SYSTEM AND METHOD FOR DETECTING CARDIAC ISCHEMIA BASED ON T-WAVES USING AN IMPLANTABLE MEDICAL DEVICE

• US 20070156056A1
• Filed: 03/15/2007
• Published: 07/05/2007
• Est. Priority Date: 06/24/2003
• Status: Active Grant

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Original Assignee: Pacesetter Incorporated (Abbott Laboratories)
• Inventors: Chitre, Yougandh, Min, Xiaoyi, Kil, Jong, Bornzin, Gene, Snell, Jeffery
• Granted Patent: US 7,643,872 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/355 Detecting T-waves
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/363 Detecting tachycardia or bradycardia
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: A61N 1/3627 for treating a mechanical deficiency of the heart, e.g. congestive heart failure or cardiomyopathy
• CPC Class Codes: A61N 1/3702 Physiological parameters A61N1/365 takes precedence; evoked response A61N1/371

Abstract

A technique is provided for detecting episodes of cardiac ischemia based on an examination of the total energy of T-waves. Since cardiac ischemia is often a precursor to acute myocardial infarction (AMI) or ventricular fibrillation (VF), the technique thereby provides a method for predicting the possible onset of AMI or VF. Briefly, the technique integrates internal electrical cardiac signals occurring during T-waves and then compares the result against a running average. If the result exceeds the average by some predetermined amount, ischemia is thereby detected and a warning signal is provided to the patient. The maximum slope of the T-wave is also exploited. Techniques are also set forth herein for reliably detecting T-waves, which help prevent P-waves from being misinterpreted as T-waves on unipolar sensing channels. The T-wave detection technique may be used in conjunction with ischemia detection or for other purposes.

Claims

1. In an implantable medical device for implant within a patient, a system comprising:

a T-wave detection subsystem operative to detect a plurality of individual T-waves;

a T-wave energy integration subsystem operative to detect a total energy for each of a plurality of the individual T-waves; and

a cardiac ischemia detection subsystem operative to process a total energy of one of the individual T-waves, an average of the total energies of a plurality of the T-waves and an energy threshold value, to detect cardiac ischemia.

2. The system of claim 1 wherein the detection subsystem detects an onset of ischemia when the difference between the total energy and the average of the total energies exceeds the energy threshold value.

3. The system of claim 2 wherein the detection subsystem detects termination of an episode of ischemia when the difference between the total energy and the average of the total energies is less than the energy threshold value.

4. The system of claim 1 wherein the detection subsystem is operative to process T-waves arising from sinus ventricular beats based on a sinus-beat energy threshold corresponding to the energy threshold value and a running average of sinus beat total energies corresponding to the total energies of a plurality of the T-waves.

5. The system of claim 1 wherein the detection subsystem is operative to process T-waves arising from paced ventricular beats based on a paced-beat energy threshold corresponding to the energy threshold value and a running average of paced-beat total energies corresponding to the total energies of a plurality of the T-waves.

6. The system of claim 1 further comprising a T-wave slope determination subsystem operative to determine a maximum slope of individual T-waves and an average of the maximum slopes of a plurality of the T-waves and wherein the detection subsystem is further operative to detect ischemia based on the maximum slope, average slope and a slope threshold value.

7. The system of claim 6 wherein the detection subsystem detects an onset of ischemia when the difference between the maximum slope and the average slope exceeds the slope threshold value.

8. The system of claim 7 wherein the detection subsystem detects termination of an episode of ischemia when the difference between the maximum slope and the average slope is less than the slope threshold value.

9. The system of claim 6 wherein the detection subsystem detects an onset of ischemia when both of the following conditions are met:

the difference between the total energy and the average of the total energies exceeds the energy threshold value; and

the difference between the maximum slope and the average slope exceeds the slope threshold value.

10. A method comprising:

detecting a plurality of individual T-waves;

calculating a total energy for each of a plurality of the individual T-waves; and

detecting cardiac ischemia based on the total energy of one of the individual T-waves, an average of the total energies of a plurality of the other T-waves and an energy threshold value.

11. The method of claim 10 wherein detecting cardiac ischemia comprises:

determining the difference between the total energy and the average of the total energies;

comparing the difference to the energy threshold value; and

indicating ischemia when the difference exceeds the energy threshold value.

12. The method of claim 10 further comprising, upon detection of ischemia, detecting termination of ischemia based on a total energy of one of the individual T-waves, an average of the total energies of a plurality of the T-waves and the energy threshold value.

13. The system of claim 12 wherein detecting termination of cardiac ischemia comprises:

determining the difference between the total energy and the average of the total energies;

comparing the difference to the energy threshold value; and

indicating ischemia when the difference is less than the energy threshold value.

14. The method of claim 10 wherein detecting a plurality of individual T-waves comprises detecting a plurality of T-waves arising from sinus ventricular beats, and detecting cardiac ischemia comprises:

determining the difference between the total energy of an individual T-wave arising from a sinus ventricular beat and the average of the total energies of a plurality of T-waves arising from sinus ventricular beats;

comparing the difference to a sinus-beat energy threshold corresponding to the energy threshold value; and

indicating ischemia when the difference exceeds the sinus-beat energy threshold.

15. The method of claim 10 wherein detecting a plurality of individual T-waves comprises detecting a plurality of T-waves arising from paced ventricular beats, and detecting cardiac ischemia comprises:

determining the difference between the total energy of an individual T-wave arising from a paced ventricular beat and the average of the total energies of a plurality of T-waves arising from paced ventricular beats;

comparing the difference to a paced-beat energy threshold corresponding to the energy threshold value; and

indicating ischemia when the difference exceeds the paced-beat energy threshold.

16. The method of claim 10 further comprising:

calculating a maximum slope for each of a plurality of individual T-waves; and

detecting cardiac ischemia based on the maximum of one of the individual T-waves, an average of the maximum slopes of a plurality of the T-waves and a slope threshold value.

17. The method of claim 16 wherein detecting cardiac ischemia comprises:

calculating the difference between the maximum slope and the average maximum slope;

comparing the difference to the slope threshold value; and

indicating ischemia when the difference exceeds the slope threshold value.

18. The method of claim 17 further comprising indicating termination of an episode of ischemia when the difference between a maximum slope and an average maximum slope is less than the slope threshold value.

19. The method of claim 16 wherein detecting an onset of ischemia comprises

determining the difference between the total energy and the average of the total energies;

comparing the energy difference to the energy threshold value;

determining the difference between the maximum slope and the average maximum slope;

comparing the slope difference to the slope threshold value; and

indicating ischemia when the slope difference exceeds the slope threshold value and the energy difference exceeds the energy threshold value.

20. The method of claim 16 wherein products of the energy values and the maximum slopes are used to detect cardiac ischemia.