Maximum atrial tracking rate for cardiac rhythm management system

• US 20030078624A1
• Filed: 10/19/2001
• Published: 04/24/2003
• Est. Priority Date: 10/19/2001
• Status: Active Grant

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Spinelli, Julio C., Carlson, Gerrard M., Zhu, Qingsheng
• Granted Patent: US 7,062,323 B2
• Time in Patent Office: Days
• US Class Current: 607/9
• CPC Class Codes: A61N 1/3622 comprising two or more electrodes co-operating with different heart regions
• CPC Class Codes: A61N 1/36521 the parameter being derived from measurement of an electrical impedance
• CPC Class Codes: A61N 1/36542 controlled by body motion, e.g. acceleration

Abstract

A cardiac rhythm management system includes an operational mode in which ventricular pacing pulses are delivered at a rate that tracks a sinoatrial rate up to an appropriate maximum atrial tracking rate (MATR) value determined by the system. In one example, the MATR value is based on a patient activity level and a hemodynamic maximum rate (HMR) determined from a QRS-to-S₂ interval, where S₂ is an accelerometer-generated fiducial correlative to aortic valve closure (AVC). In a further example, a correlation between the QRS-to-S₂ interval and heart rate is established, and the MATR is based on the patient activity level and heart rate. In a further example, a lower rate threshold for providing antitachyarrhythmia therapy is modified based on the MATR. For example, when the MATR exceeds a default value of the antitachyarrhythmia therapy lower rate threshold, the threshold tracks the MATR. In another example, the MATR is based on an active time between a QRS complex and a heart impedance signal maximum slope during the same cardiac cycle.

Claims

1. A method including:

measuring a subinterval of a patient'"'"'s cardiac cycle correlative to a hemodynamic maximum rate indicator; and

establishing a maximum atrial tracking rate based at least in part on the hemodynamic maximum rate indicator.

2. The method of claim 1, in which measuring the subinterval includes:

detecting a portion of a QRS complex;

detecting an indication of an aortic valve closure; and

measuring an indication of a time interval between the detected QRS complex and the detected aortic valve closure.

3. The method of claim 2, in which detecting an indication of an aortic valve closure includes detecting an acceleration fiducial correlative to the aortic valve closure.

4. The method of claim 3, in which detecting the acceleration fiducial includes detecting an S2 heart sound.

5. The method of claim 4, in which measuring the indication of the time interval between the detected QRS complex and the detected aortic valve closure includes:

converting a measured time interval between the detected QRS complex and the S2 heart sound into a heart rate; and

adding a rate offset thereto to obtain the indication of the time interval between the detected QRS complex and the detected aortic valve closure.

6. The method of claim 1, in which establishing the maximum atrial tracking rate includes:

providing a base value of the maximum atrial tracking rate;

detecting a present activity level of the patient;

detecting a maximum activity level over a period of time; and

computing the maximum atrial tracking rate by scaling a difference between the hemodynamic maximum rate indicator and the base value of the maximum atrial tracking rate by a ratio of the present activity level to the maximum activity level, and adding the scaled difference to the base value of the maximum atrial tracking rate to establish the maximum atrial tracking rate.

7. The method of claim 1, further including:

providing a first tachyarrhythmia therapy rate threshold; and

adjusting the first tachyarrhythmia therapy rate threshold when the maximum atrial tracking rate exceeds the first tachyarrhythmia therapy rate threshold.

8. The method of claim 7, in which adjusting the first tachyarrhythmia therapy rate threshold includes substantially equating the first tachyarrhythmia therapy rate threshold to the maximum atrial tracking rate when the maximum atrial tracking rate exceeds the first tachyarrhythmia therapy rate threshold.

9. The method of claim 1, in which measuring the subinterval of the patient'"'"'s cardiac cycle correlative to the hemodynamic maximum rate indicator is carried out at a plurality of heart rates to create a correlation between heart rate and the hemodynamic maximum rate indicator.

10. The method of claim 9, in which establishing the maximum atrial tracking rate is based at least in part on the correlation between heart rate and the hemodynamic maximum rate indicator.

11. The method of claim 1, further including adjusting a criteria for providing an antitachyarrhythmia therapy based on the established maximum atrial tracking rate.

12. The method of claim 11, further including increasing a rate threshold for providing an antitachyarrhythmia therapy to a value that is greater than or equal to the established maximum atrial tracking rate.

