HEMODYNAMIC STABILITY ASSESSMENT BASED ON HEART SOUNDS

• US 20100249863A1
• Filed: 06/10/2010
• Published: 09/30/2010
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: Gerrard M. Carlson, Yayun Lin
• Original Assignee: Gerrard M. Carlson, Yayun Lin
• Inventors: Lin, Yayun, Carlson, Gerrard M.
• Granted Patent: US 7,938,781 B2
• Time in Patent Office: Days
• US Class Current: 607/14
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 7/00 Instruments for auscultation
• CPC Class Codes: A61B 7/04 Electric stethoscopes microphones, acoustic transducers therefor H04R
• CPC Class Codes: A61N 1/3621 for treating or preventing abnormally high heart rate
• 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 1/36514 controlled by a physiological quantity other than heart potential, e.g. blood pressure controlled by two or more physical parameters A61N1/36585
• CPC Class Codes: A61N 1/36578 controlled by mechanical motion of the heart wall, e.g. measured by an accelerometer or microphone
• CPC Class Codes: A61N 1/37247 User interfaces, e.g. input or presentation means
• CPC Class Codes: A61N 1/37282 characterised by communication with experts in remote locations using a network
• CPC Class Codes: A61N 1/39622 Pacing therapy

Abstract

A method comprises detecting at least one episode of ventricular tachyarrhythmia in a subject using an implantable medical device (IMD), sensing at least one heart sound signal for the subject using the IMD, the heart sound signal associated with mechanical vibration of a heart of the subject; initiating, in response to and during the detected episode of tachyarrhythmia, a measurement of hemodynamic stability of the ventricular tachyarrhythmia from the heart sound signal, and deeming whether the ventricular tachyarrhythmia is stable according to the measurement of hemodynamic stability. The measurement of hemodynamic stability is determined using linear prediction.

Claims

1. A method comprising:

detecting at least one episode of ventricular tachyarrhythmia in a subject using an implantable medical device (IMD);

sensing at least one heart sound signal for the subject using the IMD, the heart sound signal associated with mechanical vibration of a heart of the subject;

initiating, in response to and during the detected episode of tachyarrhythmia, a measurement of hemodynamic stability of the ventricular tachyarrhythmia from the heart sound signal, wherein the measurement of hemodynamic stability is determined using linear prediction; and

deeming whether the ventricular tachyarrhythmia is stable according to the measurement of hemodynamic stability.

2. The method of claim 1, wherein obtaining a measurement of hemodynamic stability includes extracting a proxy measurement of aortic pressure from the heart sound signal.

3. The method of claim 1, wherein obtaining a measurement of hemodynamic stability includes:

sampling the heart sound signal to obtain a plurality of signal samples; and

determining an autocorrelation function using the signal samples.

4. The method of claim 1, wherein obtaining a measurement of hemodynamic stability from the heart sound signal includes:

establishing a baseline measurement for the measurement of hemodynamic stability; and

deeming the ventricular tachyarrhythmia to be unstable when a measured change from the baseline measurement of hemodynamic stability exceeds a predetermined threshold value.

5. The method of claim 4, including deeming the ventricular tachyarrhythmia to be unstable when a measured change from the baseline measurement of hemodynamic stability exceeds a predetermined threshold value in X of Y consecutive cardiac cycles, wherein X and Y are integers and Y>

X.

6. The method of claim 5, wherein establishing a baseline measurement includes determining a central tendency of the measurement of hemodynamic stability.

7. The method of claim 1, wherein obtaining a measurement of hemodynamic stability from the heart sound signal includes:

establishing a baseline measurement for the measurement of hemodynamic stability;

determining a measure of variability of ventricular time intervals; and

deeming the ventricular tachyarrhythmia to be unstable when both a measured change from the baseline measurement of hemodynamic stability exceeds a predetermined stability measurement threshold value and the measure of variability of ventricular time intervals exceeds a predetermined variability threshold value.

8. The method of claim 1, including delaying delivery of a predetermined shock stimulus according to the measurement of hemodynamic stability.

9. The method of claim 1, including:

initiating a predetermined anti-tachyarrhythmia pacing (ATP) regimen upon detecting the episode of ventricular tachyarrhythmia; and

extending a duration of the ATP regimen according to the measurement of hemodynamic stability.

10. The method of claim 1, including correlating the sensed heart sound signal to a sensed electrical cardiac signal representative of cardiac activity of the patient.

11. The method of claim 1, including correlating a sensed heart sound signal to sensed patient activity.

12. The method of claim 1, wherein sensing at least one heart sound signal includes:

sensing the heart sound signal with an accelerometer;

lowpass filtering the heart sound signal to obtain a filtered heart sound signal; and

pre-emphasizing higher frequencies of the filtered heart sound signal.

13. The method of claim 1, wherein detecting at least one episode of ventricular tachyarrhythmia in a subject includes determining that an average ventricular contraction rate exceeds an average atrial contraction rate by more than a specified rate threshold value.

14. The method of claim 1, including:

sampling the heart sound signal to obtain a sampled heart sound signal; and

initiating the measurement of hemodynamic stability includes initiating a determination of an autocorrelation function using the sampled heart sound signal.

15. The method of claim 1, wherein initiating the measurement of hemodynamic stability includes initiating a measurement of a hemodynamic parameter He, wherein

$\mathrm{He}=1-k_1^2,$

k 1 = - ( R 1 R 0 ) , 

R 0 = ∑

n = 0 N - 1 



s n 2 , 

and $R_1=\underset{n=0}{\overset{N-2}{\sum <br><br>}}<br><br><br><br>s_n<br><br>s_{n+1},$

where s_n are digitized samples of the heart sound signal obtained during a measured heart sound.

16. The method of claim 1, wherein sensing the heart sound signal includes sensing the heart sound signal using at least one of an accelerometer, a strain gauge, and a microphone.

17. The method of claim 1, wherein the measurement of hemodynamic stability is determined using linear prediction applied to an S1 heart sound of the sensed heart sound signal.

18. The method of claim 1, including:

communicating information about the measurement of hemodynamic stability to an external device; and

generating an alarm using the external device based on the information about the measurement of hemodynamic stability.

19. The method of claim 18, wherein communicating information about the measurement of hemodynamic stability to an external device includes communicating information about the measurement of hemodynamic stability to a server in communication with a network.

20. The method of claim 19, wherein communicating information about the measurement of hemodynamic stability to an external device includes communicating information about the measurement of hemodynamic stability to an IMD programmer.