate time series data and the second parameter value data, thereby producing filtered and averaged heart rate time series data and filtered parameter value data;

(iii) performing a cardiac event detection test that involves comparing the filtered parameter value data of at least one beat with upper and lower boundary values that are determined from upper and lower normal boundaries according to the filtered and averaged heart rate time series data.

13. The system of claim 12 wherein the processor is further configured to compute the upper and lower normal boundaries.