13. The method of claim 12, further including increasing a lower rate threshold for a lower antitachyarrhythmia therapy zone to a value that is greater than or equal to the established maximum atrial tracking rate.

14. The method of claim 1, in which establishing the maximum atrial tracking rate includes calculating the maximum atrial tracking rate (MATR) as:

MATR=Default MATR+(HMR−

Default MATR)·

(AL/MAL), where Default MATR is a previously programmed value, HMR is a hemodynamic maximum rate based at least in part on the time interval between the QRS complex and the fiducial, AL is the patient activity level, and MAL is a maximum value of the patient activity level over a preceding time period.

15. The method of claim 1, in which measuring the subinterval includes:

detecting a portion of a QRS complex;

detecting a heart impedance including variations corresponding to heart contractions;

detecting a time associated with a maximum slope of the heart impedance; and

measuring an active time interval between the detected QRS complex and the time associated with the maximum slope of the heart impedance occurring during the same cardiac cycle as the detected QRS complex.

16. The method of claim 15, in which establishing the maximum atrial tracing rate includes using a rate corresponding to the active time interval.

17. A cardiac rhythm management system including:

a ventricular sensing channel to detect a QRS complex during a cardiac cycle;

an accelerometer to detect a fiducial of a heart acceleration signal correlative to an aortic valve closure occurring during the cardiac cycle after the QRS complex, and to detect a patient activity level; and

a controller adapted for calculating a maximum atrial tracking rate based at least in part on the activity level and a time interval between the QRS complex and the fiducial.

18. The system of claim 17, further including:

an atrial sensing channel to detect an atrial heart rate; and

a ventricular therapy module to provide ventricular pacing pulses at a ventricular indicated rate that is based at least in part on the atrial heart rate up to the maximum atrial tracking rate.

19. The system of claim 18, further including atrial and ventricular electrodes adapted for being associated with an atrium and a ventricle, respectively.

20. The system of claim 18, in which the ventricular therapy module is also adapted to provide antitachyarrhythmia therapy that is based at least in part on the maximum atrial tracking rate.

21. The system of claim 20, in which the controller includes a rate threshold for triggering delivery of the antitachyarrhythmia therapy, and in which the rate threshold is increased from a default value when the maximum atrial tracking rate exceeds the default value of the rate threshold.

22. The system of claim 20, in which the controller includes a plurality of lower rate thresholds corresponding to different antitachyarrhythmia therapy zones, and in which a lower rate threshold defining a lowest rate zone is increased from a default value when the maximum atrial tracking rate exceeds the default value.

23. The system of claim 17, in which the controller calculates the maximum atrial tracking rate (MATR) as:

MATR=Default MATR+(HMR−

Default MATR)·

(AL/MAL), where Default MATR is a previously programmed value, HMR is a hemodynamic maximum rate based at least in part on the time interval between the QRS complex and the fiducial, AL is the patient activity level, and MAL is a maximum value of the patient activity level over a preceding time period.

24. The system of claim 17, in which the controller includes memory locations adapted to provide a correlation between heart rate and the time interval between the QRS complex and the fiducial, and in which the controller is adapted to calculate the maximum atrial tracking rate based at least in part on the activity level and the correlation.

25. A cardiac rhythm management system including:

a ventricular sensing channel to detect a QRS complex during a cardiac cycle;

means for detecting a fiducial of a heart acceleration signal correlative to an aortic valve closure occurring during the cardiac cycle after the QRS complex, and for detecting a patient activity level; and

a controller adapted for calculating a maximum atrial tracking rate based at least in part on the activity level and a time interval between the QRS complex and the fiducial.

26. The system of claim 25, further including:

an atrial sensing channel to detect an atrial heart rate; and

a ventricular therapy module to provide ventricular pacing pulses at a ventricular indicated rate that is based at least in part on the atrial heart rate up to the maximum atrial tracking rate.

27. A cardiac rhythm management system including:

a ventricular sensing channel to detect a QRS complex during a cardiac cycle;

an impedance sensing circuit to detect a heart impedance signal varying in response to a heart contraction; and

a controller adapted for calculating a maximum atrial tracking rate based at least in part a time interval between the QRS complex and a subsequent maximum slope of the heart impedance signal during the same cardiac cycle as the QRS complex.

28. The system of claim 27, further including:

an atrial sensing channel to detect an atrial heart rate; and

a ventricular therapy module to provide ventricular pacing pulses at a ventricular indicated rate that is based at least in part on the atrial heart rate up to the maximum atrial tracking rate.