Method and apparatus for controlling cardiac resynchronization therapy using cardiac impedance

• US 20070066905A1
• Filed: 09/21/2005
• Published: 03/22/2007
• Est. Priority Date: 09/21/2005
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Zhang, Yunlong
• Granted Patent: US 7,974,691 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• 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 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/3956 Implantable devices for applying electric shocks to the heart, e.g. for cardioversion

Abstract

This document discusses, among other things, systems, devices, and methods for measuring cardiac impedances and producing one or more resynchronization index parameters each indicative of a cardiac synchrony or asynchrony using the measured cardiac impedances. In one example, the one or more resynchronization index parameters are used to adjust one or more pacing parameters of a cardiac resynchronization therapy.

Claims

1. A machine-assisted method for monitoring a heart having first and second ventricles, the method comprising:

measuring a first impedance signal, the first impedance signal being substantially indicative of a volume of the first ventricle as the first ventricle expands and contracts during a cardiac cycle of the heart;

measuring a second impedance signal, the second impedance signal being substantially indicative of a volume of the second ventricle as the second ventricle expands and contracts during the cardiac cycle;

detecting a first peak of the first impedance signal during the cardiac cycle, the first peak being a first point at which the first impedance signal reaches a first maximum value;

detecting a second peak of the second impedance signal during the cardiac cycle, the second peak being a second point at which the second impedance signal reaches a second maximum value; and

producing a first resynchronization index parameter using at least the first and second peaks, the resynchronization index parameter indicative of a degree of cardiac mechanical synchrony or asynchrony between the first and second ventricles.

2. The method of claim 1, further comprising controlling one or more cardiac resynchronization therapy parameters using the first resynchronization index parameter.

3. The method of claim 2, in which the controlling the one or more cardiac resynchronization therapy parameters includes controlling an atrioventricular delay.

4. The method of claim 3, in which the controlling the one or more cardiac resynchronization therapy parameters further includes controlling an interventricular offset.

5. The method of claim 1, in which the first resynchronization index parameter is a time interval between the first and second peaks, and the producing the first resynchronization index parameter includes measuring the time interval between the first and second peaks.

6. The method of claim 1, further comprising:

computing a first slope of the first impedance signal at a first predetermined type point on the first impedance signal; and

computing a second slope of the second impedance signal at a second predetermined type point on the second impedance signal, and

in which the first resynchronization index parameter is a function of a difference between the first and second slopes, and the producing the first resynchronization index parameter includes computing the difference between the first and second slopes.

7. The method of claim 6, further comprising:

detecting a first baseline point of the first impedance signal during the cardiac cycle, the first baseline point being a point at which the first impedance signal rises across a predetermined first baseline impedance;

detecting a second baseline point of the second impedance signal during the cardiac cycle, the second baseline point being a point at which the second impedance signal rises across a predetermined second baseline impedance;

locating the first predetermined type point between the first baseline point and the first peak; and

locating the second predetermined type point between the second baseline point and the second peak.

8. The method of claim 1, further comprising:

detecting a first ventricular depolarization of the first ventricle during the cardiac cycle; and

detecting a second ventricular depolarization of the second ventricle during the cardiac cycle.

9. The method of claim 8, further comprising:

measuring a first time interval between the first ventricular depolarization and the first peak; and

measuring a second time interval between the second ventricular depolarization and the second peak, and

in which the first resynchronization index parameter is a function of a difference between the first and second time intervals, and the producing the first resynchronization index parameter includes computing the difference between the first and the second time intervals.

10. The method of claim 8, further comprising producing a second resynchronization index parameter indicative of a degree of cardiac electrical synchrony or asynchrony between the right and left ventricles, the second resynchronization index parameter being an interventricular interval between the first and second ventricular depolarizations, the producing the second resynchronization index parameter including measuring the interventricular interval.

11. A system for monitoring a heart having first and second ventricles, the system comprising:

a device comprising;

an impedance measurement circuit, including terminals configured to be coupled to electrodes in association with the first ventricle to measure a first impedance signal that is substantially indicative of a volume of the first ventricle as the first ventricle expands and contracts during a cardiac cycle of the heart and in association with the second ventricle to measure a second impedance signal that is substantially indicative of a volume of the second ventricle as the second ventricle expands and contracts during the cardiac cycle; and

a processor circuit, coupled to the impedance measurement circuit to receive information about the first and second impedance signals over the cardiac cycle, the processor configured to perform instructions to detect a first peak of the first impedance signal during the cardiac cycle, detect a second peak of the second impedance signal during the cardiac cycle, and produce a first resynchronization index parameter using at least the first and second peaks, the first peak being a first point at which the first impedance signal reaches a first maximum value, the second peak being a second point at which the second impedance signal reaches a second maximum value, the first resynchronization index parameter indicative of a degree of cardiac mechanical synchrony or asynchrony between the first and second ventricles.

12. The system of claim 11, in which the device includes an implantable medical device.

13. The system of claim 12, in which the implantable medical device includes a telemetry circuit, coupled to the processor circuit, to receive information about the degree of synchrony or asynchrony, the telemetry circuit configured to communicate data associated with the information about the degree of synchrony or asynchrony from the implantable medical device.

14. The system of claim 12, in which the implantable medical device further includes a therapy circuit configured to provide a cardiac resynchronization therapy, and the processor is configured to perform instructions to adjust delivery of the cardiac resynchronization therapy using the first resynchronization index parameter.

15. The system of claim 12, in which the processor is configured to perform instructions to produce the first resynchronization index parameter by measuring a time interval between the first and second peaks.

16. The system of claim 12, in which the processor is configured to perform instructions to compute a first slope of the first impedance signal at a first predetermined type point on the first impedance signal, compute a second slope of the second impedance signal at a second predetermined type point on the second impedance signal, and produce the first resynchronization index parameter by using a difference between the first slope and the second slope.

17. The system of claim 16, in which the processor is configured to perform instructions to detect a first baseline point of the first impedance signal during the cardiac cycle, detect a second baseline point of the second impedance signal during the cardiac cycle, locate the first predetermined type point between the first baseline point and the first peak, and locate the second predetermined type point between the second baseline point and the second peak, the first baseline point being a point at which the first impedance signal rises across a predetermined first baseline impedance, the second baseline point being a point at which the second impedance signal rises across a predetermined second baseline impedance.

18. The system of claim 12, in which the implantable medical device further includes a depolarization detector to detect a first ventricular depolarization of the first ventricle and a second ventricular depolarization of the second ventricle during the cardiac cycle.

19. The system of claim 18, in which the processor is configured to perform instructions to measure a first time interval between the first ventricular depolarization and the first peak, measure a second time interval between the second ventricular depolarization and the second peak, and produce the first resynchronization index parameter by using a difference between the first time interval and the second time interval.

20. The method of claim 18, in which the processor is configured to perform instructions to produce a second resynchronization index parameter indicative of a degree of cardiac electrical synchrony or asynchrony between the right and left ventricles by computing an interventricular interval between a time interval between the first ventricular depolarization and the second ventricular depolarization.