Hemodynamic stability assessment based on heart sounds

• US 7,780,606 B2
• Filed: 03/29/2006
• Issued: 08/24/2010
• Est. Priority Date: 03/29/2006
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Lin, Yayun, Carlson, Gerrard M.
• Primary Examiner(s): Layno; Carl H
• Assistant Examiner(s): Porter, Jr.; Gary A
• Application Number:
  US11/277,773
• Publication Number:
  US 20070239218A1
• Time in Patent Office: 1,609 Days
• Field of Search: 607/4, 607/14, 607 17- 19, 607/2, 607/5, 607/6, 607/7, 607/9, 607/11, 607/23, 600/528
• US Class Current: 600/508
• 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 system comprising an implantable medical device (IMD). The IMD includes an implantable sensor operable to produce an electrical signal representative of mechanical activity of a heart of a subject and a controller circuit coupled to the sensor. The IMD also includes a heart sound sensor interface circuit to produce a heart sound signal, a tachyarrhythmia detector, and a controller circuit. The controller circuit includes a hemodynamic stability assessment module configured to determine that at least one episode of ventricular tachyarrhythmia is detected in a subject and obtain a measurement of hemodynamic stability of the ventricular tachyarrhythmia from the heart sound signal.

Claims

1. A system comprising:

an implantable medical device (IMD) comprising;

an implantable heart sound sensor operable to produce an electrical signal representative of at least one heart sound, the heart sound associated with mechanical activity of a patient'"'"'s heart;

a heart sound sensor interface circuit coupled to the heart sound sensor to produce a heart sound signal;

a tachyarrhythmia detector; and

a controller circuit coupled to the heart sound sensor interface circuit and the tachyarrhythmia detector, wherein the controller circuit includes a hemodynamic stability assessment module configured to;

determine that at least one episode of ventricular tachyarrhythmia is detected in a subject;

initiate, in response to and obtain 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

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

2. The system of claim 1, wherein the hemodynamic stability assessment module includes a baseline module to establish a baseline for the measurement of hemodynamic stability obtained from the heart sound signal;

and

wherein the hemodynamic stability assessment module is further configured to deem the ventricular tachyarrhythmia to be unstable when a measured change from the baseline measurement of hemodynamic stability exceeds a predetermined threshold value.

3. The system of claim 2, wherein the baseline module is configured to establish a baseline for the measurement of hemodynamic stability by determining a central tendency of the measurement of hemodynamic stability.

4. The system of claim 2, wherein the hemodynamic stability assessment module is configured to deem 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.

5. The system of claim 1, wherein the system further includes a timer circuit coupled to the controller circuit to provide a ventricular time interval between ventricular contractions;

wherein the hemodynamic stability assessment module includes a ventricular contraction variability module to obtain a measure of variability of ventricular time intervals;

wherein the hemodynamic stability module includes a baseline module to establish a baseline for the measurement of hemodynamic stability obtained from the heart sound signal; and

wherein the hemodynamic stability assessment module is further configured to deem 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.

6. The system of claim 1, wherein the system further includes a shock circuit coupled to the controller circuit, and

wherein the controller circuit is configured to delay delivery of a predetermined shock stimulus during the detected episode of tachyarrhythmia according to the measurement of hemodynamic stability obtained by the hemodynamic stability assessment module.

7. The system of claim 1, wherein the system further includes an anti-tachyarrhythmia pacing (ATP) circuit coupled to the controller circuit, and wherein the controller circuit is configured to:

initiate a predetermined ATP regimen upon detecting the episode of ventricular tachyarrhythmia; and

extend a duration of the ATP regimen during the detected episode of tachyarrhythmia according to the measurement of hemodynamic stability.

8. The system of claim 1, including at least one implantable cardiac signal sensing circuit coupled to the controller circuit, the implantable cardiac signal sensing circuit configured to produce an electrical cardiac signal representative of cardiac activity of the patient, and wherein the hemodynamic stability assessment module is configured to obtain the measurement of hemodynamic stability from a heart sound signal in correlation with the electrical cardiac activity signal.

9. The system of claim 1, including a patient activity sensor coupled to the controller circuit, wherein the hemodynamic stability assessment module is configured to obtain the measurement of hemodynamic stability from a heart sound signal in correlation with patient activity.

10. The system of claim 1, wherein the heart sound sensor interface circuit includes:

a lowpass filter circuit; and

a pre-emphasizing circuit to add signal gain to higher frequencies of a lowpass filtered heart sound signal.

11. The system of claim 1, including an external device, and wherein the IMD includes a communication circuit coupled to the controller circuit and the IMD is configured to communicate to an external device information about at least one measurement of hemodynamic stability obtained from a heart sound signal.

12. The system of claim 11, wherein the external device is an IMD programmer.

13. The system of claim 11, wherein the external device is a server in communication with a network, and wherein the server is configured to communicate with the IMD via a third device.

14. The system of claim 11, wherein the external device generates an alarm based on the information about the measurement of hemodynamic stability.

15. The system of claim 1, including a timer circuit, coupled to the tachyarrhythmia detector, to provide a ventricular time interval between ventricular contractions;

and

wherein the tachyarrhythmia detector is configured to declare that a tachyarrhythmia has occurred when an average ventricular contraction rate exceeds an average atrial contraction rate by more than a specified rate threshold value.

16. The system of claim 1, wherein the measurement of hemodynamic stability includes a hemodynamic parameter He, wherein He=1−

k₁²,

$k_1=-\left(\frac{R_1}{R_0}\right),<br><br>R_0=\underset{n=0}{\overset{N-1}{\sum <br><br>}}<br><br><br><br>s_n^2,<br><br>\mathrm{and}<br><br><br><br>R_1=\underset{n=0}{\overset{N-2}{\sum <br><br>}}<br><br><br><br>s_n<br><br>s_{n+1},$

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

17. The system of claim 1, wherein the heart sound sensor includes at least one of an accelerometer, a strain gauge, and a microphone.